push: introduce REJECT_FETCH_FIRST and REJECT_NEEDS_FORCE

When we push to update an existing ref, if:

 * the object at the tip of the remote is not a commit; or
 * the object we are pushing is not a commit,

it won't be correct to suggest to fetch, integrate and push again,
as the old and new objects will not "merge".  We should explain that
the push must be forced when there is a non-committish object is
involved in such a case.

If we do not have the current object at the tip of the remote, we do
not even know that object, when fetched, is something that can be
merged.  In such a case, suggesting to pull first just like
non-fast-forward case may not be technically correct, but in
practice, most such failures are seen when you try to push your work
to a branch without knowing that somebody else already pushed to
update the same branch since you forked, so "pull first" would work
as a suggestion most of the time.  And if the object at the tip is
not a commit, "pull first" will fail, without making any permanent
damage.  As a side effect, it also makes the error message the user
will get during the next "push" attempt easier to understand, now
the user is aware that a non-commit object is involved.

In these cases, the current code already rejects such a push on the
client end, but we used the same error and advice messages as the
ones used when rejecting a non-fast-forward push, i.e. pull from
there and integrate before pushing again.

Introduce new rejection reasons and reword the messages
appropriately.

[jc: with help by Peff on message details]

Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 40 insertions, 0 deletions

diff --git a/builtin/push.c b/builtin/push.c
index 8491e43..a2b3fbe 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -220,10 +220,22 @@ static const char message_advice_checkout_pull_push[] =
 	   "(e.g. 'git pull') before pushing again.\n"
 	   "See the 'Note about fast-forwards' in 'git push --help' for details.");
 
+static const char message_advice_ref_fetch_first[] =
+	N_("Updates were rejected because the remote contains work that you do\n"
+	   "not have locally. This is usually caused by another repository pushing\n"
+	   "to the same ref. You may want to first merge the remote changes (e.g.,\n"
+	   "'git pull') before pushing again.\n"
+	   "See the 'Note about fast-forwards' in 'git push --help' for details.");
+
 static const char message_advice_ref_already_exists[] =
 	N_("Updates were rejected because the destination reference already exists\n"
 	   "in the remote.");
 
+static const char message_advice_ref_needs_force[] =
+	N_("You cannot update a remote ref that points at a non-commit object,\n"
+	   "or update a remote ref to make it point at a non-commit object,\n"
+	   "without using the '--force' option.\n");
+
 static void advise_pull_before_push(void)
 {
 	if (!advice_push_non_ff_current || !advice_push_update_rejected)
@@ -252,6 +264,20 @@ static void advise_ref_already_exists(void)
 	advise(_(message_advice_ref_already_exists));
 }
 
+static void advise_ref_fetch_first(void)
+{
+	if (!advice_push_fetch_first || !advice_push_update_rejected)
+		return;
+	advise(_(message_advice_ref_fetch_first));
+}
+
+static void advise_ref_needs_force(void)
+{
+	if (!advice_push_needs_force || !advice_push_update_rejected)
+		return;
+	advise(_(message_advice_ref_needs_force));
+}
+
 static int push_with_options(struct transport *transport, int flags)
 {
 	int err;
@@ -285,6 +311,10 @@ static int push_with_options(struct transport *transport, int flags)
 			advise_checkout_pull_push();
 	} else if (reject_reasons & REJECT_ALREADY_EXISTS) {
 		advise_ref_already_exists();
+	} else if (reject_reasons & REJECT_FETCH_FIRST) {
+		advise_ref_fetch_first();
+	} else if (reject_reasons & REJECT_NEEDS_FORCE) {
+		advise_ref_needs_force();
 	}
 
 	return 1;
diff --git a/builtin/send-pack.c b/builtin/send-pack.c
index f849e0a..57a46b2 100644
--- a/builtin/send-pack.c
+++ b/builtin/send-pack.c
@@ -44,6 +44,16 @@ static void print_helper_status(struct ref *ref)
 			msg = "non-fast forward";
 			break;
 
+		case REF_STATUS_REJECT_FETCH_FIRST:
+			res = "error";
+			msg = "fetch first";
+			break;
+
+		case REF_STATUS_REJECT_NEEDS_FORCE:
+			res = "error";
+			msg = "needs force";
+			break;
+
 		case REF_STATUS_REJECT_ALREADY_EXISTS:
 			res = "error";
 			msg = "already exists";