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fetch: document and test --refmap=""

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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>
This commit is contained in:
Derrick Stolee 2020-01-21 01:38:12 +00:00 committed by Junio C Hamano
parent b6d4d82bd5
commit b40a50264a
2 changed files with 28 additions and 1 deletions
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5
Documentation/fetch-options.txt
View File

@ -135,7 +135,10 @@ ifndef::git-pull[]
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::

24
t/t5510-fetch.sh
View File

@ -174,6 +174,30 @@ test_expect_success 'fetch --prune --tags with refspec prunes based on refspec'
git rev-parse sometag
'
test_expect_success '--refmap="" ignores configured refspec' '
cd "$TRASH_DIRECTORY" &&
git clone "$D" remote-refs &&
git -C remote-refs rev-parse remotes/origin/master >old &&
git -C remote-refs update-ref refs/remotes/origin/master master~1 &&
git -C remote-refs rev-parse remotes/origin/master >new &&
git -C remote-refs fetch --refmap= origin "+refs/heads/*:refs/hidden/origin/*" &&
git -C remote-refs rev-parse remotes/origin/master >actual &&
test_cmp new actual &&
git -C remote-refs fetch origin &&
git -C remote-refs rev-parse remotes/origin/master >actual &&
test_cmp old actual
'
test_expect_success '--refmap="" and --prune' '
git -C remote-refs update-ref refs/remotes/origin/foo/otherbranch master &&
git -C remote-refs update-ref refs/hidden/foo/otherbranch master &&
git -C remote-refs fetch --prune --refmap="" origin +refs/heads/*:refs/hidden/* &&
git -C remote-refs rev-parse remotes/origin/foo/otherbranch &&
test_must_fail git -C remote-refs rev-parse refs/hidden/foo/otherbranch &&
git -C remote-refs fetch --prune origin &&
test_must_fail git -C remote-refs rev-parse remotes/origin/foo/otherbranch
'
test_expect_success 'fetch tags when there is no tags' '
cd "$D" &&