Tooling

The build system, scripts, and helper utilities you'll touch as a contributor.

build-script

utils/build-script (Python) is the canonical entry point for building everything. It calls utils/build-script-impl (a CMake/Ninja driver) and utils/build-toolchain (a tarball builder).

Common invocations:

# Default debug build
./swift/utils/build-script

# Release with assertions, plus tests, plus benchmarks
./swift/utils/build-script -R --test --benchmark

# Build only the host stdlib (skip cross targets)
./swift/utils/build-script --skip-build-osx --skip-build-ios

# Build a toolchain tarball
./swift/utils/build-toolchain com.example

Presets

Common configurations live in utils/build-presets.ini:

• buildbot_incremental -- the CI baseline.
• mixin_buildbot_install_components_with_clang -- adds Clang to the toolchain.
• mixin_buildbot_tools_RA_stdlib_DA -- release-with-assertions tools, debug stdlib.

Invoke with --preset=<name>.

update-checkout

utils/update-checkout keeps the side-by-side dependent repos at compatible revisions. The list is in utils/update-checkout/update-checkout-config.json. Useful subcommands:

./utils/update-checkout --clone           # initial clone of all repos
./utils/update-checkout --scheme=main     # update to latest tested
./utils/update-checkout --tag=swift-6.3-RELEASE  # check out a specific tag

gyb

utils/gyb.py ("Generate Your Boilerplate") is a Python templating tool used heavily in the standard library. Files end in .gyb. The build runs gyb on every .gyb to produce the corresponding source. Try:

./utils/gyb stdlib/public/core/Tuple.swift.gyb -o /tmp/Tuple.swift

GYB syntax: % python_statement, ${python_expression}, %end to close blocks.

Other helpful scripts

Script	What it does
utils/run-test	Wraps lit to run subsets of test/.
utils/build-toolchain	Produces a redistributable toolchain tarball.
utils/git-clang-format-all.zsh	Run clang-format over the working tree.
utils/python_lint.py	Run pylint over the Python code.
utils/find-overlay-dependencies.sh	Visualize stdlib overlay dependencies.
utils/swift-api-dump.py	Dump a Clang module as Swift API.
utils/api_checker/	Compare two SDKs for API breakage (used by ABI check CI).
utils/generate-xcode	Produce an Xcode project for IDE use.
utils/bug_reducer/	Reducer for compiler crash repros.
utils/swift-mode.el, utils/sil-mode.el	Emacs modes.

CMake structure

Top-level CMakeLists.txt drives the build. Major subprojects:

• lib/CMakeLists.txt -- compiler libraries.
• tools/CMakeLists.txt -- driver, demangle, sourcekit, etc.
• stdlib/CMakeLists.txt -- standard library and overlays (multi-target cross-compile).
• Runtimes/CMakeLists.txt -- the newer, decoupled stdlib build (see Runtimes).
• unittests/CMakeLists.txt -- C++ unit tests.

CMake helpers live in cmake/modules/. The two most important are:

• cmake/modules/AddSwift.cmake -- add_swift_target_library, add_swift_host_library, etc.
• cmake/modules/SwiftSource.cmake -- handles .swift sources for the standard library.

Editor integrations

• VS Code: install the Swift extension; the build emits compile_commands.json for clangd.
• Xcode: utils/generate-xcode produces a .xcodeproj for the C++ sources.
• Emacs: utils/swift-mode.el, utils/sil-mode.el, utils/inferior-swift-mode.el.
• Vim: most contributors install swift-syntax for Vim externally.

CI

.github/workflows/ holds GitHub Actions configurations (mostly auxiliary). The primary CI is the Apple-internal Jenkins farm fronted by the @swift_ci bot. PR comments trigger jobs.