A pane tag wraps onto rows and can collapse to one, as acme's does

acme's frame wraps a tag at its right edge and the window grows to show
every row (wind.c wintaglines); Tagup/Tagdown shrink it to one row and back.
Pane tags used to be one row, scrolled sideways to the caret. Now a tag's
lines wrap at its width (one cell kept for the caret past a full row) and it
starts expanded; insert-mode Up on the first row collapses it, Down on the
last row expands it, and Alt-Up/Alt-Down do so in either mode. A word the
wrap breaks across rows is still one word to a click and a selection.
Column and workspace tags keep scrolling sideways.

Tests read body rows relative to the body's first row; the 41 snapshot
goldens that moved were re-recorded by name after a programmatic check that
each differs only by body rows shifting under the taller tags, and twelve
scripts whose clicks targeted fixed rows now click the same text.

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

1 files changed, 28 insertions, 3 deletions

diff --git a/src/pardes.zig b/src/pardes.zig
index a85c97ab..992311a2 100644
--- a/src/pardes.zig
+++ b/src/pardes.zig
@@ -5319,6 +5319,12 @@ pub const Pardes = struct {
             return;
         }
         const pane = p.panes[p.active] orelse return;
+        // Alt-Down and Alt-Up in a pane's tag expand and collapse it, in
+        // either mode: acme's Tagdown and Tagup (plan9port text.c:776).
+        if (pane.focus == .tag and key.alt and !key.ctrl and (key.cp == Key.down or key.cp == Key.up) and tagline.focusedHeader(p) == null) {
+            pane.tag_expanded = key.cp == Key.down;
+            return;
+        }
         // An open prompt takes the keys even when it answers for a header.
         const header = if (pane.prompt != .none) null else tagline.focusedHeader(p);
         if (header == null and pane.isTerminal() and pane.body.mode == .tty and pane.focus == .body and pane.prompt == .none) {
@@ -6142,11 +6148,30 @@ pub const Pardes = struct {
                 }
                 pane.tag_lead = lead;
             }
-            const lines = std.mem.count(u8, tagline.curTail(pane), "\n") + 1;
-            pane.tag_rows = @intCast(@min(lines, MAX_TAG_ROWS, @max(BOX_H, r.h -| 1)));
+            // A row per shown row: the tag's lines wrapped at its width.
+            var wrap_room: [32 * 1024]u8 = undefined;
+            var wrap_fba = std.heap.FixedBufferAllocator.init(&wrap_room);
+            const wa = wrap_fba.allocator();
+            var lines = std.mem.count(u8, tagline.curTail(pane), "\n") + 1;
+            var wanted = lines;
+            var caret_row: usize = @intCast(@max(0, pane.tag.cur_row));
+            if (tagline.prefixIn(wa, pane)) |prefix| {
+                if (std.mem.concat(wa, u8, &.{ prefix, tagline.curTail(pane) })) |whole| {
+                    if (tagline.wrapTag(wa, whole, tagline.tagWidth(p, id))) |shown| {
+                        lines = shown.rows();
+                        // Collapsed, one row, as acme's Tagup sets taglines to 1
+                        // (plan9port text.c:786).
+                        wanted = if (pane.tag_expanded) lines else 1;
+                        const cur = modal.offsetAt(whole, .{ .row = caret_row, .col = @intCast(@max(0, pane.tag.cur_col)) });
+                        caret_row = std.mem.count(u8, shown.text[0..@min(shown.fromReal(cur), shown.text.len)], "\n");
+                    } else |_| {}
+                } else |_| {}
+            } else |_| {}
+            if (!pane.tag_expanded) wanted = 1;
+            pane.tag_rows = @intCast(@min(wanted, MAX_TAG_ROWS, @max(BOX_H, r.h -| 1)));
             if (pane.collapsed) pane.tag_rows = BOX_H;
             if (pane.focus == .tag and pane.prompt != .name) {
-                const cur: usize = @intCast(@max(0, pane.tag.cur_row));
+                const cur: usize = caret_row;
                 var top: usize = pane.tag_top;
                 if (cur < top) top = cur;
                 if (cur >= top + pane.tag_rows) top = cur + 1 - pane.tag_rows;