push: require force for refs under refs/tags/

References are allowed to update from one commit-ish to another if the
former is an ancestor of the latter.  This behavior is oriented to
branches which are expected to move with commits.  Tag references are
expected to be static in a repository, though, thus an update to
something under refs/tags/ should be rejected unless the update is
forced.

Signed-off-by: Chris Rorvick <chris@rorvick.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-push.txt

@@ -51,11 +51,12 @@ be named. If `:`<dst> is omitted, the same ref as <src> will be
 updated.
 +
 The object referenced by <src> is used to update the <dst> reference
-on the remote side, but by default this is only allowed if the
-update can fast-forward <dst>.  By having the optional leading `+`,
-you can tell git to update the <dst> ref even when the update is not a
-fast-forward.  This does *not* attempt to merge <src> into <dst>.  See
-EXAMPLES below for details.
+on the remote side.  By default this is only allowed if <dst> is not
+under refs/tags/, and then only if it can fast-forward <dst>.  By having
+the optional leading `+`, you can tell git to update the <dst> ref even
+if it is not allowed by default (e.g., it is not a fast-forward.)  This
+does *not* attempt to merge <src> into <dst>.  See EXAMPLES below for
+details.
 +
 `tag <tag>` means the same as `refs/tags/<tag>:refs/tags/<tag>`.
 +

builtin/push.c

@@ -222,7 +222,7 @@ static const char message_advice_checkout_pull_push[] =
 
 static const char message_advice_ref_already_exists[] =
 	N_("Updates were rejected because the destination reference already exists\n"
-	   "in the remote and the update is not a fast-forward.");
+	   "in the remote.");
 
 static void advise_pull_before_push(void)
 {

builtin/send-pack.c

@@ -44,6 +44,11 @@ static void print_helper_status(struct ref *ref)
 			msg = "non-fast forward";
 			break;
 
+		case REF_STATUS_REJECT_ALREADY_EXISTS:
+			res = "error";
+			msg = "already exists";
+			break;
+
 		case REF_STATUS_REJECT_NODELETE:
 		case REF_STATUS_REMOTE_REJECT:
 			res = "error";

cache.h

@@ -1011,6 +1011,7 @@ struct ref {
 		REF_STATUS_NONE = 0,
 		REF_STATUS_OK,
 		REF_STATUS_REJECT_NONFASTFORWARD,
+		REF_STATUS_REJECT_ALREADY_EXISTS,
 		REF_STATUS_REJECT_NODELETE,
 		REF_STATUS_UPTODATE,
 		REF_STATUS_REMOTE_REJECT,

remote.c

@@ -1315,14 +1315,18 @@ void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
 		 *
 		 * (1) if the old thing does not exist, it is OK.
 		 *
-		 * (2) if you do not have the old thing, you are not allowed
+		 * (2) if the destination is under refs/tags/ you are
+		 *     not allowed to overwrite it; tags are expected
+		 *     to be static once created
+		 *
+		 * (3) if you do not have the old thing, you are not allowed
 		 *     to overwrite it; you would not know what you are losing
 		 *     otherwise.
 		 *
-		 * (3) if both new and old are commit-ish, and new is a
+		 * (4) if both new and old are commit-ish, and new is a
 		 *     descendant of old, it is OK.
 		 *
-		 * (4) regardless of all of the above, removing :B is
+		 * (5) regardless of all of the above, removing :B is
 		 *     always allowed.
 		 */
 
@@ -1337,7 +1341,13 @@ void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
 				!has_sha1_file(ref->old_sha1)
 				  || !ref_newer(ref->new_sha1, ref->old_sha1);
 
-			if (ref->nonfastforward) {
+			if (ref->not_forwardable) {
+				ref->requires_force = 1;
+				if (!force_ref_update) {
+					ref->status = REF_STATUS_REJECT_ALREADY_EXISTS;
+					continue;
+				}
+			} else if (ref->nonfastforward) {
 				ref->requires_force = 1;
 				if (!force_ref_update) {
 					ref->status = REF_STATUS_REJECT_NONFASTFORWARD;

send-pack.c

@@ -229,6 +229,7 @@ int send_pack(struct send_pack_args *args,
 		/* Check for statuses set by set_ref_status_for_push() */
 		switch (ref->status) {
 		case REF_STATUS_REJECT_NONFASTFORWARD:
+		case REF_STATUS_REJECT_ALREADY_EXISTS:
 		case REF_STATUS_UPTODATE:
 			continue;
 		default:

t/t5516-fetch-push.sh

@@ -368,7 +368,7 @@ test_expect_success 'push with colon-less refspec (2)' '
 		git branch -D frotz
 	fi &&
 	git tag -f frotz &&
-	git push testrepo frotz &&
+	git push -f testrepo frotz &&
 	check_push_result $the_commit tags/frotz &&
 	check_push_result $the_first_commit heads/frotz
 
@@ -929,6 +929,27 @@ test_expect_success 'push into aliased refs (inconsistent)' '
 	)
 '
 
+test_expect_success 'push requires --force to update lightweight tag' '
+	mk_test heads/master &&
+	mk_child child1 &&
+	mk_child child2 &&
+	(
+		cd child1 &&
+		git tag Tag &&
+		git push ../child2 Tag &&
+		git push ../child2 Tag &&
+		>file1 &&
+		git add file1 &&
+		git commit -m "file1" &&
+		git tag -f Tag &&
+		test_must_fail git push ../child2 Tag &&
+		git push --force ../child2 Tag &&
+		git tag -f Tag &&
+		test_must_fail git push ../child2 Tag HEAD~ &&
+		git push --force ../child2 Tag
+	)
+'
+
 test_expect_success 'push --porcelain' '
 	mk_empty &&
 	echo >.git/foo  "To testrepo" &&

transport-helper.c

@@ -661,6 +661,11 @@ static void push_update_ref_status(struct strbuf *buf,
 			free(msg);
 			msg = NULL;
 		}
+		else if (!strcmp(msg, "already exists")) {
+			status = REF_STATUS_REJECT_ALREADY_EXISTS;
+			free(msg);
+			msg = NULL;
+		}
 	}
 
 	if (*ref)
@@ -720,6 +725,7 @@ static int push_refs_with_push(struct transport *transport,
 		/* Check for statuses set by set_ref_status_for_push() */
 		switch (ref->status) {
 		case REF_STATUS_REJECT_NONFASTFORWARD:
+		case REF_STATUS_REJECT_ALREADY_EXISTS:
 		case REF_STATUS_UPTODATE:
 			continue;
 		default:

transport.c

@@ -695,6 +695,10 @@ static int print_one_push_status(struct ref *ref, const char *dest, int count, i
 		print_ref_status('!', "[rejected]", ref, ref->peer_ref,
 						 "non-fast-forward", porcelain);
 		break;
+	case REF_STATUS_REJECT_ALREADY_EXISTS:
+		print_ref_status('!', "[rejected]", ref, ref->peer_ref,
+						 "already exists", porcelain);
+		break;
 	case REF_STATUS_REMOTE_REJECT:
 		print_ref_status('!', "[remote rejected]", ref,
 						 ref->deletion ? NULL : ref->peer_ref,
@@ -740,12 +744,12 @@ void transport_print_push_status(const char *dest, struct ref *refs,
 		    ref->status != REF_STATUS_OK)
 			n += print_one_push_status(ref, dest, n, porcelain);
 		if (ref->status == REF_STATUS_REJECT_NONFASTFORWARD) {
-			if (ref->not_forwardable)
-				*reject_reasons |= REJECT_ALREADY_EXISTS;
 			if (!strcmp(head, ref->name))
 				*reject_reasons |= REJECT_NON_FF_HEAD;
 			else
 				*reject_reasons |= REJECT_NON_FF_OTHER;
+		} else if (ref->status == REF_STATUS_REJECT_ALREADY_EXISTS) {
+			*reject_reasons |= REJECT_ALREADY_EXISTS;
 		}
 	}
 }