master is the place for active development on Swift. If you‘re just working on Swift, that’s where you'll spend most of your time.
LLVM Project repo automatically merge changes from the latest release branch (see below) into
swift/master. This generally means
swift/master is just an alias for the latest release branch. If you want to do Swift-related development on LLVM projects, see “The Upstream Branches” below.
To switch from one set of branches to another, you can use
utils/update-checkout in the Swift repository with the
--scheme option. You can use any of the branch names as the argument to
--scheme: in this case, either
At some point before a release, a release branch will be created in every repository with a name like
release/5.3. (The actual number is chosen by Apple.) After the branch has been created, commits must make it to this branch to make it into the release. In some cases, the release manager for the branch will decide to merge in all additional changes from
master; otherwise, cherry-picking changes and making a new pull request is the way to go. If there are any “patch” releases (e.g. Swift 5.3.1), they will also come from this branch.
Note that these branches come not from the “development” branches (above), but the “upstream” branches (below). This is because they need to contain the latest changes not just from Swift, but from the LLVM project as well. For some releases, the release branch for the LLVM project will be timed to coincide with the corresponding llvm.org release branch.
swift/master-next is a branch for LLVM that includes all changes necessary to support Swift. Changes from llvm.org‘s master branch are automatically merged in. Why isn’t this just
swift/master? Well, because LLVM changes very rapidly, and that wouldn't be very stable. However, we do want to make sure the Swift stuff keeps working.
If you are making changes to LLVM to support Swift, you'll probably need to work on them in
swift/master to test them against Swift itself, but they should be committed to
swift/master-next, and cherry-picked to the current release branch (
swift/release/x.y) if needed. Remember, the release branches are automerged into
swift/master on a regular basis.
(If you‘re making changes to LLVM Project that *aren’t* about Swift, they should generally be made on llvm.org instead, then cherry-picked to the active release branch or
master-next is an effort to keep Swift building with the latest LLVM changes. Ideally when LLVM changes, no Swift updates are needed, but that isn‘t always the case. In these situations, any adjustments can go into Swift’s
master-next branch. Changes from Swift's
master are automatically merged into
master-next as well.
swift/utils/update-checkout --scheme [branch]
You can use any of the branch names as the argument to
--scheme, such as
update-checkout --help for more options.
Swift: new commits go to
LLVM Project: the destination branch depends on the kind of change that must be made:
LLVM Project changes that don't depend on Swift
New commits go to
master in the upstream llvm-project.
Then cherry-pick these commits to an appropriate,
apple/stable/* branch in Apple's fork of llvm-project. Please see Apple's branching scheme document to determine which
apple/stable/* branch you should cherry-pick to.
Note that no new changes should be submitted directly to
apple/master. We are actively working on eliminating the differences from upstream LLVM.
Changes that depend on Swift (this only applies to LLDB)
New commits go to
swift/master (not an
apple/stable/* branch, as these shouldn't contain changes that depend on Swift).
Then cherry-pick these commits to
If necessary, cherry-pick to the release branch (
swift/release/x.y), following the appropriate release process. (Usually this means filling out a standard template, finding someone to review your code if that hasn‘t already happened, and getting approval from that repo’s release manager.)
In the long term we want to eliminate the differences from upstream LLVM for these changes as well, but for now there is no concrete plan. So, submitting to
swift/master-next continues to be allowed.
Some branches are automerged into other branches, to keep them in sync. This is just a process that runs
git merge at a regular interval. These are run by Apple and are either on a “frequent” (sub-hourly) or nightly schedule.
master is automerged into
swift/release/x.y (the latest release branch) is automerged into
master is automerged into
swift/release/x.y, if they are in sync