merge: use commit-slab in merge remote desc instead of commit->util

It's done so that commit->util can be removed. See more explanation in
the commit that removes commit->util.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge.c

@@ -443,6 +443,7 @@ static void merge_name(const char *remote, struct strbuf *msg)
 	struct object_id branch_head;
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf bname = STRBUF_INIT;
+	struct merge_remote_desc *desc;
 	const char *ptr;
 	char *found_ref;
 	int len, early;
@@ -515,8 +516,6 @@ static void merge_name(const char *remote, struct strbuf *msg)
 		strbuf_release(&truname);
 	}
 
-	if (remote_head->util) {
-		struct merge_remote_desc *desc;
 	desc = merge_remote_util(remote_head);
 	if (desc && desc->obj && desc->obj->type == OBJ_TAG) {
 		strbuf_addf(msg, "%s\t\t%s '%s'\n",
@@ -525,7 +524,6 @@ static void merge_name(const char *remote, struct strbuf *msg)
 			    remote);
 		goto cleanup;
 	}
-	}
 
 	strbuf_addf(msg, "%s\t\tcommit '%s'\n",
 		oid_to_hex(&remote_head->object.oid), remote);
@@ -932,8 +930,11 @@ static void write_merge_heads(struct commit_list *remoteheads)
 	for (j = remoteheads; j; j = j->next) {
 		struct object_id *oid;
 		struct commit *c = j->item;
-		if (c->util && merge_remote_util(c)->obj) {
-			oid = &merge_remote_util(c)->obj->oid;
+		struct merge_remote_desc *desc;
+
+		desc = merge_remote_util(c);
+		if (desc && desc->obj) {
+			oid = &desc->obj->oid;
 		} else {
 			oid = &c->object.oid;
 		}

commit.c

@@ -1574,13 +1574,21 @@ out:
 	return result;
 }
 
+define_commit_slab(merge_desc_slab, struct merge_remote_desc *);
+static struct merge_desc_slab merge_desc_slab = COMMIT_SLAB_INIT(1, merge_desc_slab);
+
+struct merge_remote_desc *merge_remote_util(struct commit *commit)
+{
+	return *merge_desc_slab_at(&merge_desc_slab, commit);
+}
+
 void set_merge_remote_desc(struct commit *commit,
 			   const char *name, struct object *obj)
 {
 	struct merge_remote_desc *desc;
 	FLEX_ALLOC_STR(desc, name, name);
 	desc->obj = obj;
-	commit->util = desc;
+	*merge_desc_slab_at(&merge_desc_slab, commit) = desc;
 }
 
 struct commit *get_merge_parent(const char *name)
@@ -1592,7 +1600,7 @@ struct commit *get_merge_parent(const char *name)
 		return NULL;
 	obj = parse_object(&oid);
 	commit = (struct commit *)peel_to_type(name, 0, obj, OBJ_COMMIT);
-	if (commit && !commit->util)
+	if (commit && !merge_remote_util(commit))
 		set_merge_remote_desc(commit, name, obj);
 	return commit;
 }

commit.h

@@ -303,7 +303,7 @@ struct merge_remote_desc {
 	struct object *obj; /* the named object, could be a tag */
 	char name[FLEX_ARRAY];
 };
-#define merge_remote_util(commit) ((struct merge_remote_desc *)((commit)->util))
+extern struct merge_remote_desc *merge_remote_util(struct commit *);
 extern void set_merge_remote_desc(struct commit *commit,
 				  const char *name, struct object *obj);
 

merge-recursive.c

@@ -223,10 +223,12 @@ static void output(struct merge_options *o, int v, const char *fmt, ...)
 
 static void output_commit_title(struct merge_options *o, struct commit *commit)
 {
+	struct merge_remote_desc *desc;
+
 	strbuf_addchars(&o->obuf, ' ', o->call_depth * 2);
-	if (commit->util)
-		strbuf_addf(&o->obuf, "virtual %s\n",
-			merge_remote_util(commit)->name);
+	desc = merge_remote_util(commit);
+	if (desc)
+		strbuf_addf(&o->obuf, "virtual %s\n", desc->name);
 	else {
 		strbuf_add_unique_abbrev(&o->obuf, &commit->object.oid,
 					 DEFAULT_ABBREV);