More work on merging with git-read-tree..

Add a "-u" flag to update the tree as a result of a merge.

Right now this code is way too anal about things, and fails merges it
shouldn't, but let me fix up the different cases and this will allow for
much smoother merging even in the presense of dirty data in the working
tree.

cache.h

@@ -84,6 +84,7 @@ struct cache_entry {
 
 #define CE_NAMEMASK  (0x0fff)
 #define CE_STAGEMASK (0x3000)
+#define CE_UPDATE    (0x4000)
 #define CE_STAGESHIFT 12
 
 #define create_ce_flags(len, stage) htons((len) | ((stage) << CE_STAGESHIFT))

git-resolve-script

@@ -39,14 +39,13 @@ if [ "$common" == "$head" ]; then
 	echo "Destroying all noncommitted data!"
 	echo "Kill me within 3 seconds.."
 	sleep 3
-	git-read-tree -m $merge || exit 1
-	git-checkout-cache -f -u -a
+	git-read-tree -u -m $head $merge || exit 1
 	echo $merge > "$GIT_DIR"/HEAD
 	git-diff-tree -p ORIG_HEAD HEAD | git-apply --stat
 	exit 0
 fi
 echo "Trying to merge $merge into $head"
-git-read-tree -m $common $head $merge || exit 1
+git-read-tree -u -m $common $head $merge || exit 1
 merge_msg="Merge of $merge_repo"
 result_tree=$(git-write-tree  2> /dev/null)
 if [ $? -ne 0 ]; then
@@ -58,5 +57,4 @@ fi
 result_commit=$(echo "$merge_msg" | git-commit-tree $result_tree -p $head -p $merge)
 echo "Committed merge $result_commit"
 echo $result_commit > "$GIT_DIR"/HEAD
-git-checkout-cache -f -u -a
 git-diff-tree -p ORIG_HEAD HEAD | git-apply --stat

read-tree.c

@@ -6,6 +6,7 @@
 #include "cache.h"
 
 static int stage = 0;
+static int update = 0;
 
 static int unpack_tree(unsigned char *sha1)
 {
@@ -130,27 +131,29 @@ static void trivially_merge_cache(struct cache_entry **src, int nr)
 	struct cache_entry **dst = src;
 	struct cache_entry *old = NULL;
 
-	while (nr) {
+	while (nr--) {
 		struct cache_entry *ce, *result;
 
-		ce = src[0];
+		ce = *src++;
 
 		/* We throw away original cache entries except for the stat information */
 		if (!ce_stage(ce)) {
 			if (old)
 				reject_merge(old);
 			old = ce;
-			src++;
-			nr--;
 			active_nr--;
 			continue;
 		}
 		if (old && !path_matches(old, ce))
 			reject_merge(old);
 		if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
+			result->ce_flags |= htons(CE_UPDATE);
 			/*
 			 * See if we can re-use the old CE directly?
 			 * That way we get the uptodate stat info.
+			 *
+			 * This also removes the UPDATE flag on
+			 * a match.
 			 */
 			if (old && same(old, result)) {
 				*result = *old;
@@ -172,42 +175,113 @@ static void trivially_merge_cache(struct cache_entry **src, int nr)
 		 */
 		CHECK_OLD(ce);
 		*dst++ = ce;
-		src++;
-		nr--;
 	}
 	if (old)
 		reject_merge(old);
 }
 
-static void merge_stat_info(struct cache_entry **src, int nr)
+/*
+ * 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.
+ */
+static void twoway_merge(struct cache_entry **src, int nr)
 {
 	static struct cache_entry null_entry;
+	struct cache_entry *old = NULL, *stat = &null_entry;
 	struct cache_entry **dst = src;
-	struct cache_entry *old = &null_entry;
 
-	while (nr) {
-		struct cache_entry *ce;
+	while (nr--) {
+		struct cache_entry *ce = *src++;
+		int stage = ce_stage(ce);
+
+		switch (stage) {
+		case 0:
+			if (old)
+				reject_merge(old);
+			old = ce;
+			stat = ce;
+			active_nr--;
+			continue;
+
+		case 1:
+			active_nr--;
+			if (!old)
+				continue;
+			if (!path_matches(old, ce) || !same(old, ce))
+				reject_merge(old);
+			continue;
+
+		case 2:
+			ce->ce_flags |= htons(CE_UPDATE);
+			if (old) {
+				if (!path_matches(old, ce))
+					reject_merge(old);
+				/*
+				 * This also removes the UPDATE flag on
+				 * a match
+				 */
+				if (same(old, ce))
+					*ce = *old;
+				else
+					verify_uptodate(old);
+				old = NULL;
+			}
+			ce->ce_flags &= ~htons(CE_STAGEMASK);
+			*dst++ = ce;
+			continue;
+		}
+		die("impossible two-way stage");
+	}
+	if (old)
+		reject_merge(old);
+}
+
+static void merge_stat_info(struct cache_entry **src, int nr)
+{
+	static struct cache_entry null_entry;
+	struct cache_entry **dst = src;
+	struct cache_entry *stat = &null_entry;
 
-		ce = src[0];
+	while (nr--) {
+		struct cache_entry *ce = *src++;
 
 		/* We throw away original cache entries except for the stat information */
 		if (!ce_stage(ce)) {
-			old = ce;
-			src++;
-			nr--;
+			stat = ce;
 			active_nr--;
 			continue;
 		}
-		if (path_matches(ce, old) && same(ce, old))
-			*ce = *old;
+		if (path_matches(ce, stat) && same(ce, stat))
+			*ce = *stat;
 		ce->ce_flags &= ~htons(CE_STAGEMASK);
 		*dst++ = ce;
-		src++;
-		nr--;
 	}
 }
 
-static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> <sha3>])";
+static void check_updates(struct cache_entry **src, int nr)
+{
+	static struct checkout state = {
+		.base_dir = "",
+		.force = 1,
+		.quiet = 1,
+		.refresh_cache = 1,
+	};
+	unsigned short mask = htons(CE_UPDATE);
+	while (nr--) {
+		struct cache_entry *ce = *src++;
+		if (ce->ce_flags & mask) {
+			ce->ce_flags &= ~mask;
+			if (update)
+				checkout_entry(ce, &state);
+		}
+	}
+}
+
+static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> [<sha3>]])";
 
 int main(int argc, char **argv)
 {
@@ -228,6 +302,12 @@ int main(int argc, char **argv)
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
 
+		/* "-u" means "update", meaning that a merge will update the working directory */
+		if (!strcmp(arg, "-u")) {
+			update = 1;
+			continue;
+		}
+
 		/* "-m" stands for "merge", meaning we start in stage 1 */
 		if (!strcmp(arg, "-m")) {
 			int i;
@@ -254,6 +334,11 @@ int main(int argc, char **argv)
 		switch (stage) {
 		case 4:	/* Three-way merge */
 			trivially_merge_cache(active_cache, active_nr);
+			check_updates(active_cache, active_nr);
+			break;
+		case 3:	/* Update from one tree to another */
+			twoway_merge(active_cache, active_nr);
+			check_updates(active_cache, active_nr);
 			break;
 		case 2:	/* Just read a tree, merge with old cache contents */
 			merge_stat_info(active_cache, active_nr);