Merge branch 'sp/merge' (early part)

* 'sp/merge' (early part):
  Use merge-recursive in git-am -3.
  Allow merging bare trees in merge-recursive.
  Move better_branch_name above get_ref in merge-recursive.

git-am.sh

@@ -88,10 +88,12 @@ It does not apply to blobs recorded in its index."
     # This is not so wrong.  Depending on which base we picked,
     # orig_tree may be wildly different from ours, but his_tree
     # has the same set of wildly different changes in parts the
-    # patch did not touch, so resolve ends up canceling them,
+    # patch did not touch, so recursive ends up canceling them,
     # saying that we reverted all those changes.
 
-    git-merge-resolve $orig_tree -- HEAD $his_tree || {
+    eval GITHEAD_$his_tree='"$SUBJECT"'
+    export GITHEAD_$his_tree
+    git-merge-recursive $orig_tree -- HEAD $his_tree || {
 	    if test -d "$GIT_DIR/rr-cache"
 	    then
 		git-rerere
@@ -99,6 +101,7 @@ It does not apply to blobs recorded in its index."
 	    echo Failed to merge in the changes.
 	    exit 1
     }
+    unset GITHEAD_$his_tree
 }
 
 prec=4

merge-recursive.c

@@ -1248,6 +1248,18 @@ static int merge(struct commit *h1,
 	return clean;
 }
 
+static const char *better_branch_name(const char *branch)
+{
+	static char githead_env[8 + 40 + 1];
+	char *name;
+
+	if (strlen(branch) != 40)
+		return branch;
+	sprintf(githead_env, "GITHEAD_%s", branch);
+	name = getenv(githead_env);
+	return name ? name : branch;
+}
+
 static struct commit *get_ref(const char *ref)
 {
 	unsigned char sha1[20];
@@ -1256,6 +1268,9 @@ static struct commit *get_ref(const char *ref)
 	if (get_sha1(ref, sha1))
 		die("Could not resolve ref '%s'", ref);
 	object = deref_tag(parse_object(sha1), ref, strlen(ref));
+	if (object->type == OBJ_TREE)
+		return make_virtual_commit((struct tree*)object,
+			better_branch_name(ref));
 	if (object->type != OBJ_COMMIT)
 		return NULL;
 	if (parse_commit((struct commit *)object))
@@ -1263,18 +1278,6 @@ static struct commit *get_ref(const char *ref)
 	return (struct commit *)object;
 }
 
-static const char *better_branch_name(const char *branch)
-{
-	static char githead_env[8 + 40 + 1];
-	char *name;
-
-	if (strlen(branch) != 40)
-		return branch;
-	sprintf(githead_env, "GITHEAD_%s", branch);
-	name = getenv(githead_env);
-	return name ? name : branch;
-}
-
 int main(int argc, char *argv[])
 {
 	static const char *bases[2];