Fix GC bug causing incorrect 'format' output (Bug#75754)

This fixes the correctness bug discovered in bug#75754, but not the
performance issue or excessive stack usage.

* src/editfns.c (styled_format): Split 'info' array into two arrays,
one of them allocated via SAFE_ALLOCA_LISP for GC protection.

(cherry picked from commit ed5067e689a5e38795d5c27c5a688886d259a298)

diff --git a/src/editfns.c b/src/editfns.c
index 8a5fb673fe7a19f29763f7874f95189b2389f9b0..4ba356d627c8d40af1c36d96f2c7cdb7fac8c25a 100644 (file)
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3431,10 +3431,6 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
   /* Information recorded for each format spec.  */
   struct info
   {
-    /* The corresponding argument, converted to string if conversion
-       was needed.  */
-    Lisp_Object argument;
-
     /* The start and end bytepos in the output string.  */
     ptrdiff_t start, end;
 
@@ -3461,6 +3457,10 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
       || SIZE_MAX < alloca_size)
     memory_full (SIZE_MAX);
   info = SAFE_ALLOCA (alloca_size);
+  /* One argument belonging to each spec; but needs to be allocated
+     separately so GC doesn't free the strings (bug#75754).  */
+  Lisp_Object *spec_arguments;
+  SAFE_ALLOCA_LISP (spec_arguments, nspec_bound);
   /* discarded[I] is 1 if byte I of the format
      string was not copied into the output.
      It is 2 if byte I was not the first byte of its character.  */
@@ -3610,14 +3610,15 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
          if (! (n < nargs))
            error ("Not enough arguments for format string");
 
-         struct info *spec = &info[ispec++];
+         ptrdiff_t spec_index = ispec++;
+         struct info *spec = &info[spec_index];
          if (nspec < ispec)
            {
-             spec->argument = args[n];
+             spec_arguments[spec_index] = args[n];
              spec->intervals = false;
              nspec = ispec;
            }
-         Lisp_Object arg = spec->argument;
+         Lisp_Object arg = spec_arguments[spec_index];
 
          /* For 'S', prin1 the argument, and then treat like 's'.
             For 's', princ any argument that is not a string or
@@ -3630,7 +3631,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
              if (EQ (arg, args[n]))
                {
                  Lisp_Object noescape = conversion == 'S' ? Qnil : Qt;
-                 spec->argument = arg = Fprin1_to_string (arg, noescape, Qnil);
+                 spec_arguments[spec_index] = arg = Fprin1_to_string (arg, noescape, Qnil);
                  if (STRING_MULTIBYTE (arg) && ! multibyte)
                    {
                      multibyte = true;
@@ -3648,7 +3649,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                      multibyte = true;
                      goto retry;
                    }
-                 spec->argument = arg = Fchar_to_string (arg);
+                 spec_arguments[spec_index] = arg = Fchar_to_string (arg);
                }
 
              if (!EQ (arg, args[n]))
@@ -3658,7 +3659,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
 
          if (SYMBOLP (arg))
            {
-             spec->argument = arg = SYMBOL_NAME (arg);
+             spec_arguments[spec_index] = arg = SYMBOL_NAME (arg);
              if (STRING_MULTIBYTE (arg) && ! multibyte)
                {
                  multibyte = true;
@@ -4303,9 +4304,9 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
        for (ptrdiff_t i = 0; i < nspec; i++)
          if (info[i].intervals)
            {
-             len = make_fixnum (SCHARS (info[i].argument));
+             len = make_fixnum (SCHARS (spec_arguments[i]));
              Lisp_Object new_len = make_fixnum (info[i].end - info[i].start);
-             props = text_property_list (info[i].argument,
+             props = text_property_list (spec_arguments[i],
                                           make_fixnum (0), len, Qnil);
              props = extend_property_ranges (props, len, new_len);
              /* If successive arguments have properties, be sure that