Merge branch 'ab/push-cas-doc-n-test'

Doc update.

* ab/push-cas-doc-n-test:
  push: document & test --force-with-lease with multiple remotes
This commit is contained in:
Junio C Hamano 2017-04-26 15:39:05 +09:00
commit 46bdfa3975
2 changed files with 70 additions and 0 deletions

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@ -217,6 +217,47 @@ with this feature.
+
"--no-force-with-lease" will cancel all the previous --force-with-lease on the
command line.
+
A general note on safety: supplying this option without an expected
value, i.e. as `--force-with-lease` or `--force-with-lease=<refname>`
interacts very badly with anything that implicitly runs `git fetch` on
the remote to be pushed to in the background, e.g. `git fetch origin`
on your repository in a cronjob.
+
The protection it offers over `--force` is ensuring that subsequent
changes your work wasn't based on aren't clobbered, but this is
trivially defeated if some background process is updating refs in the
background. We don't have anything except the remote tracking info to
go by as a heuristic for refs you're expected to have seen & are
willing to clobber.
+
If your editor or some other system is running `git fetch` in the
background for you a way to mitigate this is to simply set up another
remote:
+
git remote add origin-push $(git config remote.origin.url)
git fetch origin-push
+
Now when the background process runs `git fetch origin` the references
on `origin-push` won't be updated, and thus commands like:
+
git push --force-with-lease origin-push
+
Will fail unless you manually run `git fetch origin-push`. This method
is of course entirely defeated by something that runs `git fetch
--all`, in that case you'd need to either disable it or do something
more tedious like:
+
git fetch # update 'master' from remote
git tag base master # mark our base point
git rebase -i master # rewrite some commits
git push --force-with-lease=master:base master:master
+
I.e. create a `base` tag for versions of the upstream code that you've
seen and are willing to overwrite, then rewrite history, and finally
force push changes to `master` if the remote version is still at
`base`, regardless of what your local `remotes/origin/master` has been
updated to in the background.
-f::
--force::

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@ -229,4 +229,33 @@ test_expect_success 'new branch already exists' '
)
'
test_expect_success 'background updates of REMOTE can be mitigated with a non-updated REMOTE-push' '
rm -rf src dst &&
git init --bare src.bare &&
test_when_finished "rm -rf src.bare" &&
git clone --no-local src.bare dst &&
test_when_finished "rm -rf dst" &&
(
cd dst &&
test_commit G &&
git remote add origin-push ../src.bare &&
git push origin-push master:master
) &&
git clone --no-local src.bare dst2 &&
test_when_finished "rm -rf dst2" &&
(
cd dst2 &&
test_commit H &&
git push
) &&
(
cd dst &&
test_commit I &&
git fetch origin &&
test_must_fail git push --force-with-lease origin-push &&
git fetch origin-push &&
git push --force-with-lease origin-push
)
'
test_done