Improve handling of coding-system mnemonic indicators

This fixes assertion violations when the mnemonic is
given as a string, and allows non-ASCII characters be
used as mode-line mnemonic of a coding-system.
* src/xdisp.c (decode_mode_spec_coding): Handle multibyte
characters as coding-system's mnemonic.
(display_mode_element): If decode_mode_spec returns a multibyte
string, display it as multibyte.
* src/coding.c (Fdefine_coding_system_internal)
(Fcoding_system_put): If :mnemonic is a string, use its first
character.  This avoids assertion violations if someone uses a
string as the mnemonic of a coding-system.

1 files changed, 8 insertions, 2 deletions

diff --git a/src/coding.c b/src/coding.c
index 51bd441de9d..221a9cad898 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -10895,7 +10895,10 @@ usage: (define-coding-system-internal ...)  */)
   ASET (attrs, coding_attr_base_name, name);
 
   Lisp_Object val = args[coding_arg_mnemonic];
-  if (! STRINGP (val))
+  /* decode_mode_spec_coding assumes the mnemonic is a single character.  */
+  if (STRINGP (val))
+    val = make_fixnum (STRING_CHAR (SDATA (val)));
+  else
     CHECK_CHARACTER (val);
   ASET (attrs, coding_attr_mnemonic, val);
 
@@ -11408,7 +11411,10 @@ DEFUN ("coding-system-put", Fcoding_system_put, Scoding_system_put,
   attrs = AREF (spec, 0);
   if (EQ (prop, QCmnemonic))
     {
-      if (! STRINGP (val))
+      /* decode_mode_spec_coding assumes the mnemonic is a single character.  */
+      if (STRINGP (val))
+        val = make_fixnum (STRING_CHAR (SDATA (val)));
+      else
         CHECK_CHARACTER (val);
       ASET (attrs, coding_attr_mnemonic, val);
     }