Fix multi byte auto pairs (#4024)

* Fix test::print for Unicode

The print function was not generating correct translations when
the input has Unicode (non-ASCII) in it. This is due to its use of
String::len, which gives the length in bytes, not chars.

* Fix multi-code point auto pairs

The current code for auto pairs is counting offsets by summing the
length of the open and closing chars with char::len_utf8. Unfortunately,
this gives back bytes, and the offset needs to be in chars.

Additionally, it was discovered that there was a preexisting bug where
the selection was not computed correctly in the case that the cursor
was:

1. a single grapheme in width
2. this grapheme was more than one char
3. the direction of the cursor is backwards
4. a secondary range

In this case, the offset was not being added into the anchor. This was
fixed.

* migrate auto pairs tests to integration

* review comments

2 files changed, 144 insertions, 577 deletions

diff --git a/helix-core/src/auto_pairs.rs b/helix-core/src/auto_pairs.rs
index edc404ac..072c93d0 100644
--- a/helix-core/src/auto_pairs.rs
+++ b/helix-core/src/auto_pairs.rs
@@ -146,13 +146,7 @@ fn prev_char(doc: &Rope, pos: usize) -> Option<char> {
 }
 
 /// 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 {
+fn get_next_range(doc: &Rope, start_range: &Range, offset: usize, 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.
@@ -172,8 +166,8 @@ fn get_next_range(
     // 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(),
+            start_range.anchor + offset + 1,
+            start_range.head + offset + 1,
         );
     }
 
@@ -203,21 +197,18 @@ fn get_next_range(
     // 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()
+            start_range.anchor + offset + 1
         } else {
             start_range.anchor + offset
         };
 
-        return Range::new(
-            end_anchor,
-            start_range.head + offset + typed_char.len_utf8(),
-        );
+        return Range::new(end_anchor, start_range.head + offset + 1);
     }
 
     // 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()
+        start_range.head + offset + 1
     } 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
@@ -243,8 +234,7 @@ fn get_next_range(
 
         (_, Direction::Forward) => {
             if single_grapheme {
-                graphemes::prev_grapheme_boundary(doc.slice(..), start_range.head)
-                    + typed_char.len_utf8()
+                graphemes::prev_grapheme_boundary(doc.slice(..), start_range.head) + 1
 
             // if we are appending, the anchor stays where it is; only offset
             // for multiple range insertions
@@ -258,7 +248,9 @@ fn get_next_range(
                 // 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
+                graphemes::prev_grapheme_boundary(doc.slice(..), start_range.anchor)
+                    + len_inserted
+                    + offset
             } else {
                 // when we are inserting in front of a selection, we need to move
                 // the anchor over by however many characters were inserted overall
@@ -279,9 +271,12 @@ fn handle_open(doc: &Rope, selection: &Selection, pair: &Pair) -> Transaction {
         let next_char = doc.get_char(cursor);
         let len_inserted;
 
+        // Since auto pairs are currently limited to single chars, we're either
+        // inserting exactly one or two chars. When arbitrary length pairs are
+        // added, these will need to be changed.
         let change = match next_char {
             Some(_) if !pair.should_close(doc, start_range) => {
-                len_inserted = pair.open.len_utf8();
+                len_inserted = 1;
                 let mut tendril = Tendril::new();
                 tendril.push(pair.open);
                 (cursor, cursor, Some(tendril))
@@ -289,12 +284,12 @@ fn handle_open(doc: &Rope, selection: &Selection, pair: &Pair) -> Transaction {
             _ => {
                 // insert open & close
                 let pair_str = Tendril::from_iter([pair.open, pair.close]);
-                len_inserted = pair.open.len_utf8() + pair.close.len_utf8();
+                len_inserted = 2;
                 (cursor, cursor, Some(pair_str))
             }
         };
 
-        let next_range = get_next_range(doc, start_range, offs, pair.open, len_inserted);
+        let next_range = get_next_range(doc, start_range, offs, len_inserted);
         end_ranges.push(next_range);
         offs += len_inserted;
 
@@ -308,7 +303,6 @@ fn handle_open(doc: &Rope, selection: &Selection, pair: &Pair) -> Transaction {
 
 fn handle_close(doc: &Rope, selection: &Selection, pair: &Pair) -> Transaction {
     let mut end_ranges = SmallVec::with_capacity(selection.len());
-
     let mut offs = 0;
 
     let transaction = Transaction::change_by_selection(doc, selection, |start_range| {
@@ -320,13 +314,13 @@ fn handle_close(doc: &Rope, selection: &Selection, pair: &Pair) -> Transaction {
             // return transaction that moves past close
             (cursor, cursor, None) // no-op
         } else {
-            len_inserted += pair.close.len_utf8();
+            len_inserted = 1;
             let mut tendril = Tendril::new();
             tendril.push(pair.close);
             (cursor, cursor, Some(tendril))
         };
 
-        let next_range = get_next_range(doc, start_range, offs, pair.close, len_inserted);
+        let next_range = get_next_range(doc, start_range, offs, len_inserted);
         end_ranges.push(next_range);
         offs += len_inserted;
 
@@ -362,11 +356,11 @@ fn handle_same(doc: &Rope, selection: &Selection, pair: &Pair) -> Transaction {
                 pair_str.push(pair.close);
             }
 
-            len_inserted += pair_str.len();
+            len_inserted += pair_str.chars().count();
             (cursor, cursor, Some(pair_str))
         };
 
-        let next_range = get_next_range(doc, start_range, offs, pair.open, len_inserted);
+        let next_range = get_next_range(doc, start_range, offs, len_inserted);
         end_ranges.push(next_range);
         offs += len_inserted;
 
@@ -377,551 +371,3 @@ fn handle_same(doc: &Rope, selection: &Selection, pair: &Pair) -> Transaction {
     log::debug!("auto pair transaction: {:#?}", t);
     t
 }
-
-#[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)> {
-        DEFAULT_PAIRS.iter().filter(|(open, close)| open != close)
-    }
-
-    fn matching_pairs() -> impl Iterator<Item = &'static (char, char)> {
-        DEFAULT_PAIRS.iter().filter(|(open, close)| open == close)
-    }
-
-    fn test_hooks(
-        in_doc: &Rope,
-        in_sel: &Selection,
-        ch: char,
-        pairs: &[(char, char)],
-        expected_doc: &Rope,
-        expected_sel: &Selection,
-    ) {
-        let pairs = AutoPairs::new(pairs.iter());
-        let trans = hook(in_doc, in_sel, ch, &pairs).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,
-        test_pairs: I,
-        pairs: &[(char, char)],
-        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>,
-    {
-        test_pairs.into_iter().for_each(|(open, close)| {
-            test_hooks(
-                in_doc,
-                in_sel,
-                *open,
-                pairs,
-                &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),
-            DEFAULT_PAIRS,
-            DEFAULT_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()),
-            DEFAULT_PAIRS,
-            DEFAULT_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() {
-        for (_, close) in differing_pairs() {
-            test_hooks(
-                &Rope::from(format!("hello 👨‍👩‍👧‍👦 goodbye{}", LINE_END)),
-                &Selection::single(13, 6),
-                *close,
-                DEFAULT_PAIRS,
-                &Rope::from(format!("hello {}👨‍👩‍👧‍👦 goodbye{}", close, 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()),
-            DEFAULT_PAIRS,
-            DEFAULT_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()),
-            DEFAULT_PAIRS,
-            DEFAULT_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),
-            DEFAULT_PAIRS,
-            DEFAULT_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,
-            ),
-            DEFAULT_PAIRS,
-            DEFAULT_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(),
-            DEFAULT_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(),
-            DEFAULT_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(),
-            DEFAULT_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 DEFAULT_PAIRS {
-            let doc = Rope::from(format!("{}{}{}", open, close, LINE_END));
-
-            test_hooks(
-                &doc,
-                &Selection::single(2, 1),
-                *close,
-                DEFAULT_PAIRS,
-                &doc,
-                &Selection::single(2 + LINE_END.len(), 2),
-            );
-        }
-    }
-
-    /// [(]) -> append ) -> [()]
-    #[test]
-    fn test_append_close_inside_pair() {
-        for (open, close) in DEFAULT_PAIRS {
-            let doc = Rope::from(format!("{}{}{}", open, close, LINE_END));
-
-            test_hooks(
-                &doc,
-                &Selection::single(0, 2),
-                *close,
-                DEFAULT_PAIRS,
-                &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 DEFAULT_PAIRS {
-            let doc = Rope::from(format!(
-                "{open}{close}\n{open}{close}\n{open}{close}\n",
-                open = open,
-                close = close
-            ));
-
-            test_hooks(&doc, &sel, *close, DEFAULT_PAIRS, &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 DEFAULT_PAIRS {
-            let doc = Rope::from(format!(
-                "{open}{close}\n{open}{close}\n{open}{close}\n",
-                open = open,
-                close = close
-            ));
-
-            test_hooks(&doc, &sel, *close, DEFAULT_PAIRS, &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,
-                DEFAULT_PAIRS,
-                &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,
-                DEFAULT_PAIRS,
-                &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,
-                    DEFAULT_PAIRS,
-                    &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,
-                    DEFAULT_PAIRS,
-                    &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),
-            DEFAULT_PAIRS,
-            DEFAULT_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),
-            DEFAULT_PAIRS,
-            DEFAULT_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 DEFAULT_PAIRS {
-            let doc = Rope::from("word");
-            let expected_doc = Rope::from(format!("wor{}d", close));
-            test_hooks(
-                &doc,
-                &sel,
-                *close,
-                DEFAULT_PAIRS,
-                &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(),
-            DEFAULT_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,
-                DEFAULT_PAIRS,
-                &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(),
-            DEFAULT_PAIRS,
-            |open, close| format!("word{}{}{}", open, close, LINE_END),
-            &expected_sel,
-        );
-
-        test_hooks_with_pairs(
-            &doc,
-            &sel,
-            matching_pairs(),
-            DEFAULT_PAIRS,
-            |open, _| format!("word{}{}", open, LINE_END),
-            &expected_sel,
-        );
-    }
-
-    #[test]
-    fn test_configured_pairs() {
-        let test_pairs = &[('`', ':'), ('+', '-')];
-
-        test_hooks_with_pairs(
-            &Rope::from(LINE_END),
-            &Selection::single(1, 0),
-            test_pairs,
-            test_pairs,
-            |open, close| format!("{}{}{}", open, close, LINE_END),
-            &Selection::single(2, 1),
-        );
-
-        let doc = Rope::from(format!("foo`: word{}", LINE_END));
-
-        test_hooks(
-            &doc,
-            &Selection::single(9, 4),
-            ':',
-            test_pairs,
-            &doc,
-            &Selection::single(9, 5),
-        )
-    }
-}
diff --git a/helix-core/src/test.rs b/helix-core/src/test.rs
index 45503107..3e54d2c2 100644
--- a/helix-core/src/test.rs
+++ b/helix-core/src/test.rs
@@ -34,7 +34,7 @@ pub fn print(s: &str) -> (String, Selection) {
     let mut left = String::with_capacity(s.len());
 
     'outer: while let Some(c) = iter.next() {
-        let start = left.len();
+        let start = left.chars().count();
 
         if c != '#' {
             left.push(c);
@@ -63,6 +63,7 @@ pub fn print(s: &str) -> (String, Selection) {
                 left.push(c);
                 continue;
             }
+
             if !head_at_beg {
                 let prev = left.pop().unwrap();
                 if prev != '|' {
@@ -71,15 +72,18 @@ pub fn print(s: &str) -> (String, Selection) {
                     continue;
                 }
             }
+
             iter.next(); // skip "#"
 
             if is_primary {
                 primary_idx = Some(ranges.len());
             }
+
             let (anchor, head) = match head_at_beg {
-                true => (left.len(), start),
-                false => (start, left.len()),
+                true => (left.chars().count(), start),
+                false => (start, left.chars().count()),
             };
+
             ranges.push(Range::new(anchor, head));
             continue 'outer;
         }
@@ -95,6 +99,7 @@ pub fn print(s: &str) -> (String, Selection) {
         Some(i) => i,
         None => panic!("missing primary `#[|]#` {:?}", s),
     };
+
     let selection = Selection::new(ranges, primary);
     (left, selection)
 }
@@ -141,3 +146,119 @@ pub fn plain(s: &str, selection: Selection) -> String {
     }
     out
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn print_single() {
+        assert_eq!(
+            (String::from("hello"), Selection::single(1, 0)),
+            print("#[|h]#ello")
+        );
+        assert_eq!(
+            (String::from("hello"), Selection::single(0, 1)),
+            print("#[h|]#ello")
+        );
+        assert_eq!(
+            (String::from("hello"), Selection::single(4, 0)),
+            print("#[|hell]#o")
+        );
+        assert_eq!(
+            (String::from("hello"), Selection::single(0, 4)),
+            print("#[hell|]#o")
+        );
+        assert_eq!(
+            (String::from("hello"), Selection::single(5, 0)),
+            print("#[|hello]#")
+        );
+        assert_eq!(
+            (String::from("hello"), Selection::single(0, 5)),
+            print("#[hello|]#")
+        );
+    }
+
+    #[test]
+    fn print_multi() {
+        assert_eq!(
+            (
+                String::from("hello"),
+                Selection::new(
+                    SmallVec::from_slice(&[Range::new(1, 0), Range::new(5, 4)]),
+                    0
+                )
+            ),
+            print("#[|h]#ell#(|o)#")
+        );
+        assert_eq!(
+            (
+                String::from("hello"),
+                Selection::new(
+                    SmallVec::from_slice(&[Range::new(0, 1), Range::new(4, 5)]),
+                    0
+                )
+            ),
+            print("#[h|]#ell#(o|)#")
+        );
+        assert_eq!(
+            (
+                String::from("hello"),
+                Selection::new(
+                    SmallVec::from_slice(&[Range::new(2, 0), Range::new(5, 3)]),
+                    0
+                )
+            ),
+            print("#[|he]#l#(|lo)#")
+        );
+        assert_eq!(
+            (
+                String::from("hello\r\nhello\r\nhello\r\n"),
+                Selection::new(
+                    SmallVec::from_slice(&[
+                        Range::new(7, 5),
+                        Range::new(21, 19),
+                        Range::new(14, 12)
+                    ]),
+                    0
+                )
+            ),
+            print("hello#[|\r\n]#hello#(|\r\n)#hello#(|\r\n)#")
+        );
+    }
+
+    #[test]
+    fn print_multi_byte_code_point() {
+        assert_eq!(
+            (String::from("„“"), Selection::single(1, 0)),
+            print("#[|„]#“")
+        );
+        assert_eq!(
+            (String::from("„“"), Selection::single(2, 1)),
+            print("„#[|“]#")
+        );
+        assert_eq!(
+            (String::from("„“"), Selection::single(0, 1)),
+            print("#[„|]#“")
+        );
+        assert_eq!(
+            (String::from("„“"), Selection::single(1, 2)),
+            print("„#[“|]#")
+        );
+        assert_eq!(
+            (String::from("they said „hello“"), Selection::single(11, 10)),
+            print("they said #[|„]#hello“")
+        );
+    }
+
+    #[test]
+    fn print_multi_code_point_grapheme() {
+        assert_eq!(
+            (
+                String::from("hello 👨‍👩‍👧‍👦 goodbye"),
+                Selection::single(13, 6)
+            ),
+            print("hello #[|👨‍👩‍👧‍👦]# goodbye")
+        );
+    }
+}