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]>

2 files changed, 146 insertions, 0 deletions

diff --git a/test/snapshots/diffview.golden b/test/snapshots/diffview.golden
new file mode 100644
index 00000000..2da9f6e3
--- /dev/null
+++ b/test/snapshots/diffview.golden
@@ -0,0 +1,119 @@
+== snap diff-pane grid=100x31 cursor=7,3
+|Newcol Joincol Find Grep Help Changelog Tutor Dump Themes Config Debug Exit
+|   New Tty Find Grep Joincol Delcol
+|   /tmp/pardes-snap/diffview/cwd/change.diff Save Tty Collapse Del
+|     1 diff --git a/src/shape.zig b/src/shape.zig
+|     2 index 1111111..2222222 100644
+|     3 --- a/src/shape.zig
+|     4 +++ b/src/shape.zig
+|     5 @@ -1,10 +1,12 @@
+|     6  const std = @import("std");
+|     7
+|     8  pub const Shape = union(enum) {
+|     9      circle: f32,
+|    10 -    square: u8 = 7,
+|    11 +    square: f32,
+|    12 +    triangle: struct { base: f32, height: f32 },
+|    13
+|    14      const note =
+|    15 -        \\areas
+|    16 +        \\areas, defer
+|    17 +        \\summed
+|    18      ;
+|    19  };
+|    20
+== style diff-colours grid=100x31
+|0: 0-99 #b2c3b8,#1d2824,
+|1: 0-1 d,#887455, 2-2 d,#314738, 3-99 #becfc4,#314738,
+|2: 0-1 d,#add38a, 2-2 d,#314738, 3-32 #becfc4,#314738, 33-44 #dfbce5,#314738, 45-99 #becfc4,#314738,
+|3: 0-0 d,#608269, 1-1 d,#0d1410, 2-4 d,#0d1410,b 5-6 #616f64,#0d1410,b 7-99 #b9f480,#0d1410,
+|4: 0-0 d,#608269, 1-4 d,#0d1410, 5-6 #59675c,#0d1410, 7-99 #b9f480,#0d1410,
+|5: 0-0 d,#608269, 1-4 d,#0d1410, 5-6 #59675c,#0d1410, 7-99 #b9f480,#0d1410,
+|6: 0-0 d,#608269, 1-4 d,#0d1410, 5-6 #59675c,#0d1410, 7-99 #b9f480,#0d1410,
+|7: 0-0 d,#608269, 1-4 d,#0d1410, 5-6 #59675c,#0d1410, 7-99 #c9a7ed,#0d1410,
+|8: 0-0 d,#608269, 1-4 d,#0d1410, 5-7 #59675c,#0d1410, 8-19 #e5eee5,#0d1410, 20-26 #c9a7ed,#0d1410, 27-27 #e5eee5,#0d1410, 28-32 #b8d88a,#0d1410, 33-99 #e5eee5,#0d1410,
+|9: 0-0 d,#608269, 1-4 d,#0d1410, 5-99 #59675c,#0d1410,
+|10: 0-0 d,#608269, 1-4 d,#0d1410, 5-7 #59675c,#0d1410, 8-25 #e5eee5,#0d1410, 26-30 #c9a7ed,#0d1410, 31-31 #e5eee5,#0d1410, 32-35 #c9a7ed,#0d1410, 36-99 #e5eee5,#0d1410,
+|11: 0-0 d,#608269, 1-4 d,#0d1410, 5-11 #59675c,#0d1410, 12-99 #e5eee5,#0d1410,
+|12: 0-0 d,#608269, 1-3 d,#0d1410, 4-6 #59675c,#0d1410, 7-7 #f1a39b,#302b25,b 8-11 #f1a39b,#302b25, 12-24 #e5eee5,#302b25, 25-25 #f8c082,#302b25, 26-99 #e5eee5,#302b25,
+|13: 0-0 d,#608269, 1-3 d,#0d1410, 4-6 #59675c,#0d1410, 7-7 #b6ce94,#263025,b 8-11 #b6ce94,#263025, 12-99 #e5eee5,#263025,
+|14: 0-0 d,#608269, 1-3 d,#0d1410, 4-6 #59675c,#0d1410, 7-7 #b6ce94,#263025,b 8-11 #b6ce94,#263025, 12-21 #e5eee5,#263025, 22-28 #c9a7ed,#263025, 29-99 #e5eee5,#263025,
+|15: 0-0 d,#608269, 1-3 d,#0d1410, 4-99 #59675c,#0d1410,
+|16: 0-0 d,#608269, 1-3 d,#0d1410, 4-11 #59675c,#0d1410, 12-99 #e5eee5,#0d1410,
+|17: 0-0 d,#608269, 1-3 d,#0d1410, 4-6 #59675c,#0d1410, 7-7 #f1a39b,#302b25,b 8-15 #f1a39b,#302b25, 16-99 #b8d88a,#302b25,
+|18: 0-0 d,#608269, 1-3 d,#0d1410, 4-6 #59675c,#0d1410, 7-7 #b6ce94,#263025,b 8-15 #b6ce94,#263025, 16-99 #b8d88a,#263025,
+|19: 0-0 d,#608269, 1-3 d,#0d1410, 4-6 #59675c,#0d1410, 7-7 #b6ce94,#263025,b 8-15 #b6ce94,#263025, 16-99 #b8d88a,#263025,
+|20: 0-0 d,#608269, 1-3 d,#0d1410, 4-11 #59675c,#0d1410, 12-99 #e5eee5,#0d1410,
+|21: 0-0 d,#608269, 1-3 d,#0d1410, 4-7 #59675c,#0d1410, 8-99 #e5eee5,#0d1410,
+|22: 0-0 d,#608269, 1-3 d,#0d1410, 4-99 #59675c,#0d1410,
+|23: 0-0 d,#608269, 1-99 d,#0d1410,
+|24: 0-0 d,#608269, 1-99 d,#0d1410,
+|25: 0-0 d,#608269, 1-99 d,#0d1410,
+|26: 0-0 d,#608269, 1-99 d,#0d1410,
+|27: 0-0 d,#608269, 1-99 d,#0d1410,
+|28: 0-0 d,#608269, 1-99 d,#0d1410,
+|29: 0-0 d,#608269, 1-99 d,#0d1410,
+|30: 0-0 d,#608269, 1-99 d,#0d1410,
+== snap command-pane grid=100x31 cursor=7,3
+|Newcol Joincol Find Grep Help Changelog Tutor Dump Themes Config Debug Exit
+|   New Tty Find Grep Joincol Delcol
+|   /tmp/pardes-snap/diffview/cwd/cmds.txt Save Tty Collapse Del
+|     1 cat change.diff                                                                         Exec
+|     2
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|   /tmp/pardes-snap/diffview/cwd (cat change.diff) exit 0 Kill Save Collapse Del
+|       circle: f32,
+|  -    square: u8 = 7,
+|  +    square: f32,
+|  +    triangle: struct { base: f32, height: f32 },
+|
+|       const note =
+|  -        \\areas
+|  +        \\areas, defer
+|  +        \\summed
+|       ;
+|   };
+|  exit 0
+== style command-colours grid=100x31
+|0: 0-99 #b2c3b8,#1d2824,
+|1: 0-1 d,#887455, 2-2 d,#314738, 3-99 #becfc4,#314738,
+|2: 0-1 d,#add38a, 2-2 d,#314738, 3-32 #becfc4,#314738, 33-41 #dfbce5,#314738, 42-99 #becfc4,#314738,
+|3: 0-0 d,#608269, 1-1 d,#0d1410, 2-4 d,#0d1410,b 5-6 #616f64,#0d1410,b 7-93 #e5eee5,#0d1410, 94-94 #e5eee5,#1d2824, 95-99 #b2c3b8,#1d2824,
+|4: 0-0 d,#608269, 1-4 d,#0d1410, 5-99 #59675c,#0d1410,
+|5: 0-0 d,#608269, 1-99 d,#0d1410,
+|6: 0-0 d,#608269, 1-99 d,#0d1410,
+|7: 0-0 d,#608269, 1-99 d,#0d1410,
+|8: 0-0 d,#608269, 1-99 d,#0d1410,
+|9: 0-0 d,#608269, 1-99 d,#0d1410,
+|10: 0-0 d,#608269, 1-99 d,#0d1410,
+|11: 0-0 d,#608269, 1-99 d,#0d1410,
+|12: 0-0 d,#608269, 1-99 d,#0d1410,
+|13: 0-0 d,#608269, 1-99 d,#0d1410,
+|14: 0-0 d,#608269, 1-99 d,#0d1410,
+|15: 0-0 d,#608269, 1-99 d,#0d1410,
+|16: 0-0 d,#608269, 1-99 d,#0d1410,
+|17: 0-1 d,#496656, 2-2 d,#1d2824, 3-99 #b2c3b8,#1d2824,
+|18: 0-0 d,#152019, 1-6 d,#0d1410, 7-99 #e5eee5,#0d1410,
+|19: 0-0 d,#152019, 1-1 d,#0d1410, 2-2 #f1a39b,#302b25,b 3-6 #f1a39b,#302b25, 7-19 #e5eee5,#302b25, 20-20 #f8c082,#302b25, 21-99 #e5eee5,#302b25,
+|20: 0-0 d,#152019, 1-1 d,#0d1410, 2-2 #b6ce94,#263025,b 3-6 #b6ce94,#263025, 7-99 #e5eee5,#263025,
+|21: 0-0 d,#152019, 1-1 d,#0d1410, 2-2 #b6ce94,#263025,b 3-6 #b6ce94,#263025, 7-16 #e5eee5,#263025, 17-23 #c9a7ed,#263025, 24-99 #e5eee5,#263025,
+|22: 0-0 d,#152019, 1-99 d,#0d1410,
+|23: 0-0 d,#608269, 1-6 d,#0d1410, 7-99 #e5eee5,#0d1410,
+|24: 0-0 d,#608269, 1-1 d,#0d1410, 2-2 #f1a39b,#302b25,b 3-10 #f1a39b,#302b25, 11-99 #b8d88a,#302b25,
+|25: 0-0 d,#608269, 1-1 d,#0d1410, 2-2 #b6ce94,#263025,b 3-10 #b6ce94,#263025, 11-99 #b8d88a,#263025,
+|26: 0-0 d,#608269, 1-1 d,#0d1410, 2-2 #b6ce94,#263025,b 3-10 #b6ce94,#263025, 11-99 #b8d88a,#263025,
+|27: 0-0 d,#608269, 1-6 d,#0d1410, 7-99 #e5eee5,#0d1410,
+|28: 0-0 d,#608269, 1-2 d,#0d1410, 3-99 #e5eee5,#0d1410,
+|29: 0-0 d,#608269, 1-1 d,#0d1410, 2-99 #e5eee5,#0d1410,
+|30: 0-0 d,#152019, 1-99 d,#0d1410,
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