From 16c6dfb4f16bd399c70eade799ee5621614f7e83 Mon Sep 17 00:00:00 2001
From: Eli Zaretskii <eliz@gnu.org>
Date: Mon, 6 Jan 2020 21:49:24 +0200
Subject: [PATCH] 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 3d286cb22fb..f3a297a7020 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)
-- 
2.39.2