emacs-27 16c6dfb: Avoid assertion violations in very small-height windows

[Eli Zaretskii]

branch: emacs-27
commit 16c6dfb4f16bd399c70eade799ee5621614f7e83
Author: Eli Zaretskii <address@hidden>
Commit: Eli Zaretskii <address@hidden>

    Avoid assertion violations in very small-height windows
    
    * src/xdisp.c (try_cursor_movement, redisplay_window)
    (row_containing_pos): Skip tab-line glyph rows in addition to
    header-line rows, when working on the top-most glyph row of a
    window.  This avoids assertion violations in set_cursor_from_row.
    (Bug#38966)
---
 src/xdisp.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 3d286cb..f3a297a 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -16244,8 +16244,8 @@ set_cursor_from_row (struct window *w, struct glyph_row 
*row,
   bool string_from_text_prop = false;
 
   /* Don't even try doing anything if called for a mode-line or
-     header-line row, since the rest of the code isn't prepared to
-     deal with such calamities.  */
+     header-line or tab-line row, since the rest of the code isn't
+     prepared to deal with such calamities.  */
   eassert (!row->mode_line_p);
   if (row->mode_line_p)
     return false;
@@ -17504,6 +17504,9 @@ try_cursor_movement (Lisp_Object window, struct 
text_pos startp,
       else
        {
          row = MATRIX_ROW (w->current_matrix, w->last_cursor_vpos);
+         /* Skip the tab-line and header-line rows, if any.  */
+         if (row->tab_line_p)
+           ++row;
          if (row->mode_line_p)
            ++row;
          if (!row->enabled_p)
@@ -17576,6 +17579,9 @@ try_cursor_movement (Lisp_Object window, struct 
text_pos startp,
                  || row->mode_line_p)
                {
                  row = w->current_matrix->rows;
+                 /* Skip the tab-line and header-line rows, if any.  */
+                 if (row->tab_line_p)
+                   ++row;
                  if (row->mode_line_p)
                    ++row;
                }
@@ -17640,8 +17646,9 @@ try_cursor_movement (Lisp_Object window, struct 
text_pos startp,
            ;
          else if (rc != CURSOR_MOVEMENT_SUCCESS
              && MATRIX_ROW_PARTIALLY_VISIBLE_P (w, row)
-             /* Make sure this isn't a header line by any chance, since
-                then MATRIX_ROW_PARTIALLY_VISIBLE_P might yield true.  */
+             /* Make sure this isn't a header line nor a tab-line by
+                any chance, since then MATRIX_ROW_PARTIALLY_VISIBLE_P
+                might yield true.  */
              && !row->mode_line_p
              && !cursor_row_fully_visible_p (w, true, true, true))
            {
@@ -18769,11 +18776,14 @@ redisplay_window (Lisp_Object window, bool 
just_this_one_p)
            }
        }
       /* Finally, fall back on the first row of the window after the
-        header line (if any).  This is slightly better than not
-        displaying the cursor at all.  */
+        tab-line and header line (if any).  This is slightly better
+        than not displaying the cursor at all.  */
       if (!row)
        {
          row = matrix->rows;
+         /* Skip the tab-line and header-line rows, if any.  */
+         if (row->tab_line_p)
+           ++row;
          if (row->mode_line_p)
            ++row;
        }
@@ -19787,7 +19797,9 @@ row_containing_pos (struct window *w, ptrdiff_t charpos,
   ptrdiff_t mindif = BUF_ZV (XBUFFER (w->contents)) + 1;
   int last_y;
 
-  /* If we happen to start on a header-line, skip that.  */
+  /* If we happen to start on a header-line or a tab-line, skip that.  */
+  if (row->tab_line_p)
+    ++row;
   if (row->mode_line_p)
     ++row;
 
@@ -22380,7 +22392,7 @@ find_row_edges (struct it *it, struct glyph_row *row,
       if (STRINGP (it->object)
          /* this is not the first row */
          && row > it->w->desired_matrix->rows
-         /* previous row is not the header line */
+         /* previous row is not the header line or tab-line */
          && !r1->mode_line_p
          /* previous row also ends in a newline from a string */
          && r1->ends_in_newline_from_string_p)