Upstream Pulls

What is an Upstream Pull

An “upstream pull” is a pull request that pulls in commits from the upstream Rust repository back into the Ferrocene repository to keep them in sync. This procedure is usually performed by a periodic Github Action that opens a pull request automatically. Sometimes merge conflicts may occur in which case the conflict needs to to be resolved manually.

Upstream Pull without merge conflicts

To sign off a automatic upstream pull without merge conflicts, the reviewer only needs to approve the PR and comment bors merge. This will trigger the “full” CI workflow. If the workflow succeeds, the Upstream Pull is getting merged.

Upstream Pull with merge conflicts

If an automatic upstream pull creates merge conflicts, the automation commits the merge conflicts and they need to be resolved manually.

Checkout PR

Start by checking out the PR. The name of the branch is automation/pull-upstream/<ID>, e.g. automation/pull-upstream/dfvjj2s4:

git fetch
git switch automation/pull-upstream/<ID>

Fix conflict

To find the conflicting files run following command:


There are multiple kinds of merge conflicts:

General conflict

For general conflicts the output will look similar to this:

compiler/rustc_abi/Cargo.toml: conflict between lines 18 and 20

Fix the conflict manually and stage the changed files:

git add <FILE_1> <FILE_2> # stages file(s)

Deletion conflict

For deletion conflicts the output will look similar to this:

compiler/rustc_abi/src/ file deleted by one side of the merge

This conflict happens when we made changes to a file and it gets deleted by upstream.

Usually this is solved by removing the file:

git rm <FILE_1> <FILE_2> # removes file(s) and stages that change

Apart from deleting the file, it is necessary to make sure that the purpose we changed the file for is preserved. For example if we changed a bootstrap file, we need to port this change to another file. Usually this change needs to happen in the same PR.

Some changes might be deferred to a follow-up PR. For example if the deleted file was a test case used in the traceability matrix, we may need to find a new test case and finding it can be deferred.

Commit and push

After having fixed the conflicts, commit your changes, push them to the branch and ask for a code review from another member of the team.