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Unified: Bazel downloaded toolchain on macOS - #22339
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Pull request overview
Switches macOS Swift builds to a pinned, downloaded rules_swift toolchain while continuing to use the locally installed macOS SDK.
Changes:
- Adds a patched
rules_swiftregistry version with macOS toolchain support. - Registers the downloaded macOS toolchain and removes the Xcode transition.
- Updates build definitions and documentation.
Show a summary per file
| File | Description |
|---|---|
MODULE.bazel | Selects and registers the patched toolchain. |
unified/swift-syntax-rs/BUILD.bazel | Uses swift_library directly. |
unified/swift-syntax-rs/README.md | Documents downloaded macOS tooling. |
unified/swift-syntax-rs/xcode_transition.bzl | Removes the obsolete Xcode transition. |
misc/bazel/registry/modules/rules_swift/metadata.json | Registers the custom version. |
misc/bazel/registry/modules/rules_swift/4.0.0-rc5-codeql.1/MODULE.bazel | Defines custom module metadata and dependencies. |
misc/bazel/registry/modules/rules_swift/4.0.0-rc5-codeql.1/source.json | Configures the upstream archive and patch. |
misc/bazel/registry/modules/rules_swift/4.0.0-rc5-codeql.1/patches/register_downloaded_macos_toolchain.patch | Adds downloaded macOS toolchain configuration. |
Review details
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- Files reviewed: 8/8 changed files
- Comments generated: 1
- Review effort level: Balanced
| strip_prefix = filename.removesuffix(".tar.gz"), | ||
| ) | ||
| + macos_sdkroot = _run(repository_ctx, ["xcrun", "--sdk", "macosx", "--show-sdk-path"]) if repository_ctx.attr.platform == "xcode" else "" |
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Fair. Addressed in fe0e622. Note that Copilot still highlights the following problems with the fix:
- watch(macos_sdkroot) does not observe changes inside or symlink retargeting, so it won’t reliably detect xcode-select changes.
- local=True only refreshes on Bazel server restart and re-extracts the entire Swift package, which is expensive.
Recommended design: separate lightweight SDK discovery into its own local/configure repository while keeping the downloaded Swift toolchain cacheable. Also document that persistent xcode-select changes require bazel shutdown or configuration refresh.
This is fair, but follow-up work is to get rid completely of the host command line tools dependency, so I don't want to spend too much time on making this perfect.
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For prosperity I want to note that this does already more than we do internally for C++ on macOS.
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Note that this still depends on the Xcode command line tools being present.