Add layering_check support for macOS

There were 2 things with the previous implementation that needed to be improved here:

1. Apple Clang has a bug where it doesn't pass module compiler flags to the underlying -cc1 invocation, so we have to manually pass them directly to that invocation with -Xclang
2. The previous search script was too aggressive and slow for macOS. The macOS SDK has tons of files that aren't headers, and tons of symlinks pointing to other files within the SDK. This adds a fork in the script to run a version that works with Apple SDKs. The time difference on my machine is 41s->6s. 6s is still pretty long so if desired we can put this behavior behind an env var for users to opt in with.

I've added a hermetic version of this to the apple_support toolchain, but similar to the Linux setup here the modulemap file includes absolute paths.

Closes #22259.

PiperOrigin-RevId: 635735410
Change-Id: Icb3f30dd7319f147b0db54b3b42d4dc9032dc1a0

src/test/shell/bazel/bazel_layering_check_test.sh

@@ -144,11 +144,6 @@ EOF
 }
 
 function test_bazel_layering_check() {
-  if is_darwin; then
-    echo "This test doesn't run on Darwin. Skipping."
-    return
-  fi
-
   local -r clang_tool=$(which clang)
   if [[ ! -x ${clang_tool:-/usr/bin/clang_tool} ]]; then
     echo "clang not installed. Skipping test."

tools/cpp/generate_system_module_map.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 # Copyright 2020 The Bazel Authors. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -17,10 +17,19 @@ set -eu
 
 echo 'module "crosstool" [system] {'
 
-for dir in $@; do
-  find -L "${dir}" -type f 2>/dev/null | LANG=C sort | uniq | while read header; do
-    echo "  textual header \"${header}\""
+if [[ "$OSTYPE" == darwin* ]]; then
+  for dir in $@; do
+    find "$dir" -type f \( -name "*.h" -o -name "*.def" -o -path "*/c++/*" \) \
+      | LANG=C sort -u | while read -r header; do
+        echo "  textual header \"${header}\""
+      done
   done
-done
+else
+  for dir in $@; do
+    find -L "${dir}" -type f 2>/dev/null | LANG=C sort -u | while read -r header; do
+      echo "  textual header \"${header}\""
+    done
+  done
+fi
 
 echo "}"

tools/cpp/unix_cc_configure.bzl

@@ -534,7 +534,7 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
         ["/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk"],
     )
 
-    generate_modulemap = is_clang and not darwin
+    generate_modulemap = is_clang
     if generate_modulemap:
         repository_ctx.file("module.modulemap", _generate_system_module_map(
             repository_ctx,

tools/cpp/unix_cc_toolchain_config.bzl

@@ -36,7 +36,7 @@ def _target_os_version(ctx):
     xcode_config = ctx.attr._xcode_config[apple_common.XcodeVersionConfig]
     return xcode_config.minimum_os_for_platform_type(platform_type)
 
-def layering_check_features(compiler):
+def layering_check_features(compiler, is_macos):
     if compiler != "clang":
         return []
     return [
@@ -53,8 +53,10 @@ def layering_check_features(compiler):
                     ],
                     flag_groups = [
                         flag_group(
-                            flags = [
+                            # macOS requires -Xclang because of a bug in Apple Clang
+                            flags = (["-Xclang"] if is_macos else []) + [
                                 "-fmodule-name=%{module_name}",
+                            ] + (["-Xclang"] if is_macos else []) + [
                                 "-fmodule-map-file=%{module_map_file}",
                             ],
                         ),
@@ -86,7 +88,7 @@ def layering_check_features(compiler):
                         ]),
                         flag_group(
                             iterate_over = "dependent_module_map_files",
-                            flags = [
+                            flags = (["-Xclang"] if is_macos else []) + [
                                 "-fmodule-map-file=%{dependent_module_map_files}",
                             ],
                         ),
@@ -1487,7 +1489,7 @@ def _impl(ctx):
             unfiltered_compile_flags_feature,
             treat_warnings_as_errors_feature,
             archive_param_file_feature,
-        ] + layering_check_features(ctx.attr.compiler)
+        ] + layering_check_features(ctx.attr.compiler, is_macos = False)
     else:
         # macOS artifact name patterns differ from the defaults only for dynamic
         # libraries.
@@ -1528,7 +1530,7 @@ def _impl(ctx):
             treat_warnings_as_errors_feature,
             archive_param_file_feature,
             generate_linkmap_feature,
-        ]
+        ] + layering_check_features(ctx.attr.compiler, is_macos = True)
 
     parse_headers_action_configs, parse_headers_features = parse_headers_support(
         parse_headers_tool_path = ctx.attr.tool_paths.get("parse_headers"),