[1/5] support C++20 Modules, add module_interfaces attr

src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java

@@ -269,6 +269,7 @@ public CcCompilationContext getCcCompilationContext() {
   private final List<PathFragment> additionalExportedHeaders = new ArrayList<>();
   private final List<CppModuleMap> additionalCppModuleMaps = new ArrayList<>();
   private final LinkedHashMap<Artifact, CppSource> compilationUnitSources = new LinkedHashMap<>();
+  private final LinkedHashMap<Artifact, CppSource> moduleInterfaceSources = new LinkedHashMap<>();
   private ImmutableList<String> copts = ImmutableList.of();
   private CoptsFilter coptsFilter = CoptsFilter.alwaysPasses();
   private final Set<String> defines = new LinkedHashSet<>();
@@ -518,6 +519,27 @@ public CcCompilationHelper addSources(Artifact... sources) {
     return addSources(Arrays.asList(sources));
   }
 
+  @CanIgnoreReturnValue
+  public CcCompilationHelper addModuleInterfaceSources(Collection<Artifact> sources) {
+    for (Artifact source : sources) {
+      addModuleInterfaceSource(source, label);
+    }
+    return this;
+  }
+
+  @CanIgnoreReturnValue
+  public CcCompilationHelper addModuleInterfaceSources(Iterable<Pair<Artifact, Label>> sources) {
+    for (Pair<Artifact, Label> source : sources) {
+      addModuleInterfaceSource(source.first, source.second);
+    }
+    return this;
+  }
+
+  private void addModuleInterfaceSource(Artifact source, Label label) {
+    Preconditions.checkNotNull(featureConfiguration);
+    moduleInterfaceSources.put(source, CppSource.create(source, label, CppSource.Type.SOURCE));
+  }
+
   /** Add the corresponding files as non-header, non-source input files. */
   @CanIgnoreReturnValue
   public CcCompilationHelper addAdditionalInputs(Collection<Artifact> inputs) {

src/main/java/com/google/devtools/build/lib/rules/cpp/CcModule.java

@@ -2055,6 +2055,7 @@ public Tuple compile(
       Object purposeObject,
       Object coptsFilterObject,
       Object separateModuleHeadersObject,
+      Sequence<?> moduleInterfacesUnchecked, // <Artifact> expected
       Object nonCompilationAdditionalInputsObject,
       StarlarkThread thread)
       throws EvalException, InterruptedException {
@@ -2143,23 +2144,28 @@ public Tuple compile(
                 configuration.getFragment(CppConfiguration.class)));
     boolean tuple =
         (!sourcesUnchecked.isEmpty() && sourcesUnchecked.get(0) instanceof Tuple)
+            || (!moduleInterfacesUnchecked.isEmpty() && moduleInterfacesUnchecked.get(0) instanceof Tuple)
             || (!publicHeadersUnchecked.isEmpty() && publicHeadersUnchecked.get(0) instanceof Tuple)
             || (!privateHeadersUnchecked.isEmpty()
                 && privateHeadersUnchecked.get(0) instanceof Tuple);
     if (tuple) {
       ImmutableList<Pair<Artifact, Label>> sources = convertSequenceTupleToPair(sourcesUnchecked);
+      ImmutableList<Pair<Artifact, Label>> moduleInterfaces = convertSequenceTupleToPair(moduleInterfacesUnchecked);
       ImmutableList<Pair<Artifact, Label>> publicHeaders =
           convertSequenceTupleToPair(publicHeadersUnchecked);
       ImmutableList<Pair<Artifact, Label>> privateHeaders =
           convertSequenceTupleToPair(privateHeadersUnchecked);
-      helper.addPublicHeaders(publicHeaders).addPrivateHeaders(privateHeaders).addSources(sources);
+      helper.addPublicHeaders(publicHeaders).addPrivateHeaders(privateHeaders).addSources(sources)
+              .addModuleInterfaceSources(moduleInterfaces);
     } else {
       List<Artifact> sources = Sequence.cast(sourcesUnchecked, Artifact.class, "srcs");
+      List<Artifact> moduleInterfaces = Sequence.cast(moduleInterfacesUnchecked, Artifact.class, "module_interfaces");
       List<Artifact> publicHeaders =
           Sequence.cast(publicHeadersUnchecked, Artifact.class, "public_hdrs");
       List<Artifact> privateHeaders =
           Sequence.cast(privateHeadersUnchecked, Artifact.class, "private_hdrs");
-      helper.addPublicHeaders(publicHeaders).addPrivateHeaders(privateHeaders).addSources(sources);
+      helper.addPublicHeaders(publicHeaders).addPrivateHeaders(privateHeaders).addSources(sources)
+              .addModuleInterfaceSources(moduleInterfaces);
     }
 
     List<String> includes =

src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java

@@ -886,10 +886,24 @@ public boolean experimentalCcImplementationDepsForStarlark(StarlarkThread thread
     return experimentalCcImplementationDeps();
   }
 
+  @StarlarkMethod(
+      name = "experimental_cpp20_modules",
+      documented = false,
+      useStarlarkThread = true)
+  public boolean experimentalCpp20ModulesForStarlark(StarlarkThread thread)
+      throws EvalException {
+    CcModule.checkPrivateStarlarkificationAllowlist(thread);
+    return experimentalCpp20Modules();
+  }
+
   public boolean experimentalCcImplementationDeps() {
     return cppOptions.experimentalCcImplementationDeps;
   }
 
+  public boolean experimentalCpp20Modules() {
+    return cppOptions.experimentalCpp20Modules;
+  }
+
   public boolean getExperimentalCppCompileResourcesEstimation() {
     return cppOptions.experimentalCppCompileResourcesEstimation;
   }

src/main/java/com/google/devtools/build/lib/rules/cpp/CppOptions.java

@@ -1038,6 +1038,24 @@ public Label getMemProfProfileLabel() {
       help = "If enabled, cc_library targets can use attribute `implementation_deps`.")
   public boolean experimentalCcImplementationDeps;
 
+  @Option(
+      name = "experimental_cpp20_modules",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = {
+        OptionEffectTag.LOADING_AND_ANALYSIS,
+        OptionEffectTag.EXECUTION,
+        OptionEffectTag.CHANGES_INPUTS
+      },
+      metadataTags = {OptionMetadataTag.EXPERIMENTAL},
+      help =
+          "Enables experimental C++20 modules support. "
+              + "Use it with `module_interfaces` attribute on `cc_binary` and `cc_library`."
+              + "While the support is behind the experimental flag, "
+              + "there are no guarantees about incompatible changes to it or even keeping the support in the future. "
+              + "Consider those risks when using it.")
+  public boolean experimentalCpp20Modules;
+
   @Option(
       name = "experimental_link_static_libraries_once",
       defaultValue = "true",

src/main/java/com/google/devtools/build/lib/rules/cpp/CppRuleClasses.java

@@ -107,6 +107,11 @@ public static ToolchainTypeRequirement ccToolchainTypeRequirement(RuleDefinition
    */
   public static final String MODULE_MAPS = "module_maps";
 
+  /**
+   * A string constant for the cpp20_modules feature.
+   */
+  public static final String CPP20_MODULES = "cpp20_modules";
+
   /**
    * A string constant for the random_seed feature. This is used by gcc and Clangfor the
    * randomization of symbol names that are in the anonymous namespace but have external linkage.

src/main/java/com/google/devtools/build/lib/starlarkbuildapi/cpp/CcModuleApi.java

@@ -360,6 +360,14 @@ default void compilerFlagExists() {}
             named = true,
             allowedTypes = {@ParamType(type = Sequence.class)},
             defaultValue = "unbound"),
+        @Param(
+            name = "module_interfaces",
+            doc =
+                "The list of module interfaces source files to be compiled."
+                    + "Note: this is an experimental feature, only enabled with --experimental_cpp20_modules",
+            positional = false,
+            named = true,
+            defaultValue = "unbound"),
         @Param(
             name = "non_compilation_additional_inputs",
             positional = false,
@@ -405,6 +413,7 @@ Tuple compile(
       Object purposeObject,
       Object coptsFilterObject,
       Object separateModuleHeadersObject,
+      Sequence<?> moduleInterfacesUnchecked, // <Artifact> expected
       Object nonCompilationAdditionalInputsObject,
       StarlarkThread thread)
       throws EvalException, InterruptedException;

src/main/starlark/builtins_bzl/common/builtin_exec_platforms.bzl

@@ -278,6 +278,7 @@ bazel_fragments["CppOptions"] = fragment(
         "//command_line_option:target libcTop label",
         "//command_line_option:experimental_link_static_libraries_once",
         "//command_line_option:experimental_cc_implementation_deps",
+        "//command_line_option:experimental_cpp20_modules",
         "//command_line_option:start_end_lib",
         "//command_line_option:experimental_inmemory_dotd_files",
         "//command_line_option:incompatible_disable_legacy_cc_provider",

src/main/starlark/builtins_bzl/common/cc/attrs.bzl

@@ -84,6 +84,23 @@ using the C/C++ compiler.
 </p>
 """,
     ),
+    "module_interfaces": attr.label_list(
+        allow_files = True,
+        doc = """
+The list of files are regarded as C++20 Modules Interface.
+
+<p>
+C++ Standard has no restriction about module interface file extension
+<ul>
+<li>Clang use cppm </li>
+<li>GCC can use any source file extension </li>
+<li>MSVC use ixx </li>
+</ul>
+</p>
+<p>The use is guarded by the flag
+<code>--experimental_cpp20_modules</code>.</p>
+        """,
+    ),
     "data": attr.label_list(
         allow_files = True,
         flags = ["SKIP_CONSTRAINTS_OVERRIDE"],

src/main/starlark/builtins_bzl/common/cc/cc_binary.bzl

@@ -486,6 +486,9 @@ def cc_binary_impl(ctx, additional_linkopts, force_linkstatic = False):
         requested_features = features,
         unsupported_features = disabled_features,
     )
+
+    cc_helper.check_cpp20_modules(ctx, feature_configuration)
+
     all_deps = ctx.attr.deps + semantics.get_cc_runtimes(ctx, _is_link_shared(ctx))
     compilation_context_deps = [dep[CcInfo].compilation_context for dep in all_deps if CcInfo in dep]
 
@@ -507,6 +510,7 @@ def cc_binary_impl(ctx, additional_linkopts, force_linkstatic = False):
         public_hdrs = cc_helper.get_public_hdrs(ctx),
         copts_filter = cc_helper.copts_filter(ctx, additional_make_variable_substitutions),
         srcs = cc_helper.get_srcs(ctx),
+        module_interfaces = cc_helper.get_cpp20module_interfaces(ctx),
         compilation_contexts = compilation_context_deps,
         code_coverage_enabled = cc_helper.is_code_coverage_enabled(ctx = ctx),
     )

src/main/starlark/builtins_bzl/common/cc/cc_common.bzl

@@ -687,6 +687,7 @@ def _compile(
         purpose = _UNBOUND,
         copts_filter = _UNBOUND,
         separate_module_headers = _UNBOUND,
+        module_interfaces = _UNBOUND,
         non_compilation_additional_inputs = _UNBOUND):
     if module_map != _UNBOUND or \
        additional_module_maps != _UNBOUND or \
@@ -699,6 +700,7 @@ def _compile(
        implementation_compilation_contexts != _UNBOUND or \
        copts_filter != _UNBOUND or \
        separate_module_headers != _UNBOUND or \
+       module_interfaces != _UNBOUND or \
        non_compilation_additional_inputs != _UNBOUND:
         cc_common_internal.check_private_api(allowlist = _PRIVATE_STARLARKIFICATION_ALLOWLIST)
 
@@ -724,10 +726,12 @@ def _compile(
         copts_filter = None
     if separate_module_headers == _UNBOUND:
         separate_module_headers = []
+    if module_interfaces == _UNBOUND:
+        module_interfaces = []
     if non_compilation_additional_inputs == _UNBOUND:
         non_compilation_additional_inputs = []
 
-    has_tuple = _check_all_sources_contain_tuples_or_none_of_them([srcs, private_hdrs, public_hdrs])
+    has_tuple = _check_all_sources_contain_tuples_or_none_of_them([srcs, module_interfaces, private_hdrs, public_hdrs])
     if has_tuple:
         cc_common_internal.check_private_api(allowlist = _PRIVATE_STARLARKIFICATION_ALLOWLIST)
 
@@ -737,6 +741,7 @@ def _compile(
         cc_toolchain = cc_toolchain,
         name = name,
         srcs = srcs,
+        module_interfaces = module_interfaces,
         public_hdrs = public_hdrs,
         private_hdrs = private_hdrs,
         textual_hdrs = textual_hdrs,

src/main/starlark/builtins_bzl/common/cc/cc_helper.bzl

@@ -944,26 +944,37 @@ def _map_to_list(m):
         result.append((k, v))
     return result
 
-# Returns a list of (Artifact, Label) tuples. Each tuple represents an input source
-# file and the label of the rule that generates it (or the label of the source file itself if it
-# is an input file).
-def _get_srcs(ctx):
-    if not hasattr(ctx.attr, "srcs"):
-        return []
+def _calculate_artifact_label_map(attr_list, attr_name):
+    """
+    Converts a label_list attribute into a list of (Artifact, Label) tuples.
 
-    # "srcs" attribute is a LABEL_LIST in cc_rules, which might also contain files.
+    Each tuple represents an input source file and the label of the rule that generates it
+    (or the label of the source file itself if it is an input file).
+    """
     artifact_label_map = {}
-    for src in ctx.attr.srcs:
-        if DefaultInfo in src:
-            for artifact in src[DefaultInfo].files.to_list():
+    for attr in attr_list:
+        if DefaultInfo in attr:
+            for artifact in attr[DefaultInfo].files.to_list():
                 if "." + artifact.extension not in CC_HEADER:
                     old_label = artifact_label_map.get(artifact, None)
-                    artifact_label_map[artifact] = src.label
-                    if old_label != None and not _are_labels_equal(old_label, src.label) and "." + artifact.extension in CC_AND_OBJC:
+                    artifact_label_map[artifact] = attr.label
+                    if old_label != None and not _are_labels_equal(old_label, attr.label) and ("." + artifact.extension in CC_AND_OBJC or attr_name == "module_interfaces"):
                         fail(
-                            "Artifact '{}' is duplicated (through '{}' and '{}')".format(artifact, old_label, src),
-                            attr = "srcs",
+                            "Artifact '{}' is duplicated (through '{}' and '{}')".format(artifact, old_label, attr),
+                            attr = attr_name,
                         )
+    return artifact_label_map
+
+def _get_srcs(ctx):
+    if not hasattr(ctx.attr, "srcs"):
+        return []
+    artifact_label_map = _calculate_artifact_label_map(ctx.attr.srcs, "srcs")
+    return _map_to_list(artifact_label_map)
+
+def _get_cpp20module_interfaces(ctx):
+    if not hasattr(ctx.attr, "module_interfaces"):
+        return []
+    artifact_label_map = _calculate_artifact_label_map(ctx.attr.module_interfaces, "module_interfaces")
     return _map_to_list(artifact_label_map)
 
 # Returns a list of (Artifact, Label) tuples. Each tuple represents an input source
@@ -1176,6 +1187,17 @@ def _should_use_pic(ctx, cc_toolchain, feature_configuration):
         )
     )
 
+def _check_cpp20_modules(ctx, feature_configuration):
+    if len(ctx.files.module_interfaces) == 0:
+        return
+    if not ctx.fragments.cpp.experimental_cpp20_modules():
+        fail("requires --experimental_cpp20_modules", attr = "module_interfaces")
+    if not cc_common.is_enabled(
+        feature_configuration = feature_configuration,
+        feature_name = "cpp20_modules",
+    ):
+        fail("to use C++20 Modules, the feature cpp20_modules must be enabled")
+
 cc_helper = struct(
     CPP_TOOLCHAIN_TYPE = _CPP_TOOLCHAIN_TYPE,
     merge_cc_debug_contexts = _merge_cc_debug_contexts,
@@ -1225,6 +1247,7 @@ cc_helper = struct(
     get_local_defines_for_runfiles_lookup = _get_local_defines_for_runfiles_lookup,
     are_labels_equal = _are_labels_equal,
     get_srcs = _get_srcs,
+    get_cpp20module_interfaces = _get_cpp20module_interfaces,
     get_private_hdrs = _get_private_hdrs,
     get_public_hdrs = _get_public_hdrs,
     report_invalid_options = _report_invalid_options,
@@ -1242,4 +1265,5 @@ cc_helper = struct(
     package_source_root = _package_source_root,
     tokenize = _tokenize,
     should_use_pic = _should_use_pic,
+    check_cpp20_modules = _check_cpp20_modules,
 )

src/main/starlark/builtins_bzl/common/cc/cc_library.bzl

@@ -37,6 +37,8 @@ def _cc_library_impl(ctx):
         unsupported_features = ctx.disabled_features,
     )
 
+    cc_helper.check_cpp20_modules(ctx, feature_configuration)
+
     precompiled_files = cc_helper.build_precompiled_files(ctx = ctx)
 
     semantics.validate_attributes(ctx = ctx)
@@ -63,6 +65,7 @@ def _cc_library_impl(ctx):
         copts_filter = cc_helper.copts_filter(ctx, additional_make_variable_substitutions),
         purpose = "cc_library-compile",
         srcs = cc_helper.get_srcs(ctx),
+        module_interfaces = cc_helper.get_cpp20module_interfaces(ctx),
         private_hdrs = cc_helper.get_private_hdrs(ctx),
         public_hdrs = cc_helper.get_public_hdrs(ctx),
         code_coverage_enabled = cc_helper.is_code_coverage_enabled(ctx),

src/test/java/com/google/devtools/build/lib/analysis/mock/cc_toolchain_config.bzl

@@ -32,6 +32,7 @@ load(
 )
 
 _FEATURE_NAMES = struct(
+    cpp20_modules = "cpp20_modules",
     generate_pdb_file = "generate_pdb_file",
     no_legacy_features = "no_legacy_features",
     do_not_split_linking_cmdline = "do_not_split_linking_cmdline",
@@ -120,6 +121,11 @@ _FEATURE_NAMES = struct(
     generate_linkmap = "generate_linkmap",
 )
 
+_cpp20_modules_feature = feature(
+    name = _FEATURE_NAMES.cpp20_modules,
+    enabled = False,
+)
+
 _no_copts_tokenization_feature = feature(name = _FEATURE_NAMES.no_copts_tokenization)
 
 _disable_pbh_feature = feature(name = _FEATURE_NAMES.disable_pbh)
@@ -1330,6 +1336,7 @@ _generate_linkmap_feature = feature(
 )
 
 _feature_name_to_feature = {
+    _FEATURE_NAMES.cpp20_modules: _cpp20_modules_feature,
     _FEATURE_NAMES.no_legacy_features: _no_legacy_features_feature,
     _FEATURE_NAMES.do_not_split_linking_cmdline: _do_not_split_linking_cmdline_feature,
     _FEATURE_NAMES.supports_dynamic_linker: _supports_dynamic_linker_feature,

src/test/java/com/google/devtools/build/lib/packages/util/mock/osx_cc_toolchain_config.bzl

@@ -7176,7 +7176,13 @@ def _impl(ctx):
     else:
         include_system_dirs_feature = None
 
+    cpp20_modules_feature = feature(
+        name = "cpp20_modules",
+        enabled = False,
+    )
+
     features = [
+        cpp20_modules_feature,
         default_compile_flags_feature,
         default_link_flags_feature,
         no_legacy_features_feature,