Some old tmux versions can sometimes generate layout strings which have

the incorrect size for the top cell. Previously tmux didn't care but now
that panes can be partly hidden, the size matters and is checked more
strictly. So add some code to fix up the most common problem and a
sanity check to reject layouts with any other size problems. Reported by
Aleksandrs Ledovskis in GitHub issue 1930.

cmd-list-keys.c

@@ -125,7 +125,7 @@ cmd_list_keys_exec(struct cmd *self, struct cmdq_item *item)
 
 			cp = utf8_padcstr(table->name, tablewidth);
 			cplen = strlen(cp) + 1;
-			while (tmpused + cplen + 1>= tmpsize) {
+			while (tmpused + cplen + 1 >= tmpsize) {
 				tmpsize *= 2;
 				tmp = xrealloc(tmp, tmpsize);
 			}

layout-custom.c

@@ -116,13 +116,49 @@ layout_append(struct layout_cell *lc, char *buf, size_t len)
 	return (0);
 }
 
+/* Check layout sizes fit. */
+static int
+layout_check(struct layout_cell *lc)
+{
+	struct layout_cell	*lcchild;
+	u_int			 n = 0;
+
+	switch (lc->type) {
+	case LAYOUT_WINDOWPANE:
+		break;
+	case LAYOUT_LEFTRIGHT:
+		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
+			if (lcchild->sy != lc->sy)
+				return (0);
+			if (!layout_check(lcchild))
+				return (0);
+			n += lcchild->sx + 1;
+		}
+		if (n - 1 != lc->sx)
+			return (0);
+		break;
+	case LAYOUT_TOPBOTTOM:
+		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
+			if (lcchild->sx != lc->sx)
+				return (0);
+			if (!layout_check(lcchild))
+				return (0);
+			n += lcchild->sy + 1;
+		}
+		if (n - 1 != lc->sy)
+			return (0);
+		break;
+	}
+	return (1);
+}
+
 /* Parse a layout string and arrange window as layout. */
 int
 layout_parse(struct window *w, const char *layout)
 {
 	struct layout_cell	*lc, *lcchild;
 	struct window_pane	*wp;
-	u_int			 npanes, ncells;
+	u_int			 npanes, ncells, sx = 0, sy = 0;
 	u_short			 csum;
 
 	/* Check validity. */
@@ -153,6 +189,37 @@ layout_parse(struct window *w, const char *layout)
 		layout_destroy_cell(w, lcchild, &lc);
 	}
 
+	/*
+	 * It appears older versions of tmux were able to generate layouts with
+	 * an incorrect top cell size - if it is larger than the top child then
+	 * correct that (if this is still wrong the check code will catch it).
+	 */
+	switch (lc->type) {
+	case LAYOUT_WINDOWPANE:
+		break;
+	case LAYOUT_LEFTRIGHT:
+		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
+			sy = lcchild->sy + 1;
+			sx += lcchild->sx + 1;
+		}
+		break;
+	case LAYOUT_TOPBOTTOM:
+		TAILQ_FOREACH(lcchild, &lc->cells, entry) {
+			sx = lcchild->sx + 1;
+			sy += lcchild->sy + 1;
+		}
+		break;
+	}
+	if (lc->sx != sx || lc->sy != sy) {
+		log_debug("fix layout %u,%u to %u,%u", lc->sx, lc->sy, sx,sy);
+		layout_print_cell(lc, __func__, 0);
+		lc->sx = sx - 1; lc->sy = sy - 1;
+	}
+
+	/* Check the new layout. */
+	if (!layout_check(lc))
+		return (-1);
+
 	/* Resize to the layout size. */
 	window_resize(w, lc->sx, lc->sy);