The ref_transaction_update() family of functions use the following
convention for their old_sha1 parameters:
* old_sha1 == NULL: Don't check the old value at all.
* is_null_sha1(old_sha1): Ensure that the reference didn't exist
before the transaction.
* otherwise: Ensure that the reference had the specified value before
the transaction.
delete_ref() had a different convention, namely treating
is_null_sha1(old_sha1) as "don't care". Change it to adhere to the
standard convention to reduce the scope for confusion.
Please note that it is now a bug to pass old_sha1=NULL_SHA1 to
delete_ref() (because it doesn't make sense to delete a reference that
you already know doesn't exist). This is consistent with the behavior
of ref_transaction_delete().
Most of the callers of delete_ref() never pass old_sha1=NULL_SHA1 to
delete_ref(), and are therefore unaffected by this change. The
two exceptions are:
* The call in cmd_update_ref(), which passed NULL_SHA1 if the old
value passed in on the command line was 0{40} or the empty string.
Change that caller to pass NULL in those cases.
Arguably, it should be an error to call "update-ref -d" with the old
value set to "does not exist", just as it is for the `--stdin`
command "delete". But since this usage was accepted until now,
continue to accept it.
* The call in delete_branches(), which could pass NULL_SHA1 if
deleting a broken or symbolic ref. Change it to pass NULL in these
cases.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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