A diff reads as the code it changes: hunks in their file's language, added and removed rows tinted

A .diff or .patch pane, and a command pane whose output is a diff (`git
diff`, `git show`, `diff -u`; told by a `diff --git` line, or `---`/`+++`
with a `@@` under them, in its first rows), colour each hunk's code in the
language of the file its section names (`+++ b/<path>`, `--- a/<path>` for
a deleted file), with tree-sitter, as highlightLocations does for results.

src/diff.zig walks a unified diff by its `@@` counts, so a removed line
that reads `--- x` is no header. Each side of a hunk is parsed as one text
(context and removed lines the old side, context and added lines the new),
so a string or comment across lines colours as it does in the file; a side
no line takes its colours from is not parsed. A section's hunks share a
parse, in pieces of about 40 lines (a hunk past 80 is cut), only those in
view, and each piece's colours are kept by its bytes, so scrolling back and
a terminal's every repaint parse nothing again.

Added and removed lines carry a flag in their style byte; the painter tints
their rows to the pane's edge, a little way from the page toward the
theme's ANSI green or red, and draws the prefix in that hue pushed to read
on it. A file in no known language keeps the old line colours.

A command pane is read once its command has finished: its rows are copied
once (File.DiffOutput, dropped when the pane runs again), so no frame dumps
the scrollback, and painted over what git printed. A running command is
shown as it prints.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 27 insertions, 0 deletions

diff --git a/test/snapshots/diffview.snap b/test/snapshots/diffview.snap
new file mode 100644
index 00000000..b5900db9
--- /dev/null
+++ b/test/snapshots/diffview.snap
@@ -0,0 +1,27 @@
+# A diff pane, for reviewing a change: each hunk's code coloured as Zig (a
+# multi-line string over three lines, `defer` inside it no keyword), added and
+# removed rows tinted to the pane's edge with their prefix in the tint's hue,
+# headers muted.
+dirmk .git
+dirmk src
+file src/shape.zig const std = @import("std");\n\npub const Shape = union(enum) {\n    circle: f32,\n    square: f32,\n    triangle: struct { base: f32, height: f32 },\n\n    const note =\n        \\\\areas, defer\n        \\\\summed\n    ;\n};\n
+file change.diff diff --git a/src/shape.zig b/src/shape.zig\nindex 1111111..2222222 100644\n--- a/src/shape.zig\n+++ b/src/shape.zig\n@@ -1,10 +1,12 @@\n const std = @import("std");\n \n pub const Shape = union(enum) {\n     circle: f32,\n-    square: u8 = 7,\n+    square: f32,\n+    triangle: struct { base: f32, height: f32 },\n \n     const note =\n-        \\\\areas\n+        \\\\areas, defer\n+        \\\\summed\n     ;\n };\n
+start 31 100 change.diff
+wait 8000 Newcol Joincol
+stable 700 20000
+snap diff-pane
+snapstyle diff-colours
+# The same diff printed by a command (`git diff`, here `cat`) into a command
+# pane: its output is told for a diff and coloured the same, over the colours
+# the program printed.
+file cmds.txt cat change.diff\n
+start 31 100 cmds.txt
+wait 8000 cmds.txt
+stable 700 20000
+press middle 7 4
+drag middle 22 4
+release middle 22 4
+wait 10000 exit 0
+stable 700 15000
+snap command-pane
+snapstyle command-colours