Add feature detection

bazelbuild · Jun 7, 2024 · 280480b · 280480b
1 parent fd5054d
commit 280480b
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Showing 3 changed files with 23 additions and 7 deletions.
diff --git a/tools/cpp/BUILD.tpl b/tools/cpp/BUILD.tpl
@@ -113,6 +113,7 @@ cc_toolchain_config(
     coverage_compile_flags = [%{coverage_compile_flags}],
     coverage_link_flags = [%{coverage_link_flags}],
     supports_start_end_lib = %{supports_start_end_lib},
+    extra_flags_per_feature = %{extra_flags_per_feature},
 )
 
 # Android tooling requires a default toolchain for the armeabi-v7a cpu.

diff --git a/tools/cpp/unix_cc_configure.bzl b/tools/cpp/unix_cc_configure.bzl
@@ -541,6 +541,22 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
             builtin_include_directories,
             paths["@bazel_tools//tools/cpp:generate_system_module_map.sh"],
         ))
+    extra_flags_per_feature = {}
+    if is_clang:
+        # Only supported by LLVM 14 and later, but required with C++20 and
+        # layering_check as C++ modules are the default.
+        # https://github.com/llvm/llvm-project/commit/0556138624edf48621dd49a463dbe12e7101f17d
+        result = repository_ctx.execute([
+            cc,
+            "-Xclang",
+            "-fno-cxx-modules",
+            "-o",
+            "/dev/null",
+            "-c",
+            str(repository_ctx.path("tools/cpp/empty.cc")),
+        ])
+        if "-fno-cxx-modules" not in result.stderr:
+            extra_flags_per_feature["use_header_modules"] = ["-Xclang", "-fno-cxx-modules"]
 
     write_builtin_include_directory_paths(repository_ctx, cc, builtin_include_directories)
     repository_ctx.template(
@@ -696,5 +712,6 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
             "%{coverage_compile_flags}": coverage_compile_flags,
             "%{coverage_link_flags}": coverage_link_flags,
             "%{supports_start_end_lib}": "True" if gold_or_lld_linker_path else "False",
+            "%{extra_flags_per_feature}": repr(extra_flags_per_feature),
         },
     )
diff --git a/tools/cpp/unix_cc_toolchain_config.bzl b/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, is_macos):
+def layering_check_features(compiler, extra_flags_per_feature, is_macos):
     if compiler != "clang":
         return []
     return [
@@ -54,14 +54,11 @@ def layering_check_features(compiler, is_macos):
                     flag_groups = [
                         flag_group(
                             # macOS requires -Xclang because of a bug in Apple Clang
-                            # -fno-cxx-modules is necessary to avoid clang defaulting
-                            # to C++ modules with -std=c++20. The flag requires the
-                            # -Xclang prefix even on Linux.
                             flags = (["-Xclang"] if is_macos else []) + [
                                 "-fmodule-name=%{module_name}",
                             ] + (["-Xclang"] if is_macos else []) + [
                                 "-fmodule-map-file=%{module_map_file}",
-                            ] + ["-Xclang", "-fno-cxx-modules"],
+                            ] + extra_flags_per_feature.get("use_module_maps", []),
                         ),
                     ],
                 ),
@@ -1492,7 +1489,7 @@ def _impl(ctx):
             unfiltered_compile_flags_feature,
             treat_warnings_as_errors_feature,
             archive_param_file_feature,
-        ] + layering_check_features(ctx.attr.compiler, is_macos = False)
+        ] + layering_check_features(ctx.attr.compiler, ctx.attr.extra_flags_per_feature, is_macos = False)
     else:
         # macOS artifact name patterns differ from the defaults only for dynamic
         # libraries.
@@ -1533,7 +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)
+        ] + layering_check_features(ctx.attr.compiler, ctx.attr.extra_flags_per_feature, is_macos = True)
 
     parse_headers_action_configs, parse_headers_features = parse_headers_support(
         parse_headers_tool_path = ctx.attr.tool_paths.get("parse_headers"),
@@ -1586,6 +1583,7 @@ cc_toolchain_config = rule(
         "coverage_link_flags": attr.string_list(),
         "supports_start_end_lib": attr.bool(),
         "builtin_sysroot": attr.string(),
+        "extra_flags_per_feature": attr.string_list_dict(),
         "_xcode_config": attr.label(default = configuration_field(
             fragment = "apple",
             name = "xcode_config_label",