[PATCH] submodule--helper: teach push-check to handle HEAD

[Brandon Williams <bmwill@google.com>]

In 06bf4ad1d (push: propagate remote and refspec with
--recurse-submodules) push was taught how to propagate a refspec down to
submodules when the '--recurse-submodules' flag is given.  The only refspecs
that are allowed to be propagated are ones which name a ref which exists
in both the superproject and the submodule, with the caveat that 'HEAD'
was disallowed.

This patch teaches push-check (the submodule helper which determines if
a refspec can be propagated to a submodule) to permit propagating 'HEAD'
if and only if the superproject and the submodule both have the same
named branch checked out and the submodule is not in a detached head
state.

Signed-off-by: Brandon Williams <bmwill@google.com>
---
 builtin/submodule--helper.c    | 57 +++++++++++++++++++++++++++++++-----------
 submodule.c                    | 18 ++++++++++---
 t/t5531-deep-submodule-push.sh | 25 +++++++++++++++++-
 3 files changed, 82 insertions(+), 18 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 1b4d2b346..fd5020036 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1107,24 +1107,41 @@ static int resolve_remote_submodule_branch(int argc, const char **argv,
 static int push_check(int argc, const char **argv, const char *prefix)
 {
 	struct remote *remote;
+	const char *superproject_head;
+	char *head;
+	int detached_head = 0;
+	struct object_id head_oid;
 
-	if (argc < 2)
-		die("submodule--helper push-check requires at least 1 argument");
+	if (argc < 3)
+		die("submodule--helper push-check requires at least 2 argument");
+
+	/*
+	 * superproject's resolved head ref.
+	 * if HEAD then the superproject is in a detached head state, otherwise
+	 * it will be the resolved head ref.
+	 */
+	superproject_head = argv[1];
+	/* Get the submodule's head ref and determine if it is detached */
+	head = resolve_refdup("HEAD", 0, head_oid.hash, NULL);
+	if (!head)
+		die(_("Failed to resolve HEAD as a valid ref."));
+	if (!strcmp(head, "HEAD"))
+		detached_head = 1;
 
 	/*
 	 * The remote must be configured.
 	 * This is to avoid pushing to the exact same URL as the parent.
 	 */
-	remote = pushremote_get(argv[1]);
+	remote = pushremote_get(argv[2]);
 	if (!remote || remote->origin == REMOTE_UNCONFIGURED)
-		die("remote '%s' not configured", argv[1]);
+		die("remote '%s' not configured", argv[2]);
 
 	/* Check the refspec */
-	if (argc > 2) {
-		int i, refspec_nr = argc - 2;
+	if (argc > 3) {
+		int i, refspec_nr = argc - 3;
 		struct ref *local_refs = get_local_heads();
 		struct refspec *refspec = parse_push_refspec(refspec_nr,
-							     argv + 2);
+							     argv + 3);
 
 		for (i = 0; i < refspec_nr; i++) {
 			struct refspec *rs = refspec + i;
@@ -1132,18 +1149,30 @@ static int push_check(int argc, const char **argv, const char *prefix)
 			if (rs->pattern || rs->matching)
 				continue;
 
-			/*
-			 * LHS must match a single ref
-			 * NEEDSWORK: add logic to special case 'HEAD' once
-			 * working with submodules in a detached head state
-			 * ceases to be the norm.
-			 */
-			if (count_refspec_match(rs->src, local_refs, NULL) != 1)
+			/* LHS must match a single ref */
+			switch(count_refspec_match(rs->src, local_refs, NULL)) {
+			case 1:
+				break;
+			case 0:
+				/*
+				 * If LHS matches 'HEAD' then we need to ensure
+				 * that it matches the same named branch
+				 * checked out in the superproject.
+				 */
+				if (!strcmp(rs->src, "HEAD")) {
+					if (!detached_head &&
+					    !strcmp(head, superproject_head))
+						break;
+					die("HEAD does not match the named branch in the superproject");
+				}
+			default:
 				die("src refspec '%s' must name a ref",
 				    rs->src);
+			}
 		}
 		free_refspec(refspec_nr, refspec);
 	}
+	free(head);
 
 	return 0;
 }
diff --git a/submodule.c b/submodule.c
index 1b8a3b575..920b49328 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1003,7 +1003,8 @@ static int push_submodule(const char *path,
  * Perform a check in the submodule to see if the remote and refspec work.
  * Die if the submodule can't be pushed.
  */
-static void submodule_push_check(const char *path, const struct remote *remote,
+static void submodule_push_check(const char *path, const char *head,
+				 const struct remote *remote,
 				 const char **refspec, int refspec_nr)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
@@ -1011,6 +1012,7 @@ static void submodule_push_check(const char *path, const struct remote *remote,
 
 	argv_array_push(&cp.args, "submodule--helper");
 	argv_array_push(&cp.args, "push-check");
+	argv_array_push(&cp.args, head);
 	argv_array_push(&cp.args, remote->name);
 
 	for (i = 0; i < refspec_nr; i++)
@@ -1049,10 +1051,20 @@ int push_unpushed_submodules(struct oid_array *commits,
 	 * won't be propagated due to the remote being unconfigured (e.g. a URL
 	 * instead of a remote name).
 	 */
-	if (remote->origin != REMOTE_UNCONFIGURED)
+	if (remote->origin != REMOTE_UNCONFIGURED) {
+		char *head;
+		struct object_id head_oid;
+
+		head = resolve_refdup("HEAD", 0, head_oid.hash, NULL);
+		if (!head)
+			die(_("Failed to resolve HEAD as a valid ref."));
+
 		for (i = 0; i < needs_pushing.nr; i++)
 			submodule_push_check(needs_pushing.items[i].string,
-					     remote, refspec, refspec_nr);
+					     head, remote,
+					     refspec, refspec_nr);
+		free(head);
+	}
 
 	/* Actually push the submodules */
 	for (i = 0; i < needs_pushing.nr; i++) {
diff --git a/t/t5531-deep-submodule-push.sh b/t/t5531-deep-submodule-push.sh
index beff65b8a..0f84a5314 100755
--- a/t/t5531-deep-submodule-push.sh
+++ b/t/t5531-deep-submodule-push.sh
@@ -533,7 +533,8 @@ test_expect_success 'push propagating refspec to a submodule' '
 	# Fails when refspec includes an object id
 	test_must_fail git -C work push --recurse-submodules=on-demand origin \
 		"$(git -C work rev-parse branch2):refs/heads/branch2" &&
-	# Fails when refspec includes 'HEAD' as it is unsupported at this time
+	# Fails when refspec includes HEAD and parent and submodule do not
+	# have the same named branch checked out
 	test_must_fail git -C work push --recurse-submodules=on-demand origin \
 		HEAD:refs/heads/branch2 &&
 
@@ -548,4 +549,26 @@ test_expect_success 'push propagating refspec to a submodule' '
 	test_cmp expected_pub actual_pub
 '
 
+test_expect_success 'push propagating HEAD refspec to a submodule' '
+	git -C work/gar/bage checkout branch2 &&
+	> work/gar/bage/junk12 &&
+	git -C work/gar/bage add junk12 &&
+	git -C work/gar/bage commit -m "Twelfth junk" &&
+
+	git -C work checkout branch2 &&
+	git -C work add gar/bage &&
+	git -C work commit -m "updating gar/bage in branch2" &&
+
+	# Passes since the superproject and submodules HEAD are both on branch2
+	git -C work push --recurse-submodules=on-demand origin \
+		HEAD:refs/heads/branch2 &&
+
+	git -C submodule.git rev-parse branch2 >actual_submodule &&
+	git -C pub.git rev-parse branch2 >actual_pub &&
+	git -C work/gar/bage rev-parse branch2 >expected_submodule &&
+	git -C work rev-parse branch2 >expected_pub &&
+	test_cmp expected_submodule actual_submodule &&
+	test_cmp expected_pub actual_pub
+'
+
 test_done
-- 
2.13.1.704.gde00cce3c-goog