bug#37786: 26.3; Emacs crashes when calling function to decode string

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Tue, 22 Oct 2019 20:25:40 -0700, Allen Li <darkfeline@felesatra.moe> said:

    Allen> I haven't touched xft-ignore-color-fonts (and it reproduces from emacs -Q)
    >> 
    Allen> #define FC_MAJOR	2
    Allen> #define FC_MINOR	13
    Allen> #define FC_REVISION	91
    >> 

Thatʼs a very recent (and maybe even unreleased) version of
fontconfig.

    Allen> Arch Linux

Hmm. Could you try the following against emacs-26 and see if it fixes
your crash? (the character will almost certainly end up displayed
wrong). This looks more like a fontconfig bug than anything else: the
pattern we've supplied to FcFontList explicitly says "donʼt give me
color fonts".

diff --git i/lisp/international/fontset.el w/lisp/international/fontset.el
index c90d4f53bd..e80a1a87b9 100644
--- i/lisp/international/fontset.el
+++ w/lisp/international/fontset.el
@@ -804,7 +804,6 @@ setup-default-fontset
              #x2664
              (#x2667 . #x2669)
              (#x266C . #x26FF)
-             (#x2700 . #x27bF) ;; Dingbats
              (#x27C0 . #x27EF) ;; Misc Mathematical Symbols-A
              (#x27F0 . #x27FF) ;; Supplemental Arrows-A
              (#x2900 . #x297F) ;; Supplemental Arrows-B
diff --git i/src/ftfont.c w/src/ftfont.c
index 823fb2095c..017b349318 100644
--- i/src/ftfont.c
+++ w/src/ftfont.c
@@ -861,6 +861,9 @@ ftfont_list (struct frame *f, Lisp_Object spec)
 #endif /* FC_CAPABILITY */
 #ifdef FC_FONTFORMAT
                             FC_FONTFORMAT,
+#endif
+#ifdef FC_COLOR
+                             FC_COLOR,
 #endif
                             NULL);
   if (! objset)
@@ -902,6 +905,15 @@ ftfont_list (struct frame *f, Lisp_Object spec)
     {
       Lisp_Object entity;

+      {
+        FcBool b;
+        if (FcPatternGetBool (fontset->fonts[i], FC_COLOR, 0, &b)
+            == FcResultMatch && b)
+          {
+            fprintf (stderr, "Skipping Color font\n");
+            continue;
+          }
+      }
       if (spacing >= 0)
        {
          int this;