afa08f01a1
When constructing a generic signature, any redundant explicit requirements
are dropped from the final signature.
We would assume this operation is idempotent, that is, building a new
GenericSignatureBuilder from the resulting minimized signature produces
an equivalent GenericSignatureBuilder to the original one.
Unfortunately, this is not true in the case of conformance requirements.
Namely, if a conformance requirement is made redundant by a superclass
or concrete same-type requirement, then dropping the conformance
requirement changes the canonical type computation.
For example, consider the following:
public protocol P {
associatedtype Element
}
public class C<O: P>: P {
public typealias Element = O.Element
}
public func toe<T, O, E>(_: T, _: O, _: E, _: T.Element)
where T : P, O : P, O.Element == T.Element, T : C<E> {}
In the generic signature of toe(), the superclass requirement 'T : C<E>'
implies the conformance requirement 'T : P' because C conforms to P.
However, the presence of the conformance requirement makes it so that
T.Element is the canonical representative, so previously this signature
was minimized down to:
<T : C<E>, O : P, T.Element == O.Element>
If we build the signature again from the above requirements, then we
see that T.Element is no longer the canonical representative; instead,
T.Element canonicalizes as E.Element.
For this reason, we must rebuild the signature to get the correct
canonical type computation.
I realized that this is not an artifact of incorrect design in the
current GSB; my new rewrite system formalism would produce the same
result. Rather, it is a subtle consequence of the specification of our
minimization algorithm, and therefore it must be formalized in this
manner.
We used to sort-of do this with the HadAnyRedundantRequirements hack,
but it was both overly broad (we only need to rebuild if a conformance
requirement was implied by a superclass or concrete same-type
requirement) and not sufficient (when rebuilding, we need to strip any
bound associated types from our requirements to ensure the canonical
type anchors are re-computed).
Fixes rdar://problem/65263302, rdar://problem/75010156,
rdar://problem/75171977.
Swift Programming Language
| Architecture | main | Package | |
|---|---|---|---|
| macOS | x86_64 | ||
| Ubuntu 16.04 | x86_64 | ||
| Ubuntu 18.04 | x86_64 | ||
| Ubuntu 20.04 | x86_64 | ||
| CentOS 8 | x86_64 | ||
| Amazon Linux 2 | x86_64 |  |
|
Swift Community-Hosted CI Platforms
| OS | Architecture | Build |
|---|---|---|
| Ubuntu 16.04 | PPC64LE | |
| Ubuntu 18.04 | AArch64 | |
| Ubuntu 20.04 | AArch64 | |
| CentOS 8 | AArch64 | |
| Amazon Linux 2 | AArch64 |  |
| Android | ARMv7 | |
| Android | AArch64 | |
| Windows 2019 (VS 2017) | x86_64 | |
| Windows 2019 (VS 2019) | x86_64 |
Swift TensorFlow Community-Hosted CI Platforms
| OS | Architecture | Build |
|---|---|---|
| Ubuntu 18.04 | x86_64 | |
| macOS 10.13 | x86_64 |
Welcome to Swift
Swift is a high-performance system programming language. It has a clean and modern syntax, offers seamless access to existing C and Objective-C code and frameworks, and is memory safe by default.
Although inspired by Objective-C and many other languages, Swift is not itself a C-derived language. As a complete and independent language, Swift packages core features like flow control, data structures, and functions, with high-level constructs like objects, protocols, closures, and generics. Swift embraces modules, eliminating the need for headers and the code duplication they entail.
To learn more about the programming language, visit swift.org.
Contributing to Swift
Contributions to Swift are welcomed and encouraged! Please see the Contributing to Swift guide.
To be a truly great community, Swift.org needs to welcome developers from all walks of life, with different backgrounds, and with a wide range of experience. A diverse and friendly community will have more great ideas, more unique perspectives, and produce more great code. We will work diligently to make the Swift community welcoming to everyone.
To give clarity of what is expected of our members, Swift has adopted the code of conduct defined by the Contributor Covenant. This document is used across many open source communities, and we think it articulates our values well. For more, see the Code of Conduct.
Getting Started
If you are interested in:
- Contributing fixes and features to the compiler: See our How to Submit Your First Pull Request guide.
- Building the compiler as a one-off: See our Getting Started guide.
- Building a toolchain as a one-off: Follow the Getting Started guide up until the "Building the project" section. After that, follow the instructions in the Swift Toolchains section below.
We also have an FAQ that answers common questions.
Swift Toolchains
Building
Swift toolchains are created using the script build-toolchain. This script is used by swift.org's CI to produce snapshots and can allow for one to locally reproduce such builds for development or distribution purposes. A typical invocation looks like the following:
$ ./swift/utils/build-toolchain $BUNDLE_PREFIX
where $BUNDLE_PREFIX is a string that will be prepended to the build
date to give the bundle identifier of the toolchain's Info.plist. For
instance, if $BUNDLE_PREFIX was com.example, the toolchain
produced will have the bundle identifier com.example.YYYYMMDD. It
will be created in the directory you run the script with a filename
of the form: swift-LOCAL-YYYY-MM-DD-a-osx.tar.gz.
Beyond building the toolchain, build-toolchain also supports the
following (non-exhaustive) set of useful options::
--dry-run: Perform a dry run build. This is off by default.--test: Test the toolchain after it has been compiled. This is off by default.--distcc: Use distcc to speed up the build by distributing the c++ part of the swift build. This is off by default.--sccache: Use sccache to speed up subsequent builds of the compiler by caching more c++ build artifacts. This is off by default.
More options may be added over time. Please pass --help to
build-toolchain to see the full set of options.
Installing into Xcode
On macOS if one wants to install such a toolchain into Xcode:
- Untar and copy the toolchain to one of
/Library/Developer/Toolchains/or~/Library/Developer/Toolchains/. E.x.:
$ sudo tar -xzf swift-LOCAL-YYYY-MM-DD-a-osx.tar.gz -C /
$ tar -xzf swift-LOCAL-YYYY-MM-DD-a-osx.tar.gz -C ~/
The script also generates an archive containing debug symbols which can be installed over the main archive allowing symbolication of any compiler crashes.
$ sudo tar -xzf swift-LOCAL-YYYY-MM-DD-a-osx-symbols.tar.gz -C /
$ tar -xzf swift-LOCAL-YYYY-MM-DD-a-osx-symbols.tar.gz -C ~/
- Specify the local toolchain for Xcode's use via
Xcode->Toolchains.
Build Failures
Try the suggestions in Troubleshooting build issues.
Make sure you are using the correct release of Xcode.
If you have changed Xcode versions but still encounter errors that appear to
be related to the Xcode version, try passing --clean to build-script.
When a new version of Xcode is released, you can update your build without
recompiling the entire project by passing --reconfigure to build-script.
Learning More
Be sure to look at the documentation index for a bird's eye view of the available documentation. In particular, the documents titled Debugging the Swift Compiler and Continuous Integration for Swift are very helpful to understand before submitting your first PR.