X-Git-Url: https://git.verplant.org/?a=blobdiff_plain;f=read-tree.c;h=fbd0da0ebdc5c523b7f35399a39a3b8efd373112;hb=b0bf8f24e9c7bdeb7e472e6b1fa5f51de1cdcc97;hp=4acbb6b3f25cd5cb50dda3ac34b1b37edad639b1;hpb=d723c690637f2918d9861e8d602e592c5fa0bc5b;p=git.git

diff --git a/read-tree.c b/read-tree.c
index 4acbb6b3..fbd0da0e 100644
--- a/read-tree.c
+++ b/read-tree.c
@@ -155,28 +155,51 @@ static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **ds
 /*
  * Two-way merge.
  *
- * The rule is: 
- *  - every current entry has to match the old tree
- *  - if the current entry matches the new tree, we leave it
- *    as-is. Otherwise we require that it be up-to-date.
+ * The rule is to "carry forward" what is in the index without losing
+ * information across a "fast forward", favoring a successful merge
+ * over a merge failure when it makes sense.  For details of the
+ * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
+ *
  */
 static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
 {
-	struct cache_entry *old = src[0];
-	struct cache_entry *a = src[1], *b = src[2];
+	struct cache_entry *current = src[0];
+	struct cache_entry *oldtree = src[1], *newtree = src[2];
 
 	if (src[3])
 		return -1;
 
-	if (old) {
-		if (!a || !same(old, a))
+	if (current) {
+		if ((!oldtree && !newtree) || /* 4 and 5 */
+		    (!oldtree && newtree &&
+		     same(current, newtree)) || /* 6 and 7 */
+		    (oldtree && newtree &&
+		     same(oldtree, newtree)) || /* 14 and 15 */
+		    (oldtree && newtree &&
+		     !same(oldtree, newtree) && /* 18 and 19*/
+		     same(current, newtree))) {
+			*dst++ = current;
+			return 1;
+		}
+		else if (oldtree && !newtree && same(current, oldtree)) {
+			/* 10 or 11 */
+			verify_uptodate(current);
+			return 0;
+		}
+		else if (oldtree && newtree &&
+			 same(current, oldtree) && !same(current, newtree)) {
+			/* 20 or 21 */
+			verify_uptodate(current);
+			return merged_entry(newtree, NULL, dst);
+		}
+		else
+			/* all other failures */
 			return -1;
 	}
-	if (b)
-		return merged_entry(b, old, dst);
-	if (old)
-		verify_uptodate(old);
-	return 0;
+	else if (newtree)
+		return merged_entry(newtree, NULL, dst);
+	else
+		return 0;
 }
 
 /*
@@ -195,11 +218,11 @@ static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
 
 	if (!a)
 		return 0;
-	if (old && same(old, a))
-		*a = *old;
-	a->ce_flags &= ~htons(CE_STAGEMASK);
-	*dst++ = a;
-	return 1;
+	if (old && same(old, a)) {
+		*dst++ = old;
+		return 1;
+	}
+	return merged_entry(a, NULL, dst);
 }
 
 static void check_updates(struct cache_entry **src, int nr)
@@ -221,7 +244,9 @@ static void check_updates(struct cache_entry **src, int nr)
 	}
 }
 
-static void merge_cache(struct cache_entry **src, int nr, int (*fn)(struct cache_entry **, struct cache_entry **))
+typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **);
+
+static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
 {
 	struct cache_entry **dst = src;
 
@@ -250,7 +275,7 @@ static void merge_cache(struct cache_entry **src, int nr, int (*fn)(struct cache
 	check_updates(active_cache, active_nr);
 }
 
-static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> [<sha3>]])";
+static char *read_tree_usage = "git-read-tree (<sha> | -m [-u] <sha1> [<sha2> [<sha3>]])";
 
 static struct cache_file cache_file;
 
@@ -295,21 +320,17 @@ int main(int argc, char **argv)
 			die("failed to unpack tree object %s", arg);
 		stage++;
 	}
+	if (update && !merge)
+		usage(read_tree_usage);
 	if (merge) {
-		switch (stage) {
-		case 4:	/* Three-way merge */
-			merge_cache(active_cache, active_nr, threeway_merge);
-			break;
-		case 3:	/* Update from one tree to another */
-			merge_cache(active_cache, active_nr, twoway_merge);
-			check_updates(active_cache, active_nr);
-			break;
-		case 2:	/* Just read a tree, merge with old cache contents */
-			merge_cache(active_cache, active_nr, oneway_merge);
-			break;
-		default:
+		static const merge_fn_t merge_function[] = {
+			[1] = oneway_merge,
+			[2] = twoway_merge,
+			[3] = threeway_merge,
+		};
+		if (stage < 2 || stage > 4)
 			die("just how do you expect me to merge %d trees?", stage-1);
-		}
+		merge_cache(active_cache, active_nr, merge_function[stage-1]);
 	}
 	if (write_cache(newfd, active_cache, active_nr) ||
 	    commit_index_file(&cache_file))