cargo/private/cargo_build_script.bzl

"""Rules for Cargo build scripts (`build.rs` files)"""

load("@bazel_skylib//lib:paths.bzl", "paths")
load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "CPP_COMPILE_ACTION_NAME", "C_COMPILE_ACTION_NAME")
load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain")
load("//rust:defs.bzl", "rust_common")

# buildifier: disable=bzl-visibility
load("//rust/private:providers.bzl", _DepInfo = "DepInfo")

# buildifier: disable=bzl-visibility
load("//rust/private:rustc.bzl", "BuildInfo", "get_compilation_mode_opts", "get_linker_and_args")

# buildifier: disable=bzl-visibility
load("//rust/private:utils.bzl", "dedent", "expand_dict_value_locations", "find_cc_toolchain", "find_toolchain", _name_to_crate_name = "name_to_crate_name")

# Reexport for cargo_build_script_wrapper.bzl
name_to_crate_name = _name_to_crate_name

def get_cc_compile_args_and_env(cc_toolchain, feature_configuration):
    """Gather cc environment variables from the given `cc_toolchain`

    Args:
        cc_toolchain (cc_toolchain): The current rule's `cc_toolchain`.
        feature_configuration (FeatureConfiguration): Class used to construct command lines from CROSSTOOL features.

    Returns:
        tuple: A tuple of the following items:
            - (sequence): A flattened C command line flags for given action.
            - (sequence): A flattened CXX command line flags for given action.
            - (dict): C environment variables to be set for given action.
    """
    compile_variables = cc_common.create_compile_variables(
        feature_configuration = feature_configuration,
        cc_toolchain = cc_toolchain,
    )
    cc_c_args = cc_common.get_memory_inefficient_command_line(
        feature_configuration = feature_configuration,
        action_name = C_COMPILE_ACTION_NAME,
        variables = compile_variables,
    )
    cc_cxx_args = cc_common.get_memory_inefficient_command_line(
        feature_configuration = feature_configuration,
        action_name = CPP_COMPILE_ACTION_NAME,
        variables = compile_variables,
    )
    cc_env = cc_common.get_environment_variables(
        feature_configuration = feature_configuration,
        action_name = C_COMPILE_ACTION_NAME,
        variables = compile_variables,
    )
    return cc_c_args, cc_cxx_args, cc_env

def _pwd_flags(args):
    """Prefix execroot-relative paths of known arguments with ${pwd}.

    Args:
        args (list): List of tool arguments.

    Returns:
        list: The modified argument list.
    """
    res = []
    for arg in args:
        s, opt, path = arg.partition("--sysroot=")
        if s == "" and not paths.is_absolute(path):
            res.append("{}${{pwd}}/{}".format(opt, path))
        else:
            res.append(arg)
    return res

def _cargo_build_script_impl(ctx):
    """The implementation for the `cargo_build_script` rule.

    Args:
        ctx (ctx): The rules context object

    Returns:
        list: A list containing a BuildInfo provider
    """
    script = ctx.executable.script
    toolchain = find_toolchain(ctx)
    out_dir = ctx.actions.declare_directory(ctx.label.name + ".out_dir")
    env_out = ctx.actions.declare_file(ctx.label.name + ".env")
    dep_env_out = ctx.actions.declare_file(ctx.label.name + ".depenv")
    flags_out = ctx.actions.declare_file(ctx.label.name + ".flags")
    link_flags = ctx.actions.declare_file(ctx.label.name + ".linkflags")
    link_search_paths = ctx.actions.declare_file(ctx.label.name + ".linksearchpaths")  # rustc-link-search, propagated from transitive dependencies
    manifest_dir = "%s.runfiles/%s/%s" % (script.path, ctx.label.workspace_name or ctx.workspace_name, ctx.label.package)
    compilation_mode_opt_level = get_compilation_mode_opts(ctx, toolchain).opt_level

    streams = struct(
        stdout = ctx.actions.declare_file(ctx.label.name + ".stdout.log"),
        stderr = ctx.actions.declare_file(ctx.label.name + ".stderr.log"),
    )

    pkg_name = name_to_pkg_name(ctx.label.name)

    toolchain_tools = [toolchain.all_files]

    cc_toolchain = find_cpp_toolchain(ctx)

    # Start with the default shell env, which contains any --action_env
    # settings passed in on the command line.
    env = dict(ctx.configuration.default_shell_env)

    env.update({
        "CARGO_CRATE_NAME": name_to_crate_name(pkg_name),
        "CARGO_MANIFEST_DIR": manifest_dir,
        "CARGO_PKG_NAME": pkg_name,
        "HOST": toolchain.exec_triple.str,
        "NUM_JOBS": "1",
        "OPT_LEVEL": compilation_mode_opt_level,
        "RUSTC": toolchain.rustc.path,
        "TARGET": toolchain.target_flag_value,
        # OUT_DIR is set by the runner itself, rather than on the action.
    })

    # This isn't exactly right, but Bazel doesn't have exact views of "debug" and "release", so...
    env.update({
        "DEBUG": {"dbg": "true", "fastbuild": "true", "opt": "false"}.get(ctx.var["COMPILATION_MODE"], "true"),
        "PROFILE": {"dbg": "debug", "fastbuild": "debug", "opt": "release"}.get(ctx.var["COMPILATION_MODE"], "unknown"),
    })

    if ctx.attr.version:
        version = ctx.attr.version.split("+")[0].split(".")
        patch = version[2].split("-") if len(version) > 2 else [""]
        env["CARGO_PKG_VERSION_MAJOR"] = version[0]
        env["CARGO_PKG_VERSION_MINOR"] = version[1] if len(version) > 1 else ""
        env["CARGO_PKG_VERSION_PATCH"] = patch[0]
        env["CARGO_PKG_VERSION_PRE"] = patch[1] if len(patch) > 1 else ""
        env["CARGO_PKG_VERSION"] = ctx.attr.version

    # Pull in env vars which may be required for the cc_toolchain to work (e.g. on OSX, the SDK version).
    # We hope that the linker env is sufficient for the whole cc_toolchain.
    cc_toolchain, feature_configuration = find_cc_toolchain(ctx)
    linker, link_args, linker_env = get_linker_and_args(ctx, ctx.attr, "bin", cc_toolchain, feature_configuration, None)
    env.update(**linker_env)
    env["LD"] = linker
    env["LDFLAGS"] = " ".join(_pwd_flags(link_args))

    # MSVC requires INCLUDE to be set
    cc_c_args, cc_cxx_args, cc_env = get_cc_compile_args_and_env(cc_toolchain, feature_configuration)
    include = cc_env.get("INCLUDE")
    if include:
        env["INCLUDE"] = include

    if cc_toolchain:
        toolchain_tools.append(cc_toolchain.all_files)

        cc_executable = cc_toolchain.compiler_executable
        if cc_executable:
            env["CC"] = cc_executable
            env["CXX"] = cc_executable
        ar_executable = cc_toolchain.ar_executable
        if ar_executable:
            env["AR"] = ar_executable

        # Populate CFLAGS and CXXFLAGS that cc-rs relies on when building from source, in particular
        # to determine the deployment target when building for apple platforms (`macosx-version-min`
        # for example, itself derived from the `macos_minimum_os` Bazel argument).
        env["CFLAGS"] = " ".join(_pwd_flags(cc_c_args))
        env["CXXFLAGS"] = " ".join(_pwd_flags(cc_cxx_args))

    # Inform build scripts of rustc flags
    # https://github.com/rust-lang/cargo/issues/9600
    env["CARGO_ENCODED_RUSTFLAGS"] = "\\x1f".join([
        # Allow build scripts to locate the generated sysroot
        "--sysroot=${{pwd}}/{}".format(toolchain.sysroot),
    ] + ctx.attr.rustc_flags)

    for f in ctx.attr.crate_features:
        env["CARGO_FEATURE_" + f.upper().replace("-", "_")] = "1"

    # Add environment variables from the Rust toolchain.
    env.update(toolchain.env)

    # Gather data from the `toolchains` attribute.
    for target in ctx.attr.toolchains:
        if DefaultInfo in target:
            toolchain_tools.extend([
                target[DefaultInfo].files,
                target[DefaultInfo].default_runfiles.files,
            ])
        if platform_common.ToolchainInfo in target:
            all_files = getattr(target[platform_common.ToolchainInfo], "all_files", depset([]))
            if type(all_files) == "list":
                all_files = depset(all_files)
            toolchain_tools.append(all_files)

    _merge_env_dict(env, expand_dict_value_locations(
        ctx,
        ctx.attr.build_script_env,
        getattr(ctx.attr, "data", []) +
        getattr(ctx.attr, "compile_data", []) +
        getattr(ctx.attr, "tools", []),
    ))

    tools = depset(
        direct = [
            script,
            ctx.executable._cargo_build_script_runner,
        ] + ctx.files.data + ctx.files.tools + ([toolchain.target_json] if toolchain.target_json else []),
        transitive = toolchain_tools,
    )

    links = ctx.attr.links or ""

    # dep_env_file contains additional environment variables coming from
    # direct dependency sys-crates' build scripts. These need to be made
    # available to the current crate build script.
    # See https://doc.rust-lang.org/cargo/reference/build-scripts.html#-sys-packages
    # for details.
    args = ctx.actions.args()
    args.add_all([
        script.path,
        links,
        out_dir.path,
        env_out.path,
        flags_out.path,
        link_flags.path,
        link_search_paths.path,
        dep_env_out.path,
        streams.stdout.path,
        streams.stderr.path,
    ])
    build_script_inputs = []
    for dep in ctx.attr.deps:
        if rust_common.dep_info in dep and dep[rust_common.dep_info].dep_env:
            dep_env_file = dep[rust_common.dep_info].dep_env
            args.add(dep_env_file.path)
            build_script_inputs.append(dep_env_file)
            for dep_build_info in dep[rust_common.dep_info].transitive_build_infos.to_list():
                build_script_inputs.append(dep_build_info.out_dir)

    ctx.actions.run(
        executable = ctx.executable._cargo_build_script_runner,
        arguments = [args],
        outputs = [out_dir, env_out, flags_out, link_flags, link_search_paths, dep_env_out, streams.stdout, streams.stderr],
        tools = tools,
        inputs = build_script_inputs,
        mnemonic = "CargoBuildScriptRun",
        progress_message = "Running Cargo build script {}".format(pkg_name),
        env = env,
    )

    return [
        BuildInfo(
            out_dir = out_dir,
            rustc_env = env_out,
            dep_env = dep_env_out,
            flags = flags_out,
            link_flags = link_flags,
            link_search_paths = link_search_paths,
        ),
        OutputGroupInfo(
            streams = depset([streams.stdout, streams.stderr]),
            out_dir = depset([out_dir]),
        ),
    ]

cargo_build_script = rule(
    doc = (
        "A rule for running a crate's `build.rs` files to generate build information " +
        "which is then used to determine how to compile said crate."
    ),
    implementation = _cargo_build_script_impl,
    attrs = {
        "build_script_env": attr.string_dict(
            doc = "Environment variables for build scripts.",
        ),
        "crate_features": attr.string_list(
            doc = "The list of rust features that the build script should consider activated.",
        ),
        "data": attr.label_list(
            doc = "Data required by the build script.",
            allow_files = True,
        ),
        "deps": attr.label_list(
            doc = "The Rust dependencies of the crate",
            providers = [rust_common.dep_info],
            cfg = "exec",
        ),
        "links": attr.string(
            doc = "The name of the native library this crate links against.",
        ),
        "rustc_flags": attr.string_list(
            doc = dedent("""\
                List of compiler flags passed to `rustc`.

                These strings are subject to Make variable expansion for predefined
                source/output path variables like `$location`, `$execpath`, and 
                `$rootpath`. This expansion is useful if you wish to pass a generated
                file of arguments to rustc: `@$(location //package:target)`.
            """),
        ),
        # The source of truth will be the `cargo_build_script` macro until stardoc
        # implements documentation inheritence. See https://github.com/bazelbuild/stardoc/issues/27
        "script": attr.label(
            doc = "The binary script to run, generally a `rust_binary` target.",
            executable = True,
            allow_files = True,
            mandatory = True,
            cfg = "exec",
        ),
        "tools": attr.label_list(
            doc = "Tools required by the build script.",
            allow_files = True,
            cfg = "exec",
        ),
        "version": attr.string(
            doc = "The semantic version (semver) of the crate",
        ),
        "_cargo_build_script_runner": attr.label(
            executable = True,
            allow_files = True,
            default = Label("//cargo/cargo_build_script_runner:cargo_build_script_runner"),
            cfg = "exec",
        ),
        "_cc_toolchain": attr.label(
            default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
        ),
    },
    fragments = ["cpp"],
    toolchains = [
        str(Label("//rust:toolchain_type")),
        "@bazel_tools//tools/cpp:toolchain_type",
    ],
    incompatible_use_toolchain_transition = True,
)

def _merge_env_dict(prefix_dict, suffix_dict):
    """Merges suffix_dict into prefix_dict, appending rather than replacing certain env vars."""
    for key in ["CFLAGS", "CXXFLAGS", "LDFLAGS"]:
        if key in prefix_dict and key in suffix_dict and prefix_dict[key]:
            prefix_dict[key] += " " + suffix_dict.pop(key)
    prefix_dict.update(suffix_dict)

def name_to_pkg_name(name):
    """Sanitize the name of cargo_build_script targets.

    Args:
        name (str): The name value pass to the `cargo_build_script` wrapper.

    Returns:
        str: A cleaned up name for a build script target.
    """
    if name.endswith("_build_script"):
        return name[:-len("_build_script")]
    return name

def _cargo_dep_env_implementation(ctx):
    empty_file = ctx.actions.declare_file(ctx.label.name + ".empty_file")
    empty_dir = ctx.actions.declare_directory(ctx.label.name + ".empty_dir")
    ctx.actions.write(
        output = empty_file,
        content = "",
    )
    ctx.actions.run(
        outputs = [empty_dir],
        executable = "true",
    )

    build_infos = []
    out_dir = ctx.file.out_dir
    if out_dir:
        if not out_dir.is_directory:
            fail("out_dir must be a directory artifact")

        # BuildInfos in this list are collected up for all transitive cargo_build_script
        # dependencies. This is important for any flags set in `dep_env` which reference this
        # `out_dir`.
        #
        # TLDR: This BuildInfo propagates up build script dependencies.
        build_infos.append(BuildInfo(
            dep_env = empty_file,
            flags = empty_file,
            link_flags = empty_file,
            link_search_paths = empty_file,
            out_dir = out_dir,
            rustc_env = empty_file,
        ))
    return [
        DefaultInfo(files = depset(ctx.files.src)),
        # Parts of this BuildInfo is used when building all transitive dependencies
        # (cargo_build_script and otherwise), alongside the DepInfo. This is how other rules
        # identify this one as a valid dependency, but we don't otherwise have a use for it.
        #
        # TLDR: This BuildInfo propagates up normal (non build script) depenencies.
        #
        # In the future, we could consider setting rustc_env here, and also propagating dep_dir
        # so files in it can be referenced there.
        BuildInfo(
            dep_env = empty_file,
            flags = empty_file,
            link_flags = empty_file,
            link_search_paths = empty_file,
            out_dir = empty_dir,
            rustc_env = empty_file,
        ),
        # Information here is used directly by dependencies, and it is an error to have more than
        # one dependency which sets this. This is the main way to specify information from build
        # scripts, which is what we're looking to do.
        _DepInfo(
            dep_env = ctx.file.src,
            direct_crates = depset(),
            link_search_path_files = depset(),
            transitive_build_infos = depset(direct = build_infos),
            transitive_crate_outputs = depset(),
            transitive_crates = depset(),
            transitive_noncrates = depset(),
        ),
    ]

cargo_dep_env = rule(
    implementation = _cargo_dep_env_implementation,
    doc = (
        "A rule for generating variables for dependent `cargo_build_script`s " +
        "without a build script. This is useful for using Bazel rules instead " +
        "of a build script, while also generating configuration information " +
        "for build scripts which depend on this crate."
    ),
    attrs = {
        "out_dir": attr.label(
            doc = dedent("""\
                Folder containing additional inputs when building all direct dependencies.

                This has the same effect as a `cargo_build_script` which prints
                puts files into `$OUT_DIR`, but without requiring a build script.
            """),
            allow_single_file = True,
            mandatory = False,
        ),
        "src": attr.label(
            doc = dedent("""\
                File containing additional environment variables to set for build scripts of direct dependencies.

                This has the same effect as a `cargo_build_script` which prints
                `cargo:VAR=VALUE` lines, but without requiring a build script.

                This files should  contain a single variable per line, of format
                `NAME=value`, and newlines may be included in a value by ending a
                line with a trailing back-slash (`\\\\`).
            """),
            allow_single_file = True,
            mandatory = True,
        ),
    },
)