Joincol is refused, as Newcol is, when the joined column cannot give each pane its tag and 2 rows

Joincol moved every pane of the keyboard's column into the next one
whether they fit or not. Two columns of two panes in a 12-row window
became one column of four, wanting 12 rows where 10 were free, a layout
that `size` then refused as it stood. Joincol now tries the join in place
first (layout.joinFits: the panes and width moved, minimaFit asked,
everything put back, nothing dropped or logged). A join that does not
fit is refused, "Joincol: no space: the joined column cannot give each
pane its tag and 2 rows".

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

1 files changed, 26 insertions, 1 deletions

diff --git a/src/layout.zig b/src/layout.zig
index 4aebcf28..a2211dfd 100644
--- a/src/layout.zig
+++ b/src/layout.zig
@@ -360,13 +360,38 @@ pub fn noteColumn(p: *Pardes, what: []const u8, serial: u32) void {
 pub fn joinCol(p: *Pardes, c: usize) void {
     if (c + 1 >= p.ncol) return;
     const dst = c + 1;
+    joinPanes(p, c, dst);
+    dropColumn(p, c);
+}
+
+/// Whether column `c` joined into the one on its right leaves every pane
+/// its tag and 2 rows (minimaFit), tried in place and undone: nothing is
+/// dropped or logged for a join that does not fit.
+pub fn joinFits(p: *Pardes, c: usize) bool {
+    if (c + 1 >= p.ncol) return true;
+    const dst = c + 1;
+    const n = p.col_n[c];
+    const had = p.col_n[dst];
+    const weights = .{ p.col_weight[c], p.col_weight[dst] };
+    const panes_c = p.col_panes[c];
+    joinPanes(p, c, dst);
+    const fits = minimaFit(p);
+    p.col_n[dst] = had;
+    p.col_n[c] = n;
+    p.col_panes[c] = panes_c;
+    p.col_weight[c] = weights[0];
+    p.col_weight[dst] = weights[1];
+    compute(p);
+    return fits;
+}
+
+fn joinPanes(p: *Pardes, c: usize, dst: usize) void {
     for (0..p.col_n[c]) |k| p.col_panes[dst][p.col_n[dst] + k] = p.col_panes[c][k];
     p.col_n[dst] += p.col_n[c];
     p.col_n[c] = 0;
     // The width goes right, where the panes went.
     p.col_weight[dst] +|= p.col_weight[c];
     p.col_weight[c] = 0;
-    dropColumn(p, c);
 }
 
 /// Put new pane `id` in column `c` as acme's makenewwindow does