Subject: Re: bug#30874: 27.0.50; Emacs crashes

From: Robert Pluim <[email-masked]>
Date: Sat, 31 Mar 2018 15:55:13 +0200

Eli Zaretskii <[email-masked]> writes:

> Yes, it's called gc_in_progress.

Iʼm testing the following, which fixes the 20890 crash for me when
using Cairo.

diff --git i/src/ftfont.c w/src/ftfont.c
index c2e093e633..89c07e1f21 100644
--- i/src/ftfont.c
+++ w/src/ftfont.c
@@ -1242,6 +1242,11 @@ ftfont_close (struct font *font)
   struct ftfont_info *ftfont_info = (struct ftfont_info *) font;
   Lisp_Object val, cache;
 
+#ifdef USE_CAIRO
+  /* Bug#20890 workaround.  */
+  if (gc_in_progress)
+    return;
+#endif
   val = Fcons (font->props[FONT_FILE_INDEX], make_number (ftfont_info->index));
   cache = ftfont_lookup_cache (val, FTFONT_CACHE_FOR_FACE);
   eassert (CONSP (cache));

> I'm not sure it's about the font, it could be about some glyphs of the
> font.  You are probably right, but IME leaving a variable to get back
> previous behavior is good policy; at the very least, it makes it easy
> to ask users who complain about related problems to see if this
> particular change is the culprit without having to rebuild Emacs.
>
>> > Also, we should probably condition this by HAVE_XFT, since AFAIU the
>> > problem is only relevant to that build?

This is what Iʼm using at the moment. I can put the variable in
syms_of_xftfont if you prefer.

diff --git i/src/ftfont.c w/src/ftfont.c
index c2e093e633..2190186940 100644
--- i/src/ftfont.c
+++ w/src/ftfont.c
@@ -764,6 +764,13 @@ ftfont_spec_pattern (Lisp_Object spec, char *otlayout, struct OpenTypeSpec **ots
   if (scalable >= 0
       && ! FcPatternAddBool (pattern, FC_SCALABLE, scalable ? FcTrue : FcFalse))
     goto err;
+#ifdef HAVE_XFT
+  /* We really don't like color fonts, they cause Xft crashes.  See
+     bug#30874.  */
+  if (Vxft_ignore_color_fonts
+      && ! FcPatternAddBool(pattern, FC_COLOR, FcFalse))
+    goto err;
+#endif
 
   goto finish;
 
@@ -2735,6 +2742,14 @@ syms_of_ftfont (void)
   DEFSYM (Qsans, "sans");
   DEFSYM (Qsans__serif, "sans serif");
 
+#ifdef HAVE_XFT
+  DEFVAR_BOOL ("xft-ignore-color-fonts",
+	       Vxft_ignore_color_fonts,
+     doc: /* Non-nil means don't query fontconfig for color fonts,
+since they often cause Xft crashes. bug#30874.  */);
+  Vxft_ignore_color_fonts = 1;
+#endif
+
   staticpro (&freetype_font_cache);
   freetype_font_cache = list1 (Qt);