Add return value to 'traverse_tree()' callback

This allows the callback to return an error value, but it can also
specify which of the tree entries that it actually used up by returning
a positive mask value.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-tree.c

@@ -287,31 +287,32 @@ static void unresolved(const struct traverse_info *info, struct name_entry n[3])
  * The successful merge rules are the same as for the three-way merge
  * in git-read-tree.
  */
-static void threeway_callback(int n, unsigned long mask, struct name_entry *entry, struct traverse_info *info)
+static int threeway_callback(int n, unsigned long mask, struct name_entry *entry, struct traverse_info *info)
 {
 	/* Same in both? */
 	if (same_entry(entry+1, entry+2)) {
 		if (entry[0].sha1) {
 			resolve(info, NULL, entry+1);
-			return;
+			return mask;
 		}
 	}
 
 	if (same_entry(entry+0, entry+1)) {
 		if (entry[2].sha1 && !S_ISDIR(entry[2].mode)) {
 			resolve(info, entry+1, entry+2);
-			return;
+			return mask;
 		}
 	}
 
 	if (same_entry(entry+0, entry+2)) {
 		if (entry[1].sha1 && !S_ISDIR(entry[1].mode)) {
 			resolve(info, NULL, entry+1);
-			return;
+			return mask;
 		}
 	}
 
 	unresolved(info, entry);
+	return mask;
 }
 
 static void merge_trees(struct tree_desc t[3], const char *base)

tree-walk.c

@@ -135,8 +135,9 @@ char *make_traverse_path(char *path, const struct traverse_info *info, const str
 	return path;
 }
 
-void traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
+int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 {
+	int ret = 0;
 	struct name_entry *entry = xmalloc(n*sizeof(*entry));
 
 	for (;;) {
@@ -171,19 +172,26 @@ void traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 			break;
 
 		/*
-		 * Update the tree entries we've walked, and clear
-		 * all the unused name-entries.
+		 * Clear all the unused name-entries.
 		 */
 		for (i = 0; i < n; i++) {
-			if (mask & (1ul << i)) {
-				update_tree_entry(t+i);
+			if (mask & (1ul << i))
 				continue;
-			}
 			entry_clear(entry + i);
 		}
-		info->fn(n, mask, entry, info);
+		ret = info->fn(n, mask, entry, info);
+		if (ret < 0)
+			break;
+		if (ret)
+			mask &= ret;
+		ret = 0;
+		for (i = 0; i < n; i++) {
+			if (mask & (1ul << i))
+				update_tree_entry(t + i);
+		}
 	}
 	free(entry);
+	return ret;
 }
 
 static int find_tree_entry(struct tree_desc *t, const char *name, unsigned char *result, unsigned *mode)

tree-walk.h

@@ -34,8 +34,8 @@ int tree_entry(struct tree_desc *, struct name_entry *);
 void *fill_tree_descriptor(struct tree_desc *desc, const unsigned char *sha1);
 
 struct traverse_info;
-typedef void (*traverse_callback_t)(int n, unsigned long mask, struct name_entry *entry, struct traverse_info *);
-void traverse_trees(int n, struct tree_desc *t, struct traverse_info *info);
+typedef int (*traverse_callback_t)(int n, unsigned long mask, struct name_entry *entry, struct traverse_info *);
+int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info);
 
 struct traverse_info {
 	struct traverse_info *prev;