merge-recursive: split out code for determining diff_filepairs

Create a new function, get_diffpairs() to compute the diff_filepairs
between two trees.  While these are currently only used in
get_renames(), I want them to be available to some new functions.  No
actual logic changes yet.

Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -1312,24 +1312,15 @@ static int conflict_rename_rename_2to1(struct merge_options *o,
 }
 
 /*
- * Get information of all renames which occurred between 'o_tree' and
- * 'tree'. We need the three trees in the merge ('o_tree', 'a_tree' and
- * 'b_tree') to be able to associate the correct cache entries with
- * the rename information. 'tree' is always equal to either a_tree or b_tree.
+ * Get the diff_filepairs changed between o_tree and tree.
  */
-static struct string_list *get_renames(struct merge_options *o,
-				       struct tree *tree,
-				       struct tree *o_tree,
-				       struct tree *a_tree,
-				       struct tree *b_tree,
-				       struct string_list *entries)
+static struct diff_queue_struct *get_diffpairs(struct merge_options *o,
+					       struct tree *o_tree,
+					       struct tree *tree)
 {
-	int i;
-	struct string_list *renames;
+	struct diff_queue_struct *ret;
 	struct diff_options opts;
 
-	renames = xcalloc(1, sizeof(struct string_list));
-
 	diff_setup(&opts);
 	opts.flags.recursive = 1;
 	opts.flags.rename_empty = 0;
@@ -1345,10 +1336,41 @@ static struct string_list *get_renames(struct merge_options *o,
 	diffcore_std(&opts);
 	if (opts.needed_rename_limit > o->needed_rename_limit)
 		o->needed_rename_limit = opts.needed_rename_limit;
-	for (i = 0; i < diff_queued_diff.nr; ++i) {
+
+	ret = xmalloc(sizeof(*ret));
+	*ret = diff_queued_diff;
+
+	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
+	diff_queued_diff.nr = 0;
+	diff_queued_diff.queue = NULL;
+	diff_flush(&opts);
+	return ret;
+}
+
+/*
+ * Get information of all renames which occurred in 'pairs', making use of
+ * any implicit directory renames inferred from the other side of history.
+ * We need the three trees in the merge ('o_tree', 'a_tree' and 'b_tree')
+ * to be able to associate the correct cache entries with the rename
+ * information; tree is always equal to either a_tree or b_tree.
+ */
+static struct string_list *get_renames(struct merge_options *o,
+				       struct diff_queue_struct *pairs,
+				       struct tree *tree,
+				       struct tree *o_tree,
+				       struct tree *a_tree,
+				       struct tree *b_tree,
+				       struct string_list *entries)
+{
+	int i;
+	struct string_list *renames;
+
+	renames = xcalloc(1, sizeof(struct string_list));
+
+	for (i = 0; i < pairs->nr; ++i) {
 		struct string_list_item *item;
 		struct rename *re;
-		struct diff_filepair *pair = diff_queued_diff.queue[i];
+		struct diff_filepair *pair = pairs->queue[i];
 
 		if (pair->status != 'R') {
 			diff_free_filepair(pair);
@@ -1373,9 +1395,6 @@ static struct string_list *get_renames(struct merge_options *o,
 		item = string_list_insert(renames, pair->one->path);
 		item->util = re;
 	}
-	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
-	diff_queued_diff.nr = 0;
-	diff_flush(&opts);
 	return renames;
 }
 
@@ -1646,15 +1665,36 @@ static int handle_renames(struct merge_options *o,
 			  struct string_list *entries,
 			  struct rename_info *ri)
 {
+	struct diff_queue_struct *head_pairs, *merge_pairs;
+	int clean;
+
 	ri->head_renames = NULL;
 	ri->merge_renames = NULL;
 
 	if (!o->detect_rename)
 		return 1;
 
-	ri->head_renames  = get_renames(o, head, common, head, merge, entries);
-	ri->merge_renames = get_renames(o, merge, common, head, merge, entries);
-	return process_renames(o, ri->head_renames, ri->merge_renames);
+	head_pairs = get_diffpairs(o, common, head);
+	merge_pairs = get_diffpairs(o, common, merge);
+
+	ri->head_renames  = get_renames(o, head_pairs, head,
+					 common, head, merge, entries);
+	ri->merge_renames = get_renames(o, merge_pairs, merge,
+					 common, head, merge, entries);
+	clean = process_renames(o, ri->head_renames, ri->merge_renames);
+
+	/*
+	 * Some cleanup is deferred until cleanup_renames() because the
+	 * data structures are still needed and referenced in
+	 * process_entry().  But there are a few things we can free now.
+	 */
+
+	free(head_pairs->queue);
+	free(head_pairs);
+	free(merge_pairs->queue);
+	free(merge_pairs);
+
+	return clean;
 }
 
 static void cleanup_rename(struct string_list *rename)