From e6ff64843b4a8986e9740c576f346690217cf5a7 Mon Sep 17 00:00:00 2001
From: Gabriel Schneider <gbrls@0x4200.cafe>
Date: Thu, 1 Oct 2026 01:14:37 -0300
Subject: A +Pager pane whose text is a diff is drawn and looked at as a diff,
 as a diff command pane is: git diff, show and log -p page into review

With git paging into +Pager, a diff arrived as plain text: no colour
for its sides and a right click on a hunk line searched the word. A
+Pager pane now notes, as its text is set, whether its first 64 KiB
holds a diff header or a unified hunk, and such a pane takes the diff
highlighting and the diff look every diff pane has.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/File.zig   | 33 +++++++++++++++++++++++++++++++++
 src/panes.zig  |  2 +-
 src/pardes.zig |  1 +
 3 files changed, 35 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/File.zig b/src/File.zig
index d16d4fc0..c738ee58 100644
--- a/src/File.zig
+++ b/src/File.zig
@@ -72,6 +72,9 @@ pub const State = struct {
     /// Its file was deleted on disk: said once (`deleted`) until it is
     /// written or found again.
     disk_gone: bool = false,
+    /// A +Pager pane (`pardes -`) whose text is a diff (`git diff`, `show`,
+    /// `log -p`): drawn and looked at as a diff (Pane.colorAlgo).
+    pager_diff: bool = false,
     /// Seconds of the last content change, for the filesystem's stat; zero until edited.
     mtime: u32 = 0,
     /// Non-null for a generated output buffer rather than an on-disk file.
@@ -998,6 +1001,36 @@ pub fn setContentSpan(p: *Pardes, f: *State, new: []u8, span: ?Span) void {
     f.highlights = &.{};
     f.highlight_start = 0;
     f.syntax_dirty = true;
+    if (std.mem.endsWith(u8, f.path, "/+Pager")) f.pager_diff = looksLikeDiff(new[0..@min(new.len, 64 * 1024)]);
+}
+
+/// Whether `head`, a text's first bytes, holds a diff: a `diff` header, or
+/// a unified hunk's `---`, `+++` and `@@` lines.
+pub fn looksLikeDiff(head: []const u8) bool {
+    if (std.mem.startsWith(u8, head, "diff ") or std.mem.indexOf(u8, head, "\ndiff ") != null) return true;
+    const minus = std.mem.indexOf(u8, head, "--- ") orelse return false;
+    const plus = std.mem.indexOfPos(u8, head, minus, "\n+++ ") orelse return false;
+    return std.mem.indexOfPos(u8, head, plus, "\n@@ ") != null;
+}
+
+test "a +Pager pane holding a diff is drawn and looked at as one; holding other text, as text" {
+    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true });
+    defer p.deinit();
+    const pane = try p.setTestFile("");
+    const f = &pane.file.?;
+    p.gpa.free(f.path);
+    f.path = try p.gpa.dupe(u8, "/tmp/+Pager");
+    setContent(p, f, try p.gpa.dupe(u8, "commit abc\n\ndiff --git a/x b/x\n--- a/x\n+++ b/x\n@@ -1 +1 @@\n-a\n+b\n"));
+    try std.testing.expect(pane.colorAlgo() == .diff);
+    try std.testing.expect(pardes.look.diffLines(p, pane) != null);
+    setContent(p, f, try p.gpa.dupe(u8, "commit abc\n\n    a plain log\n"));
+    try std.testing.expect(pane.colorAlgo() != .diff);
+}
+
+test "a pager's text is a diff when it holds a diff header or a unified hunk" {
+    try std.testing.expect(looksLikeDiff("commit abc\nAuthor: x\n\n    msg\n\ndiff --git a/f b/f\n"));
+    try std.testing.expect(looksLikeDiff("--- a/f\n+++ b/f\n@@ -1 +1 @@\n-a\n+b\n"));
+    try std.testing.expect(!looksLikeDiff("commit abc\nAuthor: x\n\n    plain log\n"));
 }
 
 pub fn restoreSnap(pane: *Pane, f: *State, snap: Snapshot) void {
diff --git a/src/panes.zig b/src/panes.zig
index a395d6ed..9d1b7571 100644
--- a/src/panes.zig
+++ b/src/panes.zig
@@ -448,7 +448,7 @@ pub const Pane = struct {
         if (pane.isTerminal()) return .tty;
         if (pane.file) |f| {
             if (f.mini != null) return .source;
-            if (std.mem.endsWith(u8, f.path, ".diff") or std.mem.endsWith(u8, f.path, ".patch")) return .diff;
+            if (std.mem.endsWith(u8, f.path, ".diff") or std.mem.endsWith(u8, f.path, ".patch") or f.pager_diff) return .diff;
             if (f.output != null) {
                 const tr = Output.fileTraits(f.output);
                 if (tr.locations) return .locations;
diff --git a/src/pardes.zig b/src/pardes.zig
index 84b891e5..5d0ab7e8 100644
--- a/src/pardes.zig
+++ b/src/pardes.zig
@@ -4640,6 +4640,7 @@ pub const Pardes = struct {
                 const named = try std.fs.path.join(gpa, &.{ dir, "+Pager" });
                 gpa.free(shown.file.?.path);
                 shown.file.?.path = named;
+                shown.file.?.pager_diff = panes.File.looksLikeDiff(content[0..@min(content.len, 64 * 1024)]);
                 p.oneColumn();
             },
             .embedded => {
-- 
cgit v1.3