object-file: make buf parameter of index_mem() a constant

The `buf` parameter of `index_mem()` is a non-constant string. This will
break once we enable `-Wwrite-strings` because we also pass constants
from at least one callsite.

Adapt the parameter to be a constant. As we cannot free the buffer
without casting now, this also requires us to move the lifetime of the
nested buffer around.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

object-file.c

@@ -2484,12 +2484,13 @@ static int hash_format_check_report(struct fsck_options *opts UNUSED,
 }
 
 static int index_mem(struct index_state *istate,
-		     struct object_id *oid, void *buf, size_t size,
+		     struct object_id *oid,
+		     const void *buf, size_t size,
 		     enum object_type type,
 		     const char *path, unsigned flags)
 {
+	struct strbuf nbuf = STRBUF_INIT;
 	int ret = 0;
-	int re_allocated = 0;
 	int write_object = flags & HASH_WRITE_OBJECT;
 
 	if (!type)
@@ -2499,11 +2500,10 @@ static int index_mem(struct index_state *istate,
 	 * Convert blobs to git internal format
 	 */
 	if ((type == OBJ_BLOB) && path) {
-		struct strbuf nbuf = STRBUF_INIT;
 		if (convert_to_git(istate, path, buf, size, &nbuf,
 				   get_conv_flags(flags))) {
-			buf = strbuf_detach(&nbuf, &size);
-			re_allocated = 1;
+			buf = nbuf.buf;
+			size = nbuf.len;
 		}
 	}
 	if (flags & HASH_FORMAT_CHECK) {
@@ -2520,8 +2520,8 @@ static int index_mem(struct index_state *istate,
 		ret = write_object_file(buf, size, type, oid);
 	else
 		hash_object_file(the_hash_algo, buf, size, type, oid);
-	if (re_allocated)
-		free(buf);
+
+	strbuf_release(&nbuf);
 	return ret;
 }