bazel/emscripten_cache.bzl

BUILD_FILE_CONTENT_TEMPLATE = """
package(default_visibility = ['//visibility:public'])
exports_files(['emscripten_config'])
"""

BUILD_FILE_USE_BUILTIN_CACHE = """
alias(
    name = "emscripten_cache",
    actual = "{}//:builtin_cache",
)
"""

BUILD_FILE_USE_SECONDARY_CACHE = """
filegroup(
    name = "emscripten_cache",
    srcs = glob(["cache/**"]),
    visibility = ["//visibility:public"],
)
"""

EMBUILDER_CONFIG_TEMPLATE = """
CACHE = '{cache}'
BINARYEN_ROOT = '{binaryen_root}'
LLVM_ROOT = '{llvm_root}'
"""

def get_root_and_script_ext(repository_ctx):
    if repository_ctx.os.name.startswith("linux"):
        if "amd64" in repository_ctx.os.arch or "x86_64" in repository_ctx.os.arch:
            return (repository_ctx.path(Label("@emscripten_bin_linux//:BUILD.bazel")).dirname, "")
        elif "aarch64" in repository_ctx.os.arch:
            return (repository_ctx.path(Label("@emscripten_bin_linux_arm64//:BUILD.bazel")).dirname, "")
        else:
            fail("Unsupported architecture for Linux")
    elif repository_ctx.os.name.startswith("mac"):
        if "amd64" in repository_ctx.os.arch or "x86_64" in repository_ctx.os.arch:
            return (repository_ctx.path(Label("@emscripten_bin_mac//:BUILD.bazel")).dirname, "")
        elif "aarch64" in repository_ctx.os.arch:
            return (repository_ctx.path(Label("@emscripten_bin_mac_arm64//:BUILD.bazel")).dirname, "")
        else:
            fail("Unsupported architecture for MacOS")
    elif repository_ctx.os.name.startswith("windows"):
        return (repository_ctx.path(Label("@emscripten_bin_win//:BUILD.bazel")).dirname, ".bat")
    else:
        fail("Unsupported operating system")

def get_bin_deps_repo_name(repository_ctx):
    if repository_ctx.os.name.startswith("linux"):
        if "amd64" in repository_ctx.os.arch or "x86_64" in repository_ctx.os.arch:
            return "@emscripten_bin_linux"
        elif "aarch64" in repository_ctx.os.arch:
            return "@emscripten_bin_linux_arm64"
        else:
            fail("Unsupported architecture for Linux")
    elif repository_ctx.os.name.startswith("mac"):
        if "amd64" in repository_ctx.os.arch or "x86_64" in repository_ctx.os.arch:
            return "@emscripten_bin_mac"
        elif "aarch64" in repository_ctx.os.arch:
            return "@emscripten_bin_mac_arm64"
        else:
            fail("Unsupported architecture for MacOS")
    elif repository_ctx.os.name.startswith("windows"):
        return "@emscripten_bin_win"
    else:
        fail("Unsupported operating system")

def _emscripten_cache_repository_impl(repository_ctx):
    # Read the default emscripten configuration file
    default_config = repository_ctx.read(
        repository_ctx.path(
            Label("@emsdk//emscripten_toolchain:default_config"),
        ),
    )

    repo_metadata = None
    build_file_content = BUILD_FILE_CONTENT_TEMPLATE
    use_builtin_cache = True

    if repository_ctx.attr.prebuilt_cache_url:
        repository_ctx.download_and_extract(
            url = repository_ctx.attr.prebuilt_cache_url,
            output = "cache",
            sha256 = repository_ctx.attr.prebuilt_cache_sha256,
            stripPrefix = repository_ctx.attr.prebuilt_cache_strip_prefix,
        )

        # Use the prebuilt cache
        use_builtin_cache = False

        # Bazel 7 does not have the repo_metadata API, so prebuilt cache on Bazel 7 will not be marked as reproducible. This is not ideal, but it is a limitation of Bazel 7.
        if hasattr(repository_ctx, "repo_metadata"):
            repo_metadata = repository_ctx.repo_metadata(reproducible = True)

    elif repository_ctx.attr.targets or repository_ctx.attr.configuration:
        root, script_ext = get_root_and_script_ext(repository_ctx)
        llvm_root = root.get_child("bin")
        cache = repository_ctx.path("cache")

        # Create configuration file
        embuilder_config_content = EMBUILDER_CONFIG_TEMPLATE.format(
            cache = cache,
            binaryen_root = root,
            llvm_root = llvm_root,
        )
        repository_ctx.file("embuilder_config", embuilder_config_content)
        embuilder_config_path = repository_ctx.path("embuilder_config")
        embuilder_path = "{}{}".format(root.get_child("emscripten").get_child("embuilder"), script_ext)

        # Prepare the command line
        if repository_ctx.attr.targets:
            targets = repository_ctx.attr.targets
        else:
            # If no targets are requested, build everything
            targets = ["ALL"]
        flags = ["--em-config", embuilder_config_path] + repository_ctx.attr.configuration
        embuilder_args = [embuilder_path] + flags + ["build"] + targets

        # Run embuilder
        repository_ctx.report_progress("Building secondary cache")
        result = repository_ctx.execute(
            embuilder_args,
            quiet = False,
            environment = {
                "EM_IGNORE_SANITY": "1",
                "EM_NODE_JS": "empty",
            },
        )
        if result.return_code != 0:
            fail("Embuilder exited with a non-zero return code")

        use_builtin_cache = False

    if use_builtin_cache:
        build_file_content += BUILD_FILE_USE_BUILTIN_CACHE.format(get_bin_deps_repo_name(repository_ctx))
    else:
        default_config += 'CACHE = os.path.join(os.path.dirname(os.environ["EM_CONFIG_PATH"]), "cache")\n'
        build_file_content += BUILD_FILE_USE_SECONDARY_CACHE

    # Create the configuration file for the toolchain and export
    repository_ctx.file("emscripten_config", default_config)
    repository_ctx.file("BUILD.bazel", build_file_content)

    return repo_metadata

_emscripten_cache_repository = repository_rule(
    implementation = _emscripten_cache_repository_impl,
    attrs = {
        "configuration": attr.string_list(),
        "targets": attr.string_list(),
        "prebuilt_cache_url": attr.string(),
        "prebuilt_cache_sha256": attr.string(),
        "prebuilt_cache_strip_prefix": attr.string(),
    },
)

def _emscripten_cache_impl(ctx):
    all_configuration = []
    all_targets = []

    prebuilt_cache_url = ""
    prebuilt_cache_sha256 = ""
    prebuilt_cache_strip_prefix = ""
    prebuilt_cache_seen = False
    for mod in ctx.modules:
        for configuration in mod.tags.configuration:
            all_configuration += configuration.flags
        for targets in mod.tags.targets:
            all_targets += targets.targets
        for prebuilt_cache in mod.tags.prebuilt_cache:
            if prebuilt_cache_seen:
                fail("Only one prebuilt_cache tag is allowed")
            prebuilt_cache_url = prebuilt_cache.http_archive_url
            prebuilt_cache_sha256 = prebuilt_cache.sha256
            prebuilt_cache_strip_prefix = prebuilt_cache.strip_prefix
            prebuilt_cache_seen = True

    _emscripten_cache_repository(
        name = "emscripten_cache",
        configuration = all_configuration,
        targets = all_targets,
        prebuilt_cache_url = prebuilt_cache_url,
        prebuilt_cache_sha256 = prebuilt_cache_sha256,
        prebuilt_cache_strip_prefix = prebuilt_cache_strip_prefix,
    )

emscripten_cache = module_extension(
    tag_classes = {
        "configuration": tag_class(attrs = {"flags": attr.string_list()}),
        "targets": tag_class(attrs = {"targets": attr.string_list()}),
        "prebuilt_cache": tag_class(attrs = {
            "http_archive_url": attr.string(mandatory = True),
            "sha256": attr.string(mandatory = True),
            "strip_prefix": attr.string(),
        }),
    },
    implementation = _emscripten_cache_impl,
)