22 files changed, 2420 insertions, 931 deletions

diff --git a/helix-core/src/auto_pairs.rs b/helix-core/src/auto_pairs.rs
index cc966852..f4359a34 100644
--- a/helix-core/src/auto_pairs.rs
+++ b/helix-core/src/auto_pairs.rs
@@ -1,7 +1,10 @@
 //! When typing the opening character of one of the possible pairs defined below,
 //! this module provides the functionality to insert the paired closing character.
 
-use crate::{Range, Rope, Selection, Tendril, Transaction};
+use crate::{
+    graphemes, movement::Direction, Range, Rope, RopeGraphemes, Selection, Tendril, Transaction,
+};
+use log::debug;
 use smallvec::SmallVec;
 
 // Heavily based on https://github.com/codemirror/closebrackets/
@@ -15,7 +18,9 @@ pub const PAIRS: &[(char, char)] = &[
     ('`', '`'),
 ];
 
-const CLOSE_BEFORE: &str = ")]}'\":;> \n\r\u{000B}\u{000C}\u{0085}\u{2028}\u{2029}"; // includes space and newlines
+// [TODO] build this dynamically in language config. see #992
+const OPEN_BEFORE: &str = "([{'\":;,> \n\r\u{000B}\u{000C}\u{0085}\u{2028}\u{2029}";
+const CLOSE_BEFORE: &str = ")]}'\":;,> \n\r\u{000B}\u{000C}\u{0085}\u{2028}\u{2029}"; // includes space and newlines
 
 // insert hook:
 // Fn(doc, selection, char) => Option<Transaction>
@@ -25,14 +30,19 @@ const CLOSE_BEFORE: &str = ")]}'\":;> \n\r\u{000B}\u{000C}\u{0085}\u{2028}\u{202
 //
 // to simplify, maybe return Option<Transaction> and just reimplement the default
 
-// TODO: delete implementation where it erases the whole bracket (|) -> |
+// [TODO]
+// * delete implementation where it erases the whole bracket (|) -> |
+// * change to multi character pairs to handle cases like placing the cursor in the
+//   middle of triple quotes, and more exotic pairs like Jinja's {% %}
 
 #[must_use]
 pub fn hook(doc: &Rope, selection: &Selection, ch: char) -> Option<Transaction> {
+    debug!("autopairs hook selection: {:#?}", selection);
+
     for &(open, close) in PAIRS {
         if open == ch {
             if open == close {
-                return handle_same(doc, selection, open);
+                return Some(handle_same(doc, selection, open, CLOSE_BEFORE, OPEN_BEFORE));
             } else {
                 return Some(handle_open(doc, selection, open, close, CLOSE_BEFORE));
             }
@@ -47,18 +57,145 @@ pub fn hook(doc: &Rope, selection: &Selection, ch: char) -> Option<Transaction>
     None
 }
 
-// TODO: special handling for lifetimes in rust: if preceeded by & or < don't auto close '
-// for example "&'a mut", or "fn<'a>"
-
-fn next_char(doc: &Rope, pos: usize) -> Option<char> {
-    if pos >= doc.len_chars() {
+fn prev_char(doc: &Rope, pos: usize) -> Option<char> {
+    if pos == 0 {
         return None;
     }
-    Some(doc.char(pos))
+
+    doc.get_char(pos - 1)
+}
+
+fn is_single_grapheme(doc: &Rope, range: &Range) -> bool {
+    let mut graphemes = RopeGraphemes::new(doc.slice(range.from()..range.to()));
+    let first = graphemes.next();
+    let second = graphemes.next();
+    debug!("first: {:#?}, second: {:#?}", first, second);
+    first.is_some() && second.is_none()
+}
+
+/// calculate what the resulting range should be for an auto pair insertion
+fn get_next_range(
+    doc: &Rope,
+    start_range: &Range,
+    offset: usize,
+    typed_char: char,
+    len_inserted: usize,
+) -> Range {
+    // When the character under the cursor changes due to complete pair
+    // insertion, we must look backward a grapheme and then add the length
+    // of the insertion to put the resulting cursor in the right place, e.g.
+    //
+    // foo[\r\n] - anchor: 3, head: 5
+    // foo([)]\r\n - anchor: 4, head: 5
+    //
+    // foo[\r\n] - anchor: 3, head: 5
+    // foo'[\r\n] - anchor: 4, head: 6
+    //
+    // foo([)]\r\n - anchor: 4, head: 5
+    // foo()[\r\n] - anchor: 5, head: 7
+    //
+    // [foo]\r\n - anchor: 0, head: 3
+    // [foo(])\r\n - anchor: 0, head: 5
+
+    // inserting at the very end of the document after the last newline
+    if start_range.head == doc.len_chars() && start_range.anchor == doc.len_chars() {
+        return Range::new(
+            start_range.anchor + offset + typed_char.len_utf8(),
+            start_range.head + offset + typed_char.len_utf8(),
+        );
+    }
+
+    let single_grapheme = is_single_grapheme(doc, start_range);
+    let doc_slice = doc.slice(..);
+
+    // just skip over graphemes
+    if len_inserted == 0 {
+        let end_anchor = if single_grapheme {
+            graphemes::next_grapheme_boundary(doc_slice, start_range.anchor) + offset
+
+        // even for backward inserts with multiple grapheme selections,
+        // we want the anchor to stay where it is so that the relative
+        // selection does not change, e.g.:
+        //
+        // foo([) wor]d -> insert ) -> foo()[ wor]d
+        } else {
+            start_range.anchor + offset
+        };
+
+        return Range::new(
+            end_anchor,
+            graphemes::next_grapheme_boundary(doc_slice, start_range.head) + offset,
+        );
+    }
+
+    // trivial case: only inserted a single-char opener, just move the selection
+    if len_inserted == 1 {
+        let end_anchor = if single_grapheme || start_range.direction() == Direction::Backward {
+            start_range.anchor + offset + typed_char.len_utf8()
+        } else {
+            start_range.anchor + offset
+        };
+
+        return Range::new(
+            end_anchor,
+            start_range.head + offset + typed_char.len_utf8(),
+        );
+    }
+
+    // If the head = 0, then we must be in insert mode with a backward
+    // cursor, which implies the head will just move
+    let end_head = if start_range.head == 0 || start_range.direction() == Direction::Backward {
+        start_range.head + offset + typed_char.len_utf8()
+    } else {
+        // We must have a forward cursor, which means we must move to the
+        // other end of the grapheme to get to where the new characters
+        // are inserted, then move the head to where it should be
+        let prev_bound = graphemes::prev_grapheme_boundary(doc_slice, start_range.head);
+        debug!(
+            "prev_bound: {}, offset: {}, len_inserted: {}",
+            prev_bound, offset, len_inserted
+        );
+        prev_bound + offset + len_inserted
+    };
+
+    let end_anchor = match (start_range.len(), start_range.direction()) {
+        // if we have a zero width cursor, it shifts to the same number
+        (0, _) => end_head,
+
+        // If we are inserting for a regular one-width cursor, the anchor
+        // moves with the head. This is the fast path for ASCII.
+        (1, Direction::Forward) => end_head - 1,
+        (1, Direction::Backward) => end_head + 1,
+
+        (_, Direction::Forward) => {
+            if single_grapheme {
+                graphemes::prev_grapheme_boundary(doc.slice(..), start_range.head)
+                    + typed_char.len_utf8()
+
+            // if we are appending, the anchor stays where it is; only offset
+            // for multiple range insertions
+            } else {
+                start_range.anchor + offset
+            }
+        }
+
+        (_, Direction::Backward) => {
+            if single_grapheme {
+                // if we're backward, then the head is at the first char
+                // of the typed char, so we need to add the length of
+                // the closing char
+                graphemes::prev_grapheme_boundary(doc.slice(..), start_range.anchor) + len_inserted
+            } else {
+                // when we are inserting in front of a selection, we need to move
+                // the anchor over by however many characters were inserted overall
+                start_range.anchor + offset + len_inserted
+            }
+        }
+    };
+
+    Range::new(end_anchor, end_head)
 }
-// TODO: selections should be extended if range, moved if point.
 
-// TODO: if not cursor but selection, wrap on both sides of selection (surround)
 fn handle_open(
     doc: &Rope,
     selection: &Selection,
@@ -66,98 +203,584 @@ fn handle_open(
     close: char,
     close_before: &str,
 ) -> Transaction {
-    let mut ranges = SmallVec::with_capacity(selection.len());
-
+    let mut end_ranges = SmallVec::with_capacity(selection.len());
     let mut offs = 0;
 
-    let transaction = Transaction::change_by_selection(doc, selection, |range| {
-        let pos = range.head;
-        let next = next_char(doc, pos);
-
-        let head = pos + offs + open.len_utf8();
-        // if selection, retain anchor, if cursor, move over
-        ranges.push(Range::new(
-            if range.is_empty() {
-                head
-            } else {
-                range.anchor + offs
-            },
-            head,
-        ));
+    let transaction = Transaction::change_by_selection(doc, selection, |start_range| {
+        let cursor = start_range.cursor(doc.slice(..));
+        let next_char = doc.get_char(cursor);
+        let len_inserted;
 
-        match next {
+        let change = match next_char {
             Some(ch) if !close_before.contains(ch) => {
-                offs += 1;
-                // TODO: else return (use default handler that inserts open)
-                (pos, pos, Some(Tendril::from_char(open)))
+                len_inserted = open.len_utf8();
+                let mut tendril = Tendril::new();
+                tendril.push(open);
+                (cursor, cursor, Some(tendril))
             }
             // None | Some(ch) if close_before.contains(ch) => {}
             _ => {
                 // insert open & close
-                let mut pair = Tendril::with_capacity(2);
-                pair.push_char(open);
-                pair.push_char(close);
+                let pair = Tendril::from_iter([open, close]);
+                len_inserted = open.len_utf8() + close.len_utf8();
+                (cursor, cursor, Some(pair))
+            }
+        };
 
-                offs += 2;
+        let next_range = get_next_range(doc, start_range, offs, open, len_inserted);
+        end_ranges.push(next_range);
+        offs += len_inserted;
 
-                (pos, pos, Some(pair))
-            }
-        }
+        change
     });
 
-    transaction.with_selection(Selection::new(ranges, selection.primary_index()))
+    let t = transaction.with_selection(Selection::new(end_ranges, selection.primary_index()));
+    debug!("auto pair transaction: {:#?}", t);
+    t
 }
 
 fn handle_close(doc: &Rope, selection: &Selection, _open: char, close: char) -> Transaction {
-    let mut ranges = SmallVec::with_capacity(selection.len());
+    let mut end_ranges = SmallVec::with_capacity(selection.len());
 
     let mut offs = 0;
 
-    let transaction = Transaction::change_by_selection(doc, selection, |range| {
-        let pos = range.head;
-        let next = next_char(doc, pos);
+    let transaction = Transaction::change_by_selection(doc, selection, |start_range| {
+        let cursor = start_range.cursor(doc.slice(..));
+        let next_char = doc.get_char(cursor);
+        let mut len_inserted = 0;
 
-        let head = pos + offs + close.len_utf8();
-        // if selection, retain anchor, if cursor, move over
-        ranges.push(Range::new(
-            if range.is_empty() {
-                head
-            } else {
-                range.anchor + offs
-            },
-            head,
-        ));
+        let change = if next_char == Some(close) {
+            // return transaction that moves past close
+            (cursor, cursor, None) // no-op
+        } else {
+            len_inserted += close.len_utf8();
+            let mut tendril = Tendril::new();
+            tendril.push(close);
+            (cursor, cursor, Some(tendril))
+        };
+
+        let next_range = get_next_range(doc, start_range, offs, close, len_inserted);
+        end_ranges.push(next_range);
+        offs += len_inserted;
+
+        change
+    });
+
+    let t = transaction.with_selection(Selection::new(end_ranges, selection.primary_index()));
+    debug!("auto pair transaction: {:#?}", t);
+    t
+}
+
+/// handle cases where open and close is the same, or in triples ("""docstring""")
+fn handle_same(
+    doc: &Rope,
+    selection: &Selection,
+    token: char,
+    close_before: &str,
+    open_before: &str,
+) -> Transaction {
+    let mut end_ranges = SmallVec::with_capacity(selection.len());
+
+    let mut offs = 0;
 
-        if next == Some(close) {
+    let transaction = Transaction::change_by_selection(doc, selection, |start_range| {
+        let cursor = start_range.cursor(doc.slice(..));
+        let mut len_inserted = 0;
+
+        let next_char = doc.get_char(cursor);
+        let prev_char = prev_char(doc, cursor);
+
+        let change = if next_char == Some(token) {
             //  return transaction that moves past close
-            (pos, pos, None) // no-op
+            (cursor, cursor, None) // no-op
         } else {
-            offs += close.len_utf8();
+            let mut pair = Tendril::new();
+            pair.push(token);
 
-            // TODO: else return (use default handler that inserts close)
-            (pos, pos, Some(Tendril::from_char(close)))
-        }
+            // for equal pairs, don't insert both open and close if either
+            // side has a non-pair char
+            if (next_char.is_none() || close_before.contains(next_char.unwrap()))
+                && (prev_char.is_none() || open_before.contains(prev_char.unwrap()))
+            {
+                pair.push(token);
+            }
+
+            len_inserted += pair.len();
+            (cursor, cursor, Some(pair))
+        };
+
+        let next_range = get_next_range(doc, start_range, offs, token, len_inserted);
+        end_ranges.push(next_range);
+        offs += len_inserted;
+
+        change
     });
 
-    transaction.with_selection(Selection::new(ranges, selection.primary_index()))
+    let t = transaction.with_selection(Selection::new(end_ranges, selection.primary_index()));
+    debug!("auto pair transaction: {:#?}", t);
+    t
 }
 
-// handle cases where open and close is the same, or in triples ("""docstring""")
-fn handle_same(_doc: &Rope, _selection: &Selection, _token: char) -> Option<Transaction> {
-    // if not cursor but selection, wrap
-    // let next = next char
-
-    // if next == bracket {
-    //   // if start of syntax node, insert token twice (new pair because node is complete)
-    //   // elseif colsedBracketAt
-    //      // is_triple == allow triple && next 3 is equal
-    //      // cursor jump over
-    // }
-    //} else if allow_triple && followed by triple {
-    //}
-    //} else if next != word char && prev != bracket && prev != word char {
-    // // condition checks for cases like I' where you don't want I'' (or I'm)
-    //  insert pair ("")
-    //}
-    None
+#[cfg(test)]
+mod test {
+    use super::*;
+    use smallvec::smallvec;
+
+    const LINE_END: &str = crate::DEFAULT_LINE_ENDING.as_str();
+
+    fn differing_pairs() -> impl Iterator<Item = &'static (char, char)> {
+        PAIRS.iter().filter(|(open, close)| open != close)
+    }
+
+    fn matching_pairs() -> impl Iterator<Item = &'static (char, char)> {
+        PAIRS.iter().filter(|(open, close)| open == close)
+    }
+
+    fn test_hooks(
+        in_doc: &Rope,
+        in_sel: &Selection,
+        ch: char,
+        expected_doc: &Rope,
+        expected_sel: &Selection,
+    ) {
+        let trans = hook(in_doc, in_sel, ch).unwrap();
+        let mut actual_doc = in_doc.clone();
+        assert!(trans.apply(&mut actual_doc));
+        assert_eq!(expected_doc, &actual_doc);
+        assert_eq!(expected_sel, trans.selection().unwrap());
+    }
+
+    fn test_hooks_with_pairs<I, F, R>(
+        in_doc: &Rope,
+        in_sel: &Selection,
+        pairs: I,
+        get_expected_doc: F,
+        actual_sel: &Selection,
+    ) where
+        I: IntoIterator<Item = &'static (char, char)>,
+        F: Fn(char, char) -> R,
+        R: Into<Rope>,
+        Rope: From<R>,
+    {
+        pairs.into_iter().for_each(|(open, close)| {
+            test_hooks(
+                in_doc,
+                in_sel,
+                *open,
+                &Rope::from(get_expected_doc(*open, *close)),
+                actual_sel,
+            )
+        });
+    }
+
+    // [] indicates range
+
+    /// [] -> insert ( -> ([])
+    #[test]
+    fn test_insert_blank() {
+        test_hooks_with_pairs(
+            &Rope::from(LINE_END),
+            &Selection::single(1, 0),
+            PAIRS,
+            |open, close| format!("{}{}{}", open, close, LINE_END),
+            &Selection::single(2, 1),
+        );
+
+        let empty_doc = Rope::from(format!("{line_end}{line_end}", line_end = LINE_END));
+
+        test_hooks_with_pairs(
+            &empty_doc,
+            &Selection::single(empty_doc.len_chars(), LINE_END.len()),
+            PAIRS,
+            |open, close| {
+                format!(
+                    "{line_end}{open}{close}{line_end}",
+                    open = open,
+                    close = close,
+                    line_end = LINE_END
+                )
+            },
+            &Selection::single(LINE_END.len() + 2, LINE_END.len() + 1),
+        );
+    }
+
+    #[test]
+    fn test_insert_before_multi_code_point_graphemes() {
+        test_hooks_with_pairs(
+            &Rope::from(format!("hello 👨‍👩‍👧‍👦 goodbye{}", LINE_END)),
+            &Selection::single(13, 6),
+            PAIRS,
+            |open, _| format!("hello {}👨‍👩‍👧‍👦 goodbye{}", open, LINE_END),
+            &Selection::single(14, 7),
+        );
+    }
+
+    #[test]
+    fn test_insert_at_end_of_document() {
+        test_hooks_with_pairs(
+            &Rope::from(LINE_END),
+            &Selection::single(LINE_END.len(), LINE_END.len()),
+            PAIRS,
+            |open, close| format!("{}{}{}", LINE_END, open, close),
+            &Selection::single(LINE_END.len() + 1, LINE_END.len() + 1),
+        );
+
+        test_hooks_with_pairs(
+            &Rope::from(format!("foo{}", LINE_END)),
+            &Selection::single(3 + LINE_END.len(), 3 + LINE_END.len()),
+            PAIRS,
+            |open, close| format!("foo{}{}{}", LINE_END, open, close),
+            &Selection::single(LINE_END.len() + 4, LINE_END.len() + 4),
+        );
+    }
+
+    /// [] -> append ( -> ([])
+    #[test]
+    fn test_append_blank() {
+        test_hooks_with_pairs(
+            // this is what happens when you have a totally blank document and then append
+            &Rope::from(format!("{line_end}{line_end}", line_end = LINE_END)),
+            // before inserting the pair, the cursor covers all of both empty lines
+            &Selection::single(0, LINE_END.len() * 2),
+            PAIRS,
+            |open, close| {
+                format!(
+                    "{line_end}{open}{close}{line_end}",
+                    line_end = LINE_END,
+                    open = open,
+                    close = close
+                )
+            },
+            // after inserting pair, the cursor covers the first new line and the open char
+            &Selection::single(0, LINE_END.len() + 2),
+        );
+    }
+
+    /// []              ([])
+    /// [] -> insert -> ([])
+    /// []              ([])
+    #[test]
+    fn test_insert_blank_multi_cursor() {
+        test_hooks_with_pairs(
+            &Rope::from("\n\n\n"),
+            &Selection::new(
+                smallvec!(Range::new(1, 0), Range::new(2, 1), Range::new(3, 2),),
+                0,
+            ),
+            PAIRS,
+            |open, close| {
+                format!(
+                    "{open}{close}\n{open}{close}\n{open}{close}\n",
+                    open = open,
+                    close = close
+                )
+            },
+            &Selection::new(
+                smallvec!(Range::new(2, 1), Range::new(5, 4), Range::new(8, 7),),
+                0,
+            ),
+        );
+    }
+
+    /// fo[o] -> append ( -> fo[o(])
+    #[test]
+    fn test_append() {
+        test_hooks_with_pairs(
+            &Rope::from("foo\n"),
+            &Selection::single(2, 4),
+            differing_pairs(),
+            |open, close| format!("foo{}{}\n", open, close),
+            &Selection::single(2, 5),
+        );
+    }
+
+    /// foo[] -> append to end of line ( -> foo([])
+    #[test]
+    fn test_append_single_cursor() {
+        test_hooks_with_pairs(
+            &Rope::from(format!("foo{}", LINE_END)),
+            &Selection::single(3, 3 + LINE_END.len()),
+            differing_pairs(),
+            |open, close| format!("foo{}{}{}", open, close, LINE_END),
+            &Selection::single(4, 5),
+        );
+    }
+
+    /// fo[o]                fo[o(])
+    /// fo[o] -> append ( -> fo[o(])
+    /// fo[o]                fo[o(])
+    #[test]
+    fn test_append_multi() {
+        test_hooks_with_pairs(
+            &Rope::from("foo\nfoo\nfoo\n"),
+            &Selection::new(
+                smallvec!(Range::new(2, 4), Range::new(6, 8), Range::new(10, 12)),
+                0,
+            ),
+            differing_pairs(),
+            |open, close| {
+                format!(
+                    "foo{open}{close}\nfoo{open}{close}\nfoo{open}{close}\n",
+                    open = open,
+                    close = close
+                )
+            },
+            &Selection::new(
+                smallvec!(Range::new(2, 5), Range::new(8, 11), Range::new(14, 17)),
+                0,
+            ),
+        );
+    }
+
+    /// ([)] -> insert ) -> ()[]
+    #[test]
+    fn test_insert_close_inside_pair() {
+        for (open, close) in PAIRS {
+            let doc = Rope::from(format!("{}{}{}", open, close, LINE_END));
+
+            test_hooks(
+                &doc,
+                &Selection::single(2, 1),
+                *close,
+                &doc,
+                &Selection::single(2 + LINE_END.len(), 2),
+            );
+        }
+    }
+
+    /// [(]) -> append ) -> [()]
+    #[test]
+    fn test_append_close_inside_pair() {
+        for (open, close) in PAIRS {
+            let doc = Rope::from(format!("{}{}{}", open, close, LINE_END));
+
+            test_hooks(
+                &doc,
+                &Selection::single(0, 2),
+                *close,
+                &doc,
+                &Selection::single(0, 2 + LINE_END.len()),
+            );
+        }
+    }
+
+    /// ([])                ()[]
+    /// ([]) -> insert ) -> ()[]
+    /// ([])                ()[]
+    #[test]
+    fn test_insert_close_inside_pair_multi_cursor() {
+        let sel = Selection::new(
+            smallvec!(Range::new(2, 1), Range::new(5, 4), Range::new(8, 7),),
+            0,
+        );
+
+        let expected_sel = Selection::new(
+            smallvec!(Range::new(3, 2), Range::new(6, 5), Range::new(9, 8),),
+            0,
+        );
+
+        for (open, close) in PAIRS {
+            let doc = Rope::from(format!(
+                "{open}{close}\n{open}{close}\n{open}{close}\n",
+                open = open,
+                close = close
+            ));
+
+            test_hooks(&doc, &sel, *close, &doc, &expected_sel);
+        }
+    }
+
+    /// [(])                [()]
+    /// [(]) -> append ) -> [()]
+    /// [(])                [()]
+    #[test]
+    fn test_append_close_inside_pair_multi_cursor() {
+        let sel = Selection::new(
+            smallvec!(Range::new(0, 2), Range::new(3, 5), Range::new(6, 8),),
+            0,
+        );
+
+        let expected_sel = Selection::new(
+            smallvec!(Range::new(0, 3), Range::new(3, 6), Range::new(6, 9),),
+            0,
+        );
+
+        for (open, close) in PAIRS {
+            let doc = Rope::from(format!(
+                "{open}{close}\n{open}{close}\n{open}{close}\n",
+                open = open,
+                close = close
+            ));
+
+            test_hooks(&doc, &sel, *close, &doc, &expected_sel);
+        }
+    }
+
+    /// ([]) -> insert ( -> (([]))
+    #[test]
+    fn test_insert_open_inside_pair() {
+        let sel = Selection::single(2, 1);
+        let expected_sel = Selection::single(3, 2);
+
+        for (open, close) in differing_pairs() {
+            let doc = Rope::from(format!("{}{}", open, close));
+            let expected_doc = Rope::from(format!(
+                "{open}{open}{close}{close}",
+                open = open,
+                close = close
+            ));
+
+            test_hooks(&doc, &sel, *open, &expected_doc, &expected_sel);
+        }
+    }
+
+    /// [word(]) -> append ( -> [word((]))
+    #[test]
+    fn test_append_open_inside_pair() {
+        let sel = Selection::single(0, 6);
+        let expected_sel = Selection::single(0, 7);
+
+        for (open, close) in differing_pairs() {
+            let doc = Rope::from(format!("word{}{}", open, close));
+            let expected_doc = Rope::from(format!(
+                "word{open}{open}{close}{close}",
+                open = open,
+                close = close
+            ));
+
+            test_hooks(&doc, &sel, *open, &expected_doc, &expected_sel);
+        }
+    }
+
+    /// ([]) -> insert " -> ("[]")
+    #[test]
+    fn test_insert_nested_open_inside_pair() {
+        let sel = Selection::single(2, 1);
+        let expected_sel = Selection::single(3, 2);
+
+        for (outer_open, outer_close) in differing_pairs() {
+            let doc = Rope::from(format!("{}{}", outer_open, outer_close,));
+
+            for (inner_open, inner_close) in matching_pairs() {
+                let expected_doc = Rope::from(format!(
+                    "{}{}{}{}",
+                    outer_open, inner_open, inner_close, outer_close
+                ));
+
+                test_hooks(&doc, &sel, *inner_open, &expected_doc, &expected_sel);
+            }
+        }
+    }
+
+    /// [(]) -> append " -> [("]")
+    #[test]
+    fn test_append_nested_open_inside_pair() {
+        let sel = Selection::single(0, 2);
+        let expected_sel = Selection::single(0, 3);
+
+        for (outer_open, outer_close) in differing_pairs() {
+            let doc = Rope::from(format!("{}{}", outer_open, outer_close,));
+
+            for (inner_open, inner_close) in matching_pairs() {
+                let expected_doc = Rope::from(format!(
+                    "{}{}{}{}",
+                    outer_open, inner_open, inner_close, outer_close
+                ));
+
+                test_hooks(&doc, &sel, *inner_open, &expected_doc, &expected_sel);
+            }
+        }
+    }
+
+    /// []word -> insert ( -> ([]word
+    #[test]
+    fn test_insert_open_before_non_pair() {
+        test_hooks_with_pairs(
+            &Rope::from("word"),
+            &Selection::single(1, 0),
+            PAIRS,
+            |open, _| format!("{}word", open),
+            &Selection::single(2, 1),
+        )
+    }
+
+    /// [wor]d -> insert ( -> ([wor]d
+    #[test]
+    fn test_insert_open_with_selection() {
+        test_hooks_with_pairs(
+            &Rope::from("word"),
+            &Selection::single(3, 0),
+            PAIRS,
+            |open, _| format!("{}word", open),
+            &Selection::single(4, 1),
+        )
+    }
+
+    /// [wor]d -> append ) -> [wor)]d
+    #[test]
+    fn test_append_close_inside_non_pair_with_selection() {
+        let sel = Selection::single(0, 4);
+        let expected_sel = Selection::single(0, 5);
+
+        for (_, close) in PAIRS {
+            let doc = Rope::from("word");
+            let expected_doc = Rope::from(format!("wor{}d", close));
+            test_hooks(&doc, &sel, *close, &expected_doc, &expected_sel);
+        }
+    }
+
+    /// foo[ wor]d -> insert ( -> foo([) wor]d
+    #[test]
+    fn test_insert_open_trailing_word_with_selection() {
+        test_hooks_with_pairs(
+            &Rope::from("foo word"),
+            &Selection::single(7, 3),
+            differing_pairs(),
+            |open, close| format!("foo{}{} word", open, close),
+            &Selection::single(9, 4),
+        )
+    }
+
+    /// foo([) wor]d -> insert ) -> foo()[ wor]d
+    #[test]
+    fn test_insert_close_inside_pair_trailing_word_with_selection() {
+        for (open, close) in differing_pairs() {
+            test_hooks(
+                &Rope::from(format!("foo{}{} word{}", open, close, LINE_END)),
+                &Selection::single(9, 4),
+                *close,
+                &Rope::from(format!("foo{}{} word{}", open, close, LINE_END)),
+                &Selection::single(9, 5),
+            )
+        }
+    }
+
+    /// we want pairs that are *not* the same char to be inserted after
+    /// a non-pair char, for cases like functions, but for pairs that are
+    /// the same char, we want to *not* insert a pair to handle cases like "I'm"
+    ///
+    /// word[]  -> insert ( -> word([])
+    /// word[]  -> insert ' -> word'[]
+    #[test]
+    fn test_insert_open_after_non_pair() {
+        let doc = Rope::from(format!("word{}", LINE_END));
+        let sel = Selection::single(5, 4);
+        let expected_sel = Selection::single(6, 5);
+
+        test_hooks_with_pairs(
+            &doc,
+            &sel,
+            differing_pairs(),
+            |open, close| format!("word{}{}{}", open, close, LINE_END),
+            &expected_sel,
+        );
+
+        test_hooks_with_pairs(
+            &doc,
+            &sel,
+            matching_pairs(),
+            |open, _| format!("word{}{}", open, LINE_END),
+            &expected_sel,
+        );
+    }
 }
diff --git a/helix-core/src/chars.rs b/helix-core/src/chars.rs
index c8e5efbd..54991574 100644
--- a/helix-core/src/chars.rs
+++ b/helix-core/src/chars.rs
@@ -91,12 +91,11 @@ mod test {
 
     #[test]
     fn test_categorize() {
-        const EOL_TEST_CASE: &'static str = "\n\r\u{000B}\u{000C}\u{0085}\u{2028}\u{2029}";
-        const WORD_TEST_CASE: &'static str =
-            "_hello_world_あいうえおー1234567890１２３４５６７８９０";
-        const PUNCTUATION_TEST_CASE: &'static str =
+        const EOL_TEST_CASE: &str = "\n\r\u{000B}\u{000C}\u{0085}\u{2028}\u{2029}";
+        const WORD_TEST_CASE: &str = "_hello_world_あいうえおー1234567890１２３４５６７８９０";
+        const PUNCTUATION_TEST_CASE: &str =
             "!\"#$%&\'()*+,-./:;<=>?@[\\]^`{|}~！”＃＄％＆’（）＊＋、。：；＜＝＞？＠「」＾｀｛｜｝～";
-        const WHITESPACE_TEST_CASE: &'static str = "  　   ";
+        const WHITESPACE_TEST_CASE: &str = "  　   ";
 
         for ch in EOL_TEST_CASE.chars() {
             assert_eq!(CharCategory::Eol, categorize_char(ch));
diff --git a/helix-core/src/diagnostic.rs b/helix-core/src/diagnostic.rs
index 4fcf51c9..210ad639 100644
--- a/helix-core/src/diagnostic.rs
+++ b/helix-core/src/diagnostic.rs
@@ -1,12 +1,19 @@
 //! LSP diagnostic utility types.
+use serde::{Deserialize, Serialize};
 
 /// Describes the severity level of a [`Diagnostic`].
-#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+#[derive(Debug, Clone, Copy, Eq, PartialEq, PartialOrd, Ord, Deserialize, Serialize)]
 pub enum Severity {
-    Error,
-    Warning,
-    Info,
     Hint,
+    Info,
+    Warning,
+    Error,
+}
+
+impl Default for Severity {
+    fn default() -> Self {
+        Self::Hint
+    }
 }
 
 /// A range of `char`s within the text.
diff --git a/helix-core/src/diff.rs b/helix-core/src/diff.rs
index a83db333..6960c679 100644
--- a/helix-core/src/diff.rs
+++ b/helix-core/src/diff.rs
@@ -11,10 +11,6 @@ pub fn compare_ropes(old: &Rope, new: &Rope) -> Transaction {
     // A timeout is set so after 1 seconds, the algorithm will start
     // approximating. This is especially important for big `Rope`s or
     // `Rope`s that are extremely dissimilar to each other.
-    //
-    // Note: Ignore the clippy warning, as the trait bounds of
-    // `Transaction::change()` require an iterator implementing
-    // `ExactIterator`.
     let mut config = similar::TextDiff::configure();
     config.timeout(std::time::Duration::from_secs(1));
 
@@ -62,7 +58,7 @@ mod tests {
             let mut old = Rope::from(a);
             let new = Rope::from(b);
             compare_ropes(&old, &new).apply(&mut old);
-            old.to_string() == new.to_string()
+            old == new
         }
     }
 }
diff --git a/helix-core/src/graphemes.rs b/helix-core/src/graphemes.rs
index c6398875..aa898684 100644
--- a/helix-core/src/graphemes.rs
+++ b/helix-core/src/graphemes.rs
@@ -120,6 +120,43 @@ pub fn nth_next_grapheme_boundary(slice: RopeSlice, char_idx: usize, n: usize) -
     chunk_char_idx + tmp
 }
 
+#[must_use]
+pub fn nth_next_grapheme_boundary_byte(slice: RopeSlice, mut byte_idx: usize, n: usize) -> usize {
+    // Bounds check
+    debug_assert!(byte_idx <= slice.len_bytes());
+
+    // Get the chunk with our byte index in it.
+    let (mut chunk, mut chunk_byte_idx, mut _chunk_char_idx, _) = slice.chunk_at_byte(byte_idx);
+
+    // Set up the grapheme cursor.
+    let mut gc = GraphemeCursor::new(byte_idx, slice.len_bytes(), true);
+
+    // Find the nth next grapheme cluster boundary.
+    for _ in 0..n {
+        loop {
+            match gc.next_boundary(chunk, chunk_byte_idx) {
+                Ok(None) => return slice.len_bytes(),
+                Ok(Some(n)) => {
+                    byte_idx = n;
+                    break;
+                }
+                Err(GraphemeIncomplete::NextChunk) => {
+                    chunk_byte_idx += chunk.len();
+                    let (a, _, _c, _) = slice.chunk_at_byte(chunk_byte_idx);
+                    chunk = a;
+                    // chunk_char_idx = c;
+                }
+                Err(GraphemeIncomplete::PreContext(n)) => {
+                    let ctx_chunk = slice.chunk_at_byte(n - 1).0;
+                    gc.provide_context(ctx_chunk, n - ctx_chunk.len());
+                }
+                _ => unreachable!(),
+            }
+        }
+    }
+    byte_idx
+}
+
 /// Finds the next grapheme boundary after the given char position.
 #[must_use]
 #[inline(always)]
@@ -127,6 +164,13 @@ pub fn next_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
     nth_next_grapheme_boundary(slice, char_idx, 1)
 }
 
+/// Finds the next grapheme boundary after the given byte position.
+#[must_use]
+#[inline(always)]
+pub fn next_grapheme_boundary_byte(slice: RopeSlice, byte_idx: usize) -> usize {
+    nth_next_grapheme_boundary_byte(slice, byte_idx, 1)
+}
+
 /// Returns the passed char index if it's already a grapheme boundary,
 /// or the next grapheme boundary char index if not.
 #[must_use]
@@ -151,6 +195,23 @@ pub fn ensure_grapheme_boundary_prev(slice: RopeSlice, char_idx: usize) -> usize
     }
 }
 
+/// Returns the passed byte index if it's already a grapheme boundary,
+/// or the next grapheme boundary byte index if not.
+#[must_use]
+#[inline]
+pub fn ensure_grapheme_boundary_next_byte(slice: RopeSlice, byte_idx: usize) -> usize {
+    if byte_idx == 0 {
+        byte_idx
+    } else {
+        // TODO: optimize so we're not constructing grapheme cursor twice
+        if is_grapheme_boundary_byte(slice, byte_idx) {
+            byte_idx
+        } else {
+            next_grapheme_boundary_byte(slice, byte_idx)
+        }
+    }
+}
+
 /// Returns whether the given char position is a grapheme boundary.
 #[must_use]
 pub fn is_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> bool {
@@ -179,6 +240,31 @@ pub fn is_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> bool {
     }
 }
 
+/// Returns whether the given byte position is a grapheme boundary.
+#[must_use]
+pub fn is_grapheme_boundary_byte(slice: RopeSlice, byte_idx: usize) -> bool {
+    // Bounds check
+    debug_assert!(byte_idx <= slice.len_bytes());
+
+    // Get the chunk with our byte index in it.
+    let (chunk, chunk_byte_idx, _, _) = slice.chunk_at_byte(byte_idx);
+
+    // Set up the grapheme cursor.
+    let mut gc = GraphemeCursor::new(byte_idx, slice.len_bytes(), true);
+
+    // Determine if the given position is a grapheme cluster boundary.
+    loop {
+        match gc.is_boundary(chunk, chunk_byte_idx) {
+            Ok(n) => return n,
+            Err(GraphemeIncomplete::PreContext(n)) => {
+                let (ctx_chunk, ctx_byte_start, _, _) = slice.chunk_at_byte(n - 1);
+                gc.provide_context(ctx_chunk, ctx_byte_start);
+            }
+            Err(_) => unreachable!(),
+        }
+    }
+}
+
 /// An iterator over the graphemes of a `RopeSlice`.
 #[derive(Clone)]
 pub struct RopeGraphemes<'a> {
diff --git a/helix-core/src/history.rs b/helix-core/src/history.rs
index 4b1c8d3b..bb95213c 100644
--- a/helix-core/src/history.rs
+++ b/helix-core/src/history.rs
@@ -448,8 +448,8 @@ mod test {
             change: crate::transaction::Change,
             instant: Instant,
         ) {
-            let txn = Transaction::change(&state.doc, vec![change.clone()].into_iter());
-            history.commit_revision_at_timestamp(&txn, &state, instant);
+            let txn = Transaction::change(&state.doc, vec![change].into_iter());
+            history.commit_revision_at_timestamp(&txn, state, instant);
             txn.apply(&mut state.doc);
         }
 
diff --git a/helix-core/src/increment/date_time.rs b/helix-core/src/increment/date_time.rs
new file mode 100644
index 00000000..91fa5963
--- /dev/null
+++ b/helix-core/src/increment/date_time.rs
@@ -0,0 +1,490 @@
+use chrono::{Datelike, Duration, NaiveDate, NaiveDateTime, NaiveTime, Timelike};
+use once_cell::sync::Lazy;
+use regex::Regex;
+use ropey::RopeSlice;
+
+use std::borrow::Cow;
+use std::cmp;
+
+use super::Increment;
+use crate::{Range, Tendril};
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct DateTimeIncrementor {
+    date_time: NaiveDateTime,
+    range: Range,
+    fmt: &'static str,
+    field: DateField,
+}
+
+impl DateTimeIncrementor {
+    pub fn from_range(text: RopeSlice, range: Range) -> Option<DateTimeIncrementor> {
+        let range = if range.is_empty() {
+            if range.anchor < text.len_chars() {
+                // Treat empty range as a cursor range.
+                range.put_cursor(text, range.anchor + 1, true)
+            } else {
+                // The range is empty and at the end of the text.
+                return None;
+            }
+        } else {
+            range
+        };
+
+        FORMATS.iter().find_map(|format| {
+            let from = range.from().saturating_sub(format.max_len);
+            let to = (range.from() + format.max_len).min(text.len_chars());
+
+            let (from_in_text, to_in_text) = (range.from() - from, range.to() - from);
+            let text: Cow<str> = text.slice(from..to).into();
+
+            let captures = format.regex.captures(&text)?;
+            if captures.len() - 1 != format.fields.len() {
+                return None;
+            }
+
+            let date_time = captures.get(0)?;
+            let offset = range.from() - from_in_text;
+            let range = Range::new(date_time.start() + offset, date_time.end() + offset);
+
+            let field = captures
+                .iter()
+                .skip(1)
+                .enumerate()
+                .find_map(|(i, capture)| {
+                    let capture = capture?;
+                    let capture_range = capture.range();
+
+                    if capture_range.contains(&from_in_text)
+                        && capture_range.contains(&(to_in_text - 1))
+                    {
+                        Some(format.fields[i])
+                    } else {
+                        None
+                    }
+                })?;
+
+            let has_date = format.fields.iter().any(|f| f.unit.is_date());
+            let has_time = format.fields.iter().any(|f| f.unit.is_time());
+
+            let date_time = &text[date_time.start()..date_time.end()];
+            let date_time = match (has_date, has_time) {
+                (true, true) => NaiveDateTime::parse_from_str(date_time, format.fmt).ok()?,
+                (true, false) => {
+                    let date = NaiveDate::parse_from_str(date_time, format.fmt).ok()?;
+
+                    date.and_hms(0, 0, 0)
+                }
+                (false, true) => {
+                    let time = NaiveTime::parse_from_str(date_time, format.fmt).ok()?;
+
+                    NaiveDate::from_ymd(0, 1, 1).and_time(time)
+                }
+                (false, false) => return None,
+            };
+
+            Some(DateTimeIncrementor {
+                date_time,
+                range,
+                fmt: format.fmt,
+                field,
+            })
+        })
+    }
+}
+
+impl Increment for DateTimeIncrementor {
+    fn increment(&self, amount: i64) -> (Range, Tendril) {
+        let date_time = match self.field.unit {
+            DateUnit::Years => add_years(self.date_time, amount),
+            DateUnit::Months => add_months(self.date_time, amount),
+            DateUnit::Days => add_duration(self.date_time, Duration::days(amount)),
+            DateUnit::Hours => add_duration(self.date_time, Duration::hours(amount)),
+            DateUnit::Minutes => add_duration(self.date_time, Duration::minutes(amount)),
+            DateUnit::Seconds => add_duration(self.date_time, Duration::seconds(amount)),
+            DateUnit::AmPm => toggle_am_pm(self.date_time),
+        }
+        .unwrap_or(self.date_time);
+
+        (self.range, date_time.format(self.fmt).to_string().into())
+    }
+}
+
+static FORMATS: Lazy<Vec<Format>> = Lazy::new(|| {
+    vec![
+        Format::new("%Y-%m-%d %H:%M:%S"), // 2021-11-24 07:12:23
+        Format::new("%Y/%m/%d %H:%M:%S"), // 2021/11/24 07:12:23
+        Format::new("%Y-%m-%d %H:%M"),    // 2021-11-24 07:12
+        Format::new("%Y/%m/%d %H:%M"),    // 2021/11/24 07:12
+        Format::new("%Y-%m-%d"),          // 2021-11-24
+        Format::new("%Y/%m/%d"),          // 2021/11/24
+        Format::new("%a %b %d %Y"),       // Wed Nov 24 2021
+        Format::new("%d-%b-%Y"),          // 24-Nov-2021
+        Format::new("%Y %b %d"),          // 2021 Nov 24
+        Format::new("%b %d, %Y"),         // Nov 24, 2021
+        Format::new("%-I:%M:%S %P"),      // 7:21:53 am
+        Format::new("%-I:%M %P"),         // 7:21 am
+        Format::new("%-I:%M:%S %p"),      // 7:21:53 AM
+        Format::new("%-I:%M %p"),         // 7:21 AM
+        Format::new("%H:%M:%S"),          // 23:24:23
+        Format::new("%H:%M"),             // 23:24
+    ]
+});
+
+#[derive(Debug)]
+struct Format {
+    fmt: &'static str,
+    fields: Vec<DateField>,
+    regex: Regex,
+    max_len: usize,
+}
+
+impl Format {
+    fn new(fmt: &'static str) -> Self {
+        let mut remaining = fmt;
+        let mut fields = Vec::new();
+        let mut regex = String::new();
+        let mut max_len = 0;
+
+        while let Some(i) = remaining.find('%') {
+            let after = &remaining[i + 1..];
+            let mut chars = after.chars();
+            let c = chars.next().unwrap();
+
+            let spec_len = if c == '-' {
+                1 + chars.next().unwrap().len_utf8()
+            } else {
+                c.len_utf8()
+            };
+
+            let specifier = &after[..spec_len];
+            let field = DateField::from_specifier(specifier).unwrap();
+            fields.push(field);
+            max_len += field.max_len + remaining[..i].len();
+            regex += &remaining[..i];
+            regex += &format!("({})", field.regex);
+            remaining = &after[spec_len..];
+        }
+
+        let regex = Regex::new(&regex).unwrap();
+
+        Self {
+            fmt,
+            fields,
+            regex,
+            max_len,
+        }
+    }
+}
+
+impl PartialEq for Format {
+    fn eq(&self, other: &Self) -> bool {
+        self.fmt == other.fmt && self.fields == other.fields && self.max_len == other.max_len
+    }
+}
+
+impl Eq for Format {}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+struct DateField {
+    regex: &'static str,
+    unit: DateUnit,
+    max_len: usize,
+}
+
+impl DateField {
+    fn from_specifier(specifier: &str) -> Option<Self> {
+        match specifier {
+            "Y" => Some(Self {
+                regex: r"\d{4}",
+                unit: DateUnit::Years,
+                max_len: 5,
+            }),
+            "y" => Some(Self {
+                regex: r"\d\d",
+                unit: DateUnit::Years,
+                max_len: 2,
+            }),
+            "m" => Some(Self {
+                regex: r"[0-1]\d",
+                unit: DateUnit::Months,
+                max_len: 2,
+            }),
+            "d" => Some(Self {
+                regex: r"[0-3]\d",
+                unit: DateUnit::Days,
+                max_len: 2,
+            }),
+            "-d" => Some(Self {
+                regex: r"[1-3]?\d",
+                unit: DateUnit::Days,
+                max_len: 2,
+            }),
+            "a" => Some(Self {
+                regex: r"Sun|Mon|Tue|Wed|Thu|Fri|Sat",
+                unit: DateUnit::Days,
+                max_len: 3,
+            }),
+            "A" => Some(Self {
+                regex: r"Sunday|Monday|Tuesday|Wednesday|Thursday|Friday|Saturday",
+                unit: DateUnit::Days,
+                max_len: 9,
+            }),
+            "b" | "h" => Some(Self {
+                regex: r"Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec",
+                unit: DateUnit::Months,
+                max_len: 3,
+            }),
+            "B" => Some(Self {
+                regex: r"January|February|March|April|May|June|July|August|September|October|November|December",
+                unit: DateUnit::Months,
+                max_len: 9,
+            }),
+            "H" => Some(Self {
+                regex: r"[0-2]\d",
+                unit: DateUnit::Hours,
+                max_len: 2,
+            }),
+            "M" => Some(Self {
+                regex: r"[0-5]\d",
+                unit: DateUnit::Minutes,
+                max_len: 2,
+            }),
+            "S" => Some(Self {
+                regex: r"[0-5]\d",
+                unit: DateUnit::Seconds,
+                max_len: 2,
+            }),
+            "I" => Some(Self {
+                regex: r"[0-1]\d",
+                unit: DateUnit::Hours,
+                max_len: 2,
+            }),
+            "-I" => Some(Self {
+                regex: r"1?\d",
+                unit: DateUnit::Hours,
+                max_len: 2,
+            }),
+            "P" => Some(Self {
+                regex: r"am|pm",
+                unit: DateUnit::AmPm,
+                max_len: 2,
+            }),
+            "p" => Some(Self {
+                regex: r"AM|PM",
+                unit: DateUnit::AmPm,
+                max_len: 2,
+            }),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+enum DateUnit {
+    Years,
+    Months,
+    Days,
+    Hours,
+    Minutes,
+    Seconds,
+    AmPm,
+}
+
+impl DateUnit {
+    fn is_date(self) -> bool {
+        matches!(self, DateUnit::Years | DateUnit::Months | DateUnit::Days)
+    }
+
+    fn is_time(self) -> bool {
+        matches!(
+            self,
+            DateUnit::Hours | DateUnit::Minutes | DateUnit::Seconds
+        )
+    }
+}
+
+fn ndays_in_month(year: i32, month: u32) -> u32 {
+    // The first day of the next month...
+    let (y, m) = if month == 12 {
+        (year + 1, 1)
+    } else {
+        (year, month + 1)
+    };
+    let d = NaiveDate::from_ymd(y, m, 1);
+
+    // ...is preceded by the last day of the original month.
+    d.pred().day()
+}
+
+fn add_months(date_time: NaiveDateTime, amount: i64) -> Option<NaiveDateTime> {
+    let month = (date_time.month0() as i64).checked_add(amount)?;
+    let year = date_time.year() + i32::try_from(month / 12).ok()?;
+    let year = if month.is_negative() { year - 1 } else { year };
+
+    // Normalize month
+    let month = month % 12;
+    let month = if month.is_negative() {
+        month + 12
+    } else {
+        month
+    } as u32
+        + 1;
+
+    let day = cmp::min(date_time.day(), ndays_in_month(year, month));
+
+    Some(NaiveDate::from_ymd(year, month, day).and_time(date_time.time()))
+}
+
+fn add_years(date_time: NaiveDateTime, amount: i64) -> Option<NaiveDateTime> {
+    let year = i32::try_from((date_time.year() as i64).checked_add(amount)?).ok()?;
+    let ndays = ndays_in_month(year, date_time.month());
+
+    if date_time.day() > ndays {
+        let d = NaiveDate::from_ymd(year, date_time.month(), ndays);
+        Some(d.succ().and_time(date_time.time()))
+    } else {
+        date_time.with_year(year)
+    }
+}
+
+fn add_duration(date_time: NaiveDateTime, duration: Duration) -> Option<NaiveDateTime> {
+    date_time.checked_add_signed(duration)
+}
+
+fn toggle_am_pm(date_time: NaiveDateTime) -> Option<NaiveDateTime> {
+    if date_time.hour() < 12 {
+        add_duration(date_time, Duration::hours(12))
+    } else {
+        add_duration(date_time, Duration::hours(-12))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::Rope;
+
+    #[test]
+    fn test_increment_date_times() {
+        let tests = [
+            // (original, cursor, amount, expected)
+            ("2020-02-28", 0, 1, "2021-02-28"),
+            ("2020-02-29", 0, 1, "2021-03-01"),
+            ("2020-01-31", 5, 1, "2020-02-29"),
+            ("2020-01-20", 5, 1, "2020-02-20"),
+            ("2021-01-01", 5, -1, "2020-12-01"),
+            ("2021-01-31", 5, -2, "2020-11-30"),
+            ("2020-02-28", 8, 1, "2020-02-29"),
+            ("2021-02-28", 8, 1, "2021-03-01"),
+            ("2021-02-28", 0, -1, "2020-02-28"),
+            ("2021-03-01", 0, -1, "2020-03-01"),
+            ("2020-02-29", 5, -1, "2020-01-29"),
+            ("2020-02-20", 5, -1, "2020-01-20"),
+            ("2020-02-29", 8, -1, "2020-02-28"),
+            ("2021-03-01", 8, -1, "2021-02-28"),
+            ("1980/12/21", 8, 100, "1981/03/31"),
+            ("1980/12/21", 8, -100, "1980/09/12"),
+            ("1980/12/21", 8, 1000, "1983/09/17"),
+            ("1980/12/21", 8, -1000, "1978/03/27"),
+            ("2021-11-24 07:12:23", 0, 1, "2022-11-24 07:12:23"),
+            ("2021-11-24 07:12:23", 5, 1, "2021-12-24 07:12:23"),
+            ("2021-11-24 07:12:23", 8, 1, "2021-11-25 07:12:23"),
+            ("2021-11-24 07:12:23", 11, 1, "2021-11-24 08:12:23"),
+            ("2021-11-24 07:12:23", 14, 1, "2021-11-24 07:13:23"),
+            ("2021-11-24 07:12:23", 17, 1, "2021-11-24 07:12:24"),
+            ("2021/11/24 07:12:23", 0, 1, "2022/11/24 07:12:23"),
+            ("2021/11/24 07:12:23", 5, 1, "2021/12/24 07:12:23"),
+            ("2021/11/24 07:12:23", 8, 1, "2021/11/25 07:12:23"),
+            ("2021/11/24 07:12:23", 11, 1, "2021/11/24 08:12:23"),
+            ("2021/11/24 07:12:23", 14, 1, "2021/11/24 07:13:23"),
+            ("2021/11/24 07:12:23", 17, 1, "2021/11/24 07:12:24"),
+            ("2021-11-24 07:12", 0, 1, "2022-11-24 07:12"),
+            ("2021-11-24 07:12", 5, 1, "2021-12-24 07:12"),
+            ("2021-11-24 07:12", 8, 1, "2021-11-25 07:12"),
+            ("2021-11-24 07:12", 11, 1, "2021-11-24 08:12"),
+            ("2021-11-24 07:12", 14, 1, "2021-11-24 07:13"),
+            ("2021/11/24 07:12", 0, 1, "2022/11/24 07:12"),
+            ("2021/11/24 07:12", 5, 1, "2021/12/24 07:12"),
+            ("2021/11/24 07:12", 8, 1, "2021/11/25 07:12"),
+            ("2021/11/24 07:12", 11, 1, "2021/11/24 08:12"),
+            ("2021/11/24 07:12", 14, 1, "2021/11/24 07:13"),
+            ("Wed Nov 24 2021", 0, 1, "Thu Nov 25 2021"),
+            ("Wed Nov 24 2021", 4, 1, "Fri Dec 24 2021"),
+            ("Wed Nov 24 2021", 8, 1, "Thu Nov 25 2021"),
+            ("Wed Nov 24 2021", 11, 1, "Thu Nov 24 2022"),
+            ("24-Nov-2021", 0, 1, "25-Nov-2021"),
+            ("24-Nov-2021", 3, 1, "24-Dec-2021"),
+            ("24-Nov-2021", 7, 1, "24-Nov-2022"),
+            ("2021 Nov 24", 0, 1, "2022 Nov 24"),
+            ("2021 Nov 24", 5, 1, "2021 Dec 24"),
+            ("2021 Nov 24", 9, 1, "2021 Nov 25"),
+            ("Nov 24, 2021", 0, 1, "Dec 24, 2021"),
+            ("Nov 24, 2021", 4, 1, "Nov 25, 2021"),
+            ("Nov 24, 2021", 8, 1, "Nov 24, 2022"),
+            ("7:21:53 am", 0, 1, "8:21:53 am"),
+            ("7:21:53 am", 3, 1, "7:22:53 am"),
+            ("7:21:53 am", 5, 1, "7:21:54 am"),
+            ("7:21:53 am", 8, 1, "7:21:53 pm"),
+            ("7:21:53 AM", 0, 1, "8:21:53 AM"),
+            ("7:21:53 AM", 3, 1, "7:22:53 AM"),
+            ("7:21:53 AM", 5, 1, "7:21:54 AM"),
+            ("7:21:53 AM", 8, 1, "7:21:53 PM"),
+            ("7:21 am", 0, 1, "8:21 am"),
+            ("7:21 am", 3, 1, "7:22 am"),
+            ("7:21 am", 5, 1, "7:21 pm"),
+            ("7:21 AM", 0, 1, "8:21 AM"),
+            ("7:21 AM", 3, 1, "7:22 AM"),
+            ("7:21 AM", 5, 1, "7:21 PM"),
+            ("23:24:23", 1, 1, "00:24:23"),
+            ("23:24:23", 3, 1, "23:25:23"),
+            ("23:24:23", 6, 1, "23:24:24"),
+            ("23:24", 1, 1, "00:24"),
+            ("23:24", 3, 1, "23:25"),
+        ];
+
+        for (original, cursor, amount, expected) in tests {
+            let rope = Rope::from_str(original);
+            let range = Range::new(cursor, cursor + 1);
+            assert_eq!(
+                DateTimeIncrementor::from_range(rope.slice(..), range)
+                    .unwrap()
+                    .increment(amount)
+                    .1,
+                Tendril::from(expected)
+            );
+        }
+    }
+
+    #[test]
+    fn test_invalid_date_times() {
+        let tests = [
+            "0000-00-00",
+            "1980-2-21",
+            "1980-12-1",
+            "12345",
+            "2020-02-30",
+            "1999-12-32",
+            "19-12-32",
+            "1-2-3",
+            "0000/00/00",
+            "1980/2/21",
+            "1980/12/1",
+            "12345",
+            "2020/02/30",
+            "1999/12/32",
+            "19/12/32",
+            "1/2/3",
+            "123:456:789",
+            "11:61",
+            "2021-55-12 08:12:54",
+        ];
+
+        for invalid in tests {
+            let rope = Rope::from_str(invalid);
+            let range = Range::new(0, 1);
+
+            assert_eq!(DateTimeIncrementor::from_range(rope.slice(..), range), None)
+        }
+    }
+}
diff --git a/helix-core/src/increment/mod.rs b/helix-core/src/increment/mod.rs
new file mode 100644
index 00000000..f5945774
--- /dev/null
+++ b/helix-core/src/increment/mod.rs
@@ -0,0 +1,8 @@
+pub mod date_time;
+pub mod number;
+
+use crate::{Range, Tendril};
+
+pub trait Increment {
+    fn increment(&self, amount: i64) -> (Range, Tendril);
+}
diff --git a/helix-core/src/numbers.rs b/helix-core/src/increment/number.rs
index e9f3c898..57171f67 100644
--- a/helix-core/src/numbers.rs
+++ b/helix-core/src/increment/number.rs
@@ -2,6 +2,8 @@ use std::borrow::Cow;
 
 use ropey::RopeSlice;
 
+use super::Increment;
+
 use crate::{
     textobject::{textobject_word, TextObject},
     Range, Tendril,
@@ -9,9 +11,9 @@ use crate::{
 
 #[derive(Debug, PartialEq, Eq)]
 pub struct NumberIncrementor<'a> {
-    pub range: Range,
-    pub value: i64,
-    pub radix: u32,
+    value: i64,
+    radix: u32,
+    range: Range,
 
     text: RopeSlice<'a>,
 }
@@ -71,9 +73,10 @@ impl<'a> NumberIncrementor<'a> {
             text,
         })
     }
+}
 
-    /// Add `amount` to the number and return the formatted text.
-    pub fn incremented_text(&self, amount: i64) -> Tendril {
+impl<'a> Increment for NumberIncrementor<'a> {
+    fn increment(&self, amount: i64) -> (Range, Tendril) {
         let old_text: Cow<str> = self.text.slice(self.range.from()..self.range.to()).into();
         let old_length = old_text.len();
         let new_value = self.value.wrapping_add(amount);
@@ -144,7 +147,7 @@ impl<'a> NumberIncrementor<'a> {
             }
         }
 
-        new_text.into()
+        (self.range, new_text.into())
     }
 }
 
@@ -366,8 +369,9 @@ mod test {
             assert_eq!(
                 NumberIncrementor::from_range(rope.slice(..), range)
                     .unwrap()
-                    .incremented_text(amount),
-                expected.into()
+                    .increment(amount)
+                    .1,
+                Tendril::from(expected)
             );
         }
     }
@@ -392,8 +396,9 @@ mod test {
             assert_eq!(
                 NumberIncrementor::from_range(rope.slice(..), range)
                     .unwrap()
-                    .incremented_text(amount),
-                expected.into()
+                    .increment(amount)
+                    .1,
+                Tendril::from(expected)
             );
         }
     }
@@ -419,8 +424,9 @@ mod test {
             assert_eq!(
                 NumberIncrementor::from_range(rope.slice(..), range)
                     .unwrap()
-                    .incremented_text(amount),
-                expected.into()
+                    .increment(amount)
+                    .1,
+                Tendril::from(expected)
             );
         }
     }
@@ -464,8 +470,9 @@ mod test {
             assert_eq!(
                 NumberIncrementor::from_range(rope.slice(..), range)
                     .unwrap()
-                    .incremented_text(amount),
-                expected.into()
+                    .increment(amount)
+                    .1,
+                Tendril::from(expected)
             );
         }
     }
@@ -491,8 +498,9 @@ mod test {
             assert_eq!(
                 NumberIncrementor::from_range(rope.slice(..), range)
                     .unwrap()
-                    .incremented_text(amount),
-                expected.into()
+                    .increment(amount)
+                    .1,
+                Tendril::from(expected)
             );
         }
     }
diff --git a/helix-core/src/indent.rs b/helix-core/src/indent.rs
index 8ccc0120..5d20edc1 100644
--- a/helix-core/src/indent.rs
+++ b/helix-core/src/indent.rs
@@ -1,6 +1,5 @@
 use crate::{
     chars::{char_is_line_ending, char_is_whitespace},
-    find_first_non_whitespace_char,
     syntax::{IndentQuery, LanguageConfiguration, Syntax},
     tree_sitter::Node,
     Rope, RopeSlice,
@@ -174,8 +173,7 @@ pub fn auto_detect_indent_style(document_text: &Rope) -> Option<IndentStyle> {
 
 /// To determine indentation of a newly inserted line, figure out the indentation at the last col
 /// of the previous line.
-#[allow(dead_code)]
-fn indent_level_for_line(line: RopeSlice, tab_width: usize) -> usize {
+pub fn indent_level_for_line(line: RopeSlice, tab_width: usize) -> usize {
     let mut len = 0;
     for ch in line.chars() {
         match ch {
@@ -207,10 +205,15 @@ fn get_highest_syntax_node_at_bytepos(syntax: &Syntax, pos: usize) -> Option<Nod
     Some(node)
 }
 
-fn calculate_indentation(query: &IndentQuery, node: Option<Node>, newline: bool) -> usize {
-    // NOTE: can't use contains() on query because of comparing Vec<String> and &str
-    // https://doc.rust-lang.org/std/vec/struct.Vec.html#method.contains
-
+/// Calculate the indentation at a given treesitter node.
+/// If newline is false, then any "indent" nodes on the line are ignored ("outdent" still applies).
+/// This is because the indentation is only increased starting at the second line of the node.
+fn calculate_indentation(
+    query: &IndentQuery,
+    node: Option<Node>,
+    line: usize,
+    newline: bool,
+) -> usize {
     let mut increment: isize = 0;
 
     let mut node = match node {
@@ -218,70 +221,45 @@ fn calculate_indentation(query: &IndentQuery, node: Option<Node>, newline: bool)
         None => return 0,
     };
 
-    let mut prev_start = node.start_position().row;
-
-    // if we're calculating indentation for a brand new line then the current node will become the
-    // parent node. We need to take it's indentation level into account too.
-    let node_kind = node.kind();
-    if newline && query.indent.contains(node_kind) {
-        increment += 1;
-    }
-
-    while let Some(parent) = node.parent() {
-        let parent_kind = parent.kind();
-        let start = parent.start_position().row;
-
-        // detect deeply nested indents in the same line
-        // .map(|a| {       <-- ({ is two scopes
-        //     let len = 1; <-- indents one level
-        // })               <-- }) is two scopes
-        let starts_same_line = start == prev_start;
-
-        if query.outdent.contains(node.kind()) && !starts_same_line {
-            // we outdent by skipping the rules for the current level and jumping up
-            // node = parent;
-            increment -= 1;
-            // continue;
+    let mut current_line = line;
+    let mut consider_indent = newline;
+    let mut increment_from_line: isize = 0;
+
+    loop {
+        let node_kind = node.kind();
+        let start = node.start_position().row;
+        if current_line != start {
+            // Indent/dedent by at most one per line:
+            // .map(|a| {       <-- ({ is two scopes
+            //     let len = 1; <-- indents one level
+            // })               <-- }) is two scopes
+            if consider_indent || increment_from_line < 0 {
+                increment += increment_from_line.signum();
+            }
+            increment_from_line = 0;
+            current_line = start;
+            consider_indent = true;
         }
 
-        if query.indent.contains(parent_kind) // && not_first_or_last_sibling
-            && !starts_same_line
-        {
-            // println!("is_scope {}", parent_kind);
-            prev_start = start;
-            increment += 1
+        if query.outdent.contains(node_kind) {
+            increment_from_line -= 1;
+        }
+        if query.indent.contains(node_kind) {
+            increment_from_line += 1;
         }
 
-        // if last_scope && increment > 0 && ...{ ignore }
-
-        node = parent;
+        if let Some(parent) = node.parent() {
+            node = parent;
+        } else {
+            break;
+        }
+    }
+    if consider_indent || increment_from_line < 0 {
+        increment += increment_from_line.signum();
     }
-
     increment.max(0) as usize
 }
 
-#[allow(dead_code)]
-fn suggested_indent_for_line(
-    language_config: &LanguageConfiguration,
-    syntax: Option<&Syntax>,
-    text: RopeSlice,
-    line_num: usize,
-    _tab_width: usize,
-) -> usize {
-    if let Some(start) = find_first_non_whitespace_char(text.line(line_num)) {
-        return suggested_indent_for_pos(
-            Some(language_config),
-            syntax,
-            text,
-            start + text.line_to_char(line_num),
-            false,
-        );
-    };
-
-    // if the line is blank, indent should be zero
-    0
-}
-
 // TODO: two usecases: if we are triggering this for a new, blank line:
 // - it should return 0 when mass indenting stuff
 // - it should look up the wrapper node and count it too when we press o/O
@@ -290,23 +268,20 @@ pub fn suggested_indent_for_pos(
     syntax: Option<&Syntax>,
     text: RopeSlice,
     pos: usize,
+    line: usize,
     new_line: bool,
-) -> usize {
+) -> Option<usize> {
     if let (Some(query), Some(syntax)) = (
         language_config.and_then(|config| config.indent_query()),
         syntax,
     ) {
         let byte_start = text.char_to_byte(pos);
         let node = get_highest_syntax_node_at_bytepos(syntax, byte_start);
-
-        // let config = load indentation query config from Syntax(should contain language_config)
-
         // TODO: special case for comments
         // TODO: if preserve_leading_whitespace
-        calculate_indentation(query, node, new_line)
+        Some(calculate_indentation(query, node, line, new_line))
     } else {
-        // TODO: heuristics for non-tree sitter grammars
-        0
+        None
     }
 }
 
@@ -438,7 +413,8 @@ where
 ",
         );
 
-        let doc = Rope::from(doc);
+        let doc = doc;
+        use crate::diagnostic::Severity;
         use crate::syntax::{
             Configuration, IndentationConfiguration, LanguageConfiguration, Loader,
         };
@@ -456,6 +432,8 @@ where
                 roots: vec![],
                 comment_token: None,
                 auto_format: false,
+                diagnostic_severity: Severity::Warning,
+                tree_sitter_library: None,
                 language_server: None,
                 indent: Some(IndentationConfiguration {
                     tab_width: 4,
@@ -474,20 +452,29 @@ where
 
         let language_config = loader.language_config_for_scope("source.rust").unwrap();
         let highlight_config = language_config.highlight_config(&[]).unwrap();
-        let syntax = Syntax::new(&doc, highlight_config.clone());
+        let syntax = Syntax::new(&doc, highlight_config, std::sync::Arc::new(loader));
         let text = doc.slice(..);
         let tab_width = 4;
 
         for i in 0..doc.len_lines() {
             let line = text.line(i);
-            let indent = indent_level_for_line(line, tab_width);
-            assert_eq!(
-                suggested_indent_for_line(&language_config, Some(&syntax), text, i, tab_width),
-                indent,
-                "line {}: {}",
-                i,
-                line
-            );
+            if let Some(pos) = crate::find_first_non_whitespace_char(line) {
+                let indent = indent_level_for_line(line, tab_width);
+                assert_eq!(
+                    suggested_indent_for_pos(
+                        Some(&language_config),
+                        Some(&syntax),
+                        text,
+                        text.line_to_char(i) + pos,
+                        i,
+                        false
+                    ),
+                    Some(indent),
+                    "line {}: \"{}\"",
+                    i,
+                    line
+                );
+            }
         }
     }
 }
diff --git a/helix-core/src/lib.rs b/helix-core/src/lib.rs
index 7d790406..fa8566ab 100644
--- a/helix-core/src/lib.rs
+++ b/helix-core/src/lib.rs
@@ -1,3 +1,5 @@
+pub use encoding_rs as encoding;
+
 pub mod auto_pairs;
 pub mod chars;
 pub mod comment;
@@ -5,18 +7,19 @@ pub mod diagnostic;
 pub mod diff;
 pub mod graphemes;
 pub mod history;
+pub mod increment;
 pub mod indent;
 pub mod line_ending;
 pub mod macros;
 pub mod match_brackets;
 pub mod movement;
-pub mod numbers;
 pub mod object;
 pub mod path;
 mod position;
 pub mod register;
 pub mod search;
 pub mod selection;
+pub mod shellwords;
 mod state;
 pub mod surround;
 pub mod syntax;
@@ -36,8 +39,14 @@ pub fn find_first_non_whitespace_char(line: RopeSlice) -> Option<usize> {
     line.chars().position(|ch| !ch.is_whitespace())
 }
 
-/// Find `.git` root.
-pub fn find_root(root: Option<&str>) -> Option<std::path::PathBuf> {
+/// Find project root.
+///
+/// Order of detection:
+/// * Top-most folder containing a root marker in current git repository
+/// * Git repostory root if no marker detected
+/// * Top-most folder containing a root marker if not git repository detected
+/// * Current working directory as fallback
+pub fn find_root(root: Option<&str>, root_markers: &[String]) -> Option<std::path::PathBuf> {
     let current_dir = std::env::current_dir().expect("unable to determine current directory");
 
     let root = match root {
@@ -49,16 +58,30 @@ pub fn find_root(root: Option<&str>) -> Option<std::path::PathBuf> {
                 current_dir.join(root)
             }
         }
-        None => current_dir,
+        None => current_dir.clone(),
     };
 
+    let mut top_marker = None;
     for ancestor in root.ancestors() {
-        // TODO: also use defined roots if git isn't found
+        for marker in root_markers {
+            if ancestor.join(marker).exists() {
+                top_marker = Some(ancestor);
+                break;
+            }
+        }
+        // don't go higher than repo
         if ancestor.join(".git").is_dir() {
-            return Some(ancestor.to_path_buf());
+            // Use workspace if detected from marker
+            return Some(top_marker.unwrap_or(ancestor).to_path_buf());
         }
     }
-    None
+
+    // In absence of git repo, use workspace if detected
+    if top_marker.is_some() {
+        top_marker.map(|a| a.to_path_buf())
+    } else {
+        Some(current_dir)
+    }
 }
 
 pub fn runtime_dir() -> std::path::PathBuf {
@@ -158,7 +181,7 @@ mod merge_toml_tests {
         ";
 
         let base: Value = toml::from_slice(include_bytes!("../../languages.toml"))
-            .expect("Couldn't parse built-in langauges config");
+            .expect("Couldn't parse built-in languages config");
         let user: Value = toml::from_str(USER).unwrap();
 
         let merged = merge_toml_values(base, user);
@@ -189,7 +212,10 @@ use etcetera::base_strategy::{choose_base_strategy, BaseStrategy};
 
 pub use ropey::{Rope, RopeBuilder, RopeSlice};
 
-pub use tendril::StrTendril as Tendril;
+// pub use tendril::StrTendril as Tendril;
+pub use smartstring::SmartString;
+
+pub type Tendril = SmartString<smartstring::LazyCompact>;
 
 #[doc(inline)]
 pub use {regex, tree_sitter};
diff --git a/helix-core/src/line_ending.rs b/helix-core/src/line_ending.rs
index 3541305c..8eb426e1 100644
--- a/helix-core/src/line_ending.rs
+++ b/helix-core/src/line_ending.rs
@@ -250,7 +250,7 @@ mod line_ending_tests {
         assert_eq!(get_line_ending_of_str(&text[..6]), Some(LineEnding::CR));
         assert_eq!(get_line_ending_of_str(&text[..12]), Some(LineEnding::LF));
         assert_eq!(get_line_ending_of_str(&text[..17]), Some(LineEnding::Crlf));
-        assert_eq!(get_line_ending_of_str(&text[..]), None);
+        assert_eq!(get_line_ending_of_str(text), None);
     }
 
     #[test]
diff --git a/helix-core/src/match_brackets.rs b/helix-core/src/match_brackets.rs
index cd554005..0189dedd 100644
--- a/helix-core/src/match_brackets.rs
+++ b/helix-core/src/match_brackets.rs
@@ -11,7 +11,7 @@ const PAIRS: &[(char, char)] = &[
     ('\"', '\"'),
 ];
 
-// limit matching pairs to only ( ) { } [ ] < >
+// limit matching pairs to only ( ) { } [ ] < > ' ' " "
 
 // Returns the position of the matching bracket under cursor.
 //
diff --git a/helix-core/src/movement.rs b/helix-core/src/movement.rs
index 01a8f890..47fe6827 100644
--- a/helix-core/src/movement.rs
+++ b/helix-core/src/movement.rs
@@ -307,8 +307,6 @@ fn reached_target(target: WordMotionTarget, prev_ch: char, next_ch: char) -> boo
 
 #[cfg(test)]
 mod test {
-    use std::array::{self, IntoIter};
-
     use ropey::Rope;
 
     use super::*;
@@ -360,7 +358,7 @@ mod test {
             ((Direction::Backward, 999usize), (0, 0)), // |This is a simple alphabetic line
         ];
 
-        for ((direction, amount), coordinates) in IntoIter::new(moves_and_expected_coordinates) {
+        for ((direction, amount), coordinates) in moves_and_expected_coordinates {
             range = move_horizontally(slice, range, direction, amount, Movement::Move);
             assert_eq!(coords_at_pos(slice, range.head), coordinates.into())
         }
@@ -374,7 +372,7 @@ mod test {
 
         let mut range = Range::point(position);
 
-        let moves_and_expected_coordinates = IntoIter::new([
+        let moves_and_expected_coordinates = [
             ((Direction::Forward, 11usize), (1, 1)), // Multiline\nt|ext sample\n...
             ((Direction::Backward, 1usize), (1, 0)), // Multiline\n|text sample\n...
             ((Direction::Backward, 5usize), (0, 5)), // Multi|line\ntext sample\n...
@@ -384,7 +382,7 @@ mod test {
             ((Direction::Backward, 0usize), (0, 3)), // Mul|tiline\ntext sample\n...
             ((Direction::Forward, 999usize), (5, 0)), // ...and whitespaced\n|
             ((Direction::Forward, 999usize), (5, 0)), // ...and whitespaced\n|
-        ]);
+        ];
 
         for ((direction, amount), coordinates) in moves_and_expected_coordinates {
             range = move_horizontally(slice, range, direction, amount, Movement::Move);
@@ -402,11 +400,11 @@ mod test {
         let mut range = Range::point(position);
         let original_anchor = range.anchor;
 
-        let moves = IntoIter::new([
+        let moves = [
             (Direction::Forward, 1usize),
             (Direction::Forward, 5usize),
             (Direction::Backward, 3usize),
-        ]);
+        ];
 
         for (direction, amount) in moves {
             range = move_horizontally(slice, range, direction, amount, Movement::Extend);
@@ -420,7 +418,7 @@ mod test {
         let slice = text.slice(..);
         let position = pos_at_coords(slice, (0, 0).into(), true);
         let mut range = Range::point(position);
-        let moves_and_expected_coordinates = IntoIter::new([
+        let moves_and_expected_coordinates = [
             ((Direction::Forward, 1usize), (1, 0)),
             ((Direction::Forward, 2usize), (3, 0)),
             ((Direction::Forward, 1usize), (4, 0)),
@@ -430,7 +428,7 @@ mod test {
             ((Direction::Backward, 0usize), (4, 0)),
             ((Direction::Forward, 5), (5, 0)),
             ((Direction::Forward, 999usize), (5, 0)),
-        ]);
+        ];
 
         for ((direction, amount), coordinates) in moves_and_expected_coordinates {
             range = move_vertically(slice, range, direction, amount, Movement::Move);
@@ -450,7 +448,7 @@ mod test {
             H,
             V,
         }
-        let moves_and_expected_coordinates = IntoIter::new([
+        let moves_and_expected_coordinates = [
             // Places cursor at the end of line
             ((Axis::H, Direction::Forward, 8usize), (0, 8)),
             // First descent preserves column as the target line is wider
@@ -463,7 +461,7 @@ mod test {
             ((Axis::V, Direction::Backward, 999usize), (0, 8)),
             ((Axis::V, Direction::Forward, 4usize), (4, 8)),
             ((Axis::V, Direction::Forward, 999usize), (5, 0)),
-        ]);
+        ];
 
         for ((axis, direction, amount), coordinates) in moves_and_expected_coordinates {
             range = match axis {
@@ -489,7 +487,7 @@ mod test {
             H,
             V,
         }
-        let moves_and_expected_coordinates = IntoIter::new([
+        let moves_and_expected_coordinates = [
             // Places cursor at the fourth kana.
             ((Axis::H, Direction::Forward, 4), (0, 4)),
             // Descent places cursor at the 4th character.
@@ -498,7 +496,7 @@ mod test {
             ((Axis::H, Direction::Backward, 1usize), (1, 3)),
             // Jumping back up 1 line.
             ((Axis::V, Direction::Backward, 1usize), (0, 3)),
-        ]);
+        ];
 
         for ((axis, direction, amount), coordinates) in moves_and_expected_coordinates {
             range = match axis {
@@ -530,7 +528,7 @@ mod test {
 
     #[test]
     fn test_behaviour_when_moving_to_start_of_next_words() {
-        let tests = array::IntoIter::new([
+        let tests = [
             ("Basic forward motion stops at the first space",
                 vec![(1, Range::new(0, 0), Range::new(0, 6))]),
             (" Starting from a boundary advances the anchor",
@@ -604,7 +602,7 @@ mod test {
                 vec![
                     (1, Range::new(0, 0), Range::new(0, 6)),
                 ]),
-        ]);
+        ];
 
         for (sample, scenario) in tests {
             for (count, begin, expected_end) in scenario.into_iter() {
@@ -616,7 +614,7 @@ mod test {
 
     #[test]
     fn test_behaviour_when_moving_to_start_of_next_long_words() {
-        let tests = array::IntoIter::new([
+        let tests = [
             ("Basic forward motion stops at the first space",
                 vec![(1, Range::new(0, 0), Range::new(0, 6))]),
             (" Starting from a boundary advances the anchor",
@@ -688,7 +686,7 @@ mod test {
                 vec![
                     (1, Range::new(0, 0), Range::new(0, 8)),
                 ]),
-        ]);
+        ];
 
         for (sample, scenario) in tests {
             for (count, begin, expected_end) in scenario.into_iter() {
@@ -700,7 +698,7 @@ mod test {
 
     #[test]
     fn test_behaviour_when_moving_to_start_of_previous_words() {
-        let tests = array::IntoIter::new([
+        let tests = [
             ("Basic backward motion from the middle of a word",
                 vec![(1, Range::new(3, 3), Range::new(4, 0))]),
 
@@ -773,7 +771,7 @@ mod test {
                 vec![
                     (1, Range::new(0, 6), Range::new(6, 0)),
                 ]),
-        ]);
+        ];
 
         for (sample, scenario) in tests {
             for (count, begin, expected_end) in scenario.into_iter() {
@@ -785,7 +783,7 @@ mod test {
 
     #[test]
     fn test_behaviour_when_moving_to_start_of_previous_long_words() {
-        let tests = array::IntoIter::new([
+        let tests = [
             (
                 "Basic backward motion from the middle of a word",
                 vec![(1, Range::new(3, 3), Range::new(4, 0))],
@@ -870,7 +868,7 @@ mod test {
                 vec![
                     (1, Range::new(0, 8), Range::new(8, 0)),
                 ]),
-        ]);
+        ];
 
         for (sample, scenario) in tests {
             for (count, begin, expected_end) in scenario.into_iter() {
@@ -882,7 +880,7 @@ mod test {
 
     #[test]
     fn test_behaviour_when_moving_to_end_of_next_words() {
-        let tests = array::IntoIter::new([
+        let tests = [
             ("Basic forward motion from the start of a word to the end of it",
                 vec![(1, Range::new(0, 0), Range::new(0, 5))]),
             ("Basic forward motion from the end of a word to the end of the next",
@@ -954,7 +952,7 @@ mod test {
                 vec![
                     (1, Range::new(0, 0), Range::new(0, 5)),
                 ]),
-        ]);
+        ];
 
         for (sample, scenario) in tests {
             for (count, begin, expected_end) in scenario.into_iter() {
@@ -966,7 +964,7 @@ mod test {
 
     #[test]
     fn test_behaviour_when_moving_to_end_of_previous_words() {
-        let tests = array::IntoIter::new([
+        let tests = [
             ("Basic backward motion from the middle of a word",
                 vec![(1, Range::new(9, 9), Range::new(10, 5))]),
             ("Starting from after boundary retreats the anchor",
@@ -1036,7 +1034,7 @@ mod test {
                 vec![
                     (1, Range::new(0, 10), Range::new(10, 4)),
                 ]),
-        ]);
+        ];
 
         for (sample, scenario) in tests {
             for (count, begin, expected_end) in scenario.into_iter() {
@@ -1048,7 +1046,7 @@ mod test {
 
     #[test]
     fn test_behaviour_when_moving_to_end_of_next_long_words() {
-        let tests = array::IntoIter::new([
+        let tests = [
             ("Basic forward motion from the start of a word to the end of it",
                 vec![(1, Range::new(0, 0), Range::new(0, 5))]),
             ("Basic forward motion from the end of a word to the end of the next",
@@ -1118,7 +1116,7 @@ mod test {
                 vec![
                     (1, Range::new(0, 0), Range::new(0, 7)),
                 ]),
-        ]);
+        ];
 
         for (sample, scenario) in tests {
             for (count, begin, expected_end) in scenario.into_iter() {
diff --git a/helix-core/src/object.rs b/helix-core/src/object.rs
index 717c5994..b06f4144 100644
--- a/helix-core/src/object.rs
+++ b/helix-core/src/object.rs
@@ -1,31 +1,72 @@
 use crate::{Range, RopeSlice, Selection, Syntax};
+use tree_sitter::Node;
 
-// TODO: to contract_selection we'd need to store the previous ranges before expand.
-// Maybe just contract to the first child node?
-pub fn expand_selection(syntax: &Syntax, text: RopeSlice, selection: &Selection) -> Selection {
+pub fn expand_selection(syntax: &Syntax, text: RopeSlice, selection: Selection) -> Selection {
+    select_node_impl(syntax, text, selection, |descendant, from, to| {
+        if descendant.start_byte() == from && descendant.end_byte() == to {
+            descendant.parent()
+        } else {
+            Some(descendant)
+        }
+    })
+}
+
+pub fn shrink_selection(syntax: &Syntax, text: RopeSlice, selection: Selection) -> Selection {
+    select_node_impl(syntax, text, selection, |descendant, _from, _to| {
+        descendant.child(0).or(Some(descendant))
+    })
+}
+
+pub fn select_sibling<F>(
+    syntax: &Syntax,
+    text: RopeSlice,
+    selection: Selection,
+    sibling_fn: &F,
+) -> Selection
+where
+    F: Fn(Node) -> Option<Node>,
+{
+    select_node_impl(syntax, text, selection, |descendant, _from, _to| {
+        find_sibling_recursive(descendant, sibling_fn)
+    })
+}
+
+fn find_sibling_recursive<F>(node: Node, sibling_fn: F) -> Option<Node>
+where
+    F: Fn(Node) -> Option<Node>,
+{
+    sibling_fn(node).or_else(|| {
+        node.parent()
+            .and_then(|node| find_sibling_recursive(node, sibling_fn))
+    })
+}
+
+fn select_node_impl<F>(
+    syntax: &Syntax,
+    text: RopeSlice,
+    selection: Selection,
+    select_fn: F,
+) -> Selection
+where
+    F: Fn(Node, usize, usize) -> Option<Node>,
+{
     let tree = syntax.tree();
 
-    selection.clone().transform(|range| {
+    selection.transform(|range| {
         let from = text.char_to_byte(range.from());
         let to = text.char_to_byte(range.to());
 
-        // find parent of a descendant that matches the range
-        let parent = match tree
+        let node = match tree
             .root_node()
             .descendant_for_byte_range(from, to)
-            .and_then(|node| {
-                if node.child_count() == 0 || (node.start_byte() == from && node.end_byte() == to) {
-                    node.parent()
-                } else {
-                    Some(node)
-                }
-            }) {
-            Some(parent) => parent,
+            .and_then(|node| select_fn(node, from, to))
+        {
+            Some(node) => node,
             None => return range,
         };
 
-        let from = text.byte_to_char(parent.start_byte());
-        let to = text.byte_to_char(parent.end_byte());
+        let from = text.byte_to_char(node.start_byte());
+        let to = text.byte_to_char(node.end_byte());
 
         if range.head < range.anchor {
             Range::new(to, from)
diff --git a/helix-core/src/position.rs b/helix-core/src/position.rs
index c6018ce6..93362c77 100644
--- a/helix-core/src/position.rs
+++ b/helix-core/src/position.rs
@@ -109,7 +109,10 @@ pub fn visual_coords_at_pos(text: RopeSlice, pos: usize, tab_width: usize) -> Po
 /// TODO: this should be changed to work in terms of visual row/column, not
 /// graphemes.
 pub fn pos_at_coords(text: RopeSlice, coords: Position, limit_before_line_ending: bool) -> usize {
-    let Position { row, col } = coords;
+    let Position { mut row, col } = coords;
+    if limit_before_line_ending {
+        row = row.min(text.len_lines() - 1);
+    };
     let line_start = text.line_to_char(row);
     let line_end = if limit_before_line_ending {
         line_end_char_index(&text, row)
@@ -290,5 +293,12 @@ mod test {
         assert_eq!(pos_at_coords(slice, (0, 0).into(), false), 0);
         assert_eq!(pos_at_coords(slice, (0, 1).into(), false), 1);
         assert_eq!(pos_at_coords(slice, (0, 2).into(), false), 2);
+
+        // Test out of bounds.
+        let text = Rope::new();
+        let slice = text.slice(..);
+        assert_eq!(pos_at_coords(slice, (10, 0).into(), true), 0);
+        assert_eq!(pos_at_coords(slice, (0, 10).into(), true), 0);
+        assert_eq!(pos_at_coords(slice, (10, 10).into(), true), 0);
     }
 }
diff --git a/helix-core/src/register.rs b/helix-core/src/register.rs
index b9eb497d..b39e4034 100644
--- a/helix-core/src/register.rs
+++ b/helix-core/src/register.rs
@@ -68,4 +68,8 @@ impl Registers {
     pub fn read(&self, name: char) -> Option<&[String]> {
         self.get(name).map(|reg| reg.read())
     }
+
+    pub fn inner(&self) -> &HashMap<char, Register> {
+        &self.inner
+    }
 }
diff --git a/helix-core/src/selection.rs b/helix-core/src/selection.rs
index 116a1c7c..c6eceb4b 100644
--- a/helix-core/src/selection.rs
+++ b/helix-core/src/selection.rs
@@ -7,6 +7,7 @@ use crate::{
         ensure_grapheme_boundary_next, ensure_grapheme_boundary_prev, next_grapheme_boundary,
         prev_grapheme_boundary,
     },
+    movement::Direction,
     Assoc, ChangeSet, RopeSlice,
 };
 use smallvec::{smallvec, SmallVec};
@@ -82,6 +83,13 @@ impl Range {
         std::cmp::max(self.anchor, self.head)
     }
 
+    /// Total length of the range.
+    #[inline]
+    #[must_use]
+    pub fn len(&self) -> usize {
+        self.to() - self.from()
+    }
+
     /// The (inclusive) range of lines that the range overlaps.
     #[inline]
     #[must_use]
@@ -102,6 +110,27 @@ impl Range {
         self.anchor == self.head
     }
 
+    /// `Direction::Backward` when head < anchor.
+    /// `Direction::Backward` otherwise.
+    #[inline]
+    #[must_use]
+    pub fn direction(&self) -> Direction {
+        if self.head < self.anchor {
+            Direction::Backward
+        } else {
+            Direction::Forward
+        }
+    }
+
+    // flips the direction of the selection
+    pub fn flip(&self) -> Self {
+        Self {
+            anchor: self.head,
+            head: self.anchor,
+            horiz: self.horiz,
+        }
+    }
+
     /// Check two ranges for overlap.
     #[must_use]
     pub fn overlaps(&self, other: &Self) -> bool {
@@ -111,6 +140,11 @@ impl Range {
         self.from() == other.from() || (self.to() > other.from() && other.to() > self.from())
     }
 
+    #[inline]
+    pub fn contains_range(&self, other: &Self) -> bool {
+        self.from() <= other.from() && self.to() >= other.to()
+    }
+
     pub fn contains(&self, pos: usize) -> bool {
         self.from() <= pos && pos < self.to()
     }
@@ -515,6 +549,39 @@ impl Selection {
     pub fn len(&self) -> usize {
         self.ranges.len()
     }
+
+    // returns true if self ⊇ other
+    pub fn contains(&self, other: &Selection) -> bool {
+        // can't contain other if it is larger
+        if other.len() > self.len() {
+            return false;
+        }
+
+        let (mut iter_self, mut iter_other) = (self.iter(), other.iter());
+        let (mut ele_self, mut ele_other) = (iter_self.next(), iter_other.next());
+
+        loop {
+            match (ele_self, ele_other) {
+                (Some(ra), Some(rb)) => {
+                    if !ra.contains_range(rb) {
+                        // `self` doesn't contain next element from `other`, advance `self`, we need to match all from `other`
+                        ele_self = iter_self.next();
+                    } else {
+                        // matched element from `other`, advance `other`
+                        ele_other = iter_other.next();
+                    };
+                }
+                (None, Some(_)) => {
+                    // exhausted `self`, we can't match the reminder of `other`
+                    return false;
+                }
+                (_, None) => {
+                    // no elements from `other` left to match, `self` contains `other`
+                    return true;
+                }
+            }
+        }
+    }
 }
 
 impl<'a> IntoIterator for &'a Selection {
@@ -699,16 +766,16 @@ mod test {
     fn test_contains() {
         let range = Range::new(10, 12);
 
-        assert_eq!(range.contains(9), false);
-        assert_eq!(range.contains(10), true);
-        assert_eq!(range.contains(11), true);
-        assert_eq!(range.contains(12), false);
-        assert_eq!(range.contains(13), false);
+        assert!(!range.contains(9));
+        assert!(range.contains(10));
+        assert!(range.contains(11));
+        assert!(!range.contains(12));
+        assert!(!range.contains(13));
 
         let range = Range::new(9, 6);
-        assert_eq!(range.contains(9), false);
-        assert_eq!(range.contains(7), true);
-        assert_eq!(range.contains(6), true);
+        assert!(!range.contains(9));
+        assert!(range.contains(7));
+        assert!(range.contains(6));
     }
 
     #[test]
@@ -953,4 +1020,30 @@ mod test {
             &["", "abcd", "efg", "rs", "xyz"]
         );
     }
+    #[test]
+    fn test_selection_contains() {
+        fn contains(a: Vec<(usize, usize)>, b: Vec<(usize, usize)>) -> bool {
+            let sela = Selection::new(a.iter().map(|a| Range::new(a.0, a.1)).collect(), 0);
+            let selb = Selection::new(b.iter().map(|b| Range::new(b.0, b.1)).collect(), 0);
+            sela.contains(&selb)
+        }
+
+        // exact match
+        assert!(contains(vec!((1, 1)), vec!((1, 1))));
+
+        // larger set contains smaller
+        assert!(contains(vec!((1, 1), (2, 2), (3, 3)), vec!((2, 2))));
+
+        // multiple matches
+        assert!(contains(vec!((1, 1), (2, 2)), vec!((1, 1), (2, 2))));
+
+        // smaller set can't contain bigger
+        assert!(!contains(vec!((1, 1)), vec!((1, 1), (2, 2))));
+
+        assert!(contains(
+            vec!((1, 1), (2, 4), (5, 6), (7, 9), (10, 13)),
+            vec!((3, 4), (7, 9))
+        ));
+        assert!(!contains(vec!((1, 1), (5, 6)), vec!((1, 6))));
+    }
 }
diff --git a/helix-core/src/shellwords.rs b/helix-core/src/shellwords.rs
new file mode 100644
index 00000000..13f6f3e9
--- /dev/null
+++ b/helix-core/src/shellwords.rs
@@ -0,0 +1,164 @@
+use std::borrow::Cow;
+
+/// Get the vec of escaped / quoted / doublequoted filenames from the input str
+pub fn shellwords(input: &str) -> Vec<Cow<'_, str>> {
+    enum State {
+        Normal,
+        NormalEscaped,
+        Quoted,
+        QuoteEscaped,
+        Dquoted,
+        DquoteEscaped,
+    }
+
+    use State::*;
+
+    let mut state = Normal;
+    let mut args: Vec<Cow<str>> = Vec::new();
+    let mut escaped = String::with_capacity(input.len());
+
+    let mut start = 0;
+    let mut end = 0;
+
+    for (i, c) in input.char_indices() {
+        state = match state {
+            Normal => match c {
+                '\\' => {
+                    escaped.push_str(&input[start..i]);
+                    start = i + 1;
+                    NormalEscaped
+                }
+                '"' => {
+                    end = i;
+                    Dquoted
+                }
+                '\'' => {
+                    end = i;
+                    Quoted
+                }
+                c if c.is_ascii_whitespace() => {
+                    end = i;
+                    Normal
+                }
+                _ => Normal,
+            },
+            NormalEscaped => Normal,
+            Quoted => match c {
+                '\\' => {
+                    escaped.push_str(&input[start..i]);
+                    start = i + 1;
+                    QuoteEscaped
+                }
+                '\'' => {
+                    end = i;
+                    Normal
+                }
+                _ => Quoted,
+            },
+            QuoteEscaped => Quoted,
+            Dquoted => match c {
+                '\\' => {
+                    escaped.push_str(&input[start..i]);
+                    start = i + 1;
+                    DquoteEscaped
+                }
+                '"' => {
+                    end = i;
+                    Normal
+                }
+                _ => Dquoted,
+            },
+            DquoteEscaped => Dquoted,
+        };
+
+        if i >= input.len() - 1 && end == 0 {
+            end = i + 1;
+        }
+
+        if end > 0 {
+            let esc_trim = escaped.trim();
+            let inp = &input[start..end];
+
+            if !(esc_trim.is_empty() && inp.trim().is_empty()) {
+                if esc_trim.is_empty() {
+                    args.push(inp.into());
+                } else {
+                    args.push([escaped, inp.into()].concat().into());
+                    escaped = "".to_string();
+                }
+            }
+            start = i + 1;
+            end = 0;
+        }
+    }
+    args
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_normal() {
+        let input = r#":o single_word twó wörds \three\ \"with\ escaping\\"#;
+        let result = shellwords(input);
+        let expected = vec![
+            Cow::from(":o"),
+            Cow::from("single_word"),
+            Cow::from("twó"),
+            Cow::from("wörds"),
+            Cow::from(r#"three "with escaping\"#),
+        ];
+        // TODO test is_owned and is_borrowed, once they get stabilized.
+        assert_eq!(expected, result);
+    }
+
+    #[test]
+    fn test_quoted() {
+        let quoted =
+            r#":o 'single_word' 'twó wörds' '' ' ''\three\' \"with\ escaping\\' 'quote incomplete"#;
+        let result = shellwords(quoted);
+        let expected = vec![
+            Cow::from(":o"),
+            Cow::from("single_word"),
+            Cow::from("twó wörds"),
+            Cow::from(r#"three' "with escaping\"#),
+            Cow::from("quote incomplete"),
+        ];
+        assert_eq!(expected, result);
+    }
+
+    #[test]
+    fn test_dquoted() {
+        let dquoted = r#":o "single_word" "twó wörds" "" "  ""\three\' \"with\ escaping\\" "dquote incomplete"#;
+        let result = shellwords(dquoted);
+        let expected = vec![
+            Cow::from(":o"),
+            Cow::from("single_word"),
+            Cow::from("twó wörds"),
+            Cow::from(r#"three' "with escaping\"#),
+            Cow::from("dquote incomplete"),
+        ];
+        assert_eq!(expected, result);
+    }
+
+    #[test]
+    fn test_mixed() {
+        let dquoted = r#":o single_word 'twó wörds' "\three\' \"with\ escaping\\""no space before"'and after' $#%^@ "%^&(%^" ')(*&^%''a\\\\\b' '"#;
+        let result = shellwords(dquoted);
+        let expected = vec![
+            Cow::from(":o"),
+            Cow::from("single_word"),
+            Cow::from("twó wörds"),
+            Cow::from("three' \"with escaping\\"),
+            Cow::from("no space before"),
+            Cow::from("and after"),
+            Cow::from("$#%^@"),
+            Cow::from("%^&(%^"),
+            Cow::from(")(*&^%"),
+            Cow::from(r#"a\\b"#),
+            //last ' just changes to quoted but since we dont have anything after it, it should be ignored
+        ];
+        assert_eq!(expected, result);
+    }
+}
diff --git a/helix-core/src/surround.rs b/helix-core/src/surround.rs
index b53b0a78..58eb23cf 100644
--- a/helix-core/src/surround.rs
+++ b/helix-core/src/surround.rs
@@ -172,6 +172,7 @@ mod test {
     use ropey::Rope;
     use smallvec::SmallVec;
 
+    #[allow(clippy::type_complexity)]
     fn check_find_nth_pair_pos(
         text: &str,
         cases: Vec<(usize, char, usize, Option<(usize, usize)>)>,
diff --git a/helix-core/src/syntax.rs b/helix-core/src/syntax.rs
index f1c399d2..a5c5e498 100644
--- a/helix-core/src/syntax.rs
+++ b/helix-core/src/syntax.rs
@@ -1,5 +1,6 @@
 use crate::{
     chars::char_is_line_ending,
+    diagnostic::Severity,
     regex::Regex,
     transaction::{ChangeSet, Operation},
     Rope, RopeSlice, Tendril,
@@ -7,12 +8,13 @@ use crate::{
 
 pub use helix_syntax::get_language;
 
-use arc_swap::ArcSwap;
+use arc_swap::{ArcSwap, Guard};
+use slotmap::{DefaultKey as LayerId, HopSlotMap};
 
 use std::{
     borrow::Cow,
     cell::RefCell,
-    collections::{HashMap, HashSet},
+    collections::{HashMap, HashSet, VecDeque},
     fmt,
     path::Path,
     sync::Arc,
@@ -50,7 +52,7 @@ pub struct Configuration {
 #[serde(rename_all = "kebab-case", deny_unknown_fields)]
 pub struct LanguageConfiguration {
     #[serde(rename = "name")]
-    pub language_id: String,
+    pub language_id: String, // c-sharp, rust
     pub scope: String,           // source.rust
     pub file_types: Vec<String>, // filename ends_with? <Gemfile, rb, etc>
     #[serde(default)]
@@ -63,6 +65,10 @@ pub struct LanguageConfiguration {
 
     #[serde(default)]
     pub auto_format: bool,
+    #[serde(default)]
+    pub diagnostic_severity: Severity,
+
+    pub tree_sitter_library: Option<String>, // tree-sitter library name, defaults to language_id
 
     // content_regex
     #[serde(default, skip_serializing, deserialize_with = "deserialize_regex")]
@@ -92,6 +98,7 @@ pub struct LanguageServerConfiguration {
     #[serde(default)]
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub args: Vec<String>,
+    pub language_id: Option<String>,
 }
 
 #[derive(Debug, PartialEq, Clone, Deserialize, Serialize)]
@@ -245,20 +252,22 @@ impl LanguageConfiguration {
         if highlights_query.is_empty() {
             None
         } else {
-            let language = get_language(&crate::RUNTIME_DIR, &self.language_id)
-                .map_err(|e| log::info!("{}", e))
-                .ok()?;
+            let language = get_language(
+                &crate::RUNTIME_DIR,
+                self.tree_sitter_library
+                    .as_deref()
+                    .unwrap_or(&self.language_id),
+            )
+            .map_err(|e| log::info!("{}", e))
+            .ok()?;
             let config = HighlightConfiguration::new(
                 language,
                 &highlights_query,
                 &injections_query,
                 &locals_query,
-            );
+            )
+            .unwrap(); // TODO: avoid panic
 
-            let config = match config {
-                Ok(config) => config,
-                Err(err) => panic!("{}", err),
-            }; // TODO: avoid panic
             config.configure(scopes);
             Some(Arc::new(config))
         }
@@ -308,12 +317,16 @@ impl LanguageConfiguration {
     }
 }
 
+// Expose loader as Lazy<> global since it's always static?
+
 #[derive(Debug)]
 pub struct Loader {
     // highlight_names ?
     language_configs: Vec<Arc<LanguageConfiguration>>,
     language_config_ids_by_file_type: HashMap<String, usize>, // Vec<usize>
     language_config_ids_by_shebang: HashMap<String, usize>,
+
+    scopes: ArcSwap<Vec<String>>,
 }
 
 impl Loader {
@@ -322,6 +335,7 @@ impl Loader {
             language_configs: Vec::new(),
             language_config_ids_by_file_type: HashMap::new(),
             language_config_ids_by_shebang: HashMap::new(),
+            scopes: ArcSwap::from_pointee(Vec::new()),
         };
 
         for config in config.language {
@@ -366,8 +380,9 @@ impl Loader {
 
     pub fn language_config_for_shebang(&self, source: &Rope) -> Option<Arc<LanguageConfiguration>> {
         let line = Cow::from(source.line(0));
-        static SHEBANG_REGEX: Lazy<Regex> =
-            Lazy::new(|| Regex::new(r"^#!\s*(?:\S*[/\\](?:env\s+)?)?([^\s\.\d]+)").unwrap());
+        static SHEBANG_REGEX: Lazy<Regex> = Lazy::new(|| {
+            Regex::new(r"^#!\s*(?:\S*[/\\](?:env\s+(?:\-\S+\s+)*)?)?([^\s\.\d]+)").unwrap()
+        });
         let configuration_id = SHEBANG_REGEX
             .captures(&line)
             .and_then(|cap| self.language_config_ids_by_shebang.get(&cap[1]));
@@ -406,8 +421,22 @@ impl Loader {
         }
         None
     }
-    pub fn language_configs_iter(&self) -> impl Iterator<Item = &Arc<LanguageConfiguration>> {
-        self.language_configs.iter()
+
+    pub fn set_scopes(&self, scopes: Vec<String>) {
+        self.scopes.store(Arc::new(scopes));
+
+        // Reconfigure existing grammars
+        for config in self
+            .language_configs
+            .iter()
+            .filter(|cfg| cfg.is_highlight_initialized())
+        {
+            config.reconfigure(&self.scopes());
+        }
+    }
+
+    pub fn scopes(&self) -> Guard<Arc<Vec<String>>> {
+        self.scopes.load()
     }
 }
 
@@ -416,12 +445,6 @@ pub struct TsParser {
     cursors: Vec<QueryCursor>,
 }
 
-impl fmt::Debug for TsParser {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("TsParser").finish()
-    }
-}
-
 // could also just use a pool, or a single instance?
 thread_local! {
     pub static PARSER: RefCell<TsParser> = RefCell::new(TsParser {
@@ -432,9 +455,9 @@ thread_local! {
 
 #[derive(Debug)]
 pub struct Syntax {
-    config: Arc<HighlightConfiguration>,
-
-    root_layer: LanguageLayer,
+    layers: HopSlotMap<LayerId, LanguageLayer>,
+    root: LayerId,
+    loader: Arc<Loader>,
 }
 
 fn byte_range_to_str(range: std::ops::Range<usize>, source: RopeSlice) -> Cow<str> {
@@ -444,38 +467,34 @@ fn byte_range_to_str(range: std::ops::Range<usize>, source: RopeSlice) -> Cow<st
 }
 
 impl Syntax {
-    // buffer, grammar, config, grammars, sync_timeout?
-    pub fn new(
-        /*language: Lang,*/ source: &Rope,
-        config: Arc<HighlightConfiguration>,
-    ) -> Self {
-        let root_layer = LanguageLayer { tree: None };
+    pub fn new(source: &Rope, config: Arc<HighlightConfiguration>, loader: Arc<Loader>) -> Self {
+        let root_layer = LanguageLayer {
+            tree: None,
+            config,
+            depth: 0,
+            ranges: vec![Range {
+                start_byte: 0,
+                end_byte: usize::MAX,
+                start_point: Point::new(0, 0),
+                end_point: Point::new(usize::MAX, usize::MAX),
+            }],
+        };
 
-        // track markers of injections
         // track scope_descriptor: a Vec of scopes for item in tree
 
+        let mut layers = HopSlotMap::default();
+        let root = layers.insert(root_layer);
+
         let mut syntax = Self {
-            // grammar,
-            config,
-            root_layer,
+            root,
+            layers,
+            loader,
         };
 
-        // update root layer
-        PARSER.with(|ts_parser| {
-            // TODO: handle the returned `Result` properly.
-            let _ = syntax.root_layer.parse(
-                &mut ts_parser.borrow_mut(),
-                &syntax.config,
-                source,
-                0,
-                vec![Range {
-                    start_byte: 0,
-                    end_byte: usize::MAX,
-                    start_point: Point::new(0, 0),
-                    end_point: Point::new(usize::MAX, usize::MAX),
-                }],
-            );
-        });
+        syntax
+            .update(source, source, &ChangeSet::new(source))
+            .unwrap();
+
         syntax
     }
 
@@ -485,32 +504,255 @@ impl Syntax {
         source: &Rope,
         changeset: &ChangeSet,
     ) -> Result<(), Error> {
+        let mut queue = VecDeque::new();
+        queue.push_back(self.root);
+
+        let scopes = self.loader.scopes.load();
+        let injection_callback = |language: &str| {
+            self.loader
+                .language_configuration_for_injection_string(language)
+                .and_then(|language_config| language_config.highlight_config(&scopes))
+        };
+
+        // Convert the changeset into tree sitter edits.
+        let edits = generate_edits(old_source, changeset);
+
+        // Use the edits to update all layers markers
+        if !edits.is_empty() {
+            fn point_add(a: Point, b: Point) -> Point {
+                if b.row > 0 {
+                    Point::new(a.row.saturating_add(b.row), b.column)
+                } else {
+                    Point::new(0, a.column.saturating_add(b.column))
+                }
+            }
+            fn point_sub(a: Point, b: Point) -> Point {
+                if a.row > b.row {
+                    Point::new(a.row.saturating_sub(b.row), a.column)
+                } else {
+                    Point::new(0, a.column.saturating_sub(b.column))
+                }
+            }
+
+            for layer in &mut self.layers.values_mut() {
+                // The root layer always covers the whole range (0..usize::MAX)
+                if layer.depth == 0 {
+                    continue;
+                }
+
+                for range in &mut layer.ranges {
+                    // Roughly based on https://github.com/tree-sitter/tree-sitter/blob/ddeaa0c7f534268b35b4f6cb39b52df082754413/lib/src/subtree.c#L691-L720
+                    for edit in edits.iter().rev() {
+                        let is_pure_insertion = edit.old_end_byte == edit.start_byte;
+
+                        // if edit is after range, skip
+                        if edit.start_byte > range.end_byte {
+                            // TODO: || (is_noop && edit.start_byte == range.end_byte)
+                            continue;
+                        }
+
+                        // if edit is before range, shift entire range by len
+                        if edit.old_end_byte < range.start_byte {
+                            range.start_byte =
+                                edit.new_end_byte + (range.start_byte - edit.old_end_byte);
+                            range.start_point = point_add(
+                                edit.new_end_position,
+                                point_sub(range.start_point, edit.old_end_position),
+                            );
+
+                            range.end_byte = edit
+                                .new_end_byte
+                                .saturating_add(range.end_byte - edit.old_end_byte);
+                            range.end_point = point_add(
+                                edit.new_end_position,
+                                point_sub(range.end_point, edit.old_end_position),
+                            );
+                        }
+                        // if the edit starts in the space before and extends into the range
+                        else if edit.start_byte < range.start_byte {
+                            range.start_byte = edit.new_end_byte;
+                            range.start_point = edit.new_end_position;
+
+                            range.end_byte = range
+                                .end_byte
+                                .saturating_sub(edit.old_end_byte)
+                                .saturating_add(edit.new_end_byte);
+                            range.end_point = point_add(
+                                edit.new_end_position,
+                                point_sub(range.end_point, edit.old_end_position),
+                            );
+                        }
+                        // If the edit is an insertion at the start of the tree, shift
+                        else if edit.start_byte == range.start_byte && is_pure_insertion {
+                            range.start_byte = edit.new_end_byte;
+                            range.start_point = edit.new_end_position;
+                        } else {
+                            range.end_byte = range
+                                .end_byte
+                                .saturating_sub(edit.old_end_byte)
+                                .saturating_add(edit.new_end_byte);
+                            range.end_point = point_add(
+                                edit.new_end_position,
+                                point_sub(range.end_point, edit.old_end_position),
+                            );
+                        }
+                    }
+                }
+            }
+        }
+
         PARSER.with(|ts_parser| {
-            self.root_layer.update(
-                &mut ts_parser.borrow_mut(),
-                &self.config,
-                old_source,
-                source,
-                changeset,
-            )
-        })
+            let ts_parser = &mut ts_parser.borrow_mut();
+            let mut cursor = ts_parser.cursors.pop().unwrap_or_else(QueryCursor::new);
+            // TODO: might need to set cursor range
+            cursor.set_byte_range(0..usize::MAX);
 
-        // TODO: deal with injections and update them too
-    }
+            let source_slice = source.slice(..);
 
-    // fn buffer_changed -> call layer.update(range, new_text) on root layer and then all marker layers
+            let mut touched = HashSet::new();
 
-    // call this on transaction.apply() -> buffer_changed(changes)
-    //
-    // fn parse(language, old_tree, ranges)
-    //
-    pub fn tree(&self) -> &Tree {
-        self.root_layer.tree()
+            // TODO: we should be able to avoid editing & parsing layers with ranges earlier in the document before the edit
+
+            while let Some(layer_id) = queue.pop_front() {
+                // Mark the layer as touched
+                touched.insert(layer_id);
+
+                let layer = &mut self.layers[layer_id];
+
+                // If a tree already exists, notify it of changes.
+                if let Some(tree) = &mut layer.tree {
+                    for edit in edits.iter().rev() {
+                        // Apply the edits in reverse.
+                        // If we applied them in order then edit 1 would disrupt the positioning of edit 2.
+                        tree.edit(edit);
+                    }
+                }
+
+                // Re-parse the tree.
+                layer.parse(&mut ts_parser.parser, source)?;
+
+                // Switch to an immutable borrow.
+                let layer = &self.layers[layer_id];
+
+                // Process injections.
+                let matches = cursor.matches(
+                    &layer.config.injections_query,
+                    layer.tree().root_node(),
+                    RopeProvider(source_slice),
+                );
+                let mut injections = Vec::new();
+                for mat in matches {
+                    let (language_name, content_node, include_children) = injection_for_match(
+                        &layer.config,
+                        &layer.config.injections_query,
+                        &mat,
+                        source_slice,
+                    );
+
+                    // Explicitly remove this match so that none of its other captures will remain
+                    // in the stream of captures.
+                    mat.remove();
+
+                    // If a language is found with the given name, then add a new language layer
+                    // to the highlighted document.
+                    if let (Some(language_name), Some(content_node)) = (language_name, content_node)
+                    {
+                        if let Some(config) = (injection_callback)(&language_name) {
+                            let ranges =
+                                intersect_ranges(&layer.ranges, &[content_node], include_children);
+
+                            if !ranges.is_empty() {
+                                injections.push((config, ranges));
+                            }
+                        }
+                    }
+                }
+
+                // Process combined injections.
+                if let Some(combined_injections_query) = &layer.config.combined_injections_query {
+                    let mut injections_by_pattern_index =
+                        vec![(None, Vec::new(), false); combined_injections_query.pattern_count()];
+                    let matches = cursor.matches(
+                        combined_injections_query,
+                        layer.tree().root_node(),
+                        RopeProvider(source_slice),
+                    );
+                    for mat in matches {
+                        let entry = &mut injections_by_pattern_index[mat.pattern_index];
+                        let (language_name, content_node, include_children) = injection_for_match(
+                            &layer.config,
+                            combined_injections_query,
+                            &mat,
+                            source_slice,
+                        );
+                        if language_name.is_some() {
+                            entry.0 = language_name;
+                        }
+                        if let Some(content_node) = content_node {
+                            entry.1.push(content_node);
+                        }
+                        entry.2 = include_children;
+                    }
+                    for (lang_name, content_nodes, includes_children) in injections_by_pattern_index
+                    {
+                        if let (Some(lang_name), false) = (lang_name, content_nodes.is_empty()) {
+                            if let Some(config) = (injection_callback)(&lang_name) {
+                                let ranges = intersect_ranges(
+                                    &layer.ranges,
+                                    &content_nodes,
+                                    includes_children,
+                                );
+                                if !ranges.is_empty() {
+                                    injections.push((config, ranges));
+                                }
+                            }
+                        }
+                    }
+                }
+
+                let depth = layer.depth + 1;
+                // TODO: can't inline this since matches borrows self.layers
+                for (config, ranges) in injections {
+                    // Find an existing layer
+                    let layer = self
+                        .layers
+                        .iter_mut()
+                        .find(|(_, layer)| {
+                            layer.depth == depth && // TODO: track parent id instead
+                            layer.config.language == config.language && layer.ranges == ranges
+                        })
+                        .map(|(id, _layer)| id);
+
+                    // ...or insert a new one.
+                    let layer_id = layer.unwrap_or_else(|| {
+                        self.layers.insert(LanguageLayer {
+                            tree: None,
+                            config,
+                            depth,
+                            ranges,
+                        })
+                    });
+
+                    queue.push_back(layer_id);
+                }
+
+                // TODO: pre-process local scopes at this time, rather than highlight?
+                // would solve problems with locals not working across boundaries
+            }
+
+            // Return the cursor back in the pool.
+            ts_parser.cursors.push(cursor);
+
+            // Remove all untouched layers
+            self.layers.retain(|id, _| touched.contains(&id));
+
+            Ok(())
+        })
     }
-    //
-    // <!--update_for_injection(grammar)-->
 
-    // Highlighting
+    pub fn tree(&self) -> &Tree {
+        self.layers[self.root].tree()
+    }
 
     /// Iterate over the highlighted regions for a given slice of source code.
     pub fn highlight_iter<'a>(
@@ -518,65 +760,76 @@ impl Syntax {
         source: RopeSlice<'a>,
         range: Option<std::ops::Range<usize>>,
         cancellation_flag: Option<&'a AtomicUsize>,
-        injection_callback: impl FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
     ) -> impl Iterator<Item = Result<HighlightEvent, Error>> + 'a {
-        // The `captures` iterator borrows the `Tree` and the `QueryCursor`, which
-        // prevents them from being moved. But both of these values are really just
-        // pointers, so it's actually ok to move them.
-
-        // reuse a cursor from the pool if possible
-        let mut cursor = PARSER.with(|ts_parser| {
-            let highlighter = &mut ts_parser.borrow_mut();
-            highlighter.cursors.pop().unwrap_or_else(QueryCursor::new)
+        let mut layers = self
+            .layers
+            .iter()
+            .filter_map(|(_, layer)| {
+                // TODO: if range doesn't overlap layer range, skip it
+
+                // Reuse a cursor from the pool if available.
+                let mut cursor = PARSER.with(|ts_parser| {
+                    let highlighter = &mut ts_parser.borrow_mut();
+                    highlighter.cursors.pop().unwrap_or_else(QueryCursor::new)
+                });
+
+                // The `captures` iterator borrows the `Tree` and the `QueryCursor`, which
+                // prevents them from being moved. But both of these values are really just
+                // pointers, so it's actually ok to move them.
+                let cursor_ref =
+                    unsafe { mem::transmute::<_, &'static mut QueryCursor>(&mut cursor) };
+
+                // if reusing cursors & no range this resets to whole range
+                cursor_ref.set_byte_range(range.clone().unwrap_or(0..usize::MAX));
+
+                let mut captures = cursor_ref
+                    .captures(
+                        &layer.config.query,
+                        layer.tree().root_node(),
+                        RopeProvider(source),
+                    )
+                    .peekable();
+
+                // If there's no captures, skip the layer
+                captures.peek()?;
+
+                Some(HighlightIterLayer {
+                    highlight_end_stack: Vec::new(),
+                    scope_stack: vec![LocalScope {
+                        inherits: false,
+                        range: 0..usize::MAX,
+                        local_defs: Vec::new(),
+                    }],
+                    cursor,
+                    _tree: None,
+                    captures,
+                    config: layer.config.as_ref(), // TODO: just reuse `layer`
+                    depth: layer.depth,            // TODO: just reuse `layer`
+                    ranges: &layer.ranges,         // TODO: temp
+                })
+            })
+            .collect::<Vec<_>>();
+
+        // HAXX: arrange layers by byte range, with deeper layers positioned first
+        layers.sort_by_key(|layer| {
+            (
+                layer.ranges.first().cloned(),
+                std::cmp::Reverse(layer.depth),
+            )
         });
-        let tree_ref = self.tree();
-        let cursor_ref = unsafe { mem::transmute::<_, &'static mut QueryCursor>(&mut cursor) };
-        let query_ref = &self.config.query;
-        let config_ref = self.config.as_ref();
-
-        // if reusing cursors & no range this resets to whole range
-        cursor_ref.set_byte_range(range.clone().unwrap_or(0..usize::MAX));
-
-        let captures = cursor_ref
-            .captures(query_ref, tree_ref.root_node(), RopeProvider(source))
-            .peekable();
-
-        // manually craft the root layer based on the existing tree
-        let layer = HighlightIterLayer {
-            highlight_end_stack: Vec::new(),
-            scope_stack: vec![LocalScope {
-                inherits: false,
-                range: 0..usize::MAX,
-                local_defs: Vec::new(),
-            }],
-            cursor,
-            depth: 0,
-            _tree: None,
-            captures,
-            config: config_ref,
-            ranges: vec![Range {
-                start_byte: 0,
-                end_byte: usize::MAX,
-                start_point: Point::new(0, 0),
-                end_point: Point::new(usize::MAX, usize::MAX),
-            }],
-        };
 
         let mut result = HighlightIter {
             source,
-            byte_offset: range.map_or(0, |r| r.start), // TODO: simplify
-            injection_callback,
+            byte_offset: range.map_or(0, |r| r.start),
             cancellation_flag,
             iter_count: 0,
-            layers: vec![layer],
+            layers,
             next_event: None,
             last_highlight_range: None,
         };
         result.sort_layers();
         result
     }
-    // on_tokenize
-    // on_change_highlighting
 
     // Commenting
     // comment_strings_for_pos
@@ -588,246 +841,157 @@ impl Syntax {
     // indent_level_for_line
 
     // TODO: Folding
-
-    // Syntax APIs
-    // get_syntax_node_containing_range ->
-    // ...
-    // get_syntax_node_at_pos
-    // buffer_range_for_scope_at_pos
 }
 
 #[derive(Debug)]
 pub struct LanguageLayer {
     // mode
     // grammar
-    // depth
+    pub config: Arc<HighlightConfiguration>,
     pub(crate) tree: Option<Tree>,
+    pub ranges: Vec<Range>,
+    pub depth: usize,
 }
 
 impl LanguageLayer {
-    // pub fn new() -> Self {
-    //     Self { tree: None }
-    // }
-
     pub fn tree(&self) -> &Tree {
         // TODO: no unwrap
         self.tree.as_ref().unwrap()
     }
 
-    fn parse(
-        &mut self,
-        ts_parser: &mut TsParser,
-        config: &HighlightConfiguration,
-        source: &Rope,
-        _depth: usize,
-        ranges: Vec<Range>,
-    ) -> Result<(), Error> {
-        if ts_parser.parser.set_included_ranges(&ranges).is_ok() {
-            ts_parser
-                .parser
-                .set_language(config.language)
-                .map_err(|_| Error::InvalidLanguage)?;
-
-            // unsafe { syntax.parser.set_cancellation_flag(cancellation_flag) };
-            let tree = ts_parser
-                .parser
-                .parse_with(
-                    &mut |byte, _| {
-                        if byte <= source.len_bytes() {
-                            let (chunk, start_byte, _, _) = source.chunk_at_byte(byte);
-                            chunk[byte - start_byte..].as_bytes()
-                        } else {
-                            // out of range
-                            &[]
-                        }
-                    },
-                    self.tree.as_ref(),
-                )
-                .ok_or(Error::Cancelled)?;
+    fn parse(&mut self, parser: &mut Parser, source: &Rope) -> Result<(), Error> {
+        parser.set_included_ranges(&self.ranges).unwrap();
 
-            self.tree = Some(tree)
-        }
+        parser
+            .set_language(self.config.language)
+            .map_err(|_| Error::InvalidLanguage)?;
+
+        // unsafe { syntax.parser.set_cancellation_flag(cancellation_flag) };
+        let tree = parser
+            .parse_with(
+                &mut |byte, _| {
+                    if byte <= source.len_bytes() {
+                        let (chunk, start_byte, _, _) = source.chunk_at_byte(byte);
+                        chunk[byte - start_byte..].as_bytes()
+                    } else {
+                        // out of range
+                        &[]
+                    }
+                },
+                self.tree.as_ref(),
+            )
+            .ok_or(Error::Cancelled)?;
+        // unsafe { ts_parser.parser.set_cancellation_flag(None) };
+        self.tree = Some(tree);
         Ok(())
     }
+}
 
-    pub(crate) fn generate_edits(
-        old_text: RopeSlice,
-        changeset: &ChangeSet,
-    ) -> Vec<tree_sitter::InputEdit> {
-        use Operation::*;
-        let mut old_pos = 0;
+pub(crate) fn generate_edits(
+    old_text: &Rope,
+    changeset: &ChangeSet,
+) -> Vec<tree_sitter::InputEdit> {
+    use Operation::*;
+    let mut old_pos = 0;
 
-        let mut edits = Vec::new();
+    let mut edits = Vec::new();
 
-        let mut iter = changeset.changes.iter().peekable();
+    if changeset.changes.is_empty() {
+        return edits;
+    }
 
-        // TODO; this is a lot easier with Change instead of Operation.
+    let mut iter = changeset.changes.iter().peekable();
 
-        fn point_at_pos(text: RopeSlice, pos: usize) -> (usize, Point) {
-            let byte = text.char_to_byte(pos); // <- attempted to index past end
-            let line = text.char_to_line(pos);
-            let line_start_byte = text.line_to_byte(line);
-            let col = byte - line_start_byte;
+    // TODO; this is a lot easier with Change instead of Operation.
 
-            (byte, Point::new(line, col))
-        }
+    fn point_at_pos(text: &Rope, pos: usize) -> (usize, Point) {
+        let byte = text.char_to_byte(pos); // <- attempted to index past end
+        let line = text.char_to_line(pos);
+        let line_start_byte = text.line_to_byte(line);
+        let col = byte - line_start_byte;
 
-        fn traverse(point: Point, text: &Tendril) -> Point {
-            let Point {
-                mut row,
-                mut column,
-            } = point;
-
-            // TODO: there should be a better way here.
-            let mut chars = text.chars().peekable();
-            while let Some(ch) = chars.next() {
-                if char_is_line_ending(ch) && !(ch == '\r' && chars.peek() == Some(&'\n')) {
-                    row += 1;
-                    column = 0;
-                } else {
-                    column += 1;
-                }
+        (byte, Point::new(line, col))
+    }
+
+    fn traverse(point: Point, text: &Tendril) -> Point {
+        let Point {
+            mut row,
+            mut column,
+        } = point;
+
+        // TODO: there should be a better way here.
+        let mut chars = text.chars().peekable();
+        while let Some(ch) = chars.next() {
+            if char_is_line_ending(ch) && !(ch == '\r' && chars.peek() == Some(&'\n')) {
+                row += 1;
+                column = 0;
+            } else {
+                column += 1;
             }
-            Point { row, column }
         }
+        Point { row, column }
+    }
 
-        while let Some(change) = iter.next() {
-            let len = match change {
-                Delete(i) | Retain(i) => *i,
-                Insert(_) => 0,
-            };
-            let mut old_end = old_pos + len;
+    while let Some(change) = iter.next() {
+        let len = match change {
+            Delete(i) | Retain(i) => *i,
+            Insert(_) => 0,
+        };
+        let mut old_end = old_pos + len;
+
+        match change {
+            Retain(_) => {}
+            Delete(_) => {
+                let (start_byte, start_position) = point_at_pos(old_text, old_pos);
+                let (old_end_byte, old_end_position) = point_at_pos(old_text, old_end);
+
+                // deletion
+                edits.push(tree_sitter::InputEdit {
+                    start_byte,                       // old_pos to byte
+                    old_end_byte,                     // old_end to byte
+                    new_end_byte: start_byte,         // old_pos to byte
+                    start_position,                   // old pos to coords
+                    old_end_position,                 // old_end to coords
+                    new_end_position: start_position, // old pos to coords
+                });
+            }
+            Insert(s) => {
+                let (start_byte, start_position) = point_at_pos(old_text, old_pos);
 
-            match change {
-                Retain(_) => {}
-                Delete(_) => {
-                    let (start_byte, start_position) = point_at_pos(old_text, old_pos);
+                // a subsequent delete means a replace, consume it
+                if let Some(Delete(len)) = iter.peek() {
+                    old_end = old_pos + len;
                     let (old_end_byte, old_end_position) = point_at_pos(old_text, old_end);
 
-                    // TODO: Position also needs to be byte based...
-                    // let byte = char_to_byte(old_pos)
-                    // let line = char_to_line(old_pos)
-                    // let line_start_byte = line_to_byte()
-                    // Position::new(line, line_start_byte - byte)
+                    iter.next();
 
-                    // deletion
+                    // replacement
                     edits.push(tree_sitter::InputEdit {
-                        start_byte,                       // old_pos to byte
-                        old_end_byte,                     // old_end to byte
-                        new_end_byte: start_byte,         // old_pos to byte
-                        start_position,                   // old pos to coords
-                        old_end_position,                 // old_end to coords
-                        new_end_position: start_position, // old pos to coords
+                        start_byte,                                    // old_pos to byte
+                        old_end_byte,                                  // old_end to byte
+                        new_end_byte: start_byte + s.len(),            // old_pos to byte + s.len()
+                        start_position,                                // old pos to coords
+                        old_end_position,                              // old_end to coords
+                        new_end_position: traverse(start_position, s), // old pos + chars, newlines matter too (iter over)
+                    });
+                } else {
+                    // insert
+                    edits.push(tree_sitter::InputEdit {
+                        start_byte,                                    // old_pos to byte
+                        old_end_byte: start_byte,                      // same
+                        new_end_byte: start_byte + s.len(),            // old_pos + s.len()
+                        start_position,                                // old pos to coords
+                        old_end_position: start_position,              // same
+                        new_end_position: traverse(start_position, s), // old pos + chars, newlines matter too (iter over)
                     });
-                }
-                Insert(s) => {
-                    let (start_byte, start_position) = point_at_pos(old_text, old_pos);
-
-                    // a subsequent delete means a replace, consume it
-                    if let Some(Delete(len)) = iter.peek() {
-                        old_end = old_pos + len;
-                        let (old_end_byte, old_end_position) = point_at_pos(old_text, old_end);
-
-                        iter.next();
-
-                        // replacement
-                        edits.push(tree_sitter::InputEdit {
-                            start_byte,                                    // old_pos to byte
-                            old_end_byte,                                  // old_end to byte
-                            new_end_byte: start_byte + s.len(), // old_pos to byte + s.len()
-                            start_position,                     // old pos to coords
-                            old_end_position,                   // old_end to coords
-                            new_end_position: traverse(start_position, s), // old pos + chars, newlines matter too (iter over)
-                        });
-                    } else {
-                        // insert
-                        edits.push(tree_sitter::InputEdit {
-                            start_byte,                                    // old_pos to byte
-                            old_end_byte: start_byte,                      // same
-                            new_end_byte: start_byte + s.len(),            // old_pos + s.len()
-                            start_position,                                // old pos to coords
-                            old_end_position: start_position,              // same
-                            new_end_position: traverse(start_position, s), // old pos + chars, newlines matter too (iter over)
-                        });
-                    }
                 }
             }
-            old_pos = old_end;
         }
-        edits
-    }
-
-    fn update(
-        &mut self,
-        ts_parser: &mut TsParser,
-        config: &HighlightConfiguration,
-        old_source: &Rope,
-        source: &Rope,
-        changeset: &ChangeSet,
-    ) -> Result<(), Error> {
-        if changeset.is_empty() {
-            return Ok(());
-        }
-
-        let edits = Self::generate_edits(old_source.slice(..), changeset);
-
-        // Notify the tree about all the changes
-        for edit in edits.iter().rev() {
-            // apply the edits in reverse. If we applied them in order then edit 1 would disrupt
-            // the positioning of edit 2
-            self.tree.as_mut().unwrap().edit(edit);
-        }
-
-        self.parse(
-            ts_parser,
-            config,
-            source,
-            0,
-            // TODO: what to do about this range on update
-            vec![Range {
-                start_byte: 0,
-                end_byte: usize::MAX,
-                start_point: Point::new(0, 0),
-                end_point: Point::new(usize::MAX, usize::MAX),
-            }],
-        )
+        old_pos = old_end;
     }
-
-    // fn highlight_iter() -> same as Mode but for this layer. Mode composits these
-    // fn buffer_changed
-    // fn update(range)
-    // fn update_injections()
+    edits
 }
 
-// -- refactored from tree-sitter-highlight to be able to retain state
-// TODO: add seek() to iter
-
-// problem: any time a layer is updated it must update it's injections on the parent (potentially
-// removing some from use)
-// can't modify to vec and exist in it at the same time since that would violate borrows
-// maybe we can do with an arena
-// maybe just caching on the top layer and nevermind the injections for now?
-//
-// Grammar {
-//  layers: Vec<Box<Layer>> to prevent memory moves when vec is modified
-// }
-// injections tracked by marker:
-// if marker areas match it's fine and update
-// if not found add new layer
-// if length 0 then area got removed, clean up the layer
-//
-// layer update:
-// if range.len = 0 then remove the layer
-// for change in changes { tree.edit(change) }
-// tree = parser.parse(.., tree, ..)
-// calculate affected range and update injections
-// injection update:
-// look for existing injections
-// if present, range = (first injection start, last injection end)
-//
-// For now cheat and just throw out non-root layers if they exist. This should still improve
-// parsing in majority of cases.
-
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::{iter, mem, ops, str, usize};
 use tree_sitter::{
@@ -864,8 +1028,8 @@ pub enum HighlightEvent {
 pub struct HighlightConfiguration {
     pub language: Grammar,
     pub query: Query,
+    injections_query: Query,
     combined_injections_query: Option<Query>,
-    locals_pattern_index: usize,
     highlights_pattern_index: usize,
     highlight_indices: ArcSwap<Vec<Option<Highlight>>>,
     non_local_variable_patterns: Vec<bool>,
@@ -892,13 +1056,9 @@ struct LocalScope<'a> {
 }
 
 #[derive(Debug)]
-struct HighlightIter<'a, F>
-where
-    F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
-{
+struct HighlightIter<'a> {
     source: RopeSlice<'a>,
     byte_offset: usize,
-    injection_callback: F,
     cancellation_flag: Option<&'a AtomicUsize>,
     layers: Vec<HighlightIterLayer<'a>>,
     iter_count: usize,
@@ -938,8 +1098,8 @@ struct HighlightIterLayer<'a> {
     config: &'a HighlightConfiguration,
     highlight_end_stack: Vec<usize>,
     scope_stack: Vec<LocalScope<'a>>,
-    ranges: Vec<Range>,
     depth: usize,
+    ranges: &'a [Range],
 }
 
 impl<'a> fmt::Debug for HighlightIterLayer<'a> {
@@ -971,38 +1131,32 @@ impl HighlightConfiguration {
     ) -> Result<Self, QueryError> {
         // Concatenate the query strings, keeping track of the start offset of each section.
         let mut query_source = String::new();
-        query_source.push_str(injection_query);
-        let locals_query_offset = query_source.len();
         query_source.push_str(locals_query);
         let highlights_query_offset = query_source.len();
         query_source.push_str(highlights_query);
 
         // Construct a single query by concatenating the three query strings, but record the
         // range of pattern indices that belong to each individual string.
-        let mut query = Query::new(language, &query_source)?;
-        let mut locals_pattern_index = 0;
+        let query = Query::new(language, &query_source)?;
         let mut highlights_pattern_index = 0;
         for i in 0..(query.pattern_count()) {
             let pattern_offset = query.start_byte_for_pattern(i);
             if pattern_offset < highlights_query_offset {
-                if pattern_offset < highlights_query_offset {
-                    highlights_pattern_index += 1;
-                }
-                if pattern_offset < locals_query_offset {
-                    locals_pattern_index += 1;
-                }
+                highlights_pattern_index += 1;
             }
         }
 
+        let mut injections_query = Query::new(language, injection_query)?;
+
         // Construct a separate query just for dealing with the 'combined injections'.
         // Disable the combined injection patterns in the main query.
         let mut combined_injections_query = Query::new(language, injection_query)?;
         let mut has_combined_queries = false;
-        for pattern_index in 0..locals_pattern_index {
-            let settings = query.property_settings(pattern_index);
+        for pattern_index in 0..injections_query.pattern_count() {
+            let settings = injections_query.property_settings(pattern_index);
             if settings.iter().any(|s| &*s.key == "injection.combined") {
                 has_combined_queries = true;
-                query.disable_pattern(pattern_index);
+                injections_query.disable_pattern(pattern_index);
             } else {
                 combined_injections_query.disable_pattern(pattern_index);
             }
@@ -1034,8 +1188,6 @@ impl HighlightConfiguration {
         for (i, name) in query.capture_names().iter().enumerate() {
             let i = Some(i as u32);
             match name.as_str() {
-                "injection.content" => injection_content_capture_index = i,
-                "injection.language" => injection_language_capture_index = i,
                 "local.definition" => local_def_capture_index = i,
                 "local.definition-value" => local_def_value_capture_index = i,
                 "local.reference" => local_ref_capture_index = i,
@@ -1044,12 +1196,21 @@ impl HighlightConfiguration {
             }
         }
 
+        for (i, name) in injections_query.capture_names().iter().enumerate() {
+            let i = Some(i as u32);
+            match name.as_str() {
+                "injection.content" => injection_content_capture_index = i,
+                "injection.language" => injection_language_capture_index = i,
+                _ => {}
+            }
+        }
+
         let highlight_indices = ArcSwap::from_pointee(vec![None; query.capture_names().len()]);
         Ok(Self {
             language,
             query,
+            injections_query,
             combined_injections_query,
-            locals_pattern_index,
             highlights_pattern_index,
             highlight_indices,
             non_local_variable_patterns,
@@ -1114,238 +1275,6 @@ impl HighlightConfiguration {
 }
 
 impl<'a> HighlightIterLayer<'a> {
-    /// Create a new 'layer' of highlighting for this document.
-    ///
-    /// In the even that the new layer contains "combined injections" (injections where multiple
-    /// disjoint ranges are parsed as one syntax tree), these will be eagerly processed and
-    /// added to the returned vector.
-    fn new<F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a>(
-        source: RopeSlice<'a>,
-        cancellation_flag: Option<&'a AtomicUsize>,
-        injection_callback: &mut F,
-        mut config: &'a HighlightConfiguration,
-        mut depth: usize,
-        mut ranges: Vec<Range>,
-    ) -> Result<Vec<Self>, Error> {
-        let mut result = Vec::with_capacity(1);
-        let mut queue = Vec::new();
-        loop {
-            // --> Tree parsing part
-
-            PARSER.with(|ts_parser| {
-                let highlighter = &mut ts_parser.borrow_mut();
-
-                if highlighter.parser.set_included_ranges(&ranges).is_ok() {
-                    highlighter
-                        .parser
-                        .set_language(config.language)
-                        .map_err(|_| Error::InvalidLanguage)?;
-
-                    unsafe { highlighter.parser.set_cancellation_flag(cancellation_flag) };
-                    let tree = highlighter
-                        .parser
-                        .parse_with(
-                            &mut |byte, _| {
-                                if byte <= source.len_bytes() {
-                                    let (chunk, start_byte, _, _) = source.chunk_at_byte(byte);
-                                    chunk[byte - start_byte..].as_bytes()
-                                } else {
-                                    // out of range
-                                    &[]
-                                }
-                            },
-                            None,
-                        )
-                        .ok_or(Error::Cancelled)?;
-                    unsafe { highlighter.parser.set_cancellation_flag(None) };
-                    let mut cursor = highlighter.cursors.pop().unwrap_or_else(QueryCursor::new);
-
-                    // Process combined injections.
-                    if let Some(combined_injections_query) = &config.combined_injections_query {
-                        let mut injections_by_pattern_index = vec![
-                            (None, Vec::new(), false);
-                            combined_injections_query
-                                .pattern_count()
-                        ];
-                        let matches = cursor.matches(
-                            combined_injections_query,
-                            tree.root_node(),
-                            RopeProvider(source),
-                        );
-                        for mat in matches {
-                            let entry = &mut injections_by_pattern_index[mat.pattern_index];
-                            let (language_name, content_node, include_children) =
-                                injection_for_match(
-                                    config,
-                                    combined_injections_query,
-                                    &mat,
-                                    source,
-                                );
-                            if language_name.is_some() {
-                                entry.0 = language_name;
-                            }
-                            if let Some(content_node) = content_node {
-                                entry.1.push(content_node);
-                            }
-                            entry.2 = include_children;
-                        }
-                        for (lang_name, content_nodes, includes_children) in
-                            injections_by_pattern_index
-                        {
-                            if let (Some(lang_name), false) = (lang_name, content_nodes.is_empty())
-                            {
-                                if let Some(next_config) = (injection_callback)(&lang_name) {
-                                    let ranges = Self::intersect_ranges(
-                                        &ranges,
-                                        &content_nodes,
-                                        includes_children,
-                                    );
-                                    if !ranges.is_empty() {
-                                        queue.push((next_config, depth + 1, ranges));
-                                    }
-                                }
-                            }
-                        }
-                    }
-
-                    // --> Highlighting query part
-
-                    // The `captures` iterator borrows the `Tree` and the `QueryCursor`, which
-                    // prevents them from being moved. But both of these values are really just
-                    // pointers, so it's actually ok to move them.
-                    let tree_ref = unsafe { mem::transmute::<_, &'static Tree>(&tree) };
-                    let cursor_ref =
-                        unsafe { mem::transmute::<_, &'static mut QueryCursor>(&mut cursor) };
-                    let captures = cursor_ref
-                        .captures(&config.query, tree_ref.root_node(), RopeProvider(source))
-                        .peekable();
-
-                    result.push(HighlightIterLayer {
-                        highlight_end_stack: Vec::new(),
-                        scope_stack: vec![LocalScope {
-                            inherits: false,
-                            range: 0..usize::MAX,
-                            local_defs: Vec::new(),
-                        }],
-                        cursor,
-                        depth,
-                        _tree: Some(tree),
-                        captures,
-                        config,
-                        ranges,
-                    });
-                }
-
-                Ok(()) // so we can use the try operator
-            })?;
-
-            if queue.is_empty() {
-                break;
-            }
-
-            let (next_config, next_depth, next_ranges) = queue.remove(0);
-            config = next_config;
-            depth = next_depth;
-            ranges = next_ranges;
-        }
-
-        Ok(result)
-    }
-
-    // Compute the ranges that should be included when parsing an injection.
-    // This takes into account three things:
-    // * `parent_ranges` - The ranges must all fall within the *current* layer's ranges.
-    // * `nodes` - Every injection takes place within a set of nodes. The injection ranges
-    //   are the ranges of those nodes.
-    // * `includes_children` - For some injections, the content nodes' children should be
-    //   excluded from the nested document, so that only the content nodes' *own* content
-    //   is reparsed. For other injections, the content nodes' entire ranges should be
-    //   reparsed, including the ranges of their children.
-    fn intersect_ranges(
-        parent_ranges: &[Range],
-        nodes: &[Node],
-        includes_children: bool,
-    ) -> Vec<Range> {
-        let mut cursor = nodes[0].walk();
-        let mut result = Vec::new();
-        let mut parent_range_iter = parent_ranges.iter();
-        let mut parent_range = parent_range_iter
-            .next()
-            .expect("Layers should only be constructed with non-empty ranges vectors");
-        for node in nodes.iter() {
-            let mut preceding_range = Range {
-                start_byte: 0,
-                start_point: Point::new(0, 0),
-                end_byte: node.start_byte(),
-                end_point: node.start_position(),
-            };
-            let following_range = Range {
-                start_byte: node.end_byte(),
-                start_point: node.end_position(),
-                end_byte: usize::MAX,
-                end_point: Point::new(usize::MAX, usize::MAX),
-            };
-
-            for excluded_range in node
-                .children(&mut cursor)
-                .filter_map(|child| {
-                    if includes_children {
-                        None
-                    } else {
-                        Some(child.range())
-                    }
-                })
-                .chain([following_range].iter().cloned())
-            {
-                let mut range = Range {
-                    start_byte: preceding_range.end_byte,
-                    start_point: preceding_range.end_point,
-                    end_byte: excluded_range.start_byte,
-                    end_point: excluded_range.start_point,
-                };
-                preceding_range = excluded_range;
-
-                if range.end_byte < parent_range.start_byte {
-                    continue;
-                }
-
-                while parent_range.start_byte <= range.end_byte {
-                    if parent_range.end_byte > range.start_byte {
-                        if range.start_byte < parent_range.start_byte {
-                            range.start_byte = parent_range.start_byte;
-                            range.start_point = parent_range.start_point;
-                        }
-
-                        if parent_range.end_byte < range.end_byte {
-                            if range.start_byte < parent_range.end_byte {
-                                result.push(Range {
-                                    start_byte: range.start_byte,
-                                    start_point: range.start_point,
-                                    end_byte: parent_range.end_byte,
-                                    end_point: parent_range.end_point,
-                                });
-                            }
-                            range.start_byte = parent_range.end_byte;
-                            range.start_point = parent_range.end_point;
-                        } else {
-                            if range.start_byte < range.end_byte {
-                                result.push(range);
-                            }
-                            break;
-                        }
-                    }
-
-                    if let Some(next_range) = parent_range_iter.next() {
-                        parent_range = next_range;
-                    } else {
-                        return result;
-                    }
-                }
-            }
-        }
-        result
-    }
-
     // First, sort scope boundaries by their byte offset in the document. At a
     // given position, emit scope endings before scope beginnings. Finally, emit
     // scope boundaries from deeper layers first.
@@ -1371,10 +1300,101 @@ impl<'a> HighlightIterLayer<'a> {
     }
 }
 
-impl<'a, F> HighlightIter<'a, F>
-where
-    F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
-{
+// Compute the ranges that should be included when parsing an injection.
+// This takes into account three things:
+// * `parent_ranges` - The ranges must all fall within the *current* layer's ranges.
+// * `nodes` - Every injection takes place within a set of nodes. The injection ranges
+//   are the ranges of those nodes.
+// * `includes_children` - For some injections, the content nodes' children should be
+//   excluded from the nested document, so that only the content nodes' *own* content
+//   is reparsed. For other injections, the content nodes' entire ranges should be
+//   reparsed, including the ranges of their children.
+fn intersect_ranges(
+    parent_ranges: &[Range],
+    nodes: &[Node],
+    includes_children: bool,
+) -> Vec<Range> {
+    let mut cursor = nodes[0].walk();
+    let mut result = Vec::new();
+    let mut parent_range_iter = parent_ranges.iter();
+    let mut parent_range = parent_range_iter
+        .next()
+        .expect("Layers should only be constructed with non-empty ranges vectors");
+    for node in nodes.iter() {
+        let mut preceding_range = Range {
+            start_byte: 0,
+            start_point: Point::new(0, 0),
+            end_byte: node.start_byte(),
+            end_point: node.start_position(),
+        };
+        let following_range = Range {
+            start_byte: node.end_byte(),
+            start_point: node.end_position(),
+            end_byte: usize::MAX,
+            end_point: Point::new(usize::MAX, usize::MAX),
+        };
+
+        for excluded_range in node
+            .children(&mut cursor)
+            .filter_map(|child| {
+                if includes_children {
+                    None
+                } else {
+                    Some(child.range())
+                }
+            })
+            .chain([following_range].iter().cloned())
+        {
+            let mut range = Range {
+                start_byte: preceding_range.end_byte,
+                start_point: preceding_range.end_point,
+                end_byte: excluded_range.start_byte,
+                end_point: excluded_range.start_point,
+            };
+            preceding_range = excluded_range;
+
+            if range.end_byte < parent_range.start_byte {
+                continue;
+            }
+
+            while parent_range.start_byte <= range.end_byte {
+                if parent_range.end_byte > range.start_byte {
+                    if range.start_byte < parent_range.start_byte {
+                        range.start_byte = parent_range.start_byte;
+                        range.start_point = parent_range.start_point;
+                    }
+
+                    if parent_range.end_byte < range.end_byte {
+                        if range.start_byte < parent_range.end_byte {
+                            result.push(Range {
+                                start_byte: range.start_byte,
+                                start_point: range.start_point,
+                                end_byte: parent_range.end_byte,
+                                end_point: parent_range.end_point,
+                            });
+                        }
+                        range.start_byte = parent_range.end_byte;
+                        range.start_point = parent_range.end_point;
+                    } else {
+                        if range.start_byte < range.end_byte {
+                            result.push(range);
+                        }
+                        break;
+                    }
+                }
+
+                if let Some(next_range) = parent_range_iter.next() {
+                    parent_range = next_range;
+                } else {
+                    return result;
+                }
+            }
+        }
+    }
+    result
+}
+
+impl<'a> HighlightIter<'a> {
     fn emit_event(
         &mut self,
         offset: usize,
@@ -1405,6 +1425,12 @@ where
                             i += 1;
                             continue;
                         }
+                    } else {
+                        let layer = self.layers.remove(i + 1);
+                        PARSER.with(|ts_parser| {
+                            let highlighter = &mut ts_parser.borrow_mut();
+                            highlighter.cursors.push(layer.cursor);
+                        });
                     }
                     break;
                 }
@@ -1421,30 +1447,9 @@ where
             }
         }
     }
-
-    fn insert_layer(&mut self, mut layer: HighlightIterLayer<'a>) {
-        if let Some(sort_key) = layer.sort_key() {
-            let mut i = 1;
-            while i < self.layers.len() {
-                if let Some(sort_key_i) = self.layers[i].sort_key() {
-                    if sort_key_i > sort_key {
-                        self.layers.insert(i, layer);
-                        return;
-                    }
-                    i += 1;
-                } else {
-                    self.layers.remove(i);
-                }
-            }
-            self.layers.push(layer);
-        }
-    }
 }
 
-impl<'a, F> Iterator for HighlightIter<'a, F>
-where
-    F: FnMut(&str) -> Option<&'a HighlightConfiguration> + 'a,
-{
+impl<'a> Iterator for HighlightIter<'a> {
     type Item = Result<HighlightEvent, Error>;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -1504,55 +1509,12 @@ where
                 layer.highlight_end_stack.pop();
                 return self.emit_event(end_byte, Some(HighlightEvent::HighlightEnd));
             } else {
-                // return self.emit_event(self.source.len(), None);
-                return None;
+                return self.emit_event(self.source.len_bytes(), None);
             };
 
             let (mut match_, capture_index) = layer.captures.next().unwrap();
             let mut capture = match_.captures[capture_index];
 
-            // If this capture represents an injection, then process the injection.
-            if match_.pattern_index < layer.config.locals_pattern_index {
-                let (language_name, content_node, include_children) =
-                    injection_for_match(layer.config, &layer.config.query, &match_, self.source);
-
-                // Explicitly remove this match so that none of its other captures will remain
-                // in the stream of captures.
-                match_.remove();
-
-                // If a language is found with the given name, then add a new language layer
-                // to the highlighted document.
-                if let (Some(language_name), Some(content_node)) = (language_name, content_node) {
-                    if let Some(config) = (self.injection_callback)(&language_name) {
-                        let ranges = HighlightIterLayer::intersect_ranges(
-                            &self.layers[0].ranges,
-                            &[content_node],
-                            include_children,
-                        );
-                        if !ranges.is_empty() {
-                            match HighlightIterLayer::new(
-                                self.source,
-                                self.cancellation_flag,
-                                &mut self.injection_callback,
-                                config,
-                                self.layers[0].depth + 1,
-                                ranges,
-                            ) {
-                                Ok(layers) => {
-                                    for layer in layers {
-                                        self.insert_layer(layer);
-                                    }
-                                }
-                                Err(e) => return Some(Err(e)),
-                            }
-                        }
-                    }
-                }
-
-                self.sort_layers();
-                continue 'main;
-            }
-
             // Remove from the local scope stack any local scopes that have already ended.
             while range.start > layer.scope_stack.last().unwrap().range.end {
                 layer.scope_stack.pop();
@@ -1747,14 +1709,6 @@ fn injection_for_match<'a>(
     (language_name, content_node, include_children)
 }
 
-// fn shrink_and_clear<T>(vec: &mut Vec<T>, capacity: usize) {
-//     if vec.len() > capacity {
-//         vec.truncate(capacity);
-//         vec.shrink_to_fit();
-//     }
-//     vec.clear();
-// }
-
 pub struct Merge<I> {
     iter: I,
     spans: Box<dyn Iterator<Item = (usize, std::ops::Range<usize>)>>,
@@ -1921,6 +1875,8 @@ mod test {
         .map(String::from)
         .collect();
 
+        let loader = Loader::new(Configuration { language: vec![] });
+
         let language = get_language(&crate::RUNTIME_DIR, "Rust").unwrap();
         let config = HighlightConfiguration::new(
             language,
@@ -1943,7 +1899,7 @@ mod test {
             fn main() {}
         ",
         );
-        let syntax = Syntax::new(&source, Arc::new(config));
+        let syntax = Syntax::new(&source, Arc::new(config), Arc::new(loader));
         let tree = syntax.tree();
         let root = tree.root_node();
         assert_eq!(root.kind(), "source_file");
@@ -1970,7 +1926,7 @@ mod test {
             &doc,
             vec![(6, 11, Some("test".into())), (12, 17, None)].into_iter(),
         );
-        let edits = LanguageLayer::generate_edits(doc.slice(..), transaction.changes());
+        let edits = generate_edits(&doc, transaction.changes());
         // transaction.apply(&mut state);
 
         assert_eq!(
@@ -1999,7 +1955,7 @@ mod test {
         let mut doc = Rope::from("fn test() {}");
         let transaction =
             Transaction::change(&doc, vec![(8, 8, Some("a: u32".into()))].into_iter());
-        let edits = LanguageLayer::generate_edits(doc.slice(..), transaction.changes());
+        let edits = generate_edits(&doc, transaction.changes());
         transaction.apply(&mut doc);
 
         assert_eq!(doc, "fn test(a: u32) {}");
diff --git a/helix-core/src/transaction.rs b/helix-core/src/transaction.rs
index dfc18fbe..2e34a986 100644
--- a/helix-core/src/transaction.rs
+++ b/helix-core/src/transaction.rs
@@ -22,7 +22,7 @@ pub enum Assoc {
 }
 
 // ChangeSpec = Change | ChangeSet | Vec<Change>
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
 pub struct ChangeSet {
     pub(crate) changes: Vec<Operation>,
     /// The required document length. Will refuse to apply changes unless it matches.
@@ -30,16 +30,6 @@ pub struct ChangeSet {
     len_after: usize,
 }
 
-impl Default for ChangeSet {
-    fn default() -> Self {
-        Self {
-            changes: Vec::new(),
-            len: 0,
-            len_after: 0,
-        }
-    }
-}
-
 impl ChangeSet {
     pub fn with_capacity(capacity: usize) -> Self {
         Self {
@@ -95,7 +85,7 @@ impl ChangeSet {
 
         let new_last = match self.changes.as_mut_slice() {
             [.., Insert(prev)] | [.., Insert(prev), Delete(_)] => {
-                prev.push_tendril(&fragment);
+                prev.push_str(&fragment);
                 return;
             }
             [.., last @ Delete(_)] => std::mem::replace(last, Insert(fragment)),
@@ -199,7 +189,7 @@ impl ChangeSet {
                             // TODO: cover this with a test
                             // figure out the byte index of the truncated string end
                             let (pos, _) = s.char_indices().nth(j).unwrap();
-                            s.pop_front(pos as u32);
+                            s.replace_range(0..pos, "");
                             head_a = Some(Insert(s));
                             head_b = changes_b.next();
                         }
@@ -221,9 +211,11 @@ impl ChangeSet {
                         Ordering::Greater => {
                             // figure out the byte index of the truncated string end
                             let (pos, _) = s.char_indices().nth(j).unwrap();
-                            let pos = pos as u32;
-                            changes.insert(s.subtendril(0, pos));
-                            head_a = Some(Insert(s.subtendril(pos, s.len() as u32 - pos)));
+                            let mut before = s;
+                            let after = before.split_off(pos);
+
+                            changes.insert(before);
+                            head_a = Some(Insert(after));
                             head_b = changes_b.next();
                         }
                     }
@@ -287,7 +279,7 @@ impl ChangeSet {
                 }
                 Delete(n) => {
                     let text = Cow::from(original_doc.slice(pos..pos + *n));
-                    changes.insert(Tendril::from_slice(&text));
+                    changes.insert(Tendril::from(text.as_ref()));
                     pos += n;
                 }
                 Insert(s) => {
@@ -330,7 +322,7 @@ impl ChangeSet {
     /// `true` when the set is empty.
     #[inline]
     pub fn is_empty(&self) -> bool {
-        self.changes.is_empty()
+        self.changes.is_empty() || self.changes == [Operation::Retain(self.len)]
     }
 
     /// Map a position through the changes.
@@ -419,7 +411,7 @@ impl ChangeSet {
 
 /// Transaction represents a single undoable unit of changes. Several changes can be grouped into
 /// a single transaction.
-#[derive(Debug, Default, Clone)]
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
 pub struct Transaction {
     changes: ChangeSet,
     selection: Option<Selection>,
@@ -720,19 +712,19 @@ mod test {
     #[test]
     fn optimized_composition() {
         let mut state = State::new("".into());
-        let t1 = Transaction::insert(&state.doc, &state.selection, Tendril::from_char('h'));
+        let t1 = Transaction::insert(&state.doc, &state.selection, Tendril::from("h"));
         t1.apply(&mut state.doc);
         state.selection = state.selection.clone().map(t1.changes());
-        let t2 = Transaction::insert(&state.doc, &state.selection, Tendril::from_char('e'));
+        let t2 = Transaction::insert(&state.doc, &state.selection, Tendril::from("e"));
         t2.apply(&mut state.doc);
         state.selection = state.selection.clone().map(t2.changes());
-        let t3 = Transaction::insert(&state.doc, &state.selection, Tendril::from_char('l'));
+        let t3 = Transaction::insert(&state.doc, &state.selection, Tendril::from("l"));
         t3.apply(&mut state.doc);
         state.selection = state.selection.clone().map(t3.changes());
-        let t4 = Transaction::insert(&state.doc, &state.selection, Tendril::from_char('l'));
+        let t4 = Transaction::insert(&state.doc, &state.selection, Tendril::from("l"));
         t4.apply(&mut state.doc);
         state.selection = state.selection.clone().map(t4.changes());
-        let t5 = Transaction::insert(&state.doc, &state.selection, Tendril::from_char('o'));
+        let t5 = Transaction::insert(&state.doc, &state.selection, Tendril::from("o"));
         t5.apply(&mut state.doc);
         state.selection = state.selection.clone().map(t5.changes());
 
@@ -771,7 +763,7 @@ mod test {
 
     #[test]
     fn combine_with_utf8() {
-        const TEST_CASE: &'static str = "Hello, これはヘリックスエディターです！";
+        const TEST_CASE: &str = "Hello, これはヘリックスエディターです！";
 
         let empty = Rope::from("");
         let a = ChangeSet::new(&empty);