windows_cc_configure.bzl

# pylint: disable=g-bad-file-header
# Copyright 2016 The Bazel Authors. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Configuring the C++ toolchain on Windows."""

load(
    ":lib_cc_configure.bzl",
    "auto_configure_fail",
    "auto_configure_warning",
    "auto_configure_warning_maybe",
    "escape_string",
    "execute",
    "resolve_labels",
    "write_builtin_include_directory_paths",
)

_targets_archs = {"arm": "amd64_arm", "arm64": "amd64_arm64", "x64": "amd64", "x86": "amd64_x86"}
_targets_lib_folder = {"arm": "arm", "arm64": "arm64", "x86": ""}

def _lookup_env_var(env, name, default = None):
    """Lookup environment variable case-insensitve.

    If a matching (case-insensitive) entry is found in the env dict both
    the key and the value are returned. The returned key might differ from
    name in casing.

    If a matching key was found its value is returned otherwise
    the default is returned.

    Return a (key, value) tuple"""
    for key, value in env.items():
        if name.lower() == key.lower():
            return (key, value)
    return (name, default)

def _get_env_var(repository_ctx, name, default = None):
    """Returns a value from an environment variable."""
    return _lookup_env_var(repository_ctx.os.environ, name, default)[1]

def _get_path_env_var(repository_ctx, name):
    """Returns a path from an environment variable.

    Removes quotes, replaces '/' with '\', and strips trailing '\'s."""
    value = _get_env_var(repository_ctx, name)
    if value != None:
        if value[0] == "\"":
            if len(value) == 1 or value[-1] != "\"":
                auto_configure_fail("'%s' environment variable has no trailing quote" % name)
            value = value[1:-1]
        if "/" in value:
            value = value.replace("/", "\\")
        if value[-1] == "\\":
            value = value.rstrip("\\")
    return value

def _get_temp_env(repository_ctx):
    """Returns the value of TMP, or TEMP, or if both undefined then C:\\Windows."""
    tmp = _get_path_env_var(repository_ctx, "TMP")
    if not tmp:
        tmp = _get_path_env_var(repository_ctx, "TEMP")
    if not tmp:
        tmp = "C:\\Windows\\Temp"
        auto_configure_warning(
            "neither 'TMP' nor 'TEMP' environment variables are set, using '%s' as default" % tmp,
        )
    return tmp

def _get_escaped_windows_msys_starlark_content(repository_ctx, use_mingw = False):
    """Return the content of msys cc toolchain rule."""
    msys_root = ""
    bazel_sh = _get_path_env_var(repository_ctx, "BAZEL_SH")
    if bazel_sh:
        bazel_sh = bazel_sh.replace("\\", "/").lower()
        tokens = bazel_sh.rsplit("/", 1)
        if tokens[0].endswith("/usr/bin"):
            msys_root = tokens[0][:len(tokens[0]) - len("usr/bin")]
        elif tokens[0].endswith("/bin"):
            msys_root = tokens[0][:len(tokens[0]) - len("bin")]

    prefix = "mingw64" if use_mingw else "usr"
    tool_path_prefix = escape_string(msys_root) + prefix
    tool_bin_path = tool_path_prefix + "/bin"
    tool_path = {}

    for tool in ["ar", "cpp", "dwp", "gcc", "gcov", "ld", "nm", "objcopy", "objdump", "strip"]:
        if msys_root:
            tool_path[tool] = tool_bin_path + "/" + tool
        else:
            tool_path[tool] = "msys_gcc_installation_error.bat"
    tool_paths = ",\n        ".join(['"%s": "%s"' % (k, v) for k, v in tool_path.items()])
    include_directories = ('        "%s/",\n        ' % tool_path_prefix) if msys_root else ""
    return tool_paths, tool_bin_path, include_directories

def _get_system_root(repository_ctx):
    """Get System root path on Windows, default is C:\\Windows. Doesn't %-escape the result."""
    systemroot = _get_path_env_var(repository_ctx, "SYSTEMROOT")
    if not systemroot:
        systemroot = "C:\\Windows"
        auto_configure_warning_maybe(
            repository_ctx,
            "SYSTEMROOT is not set, using default SYSTEMROOT=C:\\Windows",
        )
    return escape_string(systemroot)

def _add_system_root(repository_ctx, env):
    """Running VCVARSALL.BAT and VCVARSQUERYREGISTRY.BAT need %SYSTEMROOT%\\\\system32 in PATH."""
    env_key, env_value = _lookup_env_var(env, "PATH", default = "")
    env[env_key] = env_value + ";" + _get_system_root(repository_ctx) + "\\system32"
    return env

def find_vc_path(repository_ctx):
    """Find Visual C++ build tools install path. Doesn't %-escape the result.

    Args:
        repository_ctx: The repository context.

    Returns:
        The path to the Visual C++ build tools installation.
    """

    # 1. Check if BAZEL_VC or BAZEL_VS is already set by user.
    bazel_vc = _get_path_env_var(repository_ctx, "BAZEL_VC")
    if bazel_vc:
        if repository_ctx.path(bazel_vc).exists:
            return bazel_vc
        else:
            auto_configure_warning_maybe(
                repository_ctx,
                "%BAZEL_VC% is set to non-existent path, ignoring.",
            )

    bazel_vs = _get_path_env_var(repository_ctx, "BAZEL_VS")
    if bazel_vs:
        if repository_ctx.path(bazel_vs).exists:
            bazel_vc = bazel_vs + "\\VC"
            if repository_ctx.path(bazel_vc).exists:
                return bazel_vc
            else:
                auto_configure_warning_maybe(
                    repository_ctx,
                    "No 'VC' directory found under %BAZEL_VS%, ignoring.",
                )
        else:
            auto_configure_warning_maybe(
                repository_ctx,
                "%BAZEL_VS% is set to non-existent path, ignoring.",
            )

    auto_configure_warning_maybe(
        repository_ctx,
        "Neither %BAZEL_VC% nor %BAZEL_VS% are set, start looking for the latest Visual C++" +
        " installed.",
    )

    # 2. Use vswhere to locate all Visual Studio installations
    program_files_dir = _get_path_env_var(repository_ctx, "PROGRAMFILES(X86)")
    if not program_files_dir:
        program_files_dir = "C:\\Program Files (x86)"
        auto_configure_warning_maybe(
            repository_ctx,
            "'PROGRAMFILES(X86)' environment variable is not set, using '%s' as default" % program_files_dir,
        )

    vswhere_binary = program_files_dir + "\\Microsoft Visual Studio\\Installer\\vswhere.exe"
    if repository_ctx.path(vswhere_binary).exists:
        result = repository_ctx.execute([vswhere_binary, "-requires", "Microsoft.VisualStudio.Component.VC.Tools.x86.x64", "-property", "installationPath", "-latest"])
        auto_configure_warning_maybe(repository_ctx, "vswhere query result:\n\nSTDOUT(start)\n%s\nSTDOUT(end)\nSTDERR(start):\n%s\nSTDERR(end)\n" %
                                                     (result.stdout, result.stderr))
        installation_path = result.stdout.strip()
        if not result.stderr and installation_path:
            vc_dir = installation_path + "\\VC"
            auto_configure_warning_maybe(repository_ctx, "Visual C++ build tools found at %s" % vc_dir)
            return vc_dir

    # 3. Check if VS%VS_VERSION%COMNTOOLS is set, if true then try to find and use
    # vcvarsqueryregistry.bat / VsDevCmd.bat to detect VC++.
    auto_configure_warning_maybe(repository_ctx, "Looking for VS%VERSION%COMNTOOLS environment variables, " +
                                                 "eg. VS140COMNTOOLS")
    for vscommontools_env, script in [
        ("VS160COMNTOOLS", "VsDevCmd.bat"),
        ("VS150COMNTOOLS", "VsDevCmd.bat"),
        ("VS140COMNTOOLS", "vcvarsqueryregistry.bat"),
        ("VS120COMNTOOLS", "vcvarsqueryregistry.bat"),
        ("VS110COMNTOOLS", "vcvarsqueryregistry.bat"),
        ("VS100COMNTOOLS", "vcvarsqueryregistry.bat"),
        ("VS90COMNTOOLS", "vcvarsqueryregistry.bat"),
    ]:
        path = _get_path_env_var(repository_ctx, vscommontools_env)
        if path == None:
            continue
        script = path + "\\" + script
        if not repository_ctx.path(script).exists:
            continue
        repository_ctx.file(
            "get_vc_dir.bat",
            "@echo off\n" +
            "call \"" + script + "\" > NUL\n" +
            "echo %VCINSTALLDIR%",
            True,
        )
        env = _add_system_root(repository_ctx, repository_ctx.os.environ)
        vc_dir = execute(repository_ctx, ["./get_vc_dir.bat"], environment = env)

        auto_configure_warning_maybe(repository_ctx, "Visual C++ build tools found at %s" % vc_dir)
        return vc_dir

    # 4. User might have purged all environment variables. If so, look for Visual C++ in registry.
    # Works for Visual Studio 2017 and older. (Does not work for Visual Studio 2019 Preview.)
    auto_configure_warning_maybe(repository_ctx, "Looking for Visual C++ through registry")
    reg_binary = _get_system_root(repository_ctx) + "\\system32\\reg.exe"
    vc_dir = None
    for key, suffix in (("VC7", ""), ("VS7", "\\VC")):
        for version in ["15.0", "14.0", "12.0", "11.0", "10.0", "9.0", "8.0"]:
            if vc_dir:
                break
            result = repository_ctx.execute([reg_binary, "query", "HKEY_LOCAL_MACHINE\\SOFTWARE\\Wow6432Node\\Microsoft\\VisualStudio\\SxS\\" + key, "/v", version])
            auto_configure_warning_maybe(repository_ctx, "registry query result for VC %s:\n\nSTDOUT(start)\n%s\nSTDOUT(end)\nSTDERR(start):\n%s\nSTDERR(end)\n" %
                                                         (version, result.stdout, result.stderr))
            if not result.stderr:
                for line in result.stdout.split("\n"):
                    line = line.strip()
                    if line.startswith(version) and line.find("REG_SZ") != -1:
                        vc_dir = line[line.find("REG_SZ") + len("REG_SZ"):].strip() + suffix
    if vc_dir:
        auto_configure_warning_maybe(repository_ctx, "Visual C++ build tools found at %s" % vc_dir)
        return vc_dir

    # 5. Check default directories for VC installation
    auto_configure_warning_maybe(repository_ctx, "Looking for default Visual C++ installation directory")
    for path in [
        "Microsoft Visual Studio\\%s\\%s\\VC" % (year, edition)
        for year in (2022, 2019, 2017)
        for edition in ("Preview", "BuildTools", "Community", "Professional", "Enterprise")
    ] + [
        "Microsoft Visual Studio 14.0\\VC",
    ]:
        path = program_files_dir + "\\" + path
        if repository_ctx.path(path).exists:
            vc_dir = path
            break

    if not vc_dir:
        auto_configure_warning_maybe(repository_ctx, "Visual C++ build tools not found.")
        return None
    auto_configure_warning_maybe(repository_ctx, "Visual C++ build tools found at %s" % vc_dir)
    return vc_dir

def _is_vs_2017_or_newer(repository_ctx, vc_path):
    """Check if the installed VS version is Visual Studio 2017 or newer."""

    # For VS 2017 and later, a `Tools` directory should exist under `BAZEL_VC`
    return repository_ctx.path(vc_path).get_child("Tools").exists

def _is_msbuildtools(vc_path):
    """Check if the installed VC version is from MSBuildTools."""

    # In MSBuildTools (usually container setup), the location of VC is like:
    # C:\BuildTools\MSBuild\Microsoft\VC
    return vc_path.find("BuildTools") != -1 and vc_path.find("MSBuild") != -1

def _find_vcvars_bat_script(repository_ctx, vc_path):
    """Find batch script to set up environment variables for VC. Doesn't %-escape the result."""
    if _is_vs_2017_or_newer(repository_ctx, vc_path):
        vcvars_script = vc_path + "\\Auxiliary\\Build\\VCVARSALL.BAT"
    else:
        vcvars_script = vc_path + "\\VCVARSALL.BAT"

    if not repository_ctx.path(vcvars_script).exists:
        return None

    return vcvars_script

def _is_support_vcvars_ver(vc_full_version):
    """-vcvars_ver option is supported from version 14.11.25503 (VS 2017 version 15.3)."""
    version = [int(i) for i in vc_full_version.split(".")]
    min_version = [14, 11, 25503]
    return version >= min_version

def _is_support_winsdk_selection(repository_ctx, vc_path):
    """Windows SDK selection is supported with VC 2017 / 2019 or with full VS 2015 installation."""
    if _is_vs_2017_or_newer(repository_ctx, vc_path):
        return True

    # By checking the source code of VCVARSALL.BAT in VC 2015, we know that
    # when devenv.exe or wdexpress.exe exists, VCVARSALL.BAT supports Windows SDK selection.
    vc_common_ide = repository_ctx.path(vc_path).dirname.get_child("Common7", "IDE")
    for tool in ["devenv.exe", "wdexpress.exe"]:
        if vc_common_ide.get_child(tool).exists:
            return True
    return False

def _get_vc_env_vars(repository_ctx, vc_path, msvc_vars_x64, target_arch):
    """Derive the environment variables set of a given target architecture from the environment variables of the x64 target.

       This is done to avoid running VCVARSALL.BAT script for every target architecture.

    Args:
        repository_ctx: the repository_ctx object
        vc_path: Visual C++ root directory
        msvc_vars_x64: values of MSVC toolchain including the environment variables for x64 target architecture
        target_arch: the target architecture to get its environment variables

    Returns:
        dictionary of envvars
    """
    env = {}
    if _is_vs_2017_or_newer(repository_ctx, vc_path):
        lib = msvc_vars_x64["%{msvc_env_lib_x64}"]
        full_version = _get_vc_full_version(repository_ctx, vc_path)
        tools_path = "%s\\Tools\\MSVC\\%s\\bin\\HostX64\\%s" % (vc_path, full_version, target_arch)

        # For native windows(10) on arm64 builds host toolchain runs in an emulated x86 environment
        if not repository_ctx.path(tools_path).exists:
            tools_path = "%s\\Tools\\MSVC\\%s\\bin\\HostX86\\%s" % (vc_path, full_version, target_arch)
    else:
        lib = msvc_vars_x64["%{msvc_env_lib_x64}"].replace("amd64", _targets_lib_folder[target_arch])
        tools_path = vc_path + "\\bin\\" + _targets_archs[target_arch]

    env["INCLUDE"] = msvc_vars_x64["%{msvc_env_include_x64}"]
    env["LIB"] = lib.replace("x64", target_arch)
    env["PATH"] = escape_string(tools_path.replace("\\", "\\\\")) + ";" + msvc_vars_x64["%{msvc_env_path_x64}"]
    return env

def setup_vc_env_vars(repository_ctx, vc_path, envvars = [], allow_empty = False, escape = True):
    """Get environment variables set by VCVARSALL.BAT script. Doesn't %-escape the result!

    Args:
        repository_ctx: the repository_ctx object
        vc_path: Visual C++ root directory
        envvars: list of envvars to retrieve; default is ["PATH", "INCLUDE", "LIB", "WINDOWSSDKDIR"]
        allow_empty: allow unset envvars; if False then report errors for those
        escape: if True, escape "\" as "\\" and "%" as "%%" in the envvar values

    Returns:
        dictionary of the envvars
    """
    if not envvars:
        envvars = ["PATH", "INCLUDE", "LIB", "WINDOWSSDKDIR"]

    vcvars_script = _find_vcvars_bat_script(repository_ctx, vc_path)
    if not vcvars_script:
        auto_configure_fail("Cannot find VCVARSALL.BAT script under %s" % vc_path)

    # Getting Windows SDK version set by user.
    # Only supports VC 2017 & 2019 and VC 2015 with full VS installation.
    winsdk_version = _get_winsdk_full_version(repository_ctx)
    if winsdk_version and not _is_support_winsdk_selection(repository_ctx, vc_path):
        auto_configure_warning(("BAZEL_WINSDK_FULL_VERSION=%s is ignored, " +
                                "because standalone Visual C++ Build Tools 2015 doesn't support specifying Windows " +
                                "SDK version, please install the full VS 2015 or use VC 2017/2019.") % winsdk_version)
        winsdk_version = ""

    # Get VC version set by user. Only supports VC 2017 & 2019.
    vcvars_ver = ""
    if _is_vs_2017_or_newer(repository_ctx, vc_path):
        full_version = _get_vc_full_version(repository_ctx, vc_path)

        # Because VCVARSALL.BAT is from the latest VC installed, so we check if the latest
        # version supports -vcvars_ver or not.
        if _is_support_vcvars_ver(_get_latest_subversion(repository_ctx, vc_path)):
            vcvars_ver = "-vcvars_ver=" + full_version

    cmd = "\"%s\" amd64 %s %s" % (vcvars_script, winsdk_version, vcvars_ver)
    print_envvars = ",".join(["{k}=%{k}%".format(k = k) for k in envvars])
    repository_ctx.file(
        "get_env.bat",
        "@echo off\n" +
        ("call %s > NUL \n" % cmd) + ("echo %s \n" % print_envvars),
        True,
    )
    env = _add_system_root(repository_ctx, {k: "" for k in envvars})
    envs = execute(repository_ctx, ["./get_env.bat"], environment = env).split(",")
    env_map = {}
    for env in envs:
        key, value = env.split("=", 1)
        env_map[key] = escape_string(value.replace("\\", "\\\\")) if escape else value

    if not allow_empty:
        _check_env_vars(env_map, cmd, expected = envvars)
    return env_map

def _check_env_vars(env_map, cmd, expected):
    for env in expected:
        if not env_map.get(env):
            auto_configure_fail(
                "Setting up VC environment variables failed, %s is not set by the following command:\n    %s" % (env, cmd),
            )

def _get_latest_subversion(repository_ctx, vc_path):
    """Get the latest subversion of a VS 2017/2019 installation.

    For VS 2017 & 2019, there could be multiple versions of VC build tools.
    The directories are like:
      <vc_path>\\Tools\\MSVC\\14.10.24930\\bin\\HostX64\\x64
      <vc_path>\\Tools\\MSVC\\14.16.27023\\bin\\HostX64\\x64
    This function should return 14.16.27023 in this case."""
    versions = [path.basename for path in repository_ctx.path(vc_path + "\\Tools\\MSVC").readdir()]
    if len(versions) < 1:
        auto_configure_warning_maybe(repository_ctx, "Cannot find any VC installation under BAZEL_VC(%s)" % vc_path)
        return None

    # Parse the version string into integers, then sort the integers to prevent textual sorting.
    version_list = []
    for version in versions:
        parts = [int(i) for i in version.split(".")]
        version_list.append((parts, version))

    version_list = sorted(version_list)
    latest_version = version_list[-1][1]

    auto_configure_warning_maybe(repository_ctx, "Found the following VC versions:\n%s\n\nChoosing the latest version = %s" % ("\n".join(versions), latest_version))
    return latest_version

def _get_vc_full_version(repository_ctx, vc_path):
    """Return the value of BAZEL_VC_FULL_VERSION if defined, otherwise the latest version."""
    version = _get_env_var(repository_ctx, "BAZEL_VC_FULL_VERSION")
    if version != None:
        return version
    return _get_latest_subversion(repository_ctx, vc_path)

def _get_winsdk_full_version(repository_ctx):
    """Return the value of BAZEL_WINSDK_FULL_VERSION if defined, otherwise an empty string."""
    return _get_env_var(repository_ctx, "BAZEL_WINSDK_FULL_VERSION", default = "")

def _find_msvc_tools(repository_ctx, vc_path, target_arch = "x64"):
    """Find the exact paths of the build tools in MSVC for the given target. Doesn't %-escape the result."""
    build_tools_paths = {}
    tools = _get_target_tools(target_arch)
    for tool_name in tools:
        build_tools_paths[tool_name] = find_msvc_tool(repository_ctx, vc_path, tools[tool_name], target_arch)
    return build_tools_paths

def find_msvc_tool(repository_ctx, vc_path, tool, target_arch = "x64"):
    """Find the exact path of a specific build tool in MSVC. Doesn't %-escape the result.

    Args:
        repository_ctx: The repository context.
        vc_path: Visual C++ root directory.
        tool: The name of the tool to find.
        target_arch: The target architecture (default is "x64").

    Returns:
        The exact path of the specified build tool in MSVC, or None if not found.
    """
    tool_path = None
    if _is_vs_2017_or_newer(repository_ctx, vc_path) or _is_msbuildtools(vc_path):
        full_version = _get_vc_full_version(repository_ctx, vc_path)
        if full_version:
            tool_path = "%s\\Tools\\MSVC\\%s\\bin\\HostX64\\%s\\%s" % (vc_path, full_version, target_arch, tool)

            # For native windows(10) on arm64 builds host toolchain runs in an emulated x86 environment
            if not repository_ctx.path(tool_path).exists:
                tool_path = "%s\\Tools\\MSVC\\%s\\bin\\HostX86\\%s\\%s" % (vc_path, full_version, target_arch, tool)
    else:
        # For VS 2015 and older version, the tools are under:
        # C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64
        tool_path = vc_path + "\\bin\\" + _targets_archs[target_arch] + "\\" + tool

    if not tool_path or not repository_ctx.path(tool_path).exists:
        return None

    return tool_path.replace("\\", "/")

def _find_missing_vc_tools(repository_ctx, vc_path, target_arch = "x64"):
    """Check if any required tool for the given target architecture is missing under given VC path."""
    missing_tools = []
    if not _find_vcvars_bat_script(repository_ctx, vc_path):
        missing_tools.append("VCVARSALL.BAT")

    tools = _get_target_tools(target_arch)
    for tool_name in tools:
        if not find_msvc_tool(repository_ctx, vc_path, tools[tool_name], target_arch):
            missing_tools.append(tools[tool_name])
    return missing_tools

def _get_target_tools(target):
    """Return a list of required tools names and their filenames for a certain target."""
    tools = {
        "arm": {"CL": "cl.exe", "DUMPBIN": "dumpbin.exe", "LIB": "lib.exe", "LINK": "link.exe"},
        "arm64": {"CL": "cl.exe", "DUMPBIN": "dumpbin.exe", "LIB": "lib.exe", "LINK": "link.exe"},
        "x64": {"CL": "cl.exe", "DUMPBIN": "dumpbin.exe", "LIB": "lib.exe", "LINK": "link.exe", "ML": "ml64.exe"},
        "x86": {"CL": "cl.exe", "DUMPBIN": "dumpbin.exe", "LIB": "lib.exe", "LINK": "link.exe", "ML": "ml.exe"},
    }
    if tools.get(target) == None:
        auto_configure_fail("Target architecture %s is not recognized" % target)

    return tools.get(target)

def _is_support_debug_fastlink(repository_ctx, linker):
    """Run linker alone to see if it supports /DEBUG:FASTLINK."""
    if _use_clang_cl(repository_ctx):
        # LLVM's lld-link.exe doesn't support /DEBUG:FASTLINK.
        return False
    result = execute(repository_ctx, [linker], expect_failure = True)
    return result.find("/DEBUG[:{FASTLINK|FULL|NONE}]") != -1

def _is_support_parse_showincludes(repository_ctx, cl, env):
    repository_ctx.file(
        "main.cpp",
        "#include \"bazel_showincludes.h\"\nint main(){}\n",
    )
    repository_ctx.file(
        "bazel_showincludes.h",
        "\n",
    )
    result = execute(
        repository_ctx,
        [cl, "/nologo", "/showIncludes", "/c", "main.cpp", "/out", "main.exe", "/Fo", "main.obj"],
        # Attempt to force English language. This may fail if the language pack isn't installed.
        environment = env | {"VSLANG": "1033"},
    )
    for file in ["main.cpp", "bazel_showincludes.h", "main.exe", "main.obj"]:
        execute(repository_ctx, ["cmd", "/C", "del", file], expect_empty_output = True)
    return any([
        line.startswith("Note: including file:") and line.endswith("bazel_showincludes.h")
        for line in result.split("\n")
    ])

def find_llvm_path(repository_ctx):
    """Find LLVM install path.

    Args:
        repository_ctx: The repository context.

    Returns:
        The path to the LLVM installation, or None if not found.
    """

    # 1. Check if BAZEL_LLVM is already set by user.
    bazel_llvm = _get_path_env_var(repository_ctx, "BAZEL_LLVM")
    if bazel_llvm:
        return bazel_llvm

    auto_configure_warning_maybe(repository_ctx, "'BAZEL_LLVM' is not set, " +
                                                 "start looking for LLVM installation on machine.")

    # 2. Look for LLVM installation through registry.
    auto_configure_warning_maybe(repository_ctx, "Looking for LLVM installation through registry")
    reg_binary = _get_system_root(repository_ctx) + "\\system32\\reg.exe"
    llvm_dir = None
    result = repository_ctx.execute([reg_binary, "query", "HKEY_LOCAL_MACHINE\\SOFTWARE\\WOW6432Node\\LLVM\\LLVM"])
    auto_configure_warning_maybe(repository_ctx, "registry query result for LLVM:\n\nSTDOUT(start)\n%s\nSTDOUT(end)\nSTDERR(start):\n%s\nSTDERR(end)\n" %
                                                 (result.stdout, result.stderr))
    if not result.stderr:
        for line in result.stdout.split("\n"):
            line = line.strip()
            if line.startswith("(Default)") and line.find("REG_SZ") != -1:
                llvm_dir = line[line.find("REG_SZ") + len("REG_SZ"):].strip()
    if llvm_dir:
        auto_configure_warning_maybe(repository_ctx, "LLVM installation found at %s" % llvm_dir)
        return llvm_dir

    # 3. Check default directories for LLVM installation
    auto_configure_warning_maybe(repository_ctx, "Looking for default LLVM installation directory")
    program_files_dir = _get_path_env_var(repository_ctx, "PROGRAMFILES")
    if not program_files_dir:
        program_files_dir = "C:\\Program Files"
        auto_configure_warning_maybe(
            repository_ctx,
            "'PROGRAMFILES' environment variable is not set, using '%s' as default" % program_files_dir,
        )
    path = program_files_dir + "\\LLVM"
    if repository_ctx.path(path).exists:
        llvm_dir = path

    if not llvm_dir:
        auto_configure_warning_maybe(repository_ctx, "LLVM installation not found.")
        return None
    auto_configure_warning_maybe(repository_ctx, "LLVM installation found at %s" % llvm_dir)
    return llvm_dir

def find_llvm_tool(repository_ctx, llvm_path, tool):
    """Find the exact path of a specific build tool in LLVM. Doesn't %-escape the result.

    Args:
        repository_ctx: The repository context.
        llvm_path: The path to the LLVM installation.
        tool: The name of the tool to find.

    Returns:
        The exact path of the specified build tool in LLVM, or None if not found.
    """
    tool_path = llvm_path + "\\bin\\" + tool

    if not repository_ctx.path(tool_path).exists:
        return None

    return tool_path.replace("\\", "/")

def _use_clang_cl(repository_ctx):
    """Returns True if USE_CLANG_CL is set to 1."""
    return _get_env_var(repository_ctx, "USE_CLANG_CL", default = "0") == "1"

def _find_missing_llvm_tools(repository_ctx, llvm_path):
    """Check if any required tool is missing under given LLVM path."""
    missing_tools = []
    for tool in ["clang-cl.exe", "lld-link.exe", "llvm-lib.exe"]:
        if not find_llvm_tool(repository_ctx, llvm_path, tool):
            missing_tools.append(tool)

    return missing_tools

def _get_clang_version(repository_ctx, clang_cl):
    result = repository_ctx.execute([clang_cl, "-v"])
    first_line = result.stderr.strip().splitlines()[0].strip()

    # The first line of stderr should look like "[vendor ]clang version X.X.X"
    if result.return_code != 0 or first_line.find("clang version ") == -1:
        auto_configure_fail("Failed to get clang version by running \"%s -v\"" % clang_cl)
    return first_line.split(" ")[-1]

def _get_clang_dir(repository_ctx, llvm_path, clang_version):
    """Get the clang installation directory."""

    # The clang_version string format is "X.X.X"
    clang_dir = llvm_path + "\\lib\\clang\\" + clang_version
    if repository_ctx.path(clang_dir).exists:
        return clang_dir

    # Clang 16 changed the install path to use just the major number.
    clang_major_version = clang_version.split(".")[0]
    return llvm_path + "\\lib\\clang\\" + clang_major_version

def _get_msys_mingw_vars(repository_ctx):
    """Get the variables we need to populate the msys/mingw toolchains."""
    tool_paths, tool_bin_path, inc_dir_msys = _get_escaped_windows_msys_starlark_content(repository_ctx)
    tool_paths_mingw, tool_bin_path_mingw, inc_dir_mingw = _get_escaped_windows_msys_starlark_content(repository_ctx, use_mingw = True)
    write_builtin_include_directory_paths(repository_ctx, "mingw", [inc_dir_mingw], file_suffix = "_mingw")
    msys_mingw_vars = {
        "%{cxx_builtin_include_directories}": inc_dir_msys,
        "%{mingw_cxx_builtin_include_directories}": inc_dir_mingw,
        "%{mingw_tool_bin_path}": tool_bin_path_mingw,
        "%{mingw_tool_paths}": tool_paths_mingw,
        "%{tool_bin_path}": tool_bin_path,
        "%{tool_paths}": tool_paths,
    }
    return msys_mingw_vars

def _get_msvc_vars(repository_ctx, paths, target_arch = "x64", msvc_vars_x64 = None):
    """Get the variables we need to populate the MSVC toolchains."""
    vc_path = find_vc_path(repository_ctx)
    missing_tools = None

    if not vc_path:
        repository_ctx.template(
            "vc_installation_error_" + target_arch + ".bat",
            paths["@rules_cc//cc/private/toolchain:vc_installation_error.bat.tpl"],
            {"%{vc_error_message}": ""},
        )
    else:
        missing_tools = _find_missing_vc_tools(repository_ctx, vc_path, target_arch)
        if missing_tools:
            message = "\r\n".join([
                "echo. 1>&2",
                "echo Visual C++ build tools seems to be installed at %s 1>&2" % vc_path,
                "echo But Bazel can't find the following tools: 1>&2",
                "echo     %s 1>&2" % ", ".join(missing_tools),
                "echo for %s target architecture 1>&2" % target_arch,
                "echo. 1>&2",
            ])
            repository_ctx.template(
                "vc_installation_error_" + target_arch + ".bat",
                paths["@rules_cc//cc/private/toolchain:vc_installation_error.bat.tpl"],
                {"%{vc_error_message}": message},
            )

    if not vc_path or missing_tools:
        write_builtin_include_directory_paths(repository_ctx, "msvc", [], file_suffix = "_msvc")
        msvc_vars = {
            "%{msvc_env_tmp_" + target_arch + "}": "msvc_not_found",
            "%{msvc_env_include_" + target_arch + "}": "msvc_not_found",
            "%{msvc_cxx_builtin_include_directories_" + target_arch + "}": "",
            "%{msvc_env_path_" + target_arch + "}": "msvc_not_found",
            "%{msvc_env_lib_" + target_arch + "}": "msvc_not_found",
            "%{msvc_cl_path_" + target_arch + "}": "vc_installation_error_" + target_arch + ".bat",
            "%{msvc_ml_path_" + target_arch + "}": "vc_installation_error_" + target_arch + ".bat",
            "%{msvc_link_path_" + target_arch + "}": "vc_installation_error_" + target_arch + ".bat",
            "%{msvc_lib_path_" + target_arch + "}": "vc_installation_error_" + target_arch + ".bat",
            "%{dbg_mode_debug_flag_" + target_arch + "}": "/DEBUG",
            "%{fastbuild_mode_debug_flag_" + target_arch + "}": "/DEBUG",
            "%{msvc_parse_showincludes_" + target_arch + "}": repr(False),
        }
        return msvc_vars

    if msvc_vars_x64:
        env = _get_vc_env_vars(repository_ctx, vc_path, msvc_vars_x64, target_arch)
    else:
        env = setup_vc_env_vars(repository_ctx, vc_path)
    escaped_tmp_dir = escape_string(_get_temp_env(repository_ctx).replace("\\", "\\\\"))
    escaped_include_paths = escape_string(env["INCLUDE"])

    build_tools = {}
    llvm_path = ""
    if _use_clang_cl(repository_ctx):
        llvm_path = find_llvm_path(repository_ctx)
        if not llvm_path:
            auto_configure_fail("\nUSE_CLANG_CL is set to 1, but Bazel cannot find Clang installation on your system.\n" +
                                "Please install Clang via http://releases.llvm.org/download.html\n")

        build_tools["CL"] = find_llvm_tool(repository_ctx, llvm_path, "clang-cl.exe")
        build_tools["ML"] = find_msvc_tool(repository_ctx, vc_path, "ml64.exe", "x64")
        build_tools["LINK"] = find_llvm_tool(repository_ctx, llvm_path, "lld-link.exe")
        if not build_tools["LINK"]:
            build_tools["LINK"] = find_msvc_tool(repository_ctx, vc_path, "link.exe", "x64")
        build_tools["LIB"] = find_llvm_tool(repository_ctx, llvm_path, "llvm-lib.exe")
        if not build_tools["LIB"]:
            build_tools["LIB"] = find_msvc_tool(repository_ctx, vc_path, "lib.exe", "x64")
    else:
        build_tools = _find_msvc_tools(repository_ctx, vc_path, target_arch)

    escaped_cxx_include_directories = []
    for path in escaped_include_paths.split(";"):
        if path:
            escaped_cxx_include_directories.append("\"%s\"" % path)
    if llvm_path:
        clang_version = _get_clang_version(repository_ctx, build_tools["CL"])
        clang_dir = _get_clang_dir(repository_ctx, llvm_path, clang_version)
        clang_include_path = (clang_dir + "\\include").replace("\\", "\\\\")
        escaped_cxx_include_directories.append("\"%s\"" % clang_include_path)
        clang_lib_path = (clang_dir + "\\lib\\windows").replace("\\", "\\\\")
        env["LIB"] = escape_string(env["LIB"]) + ";" + clang_lib_path

    support_debug_fastlink = _is_support_debug_fastlink(repository_ctx, build_tools["LINK"])
    write_builtin_include_directory_paths(repository_ctx, "msvc", escaped_cxx_include_directories, file_suffix = "_msvc")

    support_parse_showincludes = _is_support_parse_showincludes(repository_ctx, build_tools["CL"], env)
    if not support_parse_showincludes:
        auto_configure_warning("""
Header pruning has been disabled since Bazel failed to recognize the output of /showIncludes.
This can result in unnecessary recompilation.
Fix this by installing the English language pack for the Visual Studio installation at {} and run 'bazel sync --configure'.""".format(vc_path))

    msvc_vars = {
        "%{msvc_env_tmp_" + target_arch + "}": escaped_tmp_dir,
        "%{msvc_env_include_" + target_arch + "}": escaped_include_paths,
        "%{msvc_cxx_builtin_include_directories_" + target_arch + "}": "        " + ",\n        ".join(escaped_cxx_include_directories),
        "%{msvc_env_path_" + target_arch + "}": escape_string(env["PATH"]),
        "%{msvc_env_lib_" + target_arch + "}": escape_string(env["LIB"]),
        "%{msvc_cl_path_" + target_arch + "}": build_tools["CL"],
        "%{msvc_ml_path_" + target_arch + "}": build_tools.get("ML", "msvc_arm_toolchain_does_not_support_ml"),
        "%{msvc_link_path_" + target_arch + "}": build_tools["LINK"],
        "%{msvc_lib_path_" + target_arch + "}": build_tools["LIB"],
        "%{msvc_dumpbin_path_" + target_arch + "}": build_tools["DUMPBIN"],
        "%{msvc_parse_showincludes_" + target_arch + "}": repr(support_parse_showincludes),
        "%{dbg_mode_debug_flag_" + target_arch + "}": "/DEBUG:FULL" if support_debug_fastlink else "/DEBUG",
        "%{fastbuild_mode_debug_flag_" + target_arch + "}": "/DEBUG:FASTLINK" if support_debug_fastlink else "/DEBUG",
    }
    return msvc_vars

def _get_clang_cl_vars(repository_ctx, paths, msvc_vars, target_arch):
    """Get the variables we need to populate the clang-cl toolchains."""
    llvm_path = find_llvm_path(repository_ctx)
    error_script = None
    if msvc_vars["%{msvc_cl_path_" + target_arch + "}"] == "vc_installation_error_{}.bat".format(target_arch):
        error_script = "vc_installation_error_{}.bat".format(target_arch)
    elif not llvm_path:
        repository_ctx.template(
            "clang_installation_error.bat",
            paths["@rules_cc//cc/private/toolchain:clang_installation_error.bat.tpl"],
            {"%{clang_error_message}": ""},
        )
        error_script = "clang_installation_error.bat"
    else:
        missing_tools = _find_missing_llvm_tools(repository_ctx, llvm_path)
        if missing_tools:
            message = "\r\n".join([
                "echo. 1>&2",
                "echo LLVM/Clang seems to be installed at %s 1>&2" % llvm_path,
                "echo But Bazel can't find the following tools: 1>&2",
                "echo     %s 1>&2" % ", ".join(missing_tools),
                "echo. 1>&2",
            ])
            repository_ctx.template(
                "clang_installation_error.bat",
                paths["@rules_cc//cc/private/toolchain:clang_installation_error.bat.tpl"],
                {"%{clang_error_message}": message},
            )
            error_script = "clang_installation_error.bat"

    if error_script:
        write_builtin_include_directory_paths(repository_ctx, "clang-cl", [], file_suffix = "_clangcl")
        clang_cl_vars = {
            "%{clang_cl_env_tmp_" + target_arch + "}": "clang_cl_not_found",
            "%{clang_cl_env_path_" + target_arch + "}": "clang_cl_not_found",
            "%{clang_cl_env_include_" + target_arch + "}": "clang_cl_not_found",
            "%{clang_cl_env_lib_" + target_arch + "}": "clang_cl_not_found",
            "%{clang_cl_cl_path_" + target_arch + "}": error_script,
            "%{clang_cl_link_path_" + target_arch + "}": error_script,
            "%{clang_cl_lib_path_" + target_arch + "}": error_script,
            "%{clang_cl_ml_path_" + target_arch + "}": error_script,
            "%{clang_cl_dbg_mode_debug_flag_" + target_arch + "}": "/DEBUG",
            "%{clang_cl_fastbuild_mode_debug_flag_" + target_arch + "}": "/DEBUG",
            "%{clang_cl_cxx_builtin_include_directories_" + target_arch + "}": "",
            "%{clang_cl_parse_showincludes_" + target_arch + "}": repr(False),
        }
        return clang_cl_vars

    clang_cl_path = find_llvm_tool(repository_ctx, llvm_path, "clang-cl.exe")
    lld_link_path = find_llvm_tool(repository_ctx, llvm_path, "lld-link.exe")
    llvm_lib_path = find_llvm_tool(repository_ctx, llvm_path, "llvm-lib.exe")

    clang_version = _get_clang_version(repository_ctx, clang_cl_path)
    clang_dir = _get_clang_dir(repository_ctx, llvm_path, clang_version)
    clang_include_path = (clang_dir + "\\include").replace("\\", "\\\\")
    clang_lib_path = (clang_dir + "\\lib\\windows").replace("\\", "\\\\")

    clang_cl_include_directories = msvc_vars["%{msvc_cxx_builtin_include_directories_" + target_arch + "}"] + (",\n        \"%s\"" % clang_include_path)
    write_builtin_include_directory_paths(repository_ctx, "clang-cl", [clang_cl_include_directories], file_suffix = "_clangcl")
    clang_cl_vars = {
        "%{clang_cl_env_tmp_" + target_arch + "}": msvc_vars["%{msvc_env_tmp_" + target_arch + "}"],
        "%{clang_cl_env_path_" + target_arch + "}": msvc_vars["%{msvc_env_path_" + target_arch + "}"],
        "%{clang_cl_env_include_" + target_arch + "}": msvc_vars["%{msvc_env_include_" + target_arch + "}"] + ";" + clang_include_path,
        "%{clang_cl_env_lib_" + target_arch + "}": msvc_vars["%{msvc_env_lib_" + target_arch + "}"] + ";" + clang_lib_path,
        "%{clang_cl_cxx_builtin_include_directories_" + target_arch + "}": clang_cl_include_directories,
        "%{clang_cl_cl_path_" + target_arch + "}": clang_cl_path,
        "%{clang_cl_link_path_" + target_arch + "}": lld_link_path,
        "%{clang_cl_lib_path_" + target_arch + "}": llvm_lib_path,
        "%{clang_cl_ml_path_" + target_arch + "}": clang_cl_path,
        # LLVM's lld-link.exe doesn't support /DEBUG:FASTLINK.
        "%{clang_cl_dbg_mode_debug_flag_" + target_arch + "}": "/DEBUG",
        "%{clang_cl_fastbuild_mode_debug_flag_" + target_arch + "}": "/DEBUG",
        # clang-cl always emits the English language version of the /showIncludes prefix.
        "%{clang_cl_parse_showincludes_" + target_arch + "}": repr(True),
    }
    return clang_cl_vars

def _get_msvc_deps_scanner_vars(repository_ctx, paths, template_vars, target_arch = "x64"):
    repository_ctx.template(
        "msvc_deps_scanner_wrapper_" + target_arch + ".bat",
        paths["@rules_cc//cc/private/toolchain:msvc_deps_scanner_wrapper.bat.tpl"],
        {
            "%{cc}": template_vars["%{msvc_cl_path_" + target_arch + "}"],
        },
    )

    return {
        "%{msvc_deps_scanner_wrapper_path_" + target_arch + "}": "msvc_deps_scanner_wrapper_" + target_arch + ".bat",
    }

def configure_windows_toolchain(repository_ctx):
    """Configure C++ toolchain on Windows.

    Args:
        repository_ctx: The repository context.
    """
    paths = resolve_labels(repository_ctx, [
        "@rules_cc//cc/private/toolchain:BUILD.windows.tpl",
        "@rules_cc//cc/private/toolchain:windows_cc_toolchain_config.bzl",
        "@rules_cc//cc/private/toolchain:armeabi_cc_toolchain_config.bzl",
        "@rules_cc//cc/private/toolchain:vc_installation_error.bat.tpl",
        "@rules_cc//cc/private/toolchain:msys_gcc_installation_error.bat",
        "@rules_cc//cc/private/toolchain:clang_installation_error.bat.tpl",
        "@rules_cc//cc/private/toolchain:msvc_deps_scanner_wrapper.bat.tpl",
    ])

    repository_ctx.symlink(
        paths["@rules_cc//cc/private/toolchain:windows_cc_toolchain_config.bzl"],
        "windows_cc_toolchain_config.bzl",
    )
    repository_ctx.symlink(
        paths["@rules_cc//cc/private/toolchain:armeabi_cc_toolchain_config.bzl"],
        "armeabi_cc_toolchain_config.bzl",
    )
    repository_ctx.symlink(
        paths["@rules_cc//cc/private/toolchain:msys_gcc_installation_error.bat"],
        "msys_gcc_installation_error.bat",
    )

    template_vars = dict()
    msvc_vars_x64 = _get_msvc_vars(repository_ctx, paths, "x64")
    template_vars.update(msvc_vars_x64)
    template_vars.update(_get_clang_cl_vars(repository_ctx, paths, msvc_vars_x64, "x64"))
    template_vars.update(_get_msys_mingw_vars(repository_ctx))
    template_vars.update(_get_msvc_vars(repository_ctx, paths, "x86", msvc_vars_x64))
    template_vars.update(_get_msvc_vars(repository_ctx, paths, "arm", msvc_vars_x64))
    msvc_vars_arm64 = _get_msvc_vars(repository_ctx, paths, "arm64", msvc_vars_x64)
    template_vars.update(msvc_vars_arm64)
    template_vars.update(_get_clang_cl_vars(repository_ctx, paths, msvc_vars_arm64, "arm64"))

    template_vars.update(_get_msvc_deps_scanner_vars(repository_ctx, paths, template_vars, "x64"))
    template_vars.update(_get_msvc_deps_scanner_vars(repository_ctx, paths, template_vars, "x86"))
    template_vars.update(_get_msvc_deps_scanner_vars(repository_ctx, paths, template_vars, "arm"))
    template_vars.update(_get_msvc_deps_scanner_vars(repository_ctx, paths, template_vars, "arm64"))
    repository_ctx.template(
        "BUILD",
        paths["@rules_cc//cc/private/toolchain:BUILD.windows.tpl"],
        template_vars,
    )