5 files changed, 116 insertions, 4 deletions
diff --git a/helix-core/src/indent.rs b/helix-core/src/indent.rs
new file mode 100644
index 00000000..c1a4fd6c
--- /dev/null
+++ b/helix-core/src/indent.rs
@@ -0,0 +1,111 @@
+use crate::{
+    syntax::Syntax,
+    tree_sitter::{Node, Tree},
+    Rope, RopeSlice, State,
+};
+
+const TAB_WIDTH: usize = 4;
+
+fn indent_level_for_line(line: RopeSlice) -> usize {
+    let mut len = 0;
+    for ch in line.chars() {
+        match ch {
+            '\t' => len += TAB_WIDTH,
+            ' ' => len += 1,
+            _ => break,
+        }
+    }
+
+    len / TAB_WIDTH
+}
+
+/// Find the highest syntax node at position.
+/// This is to identify the column where this node (e.g., an HTML closing tag) ends.
+fn get_highest_syntax_node_at_bytepos(syntax: &Syntax, pos: usize) -> Option<Node> {
+    let tree = syntax.root_layer.tree.as_ref().unwrap();
+
+    let mut node = match tree.root_node().named_descendant_for_byte_range(pos, pos) {
+        Some(node) => node,
+        None => return None,
+    };
+
+    while let Some(parent) = node.parent() {
+        if parent.start_byte() == node.start_byte() {
+            node = parent
+        } else {
+            break;
+        }
+    }
+
+    Some(node)
+}
+
+fn walk(node: Option<Node>) -> usize {
+    let node = match node {
+        Some(node) => node,
+        None => return 0,
+    };
+
+    let parent = match node.parent() {
+        Some(node) => node,
+        None => return 0,
+    };
+
+    let mut increment = 0;
+
+    let not_first_or_last_sibling = node.next_sibling().is_some() && node.prev_sibling().is_some();
+    let is_scope = true;
+
+    if not_first_or_last_sibling && is_scope {
+        increment += 1;
+    }
+
+    walk(Some(parent)) + increment
+}
+
+// for_line_at_col
+fn suggested_indent_for_line(state: &State, line_num: usize) -> usize {
+    let line = state.doc.line(line_num);
+    let current = indent_level_for_line(line);
+
+    let mut byte_start = state.doc.line_to_byte(line_num);
+
+    // find first non-whitespace char
+    for ch in line.chars() {
+        // TODO: could use memchr with chunks?
+        if ch != ' ' && ch != '\t' {
+            break;
+        }
+        byte_start += 1;
+    }
+
+    if let Some(syntax) = &state.syntax {
+        let node = get_highest_syntax_node_at_bytepos(state.syntax.as_ref().unwrap(), byte_start);
+
+        // let indentation = walk()
+        // special case for comments
+
+        // if preserve_leading_whitespace
+
+        unimplemented!()
+    } else {
+        // TODO: case for non-tree sitter grammars
+        0
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn indent_level() {
+        let line = Rope::from("        fn new"); // 8 spaces
+        assert_eq!(indent_level_for_line(line.slice(..)), 2);
+        let line = Rope::from("\t\t\tfn new"); // 3 tabs
+        assert_eq!(indent_level_for_line(line.slice(..)), 3);
+        // mixed indentation
+        let line = Rope::from("\t    \tfn new"); // 1 tab, 4 spaces, tab
+        assert_eq!(indent_level_for_line(line.slice(..)), 3);
+    }
+}
diff --git a/helix-core/src/lib.rs b/helix-core/src/lib.rs
index 4a7a2dd4..ccdc7297 100644
--- a/helix-core/src/lib.rs
+++ b/helix-core/src/lib.rs
@@ -1,6 +1,7 @@
 #![allow(unused)]
 pub mod graphemes;
 mod history;
+mod indent;
 pub mod macros;
 mod position;
 pub mod register;
diff --git a/helix-core/src/selection.rs b/helix-core/src/selection.rs
index bc677330..d3806cf3 100644
--- a/helix-core/src/selection.rs
+++ b/helix-core/src/selection.rs
@@ -110,7 +110,6 @@ impl Range {
 
     #[inline]
     pub fn fragment<'a>(&'a self, text: &'a RopeSlice) -> Cow<'a, str> {
-        // end inclusive
         Cow::from(text.slice(self.from()..self.to() + 1))
     }
 }
diff --git a/helix-core/src/state.rs b/helix-core/src/state.rs
index fde6a866..7035b27c 100644
--- a/helix-core/src/state.rs
+++ b/helix-core/src/state.rs
@@ -47,6 +47,7 @@ impl State {
     #[must_use]
     pub fn new(doc: Rope) -> Self {
         let changes = ChangeSet::new(&doc);
+        let old_state = Some((doc.clone(), Selection::single(0, 0)));
 
         Self {
             path: None,
@@ -56,7 +57,7 @@ impl State {
             restore_cursor: false,
             syntax: None,
             changes,
-            old_state: None,
+            old_state,
         }
     }
 
diff --git a/helix-core/src/syntax.rs b/helix-core/src/syntax.rs
index 3e5927e5..290f2652 100644
--- a/helix-core/src/syntax.rs
+++ b/helix-core/src/syntax.rs
@@ -146,7 +146,7 @@ pub struct Syntax {
 
     config: Arc<HighlightConfiguration>,
 
-    root_layer: LanguageLayer,
+    pub(crate) root_layer: LanguageLayer,
 }
 
 impl Syntax {
@@ -309,7 +309,7 @@ pub struct LanguageLayer {
     // mode
     // grammar
     // depth
-    tree: Option<Tree>,
+    pub(crate) tree: Option<Tree>,
 }
 
 use crate::state::coords_at_pos;