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| -rw-r--r-- | Documentation/git-push.txt | 41 | ||||
| -rwxr-xr-x | t/t5533-push-cas.sh | 29 |
2 files changed, 70 insertions, 0 deletions
diff --git a/Documentation/git-push.txt b/Documentation/git-push.txt index 1624a35888..0a639664fd 100644 --- a/Documentation/git-push.txt +++ b/Documentation/git-push.txt @@ -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:: diff --git a/t/t5533-push-cas.sh b/t/t5533-push-cas.sh index a2c9e7439f..d38ecee217 100755 --- a/t/t5533-push-cas.sh +++ b/t/t5533-push-cas.sh @@ -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 |