new panes reject a too-short split parent: if the chosen parent would leave the new pane under 2 body rows, splitParent swaps in a qualifying pane (same column first), else the tallest pane anywhere; applied to Alt-n, look-dir, placeDoc and ttyForDir. New splitparent.snap.

3 files changed, 161 insertions, 8 deletions

diff --git a/src/pardes.zig b/src/pardes.zig
index c14154e5..0219d474 100644
--- a/src/pardes.zig
+++ b/src/pardes.zig
@@ -1203,9 +1203,10 @@ pub const Pardes = struct {
             const free = p.freeSlot() orelse return;
             const nt = p.newShell(free, "") catch return;
             nt.greet = true;
-            const f = p.layoutFindTerm(p.active).?;
+            const src = p.splitParent(p.active);
+            const f = p.layoutFindTerm(src).?;
             p.layoutInsert(f.col, f.idx + 1, free);
-            p.splitBelow(p.active, nt);
+            p.splitBelow(src, nt);
             p.active = free;
             return;
         }
@@ -3973,6 +3974,26 @@ pub const Pardes = struct {
         if (p.panes[sib]) |s| s.vweight += @as(f32, @floatFromInt(@max(1, p.rects[id].h)));
     }
 
+    /// The parent a new pane splits from must be tall enough that splitBelow
+    /// leaves the NEW pane at least 2 body rows (the parent keeps tag+1 row,
+    /// the new pane needs tag+2). A too-short choice is swapped for a
+    /// qualifying pane (same column first, keeping the split local), else the
+    /// tallest pane anywhere.
+    fn splitParent(p: *Pardes, want: usize) usize {
+        const need = 2 * BOX_H + 3;
+        if (p.rects[want].h >= need) return want;
+        if (p.layoutFindTerm(want)) |f| for (0..p.col_n[f.col]) |k| {
+            if (p.rects[p.col_terms[f.col][k]].h >= need) return p.col_terms[f.col][k];
+        };
+        var tallest = want;
+        for (0..p.ncol) |c| for (0..p.col_n[c]) |k| {
+            const pid = p.col_terms[c][k];
+            if (p.rects[pid].h >= need) return pid;
+            if (p.rects[pid].h > p.rects[tallest].h) tallest = pid;
+        };
+        return tallest;
+    }
+
     /// Open a window BELOW `src` (acme-style) without rebalancing the column:
     /// shrink ONLY src to its content height (cursor row kept visible) and hand
     /// the freed rows to `nw` — together they fill src's old slot and the other
@@ -4039,8 +4060,12 @@ pub const Pardes = struct {
         const nt = p.newShell(free, dir) catch return null;
         nt.greet = false;
         const rc = if (p.ncol > 0) p.ncol - 1 else 0;
-        if (p.col_n[rc] > 0) p.splitBelow(p.col_terms[rc][p.col_n[rc] - 1], nt);
-        p.layoutInsert(rc, p.col_n[rc], free);
+        if (p.col_n[rc] > 0) {
+            const src = p.splitParent(p.col_terms[rc][p.col_n[rc] - 1]);
+            const f = p.layoutFindTerm(src).?;
+            p.splitBelow(src, nt);
+            p.layoutInsert(f.col, f.idx + 1, free);
+        } else p.layoutInsert(rc, p.col_n[rc], free);
         return free;
     }
 
@@ -4225,9 +4250,10 @@ pub const Pardes = struct {
                     const free = p.freeSlot() orelse return;
                     const nt = p.newShell(free, dir) catch return;
                     nt.greet = true;
-                    const f = p.layoutFindTerm(id).?;
+                    const src = p.splitParent(id);
+                    const f = p.layoutFindTerm(src).?;
                     p.layoutInsert(f.col, f.idx + 1, free);
-                    p.splitBelow(id, nt);
+                    p.splitBelow(src, nt);
                     p.active = free;
                 },
                 .file => |target| {
@@ -4359,9 +4385,10 @@ pub const Pardes = struct {
             };
         };
         if (src_id) |sid| {
-            const sf = p.layoutFindTerm(sid).?;
+            const src = p.splitParent(sid);
+            const sf = p.layoutFindTerm(src).?;
             p.layoutInsert(sf.col, sf.idx + 1, free);
-            p.splitBelow(sid, nt);
+            p.splitBelow(src, nt);
             p.active = free;
         } else {
             p.stackDocLeft(free, nt);
diff --git a/test/snapshots/splitparent.golden b/test/snapshots/splitparent.golden
new file mode 100644
index 00000000..b838cdad
--- /dev/null
+++ b/test/snapshots/splitparent.golden
@@ -0,0 +1,99 @@
+== snap shrunk grid=100x30 cursor=4,3
+|Kill Newcol Tutor Debug Colors NextColor Dump
+|  NOR /tmp/pardes-snap/splitparent/cwd Del          NOR /tmp/pardes-snap/splitparent/cwd Del
+|  NOR /tmp/pardes-snap/splitparent/cwd Del
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+== snap swap-parent grid=100x30 cursor=4,7
+|Kill Newcol Tutor Debug Colors NextColor Dump
+|  NOR /tmp/pardes-snap/splitparent/cwd Del          NOR /tmp/pardes-snap/splitparent/cwd Del
+|  NOR /tmp/pardes-snap/splitparent/cwd Del
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+|  NOR /tmp/pardes-snap/splitparent/cwd Del
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+== snap tallest grid=100x5 cursor=54,4
+|Kill Newcol Tutor Debug Colors NextColor Dump
+|  NOR /tmp/pardes-snap/splitparent/cwd Del          NOR /tmp/pardes-snap/splitparent/cwd Del
+|  NOR /tmp/pardes-snap/splitparent/cwd Del
+|  NOR /tmp/pardes-snap/splitparent/cwd Del          NOR /tmp/pardes-snap/splitparent/cwd Del
+|
+== snap regrown grid=100x30 cursor=54,18
+|Kill Newcol Tutor Debug Colors NextColor Dump
+|  NOR /tmp/pardes-snap/splitparent/cwd Del          NOR /tmp/pardes-snap/splitparent/cwd Del
+|  NOR /tmp/pardes-snap/splitparent/cwd Del
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+|  NOR /tmp/pardes-snap/splitparent/cwd Del
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+|                                                    NOR /tmp/pardes-snap/splitparent/cwd Del
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diff --git a/test/snapshots/splitparent.snap b/test/snapshots/splitparent.snap
new file mode 100644
index 00000000..77a1fba1
--- /dev/null
+++ b/test/snapshots/splitparent.snap
@@ -0,0 +1,27 @@
+# a new pane never opens under a too-short parent: Alt-n from a tag-only pane
+# splits the tall sibling in its column instead; when NO pane could leave the
+# newcomer 2 body rows, the tallest one anywhere is split
+start 30 100 -n 3
+stable 700 20000
+# shrink pane 0 (top-left) to just its tagline
+press left 20 16
+drag left 20 2
+release left 20 2
+motion 40 25
+stable 500 8000
+snap shrunk
+# Alt-n from the tag-only pane: the new shell opens below the tall sibling
+# underneath it, not as another 1-row sliver
+key a-n
+stable 700 15000
+snap swap-parent
+# squeeze the grid until no pane is 5 rows tall, then Alt-n again: the
+# tallest pane (right column) is split even though the active one is left
+resize 5 100
+stable 700 15000
+key a-n
+stable 700 15000
+snap tallest
+resize 30 100
+stable 700 15000
+snap regrown