Swift 5.1 Release Process

This post describes the goals, release process, and estimated schedule for Swift 5.1.

Motivation and Goals

The primary goal of Swift 5.1 is for the language to achieve module stability.

Binary Compatibility

On Apple platforms, since the ABI is now stabilized, Swift 5.1 is binary compatible with Swift 5.0, and is binary compatible with future releases of Swift.

On non-Apple platforms (such as Linux) the ABI is not yet fully stable in order to allow for more vetting. Such vetting will be particularly needed for the new platforms based on Linux.

Source Compatibility

As with Swift 5.0, we expect that majority of sources that built with the Swift 5.0 compiler will compile with the Swift 5.1 compiler. However, it is possible that a bug fix in Swift 5.1 may cause it to detect errors in code that were not detected before.

Snapshots of Swift 5.1

Downloadable snapshots of the Swift 5.1 release branch will be posted regularly as part of continuous integration testing.

Once Swift 5.1 is released, the official final builds will also be posted in addition to the snapshots.

Getting Changes into Swift 5.1

The development of Swift 5.0 required an unusual amount of focus and attention throughout the time it converged because every issue had to be evaluated for its permanent ABI impact. Consequently, Swift 5.1 has a significantly shorter development window than previous releases. This tighter time constraint is needed to ensure delivering a mature and stable 5.1 release, with stricter cutoff dates for disruptive changes.

The swift-5.1-branch contains the changes that will be released in Swift 5.1. The branch will be managed as follows:

Some notable exceptions to this plan are indicated in the table below. Each will merge from master into swift-5.1-branch daily. The final cutoff date for changes to each exception will extend beyond March 18 and will be announced later.

Project Cutoff date
indexstore-db To be announced
sourcekit-lsp To be announced
swift-corelibs-foundation To be announced
swift-corelibs-libdispatch To be announced
swift-corelibs-xctest To be announced
swift-llbuild April 10, 2019
swift-package-manager April 10, 2019
swift-stress-tester To be announed
swift March 18, 2019

Philosophy on Taking Changes into Swift 5.1

Impacted Repositories

The following repositories will have a swift-5.1-branch branch to track sources as part of Swift 5.1 release:

Release Managers

The overall management of the release will be overseen by the following individuals, who will announce when stricter control of change goes into effect for the Swift 5.1 release as the release converges:

Please feel free to post on the development forum or contact Ted Kremenek directly concerning any questions about the release management process.

Pull Requests for Release Branch

In order for a pull request to be considered for inclusion in the release branch after the final re-branch from master it must include the following information:

All change going into the swift-5.1-branch (outside changes being merged in automatically from master) must go through pull requests that are accepted by the corresponding release manager.