diff-lib: refactor run_diff_index() and do_diff_cache()

The latter is meant to be an API for internal callers that want to inspect
the resulting diff-queue, while the former is an implementation of "git
diff-index" command. Extract the common logic into a single helper
function and make them thin wrappers around it.

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

diff-lib.c

@@ -440,20 +440,19 @@ static int oneway_diff(struct cache_entry **src, struct unpack_trees_options *o)
 	return 0;
 }
 
-int run_diff_index(struct rev_info *revs, int cached)
+static int diff_cache(struct rev_info *revs,
+		      const unsigned char *tree_sha1,
+		      const char *tree_name,
+		      int cached)
 {
-	struct object *ent;
 	struct tree *tree;
-	const char *tree_name;
-	struct unpack_trees_options opts;
 	struct tree_desc t;
+	struct unpack_trees_options opts;
 
-	ent = revs->pending.objects[0].item;
-	tree_name = revs->pending.objects[0].name;
-	tree = parse_tree_indirect(ent->sha1);
+	tree = parse_tree_indirect(tree_sha1);
 	if (!tree)
-		return error("bad tree object %s", tree_name);
-
+		return error("bad tree object %s",
+			     tree_name ? tree_name : sha1_to_hex(tree_sha1));
 	memset(&opts, 0, sizeof(opts));
 	opts.head_idx = 1;
 	opts.index_only = cached;
@@ -466,7 +465,15 @@ int run_diff_index(struct rev_info *revs, int cached)
 	opts.dst_index = NULL;
 
 	init_tree_desc(&t, tree->buffer, tree->size);
-	if (unpack_trees(1, &t, &opts))
+	return unpack_trees(1, &t, &opts);
+}
+
+int run_diff_index(struct rev_info *revs, int cached)
+{
+	struct object_array_entry *ent;
+
+	ent = revs->pending.objects;
+	if (diff_cache(revs, ent->item->sha1, ent->name, cached))
 		exit(128);
 
 	diff_set_mnemonic_prefix(&revs->diffopt, "c/", cached ? "i/" : "w/");
@@ -478,29 +485,13 @@ int run_diff_index(struct rev_info *revs, int cached)
 
 int do_diff_cache(const unsigned char *tree_sha1, struct diff_options *opt)
 {
-	struct tree *tree;
 	struct rev_info revs;
-	struct unpack_trees_options opts;
-	struct tree_desc t;
 
 	init_revisions(&revs, NULL);
 	init_pathspec(&revs.prune_data, opt->pathspec.raw);
-	tree = parse_tree_indirect(tree_sha1);
-	if (!tree)
-		die("bad tree object %s", sha1_to_hex(tree_sha1));
+	revs.diffopt = *opt;
 
-	memset(&opts, 0, sizeof(opts));
-	opts.head_idx = 1;
-	opts.index_only = 1;
-	opts.diff_index_cached = !DIFF_OPT_TST(opt, FIND_COPIES_HARDER);
-	opts.merge = 1;
-	opts.fn = oneway_diff;
-	opts.unpack_data = &revs;
-	opts.src_index = &the_index;
-	opts.dst_index = NULL;
-
-	init_tree_desc(&t, tree->buffer, tree->size);
-	if (unpack_trees(1, &t, &opts))
+	if (diff_cache(&revs, tree_sha1, NULL, 1))
 		exit(128);
 	return 0;
 }