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>

1 files changed, 8 insertions, 3 deletions

diff --git a/remote.c b/remote.c
index 969aa11..a772e74 100644
--- a/remote.c
+++ b/remote.c
@@ -1322,8 +1322,12 @@ void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
 
 			if (!prefixcmp(ref->name, "refs/tags/"))
 				why = REF_STATUS_REJECT_ALREADY_EXISTS;
-			else if (!has_sha1_file(ref->old_sha1)
-				 || !ref_newer(ref->new_sha1, ref->old_sha1))
+			else if (!has_sha1_file(ref->old_sha1))
+				why = REF_STATUS_REJECT_FETCH_FIRST;
+			else if (!lookup_commit_reference_gently(ref->old_sha1, 1) ||
+				 !lookup_commit_reference_gently(ref->new_sha1, 1))
+				why = REF_STATUS_REJECT_NEEDS_FORCE;
+			else if (!ref_newer(ref->new_sha1, ref->old_sha1))
 				why = REF_STATUS_REJECT_NONFASTFORWARD;
 
 			if (!force_ref_update)
@@ -1512,7 +1516,8 @@ int ref_newer(const unsigned char *new_sha1, const unsigned char *old_sha1)
 	struct commit_list *list, *used;
 	int found = 0;
 
-	/* Both new and old must be commit-ish and new is descendant of
+	/*
+	 * Both new and old must be commit-ish and new is descendant of
 	 * old.  Otherwise we require --force.
 	 */
 	o = deref_tag(parse_object(old_sha1), NULL, 0);