bazel/toolchains.bzl

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

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

    if 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=True,
            environment = {
                "EM_IGNORE_SANITY": "1",
                "EM_NODE_JS": "empty",
            }
        )
        if result.return_code != 0:
            fail("Embuilder exited with a non-zero return code")
        # Override Emscripten's cache with the secondary cache
        default_config += "CACHE = '{}'\n".format(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_TEMPLATE)

_emscripten_cache = repository_rule(
    implementation = _emscripten_cache_impl,
    attrs = {
        "configuration": attr.string_list(),
        "targets": attr.string_list(),
    },
    local = True
)

def register_emscripten_toolchains(cache = {}):
    _emscripten_cache(
        name = "emscripten_cache",
        configuration = cache["configuration"] if "configuration" in cache else [],
        targets = cache["targets"] if "targets" in cache else [],
    )

    native.register_toolchains(str(Label("//emscripten_toolchain:cc-toolchain-wasm")))