ReceivePack: Prevent pointing a branch to a non-commit object

Since commit c3b0dec509fe136c5417422f31898b5a4e2d5e02, Git has
disallowed writing a non-commit to refs/heads/* refs.  JGit still
allows that, which can put users in a bad situation.  For example,

	git push origin v1.0:master

pushes the tag object v1.0 to refs/heads/master, instead of the
intended commit object v1.0^{commit}.

Prevent that by validating that the target of the ref points to a
commit object when pushing to refs/heads/*.

Git performs the same check at a lower level (in the RefDatabase).  We
could do the same here, but for now let's start conservatively by
handling it in pushes first.

[jn: fleshed out commit message]

Change-Id: I8f98ae6d8acbcd5ef7553ec732bc096cb6eb7c4e
Signed-off-by: Yunjie Li <yunjieli@google.com>
Signed-off-by: Jonathan Nieder <jrn@google.com>

0 files changed, 0 insertions, 0 deletions