Wire up apple_support xcode_config so @system_sdk selects resolve on macOS

Author: Copilot

.bazelrc

@@ -44,6 +44,20 @@ common --flag_alias=host_swiftcopt=@rules_swift//swift:exec_copt
 build:macos --swiftcopt=-target --swiftcopt=arm64-apple-macosx10.15
 build:macos --host_swiftcopt=-target --host_swiftcopt=arm64-apple-macosx10.15
 
+# Point Bazel at `apple_support`'s xcode_config on macOS.
+#
+# `xcode_swift_toolchain` pulls in `@system_sdk//:{all_modules,implicit_modules}`,
+# whose `select({":xcode_<version>": ...})` keys use the exact version string
+# from `@bazel_tools//tools/osx:xcode_locator.m` (e.g. `xcode_26_6_0_17F113`).
+# Bazel's built-in `@bazel_tools//tools/osx:host_xcodes` produces a shorter
+# version without the build number, so none of the config_settings match and
+# the select fails.
+#
+# `apple_support`'s `@local_config_xcode//:host_xcodes` uses the SAME
+# `xcode_locator.m`, so its version string agrees with the select keys.
+# Wired up in `MODULE.bazel` via the `xcode_configure` extension.
+build:macos --xcode_version_config=@local_config_xcode//:host_xcodes
+
 # Disable Android SDK auto-detection (we don't use it, and rules_android has Bazel 9 compatibility issues)
 build --repo_env=ANDROID_HOME=
 

MODULE.bazel

@@ -33,6 +33,12 @@ bazel_dep(name = "googletest", version = "1.17.0.bcr.2")
 bazel_dep(name = "rules_rust", version = "0.69.0")
 bazel_dep(name = "rules_swift", version = "4.0.0-rc4")
 bazel_dep(name = "swift-syntax", version = "602.0.0.bcr.2")
+# `apple_support` is a transitive dep of `rules_swift`, but we depend on it
+# directly so we can `use_repo` `local_config_xcode` (see below). This lets
+# `xcode_swift_toolchain`'s `system_sdk` selects — which are keyed on the
+# exact Xcode version string from `xcode_locator.m` (e.g.
+# `xcode_26_6_0_17F113`) — resolve on macOS.
+bazel_dep(name = "apple_support", version = "2.6.1")
 
 bazel_dep(name = "zstd", version = "1.5.7.bcr.1")
 
@@ -270,6 +276,23 @@ register_toolchains(
     "@swift_toolchain//:swift_toolchain_exec_ubuntu24.04",
 )
 
+# On macOS, `xcode_swift_toolchain` (auto-registered by rules_swift at
+# `@rules_swift//swift/toolchains:xcode-toolchain-*`) pulls in
+# `@system_sdk//:{all_modules,implicit_modules}`, whose targets are
+# `alias(..., select({":xcode_<version>": ...}))` keyed on the exact
+# Xcode version string produced by `@bazel_tools//tools/osx:xcode_locator.m`
+# (e.g. `xcode_26_6_0_17F113`). Bazel's built-in `@bazel_tools//tools/osx:host_xcodes`
+# reports a shorter version without the build number, so no `config_setting`
+# matches and the select fails with
+# "configurable attribute doesn't match this configuration".
+#
+# `apple_support`'s `@local_config_xcode//:host_xcodes` uses the SAME
+# `xcode_locator.m` as rules_swift's `system_sdk` extension, so its version
+# strings agree with the config_setting keys. Wire it up here and select it
+# on macOS via `--xcode_version_config` in `.bazelrc`.
+xcode_configure = use_extension("@apple_support//xcode:xcode_configure.bzl", "xcode_configure_extension")
+use_repo(xcode_configure, "local_config_xcode")
+
 node = use_extension("@rules_nodejs//nodejs:extensions.bzl", "node")
 node.toolchain(
     name = "nodejs",