fetch: document and test --refmap=""
To prevent long blocking time during a 'git fetch' call, a user
may want to set up a schedule for background 'git fetch' processes.
However, these runs will update the refs/remotes branches due to
the default refspec set in the config when Git adds a remote.
Hence the user will not notice when remote refs are updated during
their foreground fetches. In fact, they may _want_ those refs to
stay put so they can work with the refs from their last foreground
fetch call.
This can be accomplished by overriding the configured refspec using
'--refmap=' along with a custom refspec:
git fetch --refmap='' <remote> +refs/heads/*:refs/hidden/<remote>/*
to populate a custom ref space and download a pack of the new
reachable objects. This kind of call allows a few things to happen:
1. We download a new pack if refs have updated.
2. Since the refs/hidden branches exist, GC will not remove the
newly-downloaded data.
3. With fetch.writeCommitGraph enabled, the refs/hidden refs are
used to update the commit-graph file.
To avoid the refs/hidden directory from filling without bound, the
--prune option can be included. When providing a refspec like this,
the --prune option does not delete remote refs and instead only
deletes refs in the target refspace.
Update the documentation to clarify how '--refmap=""' works and
create tests to guarantee this behavior remains in the future.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index 43b9ff3..17fe086 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -135,7 +135,10 @@
specified refspec (can be given more than once) to map the
refs to remote-tracking branches, instead of the values of
`remote.*.fetch` configuration variables for the remote
- repository. See section on "Configured Remote-tracking
+ repository. Providing an empty `<refspec>` to the
+ `--refmap` option causes Git to ignore the configured
+ refspecs and rely entirely on the refspecs supplied as
+ command-line arguments. See section on "Configured Remote-tracking
Branches" for details.
-t::
