Bazel rules to build Swift on Apple and Linux platforms
Swift Rules for Bazel
This repository contains rules for Bazel that can be used to build Swift libraries, tests, and executables for macOS and Linux.
To build applications for all of Apple's platforms (macOS, iOS, tvOS, and watchOS), they can be combined with the Apple Rules.
If you run into any problems with these rules, please file an issue!
Reference Documentation
Click here
for the reference documentation for the rules and other definitions in this
repository.
Compatibility
Please refer to the
release notes for a given
release to see which version of Bazel it is compatible with.
Quick Setup
1. Install Swift
Before getting started, make sure that you have a Swift toolchain installed.
Apple users: Install Xcode.
If this is your first time installing it, make sure to open it once after
installing so that the command line tools are correctly configured.
Linux users: Follow the instructions on the
Swift download page to download and install the
appropriate Swift toolchain for your platform. Take care to ensure that you have
all of Swift's dependencies installed (such as ICU, Clang, and so forth), and
also ensure that the Swift compiler is available on your system path.
2. Configure your workspace
Add the following to your WORKSPACE file to add the external repositories,
replacing the urls and sha256 attributes with the values from the release
you wish to depend on:
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
name = "build_bazel_rules_swift",
sha256 = "f872c0388808c3f8de67e0c6d39b0beac4a65d7e07eff3ced123d0b102046fb6",
url = "https://github.com/bazelbuild/rules_swift/releases/download/0.23.0/rules_swift.0.23.0.tar.gz",
)
load(
"@build_bazel_rules_swift//swift:repositories.bzl",
"swift_rules_dependencies",
)
swift_rules_dependencies()
load(
"@build_bazel_rules_swift//swift:extras.bzl",
"swift_rules_extra_dependencies",
)
swift_rules_extra_dependencies()
The swift_rules_dependencies macro creates a toolchain appropriate for your
platform (either by locating an installation of Xcode on macOS, or looking for
swiftc on the system path on Linux).
3. Additional configuration (Linux only)
The swift_binary and swift_test rules expect to use clang as the driver
for linking, and they query the Bazel C++ API and CROSSTOOL to determine which
arguments should be passed to the linker. By default, the C++ toolchain used by
Bazel is gcc, so Swift users on Linux need to override this by setting the
environment variable CC=clang when invoking Bazel.
This step is not necessary for macOS users because the Xcode toolchain always
uses clang.
Building with Custom Toolchains
macOS hosts: You can build with a custom toolchain installed in
/Library/Developer/Toolchains instead of Xcode's default. To do so, pass the
following flag to Bazel:
--define=SWIFT_CUSTOM_TOOLCHAIN=toolchain.id
where toolchain.id is the value of the CFBundleIdentifier key in the
toolchain's Info.plist file.
To list the available toolchains and their bundle identifiers, you can run:
bazel run @build_bazel_rules_swift//tools/dump_toolchains
Linux hosts: At this time, Bazel uses whichever swift executable is
encountered first on your PATH.
Supporting remote builds
To make remote builds work correctly with debugging and general
reproducibility see this doc
Future Work
- Support for building and linking to shared libraries (
.dylib/.so) written
in Swift. - Interoperability with Swift Package Manager.
- Migration to the Bazel platforms/toolchains APIs.
- Support for multiple toolchains, and support for non-Xcode toolchains on
macOS. - Automatically download a Linux toolchain from swift.org
if one is not already installed.