sync: make --prune the default

If a remote deletes a ref, and it points to an object that doesn't
exist locally, we can get into a bad state, and the only way for the
user to recover is to run `repo sync --prune` (and to know that is
the option they need).  The error message is not helpful:

fatal: bad object refs/remotes/cros/firmware-zork-13421.B-master
error: https://chromium.googlesource.com/chromiumos/platform/ec did not send all necessary objects

This situation can also come up when the remote renames refs in a
UNIX FS incompatible way.  For example, replacing refs/heads/foo
with refs/heads/foo/bar.

Also add a --no-prune option for users to disable the behavior.

Bug: https://issuetracker.google.com/203366450
Change-Id: Icf45d838a10938feb091d29800f7e49240830ec3
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/322956
Reviewed-by: Andrew Lamb <andrewlamb@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

0 files changed, 0 insertions, 0 deletions