This post describes the goals, release process, and estimated schedule for Swift 3.1.
Swift 3.1 is intended to be source compatible with Swift 3.0.
It will contain a few additive enhancements to the core language as well as improvements to the Swift Package Manager, Swift on Linux, and general quality improvements to the compiler and Standard Library.
Swift 3.1 is intended to be released in the spring of 2017.
It is a strong goal that the vast majority of sources that built with the Swift 3.0 compiler continue to build with the Swift 3.1 compiler. The exception will be bug fixes to the compiler that cause it to reject code that should never have been accepted in the first place. These cases should be relatively rare in practice.
Please file bug reports if you encounter cases where the Swift 3.1 compiler unexpectedly rejects code that previously compiled with the Swift 3.0 compiler.
Snapshots of Swift 3.1
Previous releases of Swift have had “Developer Previews”, e.g. “Preview 1”, “Preview 2”, etc., that represent stabilized snapshots of a Swift release as it converges. Developer previews have often been irregularly spaced apart, and have sometimes not provided enough granularity for the Swift community to try out new features or verify bug fixes in a release as it converges.
For Swift 3.1 there will instead be daily downloadable snapshots of the release branch. Snapshots will be produced as part of continuous integration testing. The cadence of downloadable snapshots will thus be more frequent and granular. Snapshots will be posted daily, assuming tests are passing.
Once Swift 3.1 is released, official final builds will also be posted in addition to the snapshots.
Getting Changes into Swift 3.1
Swift 3.1 is intended to be limited in scope, with the desire to move focus early in 2017 to the development of Swift 4. To meet this goal, Swift 3.1 will include changes in mainline development (i.e. the
master branch) only until January 16. After that date there will be a “bake” period in which only select, critical fixes will go into the
swift-3.1-branch and move
master on to Swift 4 development.
master: With the exception of the swift-llvm and swift-clang repositories (see Impacted Repositories), development of Swift 3.1 happens in
master. All changes going in
masterwill be part of the final Swift 3.1 release until January 16. At that point
mastertracks development for Swift 4.
swift-3.1-branch: Release management for Swift 3.1 happens on the
swift-3.1-branch. All Swift 3.1 snapshots are built from this branch, and Swift 3.1 will GM from this branch as well.
master will be regularly merged into
swift-3.1-branch approximately every two weeks until January 16. The two week window provides a buffer between hot development on
master and a curated release branch. Changes may be cherry-picked (via pull requests) into
swift-3.1-branch between merges of
A notable exception to this plan is the swift-package-manager, which will merge from
master into the
Philosophy on Taking Changes into Swift 3.1
Source compatibility with Swift 3.0 is a top priority.
As Swift 3.1 converges only changes that align with the core goals of the release will be considered.
All language and API changes for Swift 3.1 will go through the Swift Evolution process.
Major work for Swift 3.1 should orient around the January 16 date, but changes can still land in 3.1 afterwards per the judgement of the release manager. As the release converges, the criteria for pulling changes into 3.1 will become increasingly restrictive.
The following repositories will have a
swift-3.1-branch branch to track sources as part of Swift 3.1 release:
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 3.1 release as the release converges:
Ted Kremenek is the overall release manager for Swift 3.1.
Pull Requests for Release Branch
All pull requests nominating changes for inclusion in the release branch
should include the following information:
Explanation: A description of the issue being fixed or
enhancement being made. This can be brief, but it should be
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
Testing: What specific testing has been done or needs to be done
to further validate any impact of this change?
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
All change going into the
swift-3.1-branch (outside changes being merged in automatically from
master) must go through pull requests that are accepted by the corresponding release manager.