compositor: handle invalid screen positions after resize gracefully

The screen resize logic needs to be refactored to be simpler and more
deterministic. Until then, we need to handle attempts to draw outside of the
screen size gracefully, just like the old vim code did.

fixes #9989

2 files changed, 21 insertions, 3 deletions

diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 99ccce1793..1b2143c419 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -4375,7 +4375,7 @@ static void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int endcol,
   screen_adjust_grid(&grid, &row, &coloff);
 
   // Safety check. Avoids clang warnings down the call stack.
-  if (grid->chars == NULL || row >= grid->Rows || col >= grid->Columns) {
+  if (grid->chars == NULL || row >= grid->Rows || coloff >= grid->Columns) {
     DLOG("invalid state, skipped");
     return;
   }
diff --git a/src/nvim/ui_compositor.c b/src/nvim/ui_compositor.c
index 2cb3cf7ee7..9517b362af 100644
--- a/src/nvim/ui_compositor.c
+++ b/src/nvim/ui_compositor.c
@@ -480,8 +480,26 @@ static void ui_comp_raw_line(UI *ui, Integer grid, Integer row,
   if (curgrid != &default_grid) {
     flags = flags & ~kLineFlagWrap;
   }
-  assert(row < default_grid.Rows);
-  assert(clearcol <= default_grid.Columns);
+
+  assert(endcol <= clearcol);
+
+  // TODO(bfredl): this should not really be necessary. But on some condition
+  // when resizing nvim, a window will be attempted to be drawn on the older
+  // and possibly larger global screen size.
+  if (row >= default_grid.Rows) {
+    DLOG("compositor: invalid row %"PRId64" on grid %"PRId64, row, grid);
+    return;
+  }
+  if (clearcol > default_grid.Columns) {
+    DLOG("compositor: invalid last column %"PRId64" on grid %"PRId64,
+         clearcol, grid);
+    if (startcol >= default_grid.Columns) {
+      return;
+    }
+    clearcol = default_grid.Columns;
+    endcol = MIN(endcol, clearcol);
+  }
+
   if (flags & kLineFlagInvalid
       || kv_size(layers) > curgrid->comp_index+1
       || curgrid->blending) {