Recalculate default font when switching font backend

This is an updated version of the patch by Dmitry Antipov
<dmantipov@yandex.ru> in
<https://debbugs.gnu.org/cgi/bugreport.cgi?bug=23386#43>.

Fixes Bug#23386

* src/dispextern.h (struct redisplay_interface): New member
default_font_parameter.
* src/xterm.h: Add prototype for x_default_font_parameter.
* src/xterm.c (x_redisplay_interface): Initialize
default_font_parameter member.
* src/xfns.c (x_default_font_parameter): Make non-static.
* src/w32term.h: Add prototype for w32_default_font_parameter
* src/w32fns.c (w32_default_font_parameter): Make non-static.
* src/w32term.c (w32_redisplay_interface): Initialize
default_font_parameter member.
* src/nsterm.m (ns_redisplay_interface): Add dummy
ns_default_font_parameter (there is currently only one possible font
backend on macOS).  Initialize default_font_parameter member.
* src/frame.c (gui_set_font_backend): Recalculate default font using
RIF default_font_parameter to avoid crash when changing font backend.

1 files changed, 7 insertions, 5 deletions

diff --git a/src/frame.c b/src/frame.c
index 88d6f22fc0a..ecf175f4f99 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -4565,7 +4565,11 @@ gui_set_font_backend (struct frame *f, Lisp_Object new_value, Lisp_Object old_va
     return;
 
   if (FRAME_FONT (f))
-    free_all_realized_faces (Qnil);
+    {
+      Lisp_Object frame;
+      XSETFRAME (frame, f);
+      free_all_realized_faces (frame);
+    }
 
   new_value = font_update_drivers (f, NILP (new_value) ? Qt : new_value);
   if (NILP (new_value))
@@ -4579,10 +4583,8 @@ gui_set_font_backend (struct frame *f, Lisp_Object new_value, Lisp_Object old_va
 
   if (FRAME_FONT (f))
     {
-      Lisp_Object frame;
-
-      XSETFRAME (frame, f);
-      gui_set_font (f, Fframe_parameter (frame, Qfont), Qnil);
+      /* Reconsider default font after backend(s) change (Bug#23386).  */
+      FRAME_RIF(f)->default_font_parameter (f, Qnil);
       face_change = true;
       windows_or_buffers_changed = 18;
     }