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How to use drover

What is Drover?

Drover is a tool, included with depot tools, that allows developers (committers) to rapidly merge and revert changes on our trunk/branches without any previously checked out working copy. A typical drover command to merge or revert with no conflicts takes about 1 minute to run from start to finish.

New: Since moving to Gerrit, you can now perform some cherry pick scenarios directly in Gerrit instead of using Drover.

Merging Notes

Merging to a branch and don't know the branch number? The TPM (release manager) approving the merge will have it, and it's typically sent out in an email after every branch.

After merging to a release branch, try to watch http://go/stablebuilders (for stable branches) and http://go/betabuilders (for beta branches) and here for dev/trunk branches to make sure everything's all right.

Using Gerrit to cherry-pick CLs Instead
You can use Gerrit to cherry-pick CLs directly to our release branches where no conflicts are present (if there are merge conflicts, use the Git Drover instructions below), no terminal required!  To do so, follow the steps below once you have merge approval:

Press the "More" button and select "Cherry Pick"

Enter branch details. For Chromium, use:

M63 refs/branch-heads/3239
M64 refs/branch-heads/3282
M65   refs/branch-heads/3325 

Voila, you now have a fresh CL uploaded for the branch - simply +1 and commit (or go through review where you'd like).

Git Drover

NOTE: Using Gerrit (as described above) will almost certainly be faster than using git-drover, we recommend trying it first.

git-drover is a new drover for working with git repositories. It is not:
  • The way to do all merges/reverts in the "post git migration" world.
  • If you are working with a repository that is still svn-based, see the old SVN Drover instructions below.
  • The way to do anything that is not a merge of a git commit (e.g. DEPS rolls).
  • Those changes should follow the normal commit workflow, or use other tools made for the job (e.g. roll-dep)

Requirements/ recommendations

  • Note that these instructions assume you have a working depot_tools and chromium checkout as described in the depot_tools tutorial.
  • You'll need your git (.gitcookies) credentials.
  • You'll also need your credentials (for code reviews).
  • Before working with branches, you must gclient sync --with_branch_heads at least once to fetch the branches.


  • Merge a change to a release branch
    • git drover --branch <branch_id> --cherry-pick <revision> (e.g. git drover --branch 9999 --cherry-pick b5a049)
For merges on Windows and reverts, please see man git-drover or the online git-drover doc for instructions to achieve equivalent functionality using other git and depot_tools commands.


Cannot find 'refs/branch-heads/9999'

Follow the steps for checking out a release branch to sync the branch heads.

Not in chromium-committers Gerrit group

If this is the first time you've tried to merge into a branch, you may run into the following error when trying to git cl land the change:
error: failed to push some refs to ''
ERROR:git-retry:Process failure was not known to be transient; terminating with return code 1
Push failed with exit code 1.
! HEAD:refs/pending/branch-heads/2311 [remote rejected] (prohibited by Gerrit)

If you see this error, and you are a committer (went through the process described here) you may not have been added to the chromium-committers gerrit group yet (the group update process lags behind a bit). File a bug with the Infra-Git label, so you can be added to the group manually.

Uploading merge CL after manual edit

If you've started merge with "git drover" and made any manual edit, "git cl upload" doesn't work to upload the new snapshot. Use "git drover --continue".

Build failure may be due to DEPS changes

If the merged branch doesn't build locally, you may need to port DEPS change from the version-number named branch (e.g. DEPS changes after branch cut are not made on the release branch but in the version-number named branches.

Check which branches your patch has been merged to

If you have a patch and want to check which branches it has been merged to, or which version it first got released in, you can use:
$ git find-releases eeac3e6a187e362d796fa01489927e773be705ac
commit eeac3e6a187e362d796fa01489927e773be705ac was:
  initially in 55.0.2867.0
  merged to 54.0.2840.36 (as 72308707baae9aac0bea97387c1b4426bd378f51)

Re-merging patch on Release Branch

When the initial merge attempt fails, cherry-picking the CL again with "git drover" might not work anymore with the following error message:
! [remote rejected] .... (change closed)
This can be solved by removing the entire line of "Change-Id: ..." field in the commit log. Gerrit will bypass the checking on "Change-Id" and will let you submit the cherry-pick CL.