Add Apple CC toolchain setup (#113)

This migrates the Apple CC toolchain from bazel into this repo. This
allows this to evolve and be updated without a full bazel udpate.
Bazel's built in unix toolchain can still be used to build macOS C++
targets, but this repo handles a wider variety of Apple specific flags
and requires you have Xcode installed.

.bazelci/presubmit.yml

@@ -5,9 +5,19 @@ x_defaults:
   common: &common
     platform: macos
     build_targets:
-    - "//..."
+      - "//..."
     test_targets:
-    - "//..."
+      - "//..."
+
+  toolchain_flags: &toolchain_flags
+    build_flags:
+      - "--apple_crosstool_top=@local_config_apple_cc//:toolchain"
+      - "--crosstool_top=@local_config_apple_cc//:toolchain"
+      - "--host_crosstool_top=@local_config_apple_cc//:toolchain"
+    test_flags:
+      - "--apple_crosstool_top=@local_config_apple_cc//:toolchain"
+      - "--crosstool_top=@local_config_apple_cc//:toolchain"
+      - "--host_crosstool_top=@local_config_apple_cc//:toolchain"
 
 tasks:
   macos_latest:
@@ -24,9 +34,21 @@ tasks:
     name: "Latest Bazel with Head Deps"
     bazel: latest
     shell_commands:
-    # Update the WORKSPACE to use head versions of some deps to ensure nothing
-    # has landed on them breaking this project.
-    - .bazelci/update_workspace_to_deps_heads.sh
+      # Update the WORKSPACE to use head versions of some deps to ensure nothing
+      # has landed on them breaking this project.
+      - .bazelci/update_workspace_to_deps_heads.sh
+    <<: *common
+
+  macos_latest_vendored_toolchain:
+    name: "Latest Bazel vendored toolchain"
+    bazel: latest
+    <<: *common
+    <<: *toolchain_flags
+
+  macos_last_green_vendored_toolchain:
+    name: "Last Green Bazel vendored toolchain"
+    bazel: last_green
     <<: *common
+    <<: *toolchain_flags
 
 buildifier: latest

BUILD

@@ -24,6 +24,8 @@ filegroup(
     testonly = 1,
     srcs = [
         "WORKSPACE",
+        "//constraints:for_bazel_tests",
+        "//crosstool:for_bazel_tests",
         "//lib:for_bazel_tests",
         "//rules:for_bazel_tests",
         "//tools:for_bazel_tests",

MODULE.bazel

@@ -12,3 +12,8 @@ module(
 bazel_dep(name = "bazel_skylib", version = "1.3.0")
 bazel_dep(name = "platforms", version = "0.0.4")
 bazel_dep(name = "stardoc", version = "0.5.3", dev_dependency = True, repo_name = "io_bazel_stardoc")
+
+apple_cc_configure = use_extension("//crosstool:setup.bzl", "apple_cc_configure_extension")
+use_repo(apple_cc_configure, "local_config_apple_cc", "local_config_apple_cc_toolchains")
+
+register_toolchains("@local_config_apple_cc_toolchains//:all")

README.md

@@ -1,14 +1,59 @@
 # Apple Support for [Bazel](https://bazel.build)
 
-This repository contains helper methods that support building rules that
-target Apple platforms. See [the
-docs](https://github.com/bazelbuild/apple_support/tree/master/doc) for
-how you can use these helpers. Also see
-[rules_apple](https://github.com/bazelbuild/rules_apple) and
-[rules_swift](https://github.com/bazelbuild/rules_swift) for more Apple
-platform rules.
-
-## Quick setup
-
-Copy the `WORKSPACE` snippet from [the releases
-page](https://github.com/bazelbuild/apple_support/releases).
+This repository contains the [Apple CC toolchain](#toolchain-setup),
+Apple related [platforms](platforms/BUILD) and
+[constraints](constraints/BUILD) definitions, and small helper functions
+for rules authors targeting Apple platforms.
+
+If you want to build iOS, tvOS, watchOS, or macOS apps, use
+[`rules_apple`][rules_apple].
+
+If you want to build Swift use
+[`rules_swift`](https://github.com/bazelbuild/rules_swift).
+
+See [the documentation](doc) for the helper rules provided by this
+repository.
+
+## Installation
+
+Copy the `MODULE.bazel` or `WORKSPACE` snippets from [the releases
+page](https://github.com/bazelbuild/apple_support/releases) into your
+project.
+
+## Toolchain setup
+
+The Apple CC toolchain in by this repository provides toolchains for
+building for Apple platforms besides macOS. Since Bazel 7 this toolchain
+is required when targeting those platforms but the toolchain also
+supports Bazel 6.
+
+To use the Apple CC toolchain, pull this repository into your build and
+add this to your `.bazelrc`:
+
+```bzl
+build --enable_platform_specific_config
+build:macos --apple_crosstool_top=@local_config_apple_cc//:toolchain
+build:macos --crosstool_top=@local_config_apple_cc//:toolchain
+build:macos --host_crosstool_top=@local_config_apple_cc//:toolchain
+```
+
+This ensures that all rules provided by [`rules_apple`][rules_apple], as
+well as other rules like `cc_binary`, all use the toolchain provided by
+this repository when building on macOS.
+
+NOTE: This toolchain requires a full Xcode installation, not just the
+Xcode Command Line Tools. If you only need to build for macOS and don't
+want to require a full Xcode installation in your build, use the builtin
+Unix toolchain provided by Bazel.
+
+### Incompatible toolchain resolution
+
+Bazel is currently working on migrating C++ toolchain configuration to a
+new discovery method that no longer uses the `--*crosstool_top` flags.
+If you would like to test this upcoming feature, or need to use this in
+your build for other reasons, you can use this toolchain with
+`--incompatible_enable_cc_toolchain_resolution` as long as you provide a
+`platform_mappings` file. Please file any issues you find as you test
+this work in progress configuration.
+
+[rules_apple]: https://github.com/bazelbuild/rules_apple

constraints/BUILD

@@ -29,3 +29,11 @@ constraint_value(
     name = "catalyst",
     constraint_setting = ":target_environment",
 )
+
+# Consumed by bazel tests.
+filegroup(
+    name = "for_bazel_tests",
+    testonly = True,
+    srcs = glob(["**"]),
+    visibility = ["//:__pkg__"],
+)

crosstool/BUILD

@@ -0,0 +1,22 @@
+package(default_visibility = ["//visibility:public"])
+
+# Files which shouldn't be publicly visible and dependencies of all objc_* or ios_* rules should be excluded.
+exports_files(glob(
+    ["**"],
+))
+
+cc_binary(
+    name = "wrapped_clang",
+    testonly = True,
+    srcs = [
+        "wrapped_clang.cc",
+    ],
+)
+
+# Consumed by bazel tests.
+filegroup(
+    name = "for_bazel_tests",
+    testonly = True,
+    srcs = glob(["**"]),
+    visibility = ["//:__pkg__"],
+)

crosstool/BUILD.toolchains

@@ -0,0 +1,100 @@
+package(default_visibility = ["//visibility:public"])
+
+# Target constraints for each arch.
+# TODO(apple-rules): Rename osx constraint to macOS.
+OSX_TOOLS_CONSTRAINTS = {
+    "armeabi-v7a": ["@platforms//cpu:arm"],
+    "darwin_arm64": [
+        "@platforms//os:osx",
+        "@platforms//cpu:arm64",
+    ],
+    "darwin_arm64e": [
+        "@platforms//os:osx",
+        "@platforms//cpu:arm64",
+    ],
+    "darwin_x86_64": [
+        "@platforms//os:osx",
+        "@platforms//cpu:x86_64",
+    ],
+    "ios_arm64": [
+        "@platforms//os:ios",
+        "@platforms//cpu:arm64",
+        "@build_bazel_apple_support//constraints:device",
+    ],
+    "ios_arm64e": [
+        "@platforms//os:ios",
+        "@platforms//cpu:arm64",
+    ],
+    "ios_armv7": [
+        "@platforms//os:ios",
+        "@platforms//cpu:armv7",
+    ],
+    "ios_i386": [
+        "@platforms//os:ios",
+        "@platforms//cpu:i386",
+    ],
+    "ios_x86_64": [
+        "@platforms//os:ios",
+        "@platforms//cpu:x86_64",
+    ],
+    "ios_sim_arm64": [
+        "@platforms//os:ios",
+        "@platforms//cpu:arm64",
+        "@build_bazel_apple_support//constraints:simulator",
+    ],
+    "tvos_arm64": [
+        "@platforms//os:tvos",
+        "@platforms//cpu:arm64",
+        "@build_bazel_apple_support//constraints:device",
+    ],
+    "tvos_x86_64": [
+        "@platforms//os:tvos",
+        "@platforms//cpu:x86_64",
+    ],
+    "tvos_sim_arm64": [
+        "@platforms//os:tvos",
+        "@platforms//cpu:arm64",
+        "@build_bazel_apple_support//constraints:simulator",
+    ],
+    "watchos_arm64": [
+        "@platforms//os:watchos",
+        "@platforms//cpu:arm64",
+    ],
+    "watchos_arm64_32": [
+        "@platforms//os:watchos",
+        "@platforms//cpu:arm64_32",
+    ],
+    "watchos_armv7k": [
+        "@platforms//os:watchos",
+        "@platforms//cpu:armv7k",
+    ],
+    "watchos_i386": [
+        "@platforms//os:watchos",
+        "@platforms//cpu:i386",
+    ],
+    "watchos_x86_64": [
+        "@platforms//os:watchos",
+        "@platforms//cpu:x86_64",
+    ],
+}
+
+OSX_DEVELOPER_PLATFORM_CPUS = [
+    "arm64",
+    "x86_64",
+]
+
+[
+    toolchain(
+        name = "cc-toolchain-" + arch + "-" + cpu,
+        exec_compatible_with = [
+            # These only execute on macOS.
+            "@platforms//os:osx",
+            "@platforms//cpu:" + cpu,
+        ],
+        target_compatible_with = OSX_TOOLS_CONSTRAINTS[arch],
+        toolchain = "@local_config_apple_cc//:cc-compiler-" + arch,
+        toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+    )
+    for arch in OSX_TOOLS_CONSTRAINTS.keys()
+    for cpu in OSX_DEVELOPER_PLATFORM_CPUS
+]