Enable calling decode_coding_object with both SRC and DST_OBJECT Qnil

* src/coding.c (growable_destination): A C destination is also
reallocable.
(produce_chars): Don't consider source and destination identical
if they are EQ but Qnil.

1 files changed, 23 insertions, 11 deletions

diff --git a/src/coding.c b/src/coding.c
index ff7cf56c297..3f314b46d5e 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -614,10 +614,11 @@ inhibit_flag (int encoded_flag, bool var)
 static bool
 growable_destination (struct coding_system *coding)
 {
-  return STRINGP (coding->dst_object) || BUFFERP (coding->dst_object);
+  return (STRINGP (coding->dst_object)
+          || BUFFERP (coding->dst_object)
+          || NILP (coding->dst_object));
 }
 
-
 /* Safely get one byte from the source text pointed by SRC which ends
    at SRC_END, and set C to that byte.  If there are not enough bytes
    in the source, it jumps to 'no_more_source'.  If MULTIBYTEP,
@@ -7005,7 +7006,6 @@ get_translation (Lisp_Object trans, int *buf, int *buf_end, ptrdiff_t *nchars)
   return Qnil;
 }
 
-
 static int
 produce_chars (struct coding_system *coding, Lisp_Object translation_table,
                bool last_block)
@@ -7063,7 +7063,10 @@ produce_chars (struct coding_system *coding, Lisp_Object translation_table,
                       || ckd_add (&dst_size, dst_size, buf_end - buf))
                     memory_full (SIZE_MAX);
                   dst = alloc_destination (coding, dst_size, dst);
-                  if (EQ (coding->src_object, coding->dst_object))
+                  if (EQ (coding->src_object, coding->dst_object)
+                      /* Input and output are not C buffers, which are safe to
+                         assume to be different.  */
+                      && !NILP (coding->src_object))
                     {
                       coding_set_source (coding);
                       dst_end = (((unsigned char *) coding->source)
@@ -7098,7 +7101,10 @@ produce_chars (struct coding_system *coding, Lisp_Object translation_table,
       const unsigned char *src = coding->source;
       const unsigned char *src_end = src + coding->consumed;
 
-      if (EQ (coding->dst_object, coding->src_object))
+      if (EQ (coding->dst_object, coding->src_object)
+          /* Input and output are not C buffers, which are safe to
+             assume to be different.  */
+          && !NILP (coding->src_object))
         {
           eassert (growable_destination (coding));
           dst_end = (unsigned char *) src;
@@ -7119,7 +7125,8 @@ produce_chars (struct coding_system *coding, Lisp_Object translation_table,
                   if (dst == dst_end)
                     {
                       eassert (growable_destination (coding));
-                      if (EQ (coding->src_object, coding->dst_object))
+                      if (EQ (coding->src_object, coding->dst_object)
+                          && !NILP (coding->src_object))
                         dst_end = (unsigned char *) src;
                       if (dst == dst_end)
                         {
@@ -7131,7 +7138,8 @@ produce_chars (struct coding_system *coding, Lisp_Object translation_table,
                           coding_set_source (coding);
                           src = coding->source + offset;
                           src_end = coding->source + coding->consumed;
-                          if (EQ (coding->src_object, coding->dst_object))
+                          if (EQ (coding->src_object, coding->dst_object)
+                              && !NILP (coding->src_object))
                             dst_end = (unsigned char *) src;
                         }
                     }
@@ -7150,14 +7158,16 @@ produce_chars (struct coding_system *coding, Lisp_Object translation_table,
                 if (dst >= dst_end - 1)
                   {
                     eassert (growable_destination (coding));
-                    if (EQ (coding->src_object, coding->dst_object))
+                    if (EQ (coding->src_object, coding->dst_object)
+                        && !NILP (coding->src_object))
                       dst_end = (unsigned char *) src;
                     if (dst >= dst_end - 1)
                       {
                         ptrdiff_t offset = src - coding->source;
                         ptrdiff_t more_bytes;
 
-                        if (EQ (coding->src_object, coding->dst_object))
+                        if (EQ (coding->src_object, coding->dst_object)
+                            && !NILP (coding->src_object))
                           more_bytes = ((src_end - src) / 2) + 2;
                         else
                           more_bytes = src_end - src + 2;
@@ -7166,7 +7176,8 @@ produce_chars (struct coding_system *coding, Lisp_Object translation_table,
                         coding_set_source (coding);
                         src = coding->source + offset;
                         src_end = coding->source + coding->consumed;
-                        if (EQ (coding->src_object, coding->dst_object))
+                        if (EQ (coding->src_object, coding->dst_object)
+                            && !NILP (coding->src_object))
                           dst_end = (unsigned char *) src;
                       }
                   }
@@ -7175,7 +7186,8 @@ produce_chars (struct coding_system *coding, Lisp_Object translation_table,
         }
       else
         {
-          if (!EQ (coding->src_object, coding->dst_object))
+          if (!EQ (coding->src_object, coding->dst_object)
+              && !NILP (coding->src_object))
             {
               ptrdiff_t require = coding->src_bytes - coding->dst_bytes;