blob: 0c37c6a8981511238e505fa552d538d5d2fc1b5b [file] [log] [blame]
"""
This file contains logic related to enforcing public API relationships, also known as
layering checks.
See also https://maskray.me/blog/2022-09-25-layering-check-with-clang and go/layering_check
"""
# https://github.com/bazelbuild/bazel/blob/master/tools/build_defs/cc/action_names.bzl
load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "ACTION_NAMES")
# https://github.com/bazelbuild/bazel/blob/master/tools/cpp/cc_toolchain_config_lib.bzl
load(
"@bazel_tools//tools/cpp:cc_toolchain_config_lib.bzl",
"feature",
"feature_set",
"flag_group",
"flag_set",
)
def make_layering_check_features():
"""Returns a list of features which enforce "layering checks".
Layering checks catch two types of problems:
1) A cc_library using private headers from another cc_library.
2) A cc_library using public headers from a transitive dependency instead of
directly depending on that library.
This is implemented using Clang module maps, which are generated for each cc_library
as it is being built.
This implementation is very similar to the one in the default Bazel C++ toolchain
(which is not inherited by custom toolchains).
https://github.com/bazelbuild/bazel/commit/8b9f74649512ee17ac52815468bf3d7e5e71c9fa
Returns:
A list of Bazel "features", the primary one being one called "layering_check".
"""
return [
feature(
name = "use_module_maps",
enabled = False,
requires = [feature_set(features = ["module_maps"])],
flag_sets = [
flag_set(
actions = [
ACTION_NAMES.c_compile,
ACTION_NAMES.cpp_compile,
],
flag_groups = [
flag_group(
flags = [
"-fmodule-name=%{module_name}",
"-fmodule-map-file=%{module_map_file}",
],
),
],
),
],
),
# This feature name is baked into Bazel
# https://github.com/bazelbuild/bazel/blob/8f5b626acea0086be8a314d5efbf6bc6d3473cd2/src/main/java/com/google/devtools/build/lib/rules/cpp/CompileBuildVariables.java#L471
feature(name = "module_maps", enabled = True),
feature(
name = "layering_check",
# This is currently disabled by default (although we aim to enable it by default)
# because a previous build didn't support passing a flag along.
# TODO(kjlubick): enable this by default.
enabled = False,
implies = ["use_module_maps"],
flag_sets = [
flag_set(
actions = [
ACTION_NAMES.c_compile,
ACTION_NAMES.cpp_compile,
],
flag_groups = [
flag_group(flags = [
# Identify issue #1 (see docstring)
"-Wprivate-header",
# Identify issue #2
"-fmodules-strict-decluse",
]),
flag_group(
iterate_over = "dependent_module_map_files",
flags = [
"-fmodule-map-file=%{dependent_module_map_files}",
],
),
],
),
],
),
]
def generate_system_module_map(ctx, module_file, folders):
"""Generates a module map [1] for all the "system" headers in the toolchain.
The generated map looks something like:
module "crosstool" [system] {
textual header "lib/clang/15.0.1/include/__clang_cuda_builtin_vars.h"
textual header "lib/clang/15.0.1/include/__clang_cuda_cmath.h"
...
textual header "include/c++/v1/climits"
textual header "include/c++/v1/clocale"
textual header "include/c++/v1/cmath"
textual header "symlinks/xcode/MacSDK/usr/share/man/mann/zip.n"
}
Notice how all the file paths are relative to *this* directory, where
the toolchain_system_headers.modulemap. Annoyingly, Clang will silently
ignore a file that is declared if it does not actually exist on disk.
[1] https://clang.llvm.org/docs/Modules.html#module-map-language
Args:
ctx: A repository_ctx (https://bazel.build/rules/lib/repository_ctx)
module_file: The name of the modulemap file to create.
folders: List of strings corresponding to paths in the toolchain with system headers.
"""
# https://github.com/bazelbuild/bazel/blob/8f5b626acea0086be8a314d5efbf6bc6d3473cd2/tools/cpp/generate_system_module_map.sh
script_path = ctx.path(Label("@bazel_tools//tools/cpp:generate_system_module_map.sh"))
# https://bazel.build/rules/lib/repository_ctx#execute
res = ctx.execute([script_path] + folders)
if res.return_code != 0:
fail("Could not generate module map")
# https://bazel.build/rules/lib/repository_ctx#file
ctx.file(
module_file,
content = res.stdout,
executable = False,
)