Swift 5.1 Release Process February 18, 2019 Ted Kremenek is a member of the Swift Core Team and manages the Languages and Runtimes group at Apple.

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:

The swift-5.1-branch has already been initially cut from master .

Periodically, the master development branch will be merged into swift-5.1-branch until the final branch date.

March 18, 2019 (final branching): The swift-5.1-branch will have changes merged from master one last time. After the final branch date there will be a “bake” period in which only select, critical fixes will go into the release (via pull requests).

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

All language and API changes for Swift 5.1 will go through the Swift Evolution process. Evolution proposals should aim to be completed by the branch date in order to increase their chances of impacting the Swift 5.1 release. Exceptions will be considered on a case-by-case basis, particularly if they tie in with the core goal of the release.

Other changes (e.g., bug fixes, diagnostic improvements, SourceKit interface improvements) will be accepted based on their risk and impact.

Low-risk test tweaks will also be accepted late into the release branch if it aids in the qualification of the release.

As the release converges, the criteria for accepted changes will become increasingly restrictive.

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:

Explanation : A description of the issue being fixed or enhancement being made. This can be brief, but it should be clear.

Scope : An assessment of the impact/importance of the change. For example, is the change a source-breaking language change, etc.

SR Issue : The SR if the change fixes/implements an issue/enhancement on bugs.swift.org.

Risk : What is the (specific) risk to the release for taking this change?

Testing : What specific testing has been done or needs to be done to further validate any impact of this change?

Reviewer: One or more code owners for the impacted components should review the change. Technical review can be delegated by a code owner or otherwise requested as deemed appropriate or useful.