Fix shrinking of the tab-bar

* src/haikufns.c (haiku_change_tab_bar_height):
* src/pgtkfns.c (pgtk_change_tab_bar_height):
* src/nsfns.m (ns_change_tab_bar_height):
* src/w32fns.c (w32_change_tab_bar_height):
* src/xfns.c (x_change_tab_bar_height): Don't let the number of
tab-bar lines degenerate to zero due to integer division.
(Bug#60210)

src/haikufns.c

@@ -175,19 +175,17 @@ haiku_change_tool_bar_height (struct frame *f, int height)
 void
 haiku_change_tab_bar_height (struct frame *f, int height)
 {
-  int unit, old_height, lines;
+  int unit = FRAME_LINE_HEIGHT (f);
-  Lisp_Object fullscreen;
+  int old_height = FRAME_TAB_BAR_HEIGHT (f);
-
-  unit = FRAME_LINE_HEIGHT (f);
-  old_height = FRAME_TAB_BAR_HEIGHT (f);
-  fullscreen = get_frame_param (f, Qfullscreen);
 
   /* This differs from the tool bar code in that the tab bar height is
      not rounded up.  Otherwise, if redisplay_tab_bar decides to grow
      the tab bar by even 1 pixel, FRAME_TAB_BAR_LINES will be changed,
      leading to the tab bar height being incorrectly set upon the next
      call to x_set_font.  (bug#59285) */
-  lines = height / unit;
+  int lines = height / unit;
+  if (lines == 0 && height != 0)
+    lines = 1;
 
   /* Make sure we redisplay all windows in this frame.  */
   fset_redisplay (f);
@@ -208,6 +206,8 @@ haiku_change_tab_bar_height (struct frame *f, int height)
 
   if (!f->tab_bar_resized)
     {
+      Lisp_Object fullscreen = get_frame_param (f, Qfullscreen);
+
       /* As long as tab_bar_resized is false, effectively try to change
 	 F's native height.  */
       if (NILP (fullscreen) || EQ (fullscreen, Qfullwidth))

src/nsfns.m

@@ -632,19 +632,17 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
 void
 ns_change_tab_bar_height (struct frame *f, int height)
 {
-  int unit, old_height, lines;
+  int unit = FRAME_LINE_HEIGHT (f);
-  Lisp_Object fullscreen;
+  int old_height = FRAME_TAB_BAR_HEIGHT (f);
-
-  unit = FRAME_LINE_HEIGHT (f);
-  old_height = FRAME_TAB_BAR_HEIGHT (f);
-  fullscreen = get_frame_param (f, Qfullscreen);
 
   /* This differs from the tool bar code in that the tab bar height is
      not rounded up.  Otherwise, if redisplay_tab_bar decides to grow
      the tab bar by even 1 pixel, FRAME_TAB_BAR_LINES will be changed,
      leading to the tab bar height being incorrectly set upon the next
      call to x_set_font.  (bug#59285) */
-  lines = height / unit;
+  int lines = height / unit;
+  if (lines == 0 && height != 0)
+    lines = 1;
 
   /* Make sure we redisplay all windows in this frame.  */
   fset_redisplay (f);
@@ -665,6 +663,8 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
 
   if (!f->tab_bar_resized)
     {
+      Lisp_Object fullscreen = get_frame_param (f, Qfullscreen);
+
       /* As long as tab_bar_resized is false, effectively try to change
 	 F's native height.  */
       if (NILP (fullscreen) || EQ (fullscreen, Qfullwidth))

src/pgtkfns.c

@@ -473,19 +473,17 @@ pgtk_set_tab_bar_lines (struct frame *f, Lisp_Object value, Lisp_Object oldval)
 void
 pgtk_change_tab_bar_height (struct frame *f, int height)
 {
-  int unit, old_height, lines;
+  int unit = FRAME_LINE_HEIGHT (f);
-  Lisp_Object fullscreen;
+  int old_height = FRAME_TAB_BAR_HEIGHT (f);
-
-  unit = FRAME_LINE_HEIGHT (f);
-  old_height = FRAME_TAB_BAR_HEIGHT (f);
-  fullscreen = get_frame_param (f, Qfullscreen);
 
   /* This differs from the tool bar code in that the tab bar height is
      not rounded up.  Otherwise, if redisplay_tab_bar decides to grow
      the tab bar by even 1 pixel, FRAME_TAB_BAR_LINES will be changed,
      leading to the tab bar height being incorrectly set upon the next
      call to x_set_font.  (bug#59285) */
-  lines = height / unit;
+  int lines = height / unit;
+  if (lines == 0 && height != 0)
+    lines = 1;
 
   /* Make sure we redisplay all windows in this frame.  */
   fset_redisplay (f);
@@ -506,6 +504,8 @@ pgtk_change_tab_bar_height (struct frame *f, int height)
 
   if (!f->tab_bar_resized)
     {
+      Lisp_Object fullscreen = get_frame_param (f, Qfullscreen);
+
       /* As long as tab_bar_resized is false, effectively try to change
         F's native height.  */
       if (NILP (fullscreen) || EQ (fullscreen, Qfullwidth))

src/w32fns.c

@@ -1717,19 +1717,17 @@ w32_set_tab_bar_lines (struct frame *f, Lisp_Object value, Lisp_Object oldval)
 void
 w32_change_tab_bar_height (struct frame *f, int height)
 {
-  int unit, old_height, lines;
+  int unit = FRAME_LINE_HEIGHT (f);
-  Lisp_Object fullscreen;
+  int old_height = FRAME_TAB_BAR_HEIGHT (f);
-
-  unit = FRAME_LINE_HEIGHT (f);
-  old_height = FRAME_TAB_BAR_HEIGHT (f);
-  fullscreen = get_frame_param (f, Qfullscreen);
 
   /* This differs from the tool bar code in that the tab bar height is
      not rounded up.  Otherwise, if redisplay_tab_bar decides to grow
      the tab bar by even 1 pixel, FRAME_TAB_BAR_LINES will be changed,
      leading to the tab bar height being incorrectly set upon the next
      call to x_set_font.  (bug#59285) */
-  lines = height / unit;
+  int lines = height / unit;
+  if (lines == 0 && height != 0)
+    lines = 1;
 
   /* Make sure we redisplay all windows in this frame.  */
   fset_redisplay (f);
@@ -1758,6 +1756,8 @@ w32_change_tab_bar_height (struct frame *f, int height)
 
   if (!f->tab_bar_resized)
     {
+      Lisp_Object fullscreen = get_frame_param (f, Qfullscreen);
+
       /* As long as tab_bar_resized is false, effectively try to change
 	 F's native height.  */
       if (NILP (fullscreen) || EQ (fullscreen, Qfullwidth))

src/xfns.c

@@ -1758,19 +1758,17 @@ x_set_tab_bar_lines (struct frame *f, Lisp_Object value, Lisp_Object oldval)
 void
 x_change_tab_bar_height (struct frame *f, int height)
 {
-  int unit, old_height, lines;
+  int unit = FRAME_LINE_HEIGHT (f);
-  Lisp_Object fullscreen;
+  int old_height = FRAME_TAB_BAR_HEIGHT (f);
-
-  unit = FRAME_LINE_HEIGHT (f);
-  old_height = FRAME_TAB_BAR_HEIGHT (f);
-  fullscreen = get_frame_param (f, Qfullscreen);
 
   /* This differs from the tool bar code in that the tab bar height is
      not rounded up.  Otherwise, if redisplay_tab_bar decides to grow
      the tab bar by even 1 pixel, FRAME_TAB_BAR_LINES will be changed,
      leading to the tab bar height being incorrectly set upon the next
      call to x_set_font.  (bug#59285) */
-  lines = height / unit;
+  int lines = height / unit;
+  if (lines == 0 && height != 0)
+    lines = 1;
 
   /* Make sure we redisplay all windows in this frame.  */
   fset_redisplay (f);
@@ -1791,6 +1789,8 @@ x_change_tab_bar_height (struct frame *f, int height)
 
   if (!f->tab_bar_resized)
     {
+      Lisp_Object fullscreen = get_frame_param (f, Qfullscreen);
+
       /* As long as tab_bar_resized is false, effectively try to change
 	 F's native height.  */
       if (NILP (fullscreen) || EQ (fullscreen, Qfullwidth))