From 1190c99212002db4991025c2d63a5154180e4e33 Mon Sep 17 00:00:00 2001
From: CJ van den Berg <cj@vdbonline.com>
Date: Wed, 17 Dec 2025 22:11:52 +0100
Subject: [PATCH] feat: perform gutter diffing against git HEAD if available

---
 src/diff.zig              | 10 +++++++---
 src/tui/editor_gutter.zig | 28 ++++++++++++----------------
 2 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/src/diff.zig b/src/diff.zig
index 2076650..ffded8c 100644
--- a/src/diff.zig
+++ b/src/diff.zig
@@ -47,10 +47,14 @@ pub const AsyncDiffer = struct {
 
     pub const CallBack = fn (from: tp.pid_ref, edits: []Diff) void;
 
-    pub fn diff(self: @This(), cb: *const CallBack, root_dst: Buffer.Root, root_src: Buffer.Root, eol_mode: Buffer.EolMode) tp.result {
-        const text_dst = text_from_root(root_dst, eol_mode) catch |e| return tp.exit_error(e, @errorReturnTrace());
+    pub fn diff_buffer(self: @This(), cb: *const CallBack, buffer: *const Buffer) tp.result {
+        const eol_mode = buffer.file_eol_mode;
+        const text_dst = text_from_root(buffer.root, eol_mode) catch |e| return tp.exit_error(e, @errorReturnTrace());
         errdefer std.heap.c_allocator.free(text_dst);
-        const text_src = text_from_root(root_src, eol_mode) catch |e| return tp.exit_error(e, @errorReturnTrace());
+        const text_src = if (buffer.get_vcs_content()) |vcs_content|
+            std.heap.c_allocator.dupe(u8, vcs_content) catch |e| return tp.exit_error(e, @errorReturnTrace())
+        else
+            text_from_root(buffer.last_save orelse return, eol_mode) catch |e| return tp.exit_error(e, @errorReturnTrace());
         errdefer std.heap.c_allocator.free(text_src);
         const text_dst_ptr: usize = if (text_dst.len > 0) @intFromPtr(text_dst.ptr) else 0;
         const text_src_ptr: usize = if (text_src.len > 0) @intFromPtr(text_src.ptr) else 0;
diff --git a/src/tui/editor_gutter.zig b/src/tui/editor_gutter.zig
index be7fc83..50224a1 100644
--- a/src/tui/editor_gutter.zig
+++ b/src/tui/editor_gutter.zig
@@ -338,11 +338,7 @@ fn diff_update(self: *Self) !void {
         self.diff_symbols_clear();
         return;
     }
-    const editor = self.editor;
-    const new = editor.get_current_root() orelse return;
-    const old = if (editor.buffer) |buffer| buffer.last_save orelse return else return;
-    const eol_mode = if (editor.buffer) |buffer| buffer.file_eol_mode else return;
-    return self.diff_.diff(diff_result, new, old, eol_mode);
+    return self.diff_.diff_buffer(diff_result, self.editor.buffer orelse return);
 }
 
 fn diff_result(from: tp.pid_ref, edits: []diff.Diff) void {
@@ -350,22 +346,22 @@ fn diff_result(from: tp.pid_ref, edits: []diff.Diff) void {
 }
 
 fn diff_result_send(from: tp.pid_ref, edits: []diff.Diff) !void {
-    var buf: [tp.max_message_size]u8 = undefined;
-    var writer: std.Io.Writer = .fixed(&buf);
-    try cbor.writeArrayHeader(&writer, 2);
-    try cbor.writeValue(&writer, "DIFF");
-    try cbor.writeArrayHeader(&writer, edits.len);
+    var buf: std.Io.Writer.Allocating = .init(std.heap.c_allocator);
+    defer buf.deinit();
+    try cbor.writeArrayHeader(&buf.writer, 2);
+    try cbor.writeValue(&buf.writer, "DIFF");
+    try cbor.writeArrayHeader(&buf.writer, edits.len);
     for (edits) |edit| {
-        try cbor.writeArrayHeader(&writer, 4);
-        try cbor.writeValue(&writer, switch (edit.kind) {
+        try cbor.writeArrayHeader(&buf.writer, 4);
+        try cbor.writeValue(&buf.writer, switch (edit.kind) {
             .insert => "I",
             .delete => "D",
         });
-        try cbor.writeValue(&writer, edit.line);
-        try cbor.writeValue(&writer, edit.offset);
-        try cbor.writeValue(&writer, edit.bytes);
+        try cbor.writeValue(&buf.writer, edit.line);
+        try cbor.writeValue(&buf.writer, edit.offset);
+        try cbor.writeValue(&buf.writer, edit.bytes);
     }
-    from.send_raw(tp.message{ .buf = writer.buffered() }) catch return;
+    from.send_raw(tp.message{ .buf = buf.written() }) catch return;
 }
 
 pub fn process_diff(self: *Self, cb: []const u8) MessageFilter.Error!void {