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, 11 insertions, 1 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 90e7d10bad..1f47761c89 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -143,7 +143,8 @@ advice.*::
 	pushUpdateRejected::
 		Set this variable to 'false' if you want to disable
 		'pushNonFFCurrent', 'pushNonFFDefault',
-		'pushNonFFMatching', and 'pushAlreadyExists'
+		'pushNonFFMatching', 'pushAlreadyExists',
+		'pushFetchFirst', and 'pushNeedsForce'
 		simultaneously.
 	pushNonFFCurrent::
 		Advice shown when linkgit:git-push[1] fails due to a
@@ -162,6 +163,15 @@ advice.*::
 	pushAlreadyExists::
 		Shown when linkgit:git-push[1] rejects an update that
 		does not qualify for fast-forwarding (e.g., a tag.)
+	pushFetchFirst::
+		Shown when linkgit:git-push[1] rejects an update that
+		tries to overwrite a remote ref that points at an
+		object we do not have.
+	pushNeedsForce::
+		Shown when linkgit:git-push[1] rejects an update that
+		tries to overwrite a remote ref that points at an
+		object that is not a committish, or make the remote
+		ref point at an object that is not a committish.
 	statusHints::
 		Show directions on how to proceed from the current
 		state in the output of linkgit:git-status[1] and in