bug#62867: segfault in describe_vector

[Eli Zaretskii]

> From: Xinyang Chen <chenxy@mit.edu>
> Date: Sat, 15 Apr 2023 08:07:07 -0400
> 
> to reproduce:
> 
> (package-initialize)
> (require 'evil)
> (setq testmap (make-sparse-keymap))
> (define-key testmap (kbd "SPC") #'test)
> (evil-define-key 'motion global-map (kbd "SPC") testmap)
> (evil-mode)
> (describe-keymap global-map)
> 
> This appears to be caused by keymap.c line 3313
> SYMBOL_NAME (shadowed_by)
> where shadowed_by don't have to be a symbol (In this case its a keymap)

No good deed goes unpunished...

Stefan, can we do better than the below?

diff --git a/src/keymap.c b/src/keymap.c
index efac410..b9950b9 100644
--- a/src/keymap.c
+++ b/src/keymap.c
@@ -3308,13 +3308,18 @@ describe_vector (Lisp_Object vector, Lisp_Object 
prefix, Lisp_Object args,
       if (this_shadowed)
        {
          SET_PT (PT - 1);
-         static char const fmt[] = "  (currently shadowed by `%s')";
-         USE_SAFE_ALLOCA;
-         char *buffer = SAFE_ALLOCA (sizeof fmt +
-                                     SBYTES (SYMBOL_NAME (shadowed_by)));
-         esprintf (buffer, fmt, SDATA (SYMBOL_NAME (shadowed_by)));
-         insert_string (buffer);
-         SAFE_FREE();
+         if (SYMBOLP (shadowed_by))
+           {
+             static char const fmt[] = "  (currently shadowed by `%s')";
+             USE_SAFE_ALLOCA;
+             char *buffer =
+               SAFE_ALLOCA (sizeof fmt + SBYTES (SYMBOL_NAME (shadowed_by)));
+             esprintf (buffer, fmt, SDATA (SYMBOL_NAME (shadowed_by)));
+             insert_string (buffer);
+             SAFE_FREE();
+           }
+         else
+           insert_string ("  (binding currently shadowed by a keymap)");
          SET_PT (PT + 1);
        }
     }