One diff-aware expansion for a click, a 9P whole-line look and an empty event write-back; a blank context line resolves to its path:line

The mouse expanded a diff line by its kind (a header or a hunk line's
prefix to the line's address, a hunk line's code to words), but an
empty look written back to event used the plain word expansion, so ML
on a `+` took nothing, and a 9P look of a blank context line (` `) was
refused as whitespace. look.diffClick is now the one answer: the
mouse, the whole-line look and the event write-back all ask it, and a
blank context line is a line like any other. A test asks all three on
each kind of line.

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

1 files changed, 95 insertions, 3 deletions

diff --git a/src/look.zig b/src/look.zig
index 4d23582b..17ec8a1c 100644
--- a/src/look.zig
+++ b/src/look.zig
@@ -1567,16 +1567,45 @@ pub fn diffAddress(pane: *const Pane, lines: []const []const u8, row: usize, buf
     return target.address(buf);
 }
 
+/// What a click at byte `col` of line `row` of a diff pane takes, the one
+/// answer for every way a click arrives (a mouse click, a 9P look of the
+/// whole line, an empty look or exec written back to `event`): a file or
+/// hunk header anywhere, or a hunk line on its `+`/`-`/` ` prefix, is the
+/// address the line names (diffAddress); a hunk line's code is words, from
+/// `word_from` on, the prefix never one of them. Null when the pane shows
+/// no diff or the line is no part of one.
+pub const DiffClick = struct { address: ?[]const u8 = null, word_from: usize = 0 };
+
+pub fn diffClick(p: *Pardes, pane: *Pane, row: usize, col: usize, buf: []u8) ?DiffClick {
+    const lines = diffLines(p, pane) orelse return null;
+    return diffClickIn(pane, lines, row, col, buf);
+}
+
+fn diffClickIn(pane: *const Pane, lines: []const []const u8, row: usize, col: usize, buf: []u8) ?DiffClick {
+    if (row >= lines.len) return null;
+    const line = lines[row];
+    const address = diffAddress(pane, lines, row, buf) orelse return null;
+    const target = diff.targetAt(lines, row, pane.file == null) orelse return null;
+    const prefixed = line.len > 0 and std.mem.indexOfScalar(u8, "+- ", line[0]) != null;
+    switch (target.kind) {
+        .context, .added, .removed => if (!(col == 0 and prefixed)) return .{ .word_from = @intFromBool(prefixed) },
+        else => {},
+    }
+    return .{ .address = address };
+}
+
 /// A look written over 9P of a whole line of a diff pane (the cursor's line
-/// first, then the first after it): its address, as a click there makes.
+/// first, then the first after it): what a click on its first column takes.
+/// A blank context line (` `) is a line too.
 fn diffLineAddress(p: *Pardes, pane: *Pane, operand: []const u8, buf: []u8) ?[]const u8 {
     const text = std.mem.trimEnd(u8, operand, "\r\n");
-    if (std.mem.trim(u8, text, " \t").len == 0) return null;
+    if (text.len == 0) return null;
     const lines = diffLines(p, pane) orelse return null;
     const cur: usize = @intCast(@max(0, pane.body.cur_row));
     for (0..lines.len) |k| {
         const i = (cur + k) % lines.len;
-        if (std.mem.eql(u8, std.mem.trimEnd(u8, lines[i], "\r"), text)) return diffAddress(pane, lines, i, buf);
+        if (std.mem.eql(u8, std.mem.trimEnd(u8, lines[i], "\r"), text))
+            return (diffClickIn(pane, lines, i, 0, buf) orelse return null).address;
     }
     return null;
 }
@@ -2230,6 +2259,69 @@ test "Look on a diff: headers and a hunk line's prefix are the whole line, hover
     }
 }
 
+test "a click, a 9P whole-line look and an empty event write-back take one expansion on every kind of diff line, a blank context line too" {
+    if (!platform_has_fs) return;
+    const diff_text =
+        \\diff --git a/src/new.zig b/src/new.zig
+        \\--- a/src/new.zig
+        \\+++ b/src/new.zig
+        \\@@ -2,3 +2,3 @@ fn x() void {
+        \\ two
+        \\-drei
+        \\+three
+        \\ 
+        \\
+    ;
+    var fx: DiffFixture = undefined;
+    try fx.init(true, &.{.{ "src/new.zig", "one\ntwo\nthree\n\nfive\n" }}, diff_text);
+    defer fx.tmp.cleanup();
+    const p = try Pardes.init(std.testing.allocator, .{ .cols = 100, .rows = 30 });
+    defer p.deinit();
+    const pane = try fx.open(p, diff_text);
+    pane.tag_expanded = false;
+    const Point = struct { row: u16, col: u16, want: []const u8, whole_line: bool = true };
+    const points = [_]Point{
+        .{ .row = 0, .col = 0, .want = "src/new.zig" }, // diff --git
+        .{ .row = 1, .col = 0, .want = "src/new.zig" }, // ---
+        .{ .row = 2, .col = 0, .want = "src/new.zig" }, // +++
+        .{ .row = 3, .col = 0, .want = "src/new.zig:2" }, // @@
+        .{ .row = 4, .col = 0, .want = "src/new.zig:2" }, // a context line's ` `
+        .{ .row = 5, .col = 0, .want = "src/new.zig:3" }, // `-`
+        .{ .row = 6, .col = 0, .want = "src/new.zig:3" }, // `+`
+        .{ .row = 7, .col = 0, .want = "src/new.zig:4" }, // a blank context line
+        .{ .row = 6, .col = 3, .want = "three", .whole_line = false }, // code: a word
+    };
+    var frame = std.heap.ArenaAllocator.init(std.testing.allocator);
+    defer frame.deinit();
+    for (points) |at| {
+        p.active = 0;
+        pane.file.?.scroll = 0;
+        pane.body.cur_row = 0;
+        p.sync();
+        _ = frame.reset(.retain_capacity);
+        _ = try p.render(frame.allocator());
+        // The mouse's.
+        const rect = p.rects[0];
+        const x = rect.x + config.GUTTER + panes.File.gutterWidth(pane) + at.col;
+        const y = p.bodyTop(pane, rect) + at.row;
+        const pointed = edit.pointerTextSelection(p, 0, x, y, null, null) orelse return error.NothingPointed;
+        const clicked = exec.pointerOperand(p, pane, pointed.sel).text orelse return error.NothingClicked;
+        try std.testing.expectEqualStrings(at.want, clicked);
+        // An empty record written back to event, at the same byte.
+        const body = pane.file.?.content;
+        const line_start = modal.lineStartOffset(body, at.row);
+        const written = pardes.ctlfs.events.expandAt(p, pane, body, line_start + at.col, true);
+        try std.testing.expectEqualStrings(at.want, written);
+        // A 9P look of the whole line.
+        if (at.whole_line) {
+            const lines = diffLines(p, pane).?;
+            var buf: [4096 + 32]u8 = undefined;
+            const whole = diffLineAddress(p, pane, lines[at.row], &buf) orelse return error.NoWholeLineAddress;
+            try std.testing.expectEqualStrings(at.want, whole);
+        }
+    }
+}
+
 test "Look outside a diff pane expands and looks as ever" {
     const p = try Pardes.init(std.testing.allocator, .{ .cols = 100, .rows = 30 });
     defer p.deinit();