Bazel Apple toolchain for non-Apple platforms

This repository contains toolchain configuration rules for Bazel that can be used to build apps and frameworks for Apple platforms from non-Apple platforms. Current supported host is x86_64 Linux only.

Setup

1. Install required packages (Ubuntu 20.04)

   sudo apt install \
       binutils \
       build-essential \
       ca-certificates \
       cmake \
       curl \
       doxygen \
       git \
       gnupg2 \
       gobjc \
       libc6-dev \
       libcurl4 \
       libedit2 \
       libgcc-9-dev \
       libpng-dev \
       libpython2.7 \
       libsqlite3-0 \
       libstdc++-9-dev \
       libxml2 \
       libxml2-dev \ 
       libz3-dev \
       ninja-build \
       patchelf \
       pkg-config \
       python \
       python3 \
       tzdata \
       unzip \
       vim-tiny \
       zip \
       zlib1g-dev
   

2. Clone this repository and provision your OS with:

   git clone https://github.com/apple-cross-toolchain/rules_applecross.git
   cd rules_applecross
   sudo tools/install-mandatory-tools.sh
   

This installs tools required by Apple rules (e.g. xcrun) onto the system PATH, as they are not available on non-Apple platforms.

3. Add the following to your WORKSPACE file.

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "rules_applecross",
    sha256 = "3c6b017792789714323d75f29569239855cfb223ce28768df39a910fe7842863",
    strip_prefix = "rules_applecross-0.0.2",
    url = "https://github.com/apple-cross-toolchain/rules_applecross/archive/refs/tags/0.0.2.tar.gz",
)

http_archive(
    name = "build_bazel_rules_apple",
    patch_args = ["-p1"],
    patches = ["@rules_applecross//third_party:rules_apple.patch"],
    sha256 = "5fed4c90b82006176b28d44d7642f520aa2fb9a32d30e24b22071fabcd24cbeb",
    strip_prefix = "rules_apple-0a67f1bd6c4cb9bd1bee5c51ac8d6632da537310",
    url = "https://github.com/bazelbuild/rules_apple/archive/0a67f1bd6c4cb9bd1bee5c51ac8d6632da537310.tar.gz",
)

load("@build_bazel_rules_apple//apple:repositories.bzl", "apple_rules_dependencies")

apple_rules_dependencies()

load(
    "@rules_applecross//toolchain:apple_cross_toolchain.bzl",
    "apple_cross_toolchain",
)

apple_cross_toolchain(
    name = "apple_cross_toolchain",
    clang_sha256 = "8f50330cfa4c609841e73286a3a056cff95cf55ec04b3f1280d0cd0052e96c2a",
    clang_strip_prefix = "clang+llvm-12.0.0-x86_64-linux-gnu-ubuntu-20.04",
    clang_urls = ["https://github.com/apple-cross-toolchain/ci/releases/download/0.0.6/clang+llvm-12.0.0-x86_64-linux-gnu-ubuntu-20.04-stripped.tar.xz"],
    swift_sha256 = "869edb04a932c9831922541cb354102244ca33be0aa6325d28b0f14ac0a32a4d",
    swift_strip_prefix = "swift-5.3.3-RELEASE-ubuntu20.04",
    swift_urls = ["https://github.com/apple-cross-toolchain/ci/releases/download/0.0.6/swift-5.3.3-RELEASE-ubuntu20.04-stripped.tar.xz"],
    xcode_sha256 = "44221c0f4acd48d7a33ee7e51143433dee94c649cfee44cfff3c7915ac54fdd2",
    xcode_urls = ["https://github.com/apple-cross-toolchain/apple-sdks/releases/download/0.0.4/apple-sdks-xcode-12.4.tar.xz"],
)

load("@apple_cross_toolchain//:repositories.bzl", "apple_cross_toolchain_dependencies")

apple_cross_toolchain_dependencies()

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()

4. Add the following to your .bazelrc file:

   build --apple_crosstool_top=@apple_cross_toolchain//:toolchain
   build --xcode_version_config=@rules_applecross//xcode_config:host_xcodes # or your own `xcode_config` target
   

5. From your workspace, run these commands:

   bazel fetch @rules_applecross//tests/data:dummy_lib
   DEVELOPER_DIR="$(bazel info output_base)/external/apple_cross_toolchain/Xcode.app/Contents/Developer"
   sudo xcode-select -s "$DEVELOPER_DIR"
   

These commands triggers the auto-configuration of the toolchain and selects the active developer directory. There is currently no other way to avoid this kind of workaround, because Apple rules don't include tools in their action inputs, but rely on xcrun to invoke tools.

Note:

• You can use a different rules_apple version, but it will need a patch like third_party/rules_apple.patch because the ported PlistBuddy tool can't handle multiple commands now.
• apple_cross_toolchain_dependencies() needs to be called after apple_rules_dependencies() and before swift_rules_dependencies().
• You can use the official Clang and Swift releases in clang_urls/swift_urls. The example here uses stripped-down archives (that only contain what we need) to speed up the decompression during the toolchain configuration.

Remote Build Execution Setup (for BuildBuddy)

1. Define a platform target; for example, in platforms/BUILD:

platform(
    name = "docker_image_platform",
    constraint_values = [
        "@bazel_tools//platforms:x86_64",
        "@bazel_tools//platforms:linux",
        "@bazel_tools//tools/cpp:clang",
    ],
    exec_properties = {
        "OSFamily": "Linux",
        "container-image": "docker://ghcr.io/apple-cross-toolchain/xcode:12.4",
    },
)

2. Download BuildBuddy client certificate and key and put them at the top level directory of your workspace as buildbuddy-cert.pem and buildbuddy-key.pem (make sure they aren't tracked by your version control system).

3. Add the following to your .bazelrc file:

build:remote --bes_backend=grpcs://cloud.buildbuddy.io
build:remote --bes_results_url=https://app.buildbuddy.io/invocation/
build:remote --host_platform=//platforms:docker_image_platform
build:remote --jobs=100
build:remote --remote_download_toplevel
build:remote --remote_executor=grpcs://cloud.buildbuddy.io
build:remote --remote_timeout=3600
build:remote --strategy=SwiftCompile=remote,sandboxed,worker,local
build:remote --tls_client_certificate=buildbuddy-cert.pem
build:remote --tls_client_key=buildbuddy-key.pem

Now you can build your target with --config=remote.

Examples

bazel build //examples/ios/HelloWorldSwiftUI:HelloWorld
bazel build --config=remote //examples/ios/HelloWorldSwiftUI:HelloWorld

See the examples repository for more real-world examples.