Add support for parse_headers

This feature enables bazel to validate "C++" header files through clang.
Without this you only get this type of validating when you actually
include the library elsewhere.

Similar to layering_check we have to validate this outside of normal
bazel because we are expecting build failures and need to parse the logs

This mirrors bazelbuild/bazel#21560

.bazelci/presubmit.yml

@@ -32,13 +32,14 @@ tasks:
     bazel: latest
     <<: *common
 
-  macos_latest_layering_check:
-    name: "Current layering_check"
+  macos_latest_shell_scripts:
+    name: "Current layering_check and header parsing"
     platform: macos_arm64
     xcode_version: "15.2"
     bazel: latest
     shell_commands:
       - test/shell/layering_check_test.sh
+      - test/shell/header_parsing_test.sh
 
   macos_last_green:
     name: "Last Green Bazel"

crosstool/BUILD.tpl

@@ -76,6 +76,7 @@ filegroup(
         linker_files = ":osx_tools_" + arch,
         objcopy_files = ":empty",
         strip_files = ":osx_tools_" + arch,
+        supports_header_parsing = 1,
         supports_param_files = 1,
         toolchain_config = arch,
         toolchain_identifier = arch,

crosstool/cc_toolchain_config.bzl

@@ -200,6 +200,21 @@ please file an issue at https://github.com/bazelbuild/apple_support/issues/new
         tools = [tool(path = "/usr/bin/strip")],
     )
 
+    header_parsing_env_feature = feature(
+        name = "header_parsing_env",
+        env_sets = [
+            env_set(
+                actions = [ACTION_NAMES.cpp_header_parsing],
+                env_entries = [
+                    env_entry(
+                        key = "HEADER_PARSING_OUTPUT",
+                        value = "%{output_file}",
+                    ),
+                ],
+            ),
+        ],
+    )
+
     cpp_header_parsing_action = action_config(
         action_name = ACTION_NAMES.cpp_header_parsing,
         implies = [
@@ -214,6 +229,23 @@ please file an issue at https://github.com/bazelbuild/apple_support/issues/new
             "compiler_input_flags",
             "compiler_output_flags",
             "unfiltered_cxx_flags",
+            "header_parsing_env",
+        ],
+        flag_sets = [
+            flag_set(
+                flag_groups = [
+                    flag_group(
+                        flags = [
+                            # Note: This treats all headers as C++ headers, which may lead to
+                            # parsing failures for C headers that are not valid C++.
+                            # For such headers, use features = ["-parse_headers"] to selectively
+                            # disable parsing.
+                            "-xc++-header",
+                            "-fsyntax-only",
+                        ],
+                    ),
+                ],
+            ),
         ],
         tools = [
             tool(
@@ -2619,6 +2651,7 @@ please file an issue at https://github.com/bazelbuild/apple_support/issues/new
         feature(name = "no_legacy_features"),
         feature(name = "only_doth_headers_in_module_maps"),
         feature(name = "opt"),
+        feature(name = "parse_headers"),
 
         # Features with more configuration
         link_libcpp_feature,
@@ -2689,6 +2722,7 @@ please file an issue at https://github.com/bazelbuild/apple_support/issues/new
         no_warn_duplicate_libraries_feature,
         layering_check_feature,
         external_include_paths_feature,
+        header_parsing_env_feature,
     ]
 
     if (ctx.attr.cpu == "darwin_x86_64" or

crosstool/wrapped_clang.cc

@@ -477,6 +477,12 @@ int main(int argc, char *argv[]) {
     return 1;
   }
 
+  const char *header_parsing_output = getenv("HEADER_PARSING_OUTPUT");
+  if (header_parsing_output != nullptr) {
+    std::ofstream output(header_parsing_output);
+    output.close();
+  }
+
   if (!postprocess) {
     return 0;
   }

test/header_parsing/BUILD

@@ -0,0 +1,40 @@
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
+
+package(features = ["parse_headers"])
+
+cc_library(
+    name = "invalid_header",
+    hdrs = ["invalid_header.h"],
+    tags = ["manual"],
+)
+
+objc_library(
+    name = "invalid_header_objc",
+    hdrs = ["invalid_header.h"],
+    tags = ["manual"],
+)
+
+cc_library(
+    name = "invalid_header_feature_disabled",
+    hdrs = ["invalid_header.h"],
+    features = ["-parse_headers"],
+)
+
+cc_library(
+    name = "valid_header",
+    hdrs = ["valid_header.h"],
+)
+
+objc_library(
+    name = "valid_header_objc",
+    hdrs = ["valid_header.h"],
+)
+
+build_test(
+    name = "test",
+    targets = [
+        ":invalid_header_feature_disabled",
+        ":valid_header",
+        ":valid_header_objc",
+    ],
+)

test/header_parsing/invalid_header.h

@@ -0,0 +1,2 @@
+// Missing include of cstdint, which defines uint8_t.
+uint8_t foo();

test/header_parsing/valid_header.h

@@ -0,0 +1,3 @@
+#include <cstdint>
+
+uint8_t foo();

test/shell/header_parsing_test.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+set -euo pipefail
+
+script_path="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$script_path"/unittest.bash
+
+bazel="${BAZEL:-bazel}"
+
+function test_good_header_parsing() {
+  "$bazel" test --process_headers_in_dependencies -- //test/header_parsing/... &>"$TEST_log"
+}
+
+function test_bad_header_parsing() {
+  ! "$bazel" test --process_headers_in_dependencies -- //test/header_parsing:invalid_header &> "$TEST_log" || fail "Expected build failure"
+  expect_log "test/header_parsing/invalid_header.h:2:1: error: unknown type name 'uint8_t'"
+}
+
+function test_bad_header_parsing_objc() {
+  ! "$bazel" test --process_headers_in_dependencies -- //test/header_parsing:invalid_header_objc &> "$TEST_log" || fail "Expected build failure"
+  expect_log "test/header_parsing/invalid_header.h:2:1: error: unknown type name 'uint8_t'"
+}
+
+run_suite "header_parsing tests"