1 files changed, 53 insertions, 17 deletions

diff --git a/read-tree.c b/read-tree.c
index 59e6950a4c..c4ca86f486 100644
--- a/read-tree.c
+++ b/read-tree.c
@@ -73,26 +73,61 @@ static void remove_lock_file(void)
 		unlink(".git/index.lock");
 }
 
+static int same(struct cache_entry *a, struct cache_entry *b)
+{
+	return a->ce_mode == b->ce_mode && 
+		!memcmp(a->sha1, b->sha1, 20);
+}
+
+
 /*
- * This removes all identical entries and collapses them to state 0.
+ * This removes all trivial merges that don't change the tree
+ * and collapses them to state 0.
  *
- * _Any_ other merge (even a trivial one, like both ) is left to user policy.
- * That includes "both created the same file", and "both removed the same
- * file" - which are trivial, but the user might still want to _note_ it.
+ * _Any_ other merge is left to user policy.  That includes "both
+ * created the same file", and "both removed the same file" - which are
+ * trivial, but the user might still want to _note_ it. 
  */
-static int same_entry(struct cache_entry *a,
-			struct cache_entry *b,
-			struct cache_entry *c)
+static struct cache_entry *merge_entries(struct cache_entry *a,
+					 struct cache_entry *b,
+					 struct cache_entry *c)
 {
 	int len = ce_namelen(a);
-	return	a->ce_mode == b->ce_mode &&
-		a->ce_mode == c->ce_mode &&
-		ce_namelen(b) == len &&
-		ce_namelen(c) == len &&
-		!memcmp(a->name, b->name, len) &&
-		!memcmp(a->name, c->name, len) &&
-		!memcmp(a->sha1, b->sha1, 20) &&
-		!memcmp(a->sha1, c->sha1, 20);
+
+	/*
+	 * Are they all the same filename? We won't do
+	 * any name merging
+	 */
+	if (ce_namelen(b) != len ||
+	    ce_namelen(c) != len ||
+	    memcmp(a->name, b->name, len) ||
+	    memcmp(a->name, c->name, len))
+		return NULL;
+
+	/*
+	 * Ok, all three entries describe the same
+	 * filename, but maybe the contents or file
+	 * mode have changed?
+	 *
+	 * The trivial cases end up being the ones where two
+	 * out of three files are the same:
+	 *  - both destinations the same, trivially take either
+	 *  - one of the destination versions hasn't changed,
+	 *    take the other.
+	 *
+	 * The "all entries exactly the same" case falls out as
+	 * a special case of any of the "two same" cases.
+	 *
+	 * Here "a" is "original", and "b" and "c" are the two
+	 * trees we are merging.
+	 */
+	if (same(b,c))
+		return c;
+	if (same(a,b))
+		return c;
+	if (same(a,c))
+		return b;
+	return NULL;
 }
 
 static void trivially_merge_cache(struct cache_entry **src, int nr)
@@ -100,10 +135,11 @@ static void trivially_merge_cache(struct cache_entry **src, int nr)
 	struct cache_entry **dst = src;
 
 	while (nr) {
-		struct cache_entry *ce;
+		struct cache_entry *ce, *result;
 
 		ce = src[0];
-		if (nr > 2 && same_entry(ce, src[1], src[2])) {
+		if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
+			ce = result;
 			ce->ce_flags &= ~htons(CE_STAGEMASK);
 			src += 2;
 			nr -= 2;