1 files changed, 52 insertions, 3 deletions

diff --git a/helix-view/src/gutter.rs b/helix-view/src/gutter.rs
index 61a17791..377518fb 100644
--- a/helix-view/src/gutter.rs
+++ b/helix-view/src/gutter.rs
@@ -12,7 +12,7 @@ fn count_digits(n: usize) -> usize {
     std::iter::successors(Some(n), |&n| (n >= 10).then(|| n / 10)).count()
 }
 
-pub type GutterFn<'doc> = Box<dyn Fn(usize, bool, &mut String) -> Option<Style> + 'doc>;
+pub type GutterFn<'doc> = Box<dyn FnMut(usize, bool, &mut String) -> Option<Style> + 'doc>;
 pub type Gutter =
     for<'doc> fn(&'doc Editor, &'doc Document, &View, &Theme, bool, usize) -> GutterFn<'doc>;
 
@@ -31,6 +31,7 @@ impl GutterType {
             }
             GutterType::LineNumbers => line_numbers(editor, doc, view, theme, is_focused),
             GutterType::Spacer => padding(editor, doc, view, theme, is_focused),
+            GutterType::Diff => diff(editor, doc, view, theme, is_focused),
         }
     }
 
@@ -39,6 +40,7 @@ impl GutterType {
             GutterType::Diagnostics => 1,
             GutterType::LineNumbers => line_numbers_width(_view, doc),
             GutterType::Spacer => 1,
+            GutterType::Diff => 1,
         }
     }
 }
@@ -83,6 +85,53 @@ pub fn diagnostic<'doc>(
     })
 }
 
+pub fn diff<'doc>(
+    _editor: &'doc Editor,
+    doc: &'doc Document,
+    _view: &View,
+    theme: &Theme,
+    _is_focused: bool,
+) -> GutterFn<'doc> {
+    let added = theme.get("diff.plus");
+    let deleted = theme.get("diff.minus");
+    let modified = theme.get("diff.delta");
+    if let Some(diff_handle) = doc.diff_handle() {
+        let hunks = diff_handle.hunks();
+        let mut hunk_i = 0;
+        let mut hunk = hunks.nth_hunk(hunk_i);
+        Box::new(move |line: usize, _selected: bool, out: &mut String| {
+            // truncating the line is fine here because we don't compute diffs
+            // for files with more lines than i32::MAX anyways
+            // we need to special case removals here
+            // these technically do not have a range of lines to highlight (`hunk.after.start == hunk.after.end`).
+            // However we still want to display these hunks correctly we must not yet skip to the next hunk here
+            while hunk.after.end < line as u32
+                || !hunk.is_pure_removal() && line as u32 == hunk.after.end
+            {
+                hunk_i += 1;
+                hunk = hunks.nth_hunk(hunk_i);
+            }
+
+            if hunk.after.start > line as u32 {
+                return None;
+            }
+
+            let (icon, style) = if hunk.is_pure_insertion() {
+                ("▍", added)
+            } else if hunk.is_pure_removal() {
+                ("▔", deleted)
+            } else {
+                ("▍", modified)
+            };
+
+            write!(out, "{}", icon).unwrap();
+            Some(style)
+        })
+    } else {
+        Box::new(move |_, _, _| None)
+    }
+}
+
 pub fn line_numbers<'doc>(
     editor: &'doc Editor,
     doc: &'doc Document,
@@ -226,8 +275,8 @@ pub fn diagnostics_or_breakpoints<'doc>(
     theme: &Theme,
     is_focused: bool,
 ) -> GutterFn<'doc> {
-    let diagnostics = diagnostic(editor, doc, view, theme, is_focused);
-    let breakpoints = breakpoints(editor, doc, view, theme, is_focused);
+    let mut diagnostics = diagnostic(editor, doc, view, theme, is_focused);
+    let mut breakpoints = breakpoints(editor, doc, view, theme, is_focused);
 
     Box::new(move |line, selected, out| {
         breakpoints(line, selected, out).or_else(|| diagnostics(line, selected, out))