bindgen: Pass -resource-dir Clang flag to bindgen-cli. (#3591)

For some cc_toolchain configurations, this is required to find the
builtin
headers.

So far, the bindgen rules had assumed that the builtin headers can be
found through `cc_toolchain.built_in_include_directories`. This is,
however, not guaranteed to be the case; indeed,
`built_in_include_directories` is not really intended for finding
builtin headers but merely for filtering out diagnostics in builtin
headers.

Clang itself finds the resource directory relative to its own binary,
and then finds the builtin headers in the "include" subdirectory of the
resource directory. bindgen-cli may, however, be located in a different
directory than Clang, so we pass a `-resource-dir` flag on the command
line.

Author: martinboehme

extensions/bindgen/private/bindgen.bzl

@@ -14,6 +14,7 @@
 
 """Rust Bindgen rules"""
 
+load("@bazel_skylib//lib:paths.bzl", "paths")
 load(
     "@bazel_tools//tools/build_defs/cc:action_names.bzl",
     "CPP_COMPILE_ACTION_NAME",
@@ -187,6 +188,23 @@ def _generate_cc_link_build_info(ctx, cc_lib):
         rustc_env = None,
     )
 
+def _get_resource_dir(cc_toolchain):
+    """Returns the resource directory for the given cc_toolchain."""
+
+    # We use a bit of a hack to find the resource directory: We know that the builtin header
+    # stdbool.h (chosen relatively arbitrarily) needs to appear in `cc_toolchain.all_files`, so we
+    # search for it and use the directory above the include directory as the resource directory.
+    # This isn't ideal, but [email protected] believes there is no more direct way of doing this.
+    for f in cc_toolchain.all_files.to_list():
+        if f.basename == "stdbool.h":
+            path = f.path
+            for _ in range(path.count("/") + 1):
+                if paths.basename(path) == "include":
+                    return paths.dirname(path)
+                path = paths.dirname(path)
+
+    return None
+
 def _rust_bindgen_impl(ctx):
     # nb. We can't grab the cc_library`s direct headers, so a header must be provided.
     cc_lib = ctx.attr.cc_lib
@@ -254,6 +272,10 @@ def _rust_bindgen_impl(ctx):
     # Configure Clang Arguments
     args.add("--")
 
+    resource_dir = _get_resource_dir(cc_toolchain)
+    if resource_dir:
+        args.add("-resource-dir=%s" % resource_dir)
+
     compile_variables = cc_common.create_compile_variables(
         cc_toolchain = cc_toolchain,
         feature_configuration = feature_configuration,

extensions/bindgen/test/bindgen_test.bzl

@@ -1,9 +1,64 @@
 """Analysis test for for rust_bindgen_library rule."""
 
-load("@rules_cc//cc:defs.bzl", "cc_library")
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
+load("@rules_cc//cc:defs.bzl", "cc_library", "cc_toolchain")
+load("@rules_cc//cc/common:cc_common.bzl", "cc_common")
 load("@rules_rust//rust:defs.bzl", "rust_binary")
 load("@rules_rust_bindgen//:defs.bzl", "rust_bindgen_library")
 load("@rules_testing//lib:analysis_test.bzl", "analysis_test", "test_suite")
+load("@rules_testing//lib:truth.bzl", "matching")
+
+def _fake_cc_toolchain_config_impl(ctx):
+    return cc_common.create_cc_toolchain_config_info(
+        ctx = ctx,
+        toolchain_identifier = "fake-toolchain",
+        host_system_name = "unknown",
+        target_system_name = "unknown",
+        target_cpu = "unknown",
+        target_libc = "unknown",
+        compiler = "unknown",
+        abi_version = "unknown",
+        abi_libc_version = "unknown",
+    )
+
+_fake_cc_toolchain_config = rule(
+    implementation = _fake_cc_toolchain_config_impl,
+    attrs = {},
+    provides = [CcToolchainConfigInfo],
+)
+
+def _fake_cc_toolchain(name):
+    _fake_cc_toolchain_config(name = name + "_toolchain_config")
+
+    empty_filegroup = name + "_empty_filegroup"
+    native.filegroup(name = empty_filegroup)
+
+    stdbool_file = name + "_stdbool"
+    write_file(
+        name = stdbool_file,
+        content = [],
+        out = "my/resource/dir/include/stdbool.h",
+    )
+
+    all_files = name + "_all_files"
+    native.filegroup(name = all_files, srcs = [stdbool_file])
+
+    cc_toolchain(
+        name = name + "_cc_toolchain",
+        toolchain_config = name + "_toolchain_config",
+        all_files = all_files,
+        dwp_files = empty_filegroup,
+        compiler_files = empty_filegroup,
+        linker_files = empty_filegroup,
+        objcopy_files = empty_filegroup,
+        strip_files = empty_filegroup,
+    )
+
+    native.toolchain(
+        name = name,
+        toolchain = name + "_cc_toolchain",
+        toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+    )
 
 def _test_cc_linkopt_impl(env, target):
     # Assert
@@ -100,12 +155,49 @@ def _test_cc_lib_object_merging_disabled(name):
         impl = _test_cc_lib_object_merging_disabled_impl,
     )
 
+def _test_resource_dir_impl(env, target):
+    env.expect.that_int(len(target.actions)).is_greater_than(0)
+    env.expect.that_action(target.actions[0]).mnemonic().contains("RustBindgen")
+    env.expect.that_action(target.actions[0]).argv().contains_predicate(
+        matching.all(
+            matching.str_startswith("-resource-dir="),
+            matching.str_endswith("my/resource/dir"),
+        ),
+    )
+
+def _test_resource_dir(name):
+    _fake_cc_toolchain(name + "_toolchain")
+
+    cc_library(
+        name = name + "_cc",
+        hdrs = ["simple.h"],
+        srcs = ["simple.cc"],
+    )
+
+    rust_bindgen_library(
+        name = name + "_rust_bindgen",
+        cc_lib = name + "_cc",
+        header = "simple.h",
+        tags = ["manual"],
+        edition = "2021",
+    )
+
+    analysis_test(
+        name = name,
+        target = name + "_rust_bindgen__bindgen",
+        impl = _test_resource_dir_impl,
+        config_settings = {
+            "//command_line_option:extra_toolchains": [str(native.package_relative_label(name + "_toolchain"))],
+        },
+    )
+
 def bindgen_test_suite(name):
     test_suite(
         name = name,
         tests = [
             _test_cc_linkopt,
             _test_cc_lib_object_merging,
             _test_cc_lib_object_merging_disabled,
+            _test_resource_dir,
         ],
     )