Support Using Clang Module Map to Avoid mixing #include and import pr…

cc/common/cc_helper.bzl

@@ -901,7 +901,9 @@ def _report_invalid_options(cc_toolchain, cpp_config):
         fail("The selected toolchain does not support setting --grte_top (it doesn't specify builtin_sysroot).")
 
 def _check_cpp_modules(ctx, feature_configuration):
-    if len(ctx.files.module_interfaces) == 0:
+    has_module_interfaces = len(ctx.files.module_interfaces) > 0
+    has_module_header_maps = hasattr(ctx.attr, "module_header_maps") and len(ctx.attr.module_header_maps) > 0
+    if not has_module_interfaces and not has_module_header_maps:
         return
     if not ctx.fragments.cpp.experimental_cpp_modules():
         fail("requires --experimental_cpp_modules", attr = "module_interfaces")
@@ -1016,6 +1018,28 @@ def _get_cpp_module_interfaces(ctx):
     artifact_label_map = _calculate_artifact_label_map(ctx.attr.module_interfaces, "module_interfaces")
     return _map_to_list(artifact_label_map)
 
+def _get_module_header_map_entries(ctx):
+    """Returns (module_name, map_file) tuples from module_header_maps."""
+    if not hasattr(ctx.attr, "module_header_maps"):
+        return []
+    entries = []
+    for name, map_label in ctx.attr.module_header_maps.items():
+        map_files = map_label.files.to_list()
+        if len(map_files) != 1:
+            fail(
+                "module_header_maps[%r]: label %s must provide exactly one .modulemap file, got %d" %
+                (name, map_label, len(map_files)),
+                attr = "module_header_maps",
+            )
+        map_file = map_files[0]
+        if not map_file.basename.endswith(".modulemap"):
+            fail(
+                "module_header_maps[%r]: expected a .modulemap file, got %s" % (name, map_file.basename),
+                attr = "module_header_maps",
+            )
+        entries.append((name, map_file))
+    return entries
+
 # 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).
@@ -1155,6 +1179,7 @@ cc_helper = struct(
     local_defines = _local_defines,
     get_srcs = _get_srcs,
     get_cpp_module_interfaces = _get_cpp_module_interfaces,
+    get_module_header_map_entries = _get_module_header_map_entries,
     get_private_hdrs = _get_private_hdrs,
     get_public_hdrs = _get_public_hdrs,
     is_code_coverage_enabled = _is_code_coverage_enabled,

cc/private/cc_common.bzl

@@ -489,6 +489,7 @@ def _compile(
         purpose = _UNBOUND,
         separate_module_headers = _UNBOUND,
         module_interfaces = _UNBOUND,
+        module_header_map_entries = _UNBOUND,
         non_compilation_additional_inputs = _UNBOUND):
     if module_map != _UNBOUND or \
        additional_module_maps != _UNBOUND or \
@@ -501,6 +502,7 @@ def _compile(
        implementation_compilation_contexts != _UNBOUND or \
        separate_module_headers != _UNBOUND or \
        module_interfaces != _UNBOUND or \
+       module_header_map_entries != _UNBOUND or \
        non_compilation_additional_inputs != _UNBOUND:
         _cc_internal.check_private_api(allowlist = _PRIVATE_STARLARKIFICATION_ALLOWLIST)
 
@@ -524,6 +526,8 @@ def _compile(
         separate_module_headers = []
     if module_interfaces == _UNBOUND:
         module_interfaces = []
+    if module_header_map_entries == _UNBOUND:
+        module_header_map_entries = []
     if non_compilation_additional_inputs == _UNBOUND:
         non_compilation_additional_inputs = []
 
@@ -538,6 +542,7 @@ def _compile(
         name = name,
         srcs = srcs,
         module_interfaces = module_interfaces,
+        module_header_map_entries = module_header_map_entries,
         public_hdrs = public_hdrs,
         private_hdrs = private_hdrs,
         textual_hdrs = textual_hdrs,

cc/private/compile/compile.bzl

@@ -135,6 +135,7 @@ def compile(
         purpose = None,
         separate_module_headers = [],
         module_interfaces = [],
+        module_header_map_entries = [],
         non_compilation_additional_inputs = [],
         progress_message_prefix = None):
     """Should be used for C++ compilation.
@@ -385,6 +386,7 @@ def compile(
         auxiliary_fdo_inputs = auxiliary_fdo_inputs,
         fdo_build_variables = fdo_build_variables,
         progress_message_prefix = progress_message_prefix,
+        module_header_map_entries = module_header_map_entries,
     )
 
     compilation_outputs_dict["lto_compilation_context"] = create_lto_compilation_context(
@@ -637,6 +639,77 @@ def _create_gen_modmap_action(
         toolchain = None,
     )
 
+def _create_header_map_modmap_actions(
+        *,
+        actions,
+        action_construction_context,
+        cc_toolchain,
+        configuration,
+        label,
+        use_pic,
+        module_header_map_entries,
+        modules_info_file):
+    """Creates a shared modmap for all module_header_maps on this target."""
+    if use_pic:
+        output_name_base_for_modmap = _cc_internal.get_artifact_name_for_category(
+            cc_toolchain = cc_toolchain,
+            category = artifact_category.PIC_FILE,
+            output_name = label.name,
+        )
+    else:
+        output_name_base_for_modmap = label.name
+    modmap_output_name = output_name_base_for_modmap + "_header_maps"
+    modmap_file = _get_compile_output_file(
+        action_construction_context,
+        label,
+        configuration = configuration,
+        output_name = _cc_internal.get_artifact_name_for_category(
+            cc_toolchain = cc_toolchain,
+            category = artifact_category.CPP_MODULES_MODMAP,
+            output_name = modmap_output_name,
+        ),
+    )
+    modmap_input_file = _get_compile_output_file(
+        action_construction_context,
+        label,
+        configuration = configuration,
+        output_name = _cc_internal.get_artifact_name_for_category(
+            cc_toolchain = cc_toolchain,
+            category = artifact_category.CPP_MODULES_MODMAP_INPUT,
+            output_name = modmap_output_name,
+        ),
+    )
+    ddi_file = _get_compile_output_file(
+        action_construction_context,
+        label,
+        configuration = configuration,
+        output_name = _cc_internal.get_artifact_name_for_category(
+            cc_toolchain = cc_toolchain,
+            category = artifact_category.CPP_MODULES_DDI,
+            output_name = modmap_output_name,
+        ),
+    )
+    actions.write(
+        ddi_file,
+        json.encode({
+            "rules": [{
+                "requires": [
+                    {"logical-name": name}
+                    for name, _ in module_header_map_entries
+                ],
+            }],
+        }),
+    )
+    _create_gen_modmap_action(
+        actions = actions,
+        cc_toolchain = cc_toolchain,
+        ddi_file = ddi_file,
+        modules_info_file = modules_info_file,
+        modmap_file = modmap_file,
+        modmap_input_file = modmap_input_file,
+    )
+    return modmap_file, modmap_input_file
+
 # buildifier: disable=unused-variable
 def _create_cc_compile_actions_with_cpp20_module_helper(
         *,
@@ -668,7 +741,8 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
         use_pic,
         enable_dotd_files,
         output_name_map,
-        progress_message_prefix):
+        progress_message_prefix,
+        module_header_map_entries = []):
     direct_module_files = []
     source_to_module_file_map = {}
     source_to_ddi_file_map = {}
@@ -752,6 +826,10 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
         )
         source_to_ddi_file_map[source_artifact] = ddi_file
 
+    shared_header_map_modmap_file = None
+    shared_header_map_modmap_input_file = None
+    header_map_input_files = []
+
     _create_aggregate_ddi_action(
         actions = actions,
         cc_toolchain = cc_toolchain,
@@ -760,6 +838,18 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
         transitive_modules_info_files = cc_compilation_context._pic_modules_info_files if use_pic else cc_compilation_context._modules_info_files,
         modules_info_file = modules_info_file,
     )
+    if module_header_map_entries:
+        header_map_input_files = [map_file for _, map_file in module_header_map_entries]
+        shared_header_map_modmap_file, shared_header_map_modmap_input_file = _create_header_map_modmap_actions(
+            actions = actions,
+            action_construction_context = action_construction_context,
+            cc_toolchain = cc_toolchain,
+            configuration = configuration,
+            label = label,
+            use_pic = use_pic,
+            module_header_map_entries = module_header_map_entries,
+            modules_info_file = modules_info_file,
+        )
     compiled_basenames = set()
     transitive_module_files = cc_compilation_context._pic_module_files if use_pic else cc_compilation_context._module_files
     for cpp_source in module_interfaces_sources.values():
@@ -876,9 +966,17 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
         additional_build_variables = {}
         modmap_file = None
         modmap_input_file = None
+        source_additional_compilation_inputs = additional_compilation_inputs
 
+        is_cc_source = "." + source_artifact.extension in extensions.CC_SOURCE
         # Only C++ compilation unit will be compiled with C++20 Modules.
-        if "." + source_artifact.extension in extensions.CC_SOURCE:
+        if is_cc_source and shared_header_map_modmap_file != None:
+            modmap_file = shared_header_map_modmap_file
+            modmap_input_file = shared_header_map_modmap_input_file
+            additional_build_variables["cpp_module_modmap_file"] = modmap_file
+            additional_build_variables["cpp_module_header_map_files"] = header_map_input_files
+            source_additional_compilation_inputs = additional_compilation_inputs + header_map_input_files
+        elif is_cc_source:
             modmap_file = _get_compile_output_file(
                 action_construction_context,
                 label,
@@ -933,26 +1031,6 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
                 ddi_output_name = ddi_output_name,
                 progress_message_prefix = progress_message_prefix,
             )
-            modmap_file = _get_compile_output_file(
-                action_construction_context,
-                label,
-                configuration = configuration,
-                output_name = _cc_internal.get_artifact_name_for_category(
-                    cc_toolchain = cc_toolchain,
-                    category = artifact_category.CPP_MODULES_MODMAP,
-                    output_name = output_name_base,
-                ),
-            )
-            modmap_input_file = _get_compile_output_file(
-                action_construction_context,
-                label,
-                configuration = configuration,
-                output_name = _cc_internal.get_artifact_name_for_category(
-                    cc_toolchain = cc_toolchain,
-                    category = artifact_category.CPP_MODULES_MODMAP_INPUT,
-                    output_name = output_name_base,
-                ),
-            )
             additional_build_variables["cpp_module_modmap_file"] = modmap_file
             _create_gen_modmap_action(
                 actions = actions,
@@ -989,7 +1067,7 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
             bitcode_output = bitcode_output,
             fdo_context = fdo_context,
             auxiliary_fdo_inputs = auxiliary_fdo_inputs,
-            additional_compilation_inputs = additional_compilation_inputs,
+            additional_compilation_inputs = source_additional_compilation_inputs,
             additional_include_scanning_roots = additional_include_scanning_roots,
             use_pic = use_pic,
             enable_dotd_files = enable_dotd_files,
@@ -1030,7 +1108,8 @@ def _create_cc_compile_actions_with_cpp20_module(
         auxiliary_fdo_inputs,
         fdo_build_variables,
         enable_dotd_files,
-        progress_message_prefix):
+        progress_message_prefix,
+        module_header_map_entries = []):
     """Constructs the C++ compiler actions with C++20 modules support.
     """
     output_name_prefix_dir = _cc_internal.compute_output_name_prefix_dir(configuration = configuration, purpose = purpose)
@@ -1071,6 +1150,7 @@ def _create_cc_compile_actions_with_cpp20_module(
             enable_dotd_files = enable_dotd_files,
             output_name_map = output_name_map,
             progress_message_prefix = progress_message_prefix,
+            module_header_map_entries = module_header_map_entries,
         )
 
 def _create_cc_compile_actions(
@@ -1103,7 +1183,8 @@ def _create_cc_compile_actions(
         common_compile_build_variables,
         auxiliary_fdo_inputs,
         fdo_build_variables,
-        progress_message_prefix):
+        progress_message_prefix,
+        module_header_map_entries = []):
     """Constructs the C++ compiler actions.
 
     It generally creates one action for every specified source
@@ -1148,6 +1229,7 @@ def _create_cc_compile_actions(
             fdo_build_variables = fdo_build_variables,
             enable_dotd_files = enable_dotd_files,
             progress_message_prefix = progress_message_prefix,
+            module_header_map_entries = module_header_map_entries,
         )
         return
 

cc/private/rules_impl/attrs.bzl

@@ -102,6 +102,21 @@ C++ Standard has no restriction about module interface file extension
 <code>--experimental_cpp_modules</code>.</p>
         """,
     ),
+    "module_header_maps": attr.string_keyed_label_dict(
+        allow_files = [".modulemap"],
+        doc = """
+Maps C++20 named module names to Clang module map files that redirect legacy
+<code>#include</code> to <code>import</code> for the same module.
+
+<p>Keys are logical module names (for example <code>a</code> for
+<code>export module a;</code>). Values are <code>.modulemap</code> files.</p>
+<p>All C++ sources on this target compiled with <code>cpp_modules</code> enabled
+receive every module listed here via a generated modmap, without per-source
+dependency scanning.</p>
+<p>Requires <code>--experimental_cpp_modules</code> and the
+<code>cpp_modules</code> toolchain feature.</p>
+        """,
+    ),
     "data": attr.label_list(
         allow_files = True,
         flags = ["SKIP_CONSTRAINTS_OVERRIDE"],

cc/private/rules_impl/cc_binary_impl.bzl

@@ -536,6 +536,7 @@ def cc_binary_impl(ctx, additional_linkopts, force_linkstatic = False):
         public_hdrs = cc_helper.get_public_hdrs(ctx),
         srcs = cc_helper.get_srcs(ctx),
         module_interfaces = cc_helper.get_cpp_module_interfaces(ctx),
+        module_header_map_entries = cc_helper.get_module_header_map_entries(ctx),
         compilation_contexts = compilation_context_deps,
         code_coverage_enabled = cc_helper.is_code_coverage_enabled(ctx = ctx),
         additional_inputs = ctx.files.additional_compiler_inputs,

cc/private/rules_impl/cc_library_impl.bzl

@@ -68,6 +68,7 @@ def _cc_library_impl(ctx):
         purpose = "cc_library-compile",
         srcs = cc_helper.get_srcs(ctx),
         module_interfaces = cc_helper.get_cpp_module_interfaces(ctx),
+        module_header_map_entries = cc_helper.get_module_header_map_entries(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),

cc/private/toolchain/unix_cc_toolchain_config.bzl

@@ -1865,6 +1865,24 @@ def _impl(ctx):
         enabled = True,
     )
 
+    cpp_module_header_map_files_feature = feature(
+        name = "cpp_module_header_map_files",
+        flag_sets = [
+            flag_set(
+                actions = [
+                    ACTION_NAMES.cpp_compile,
+                ],
+                flag_groups = [
+                    flag_group(
+                        iterate_over = "cpp_module_header_map_files",
+                        flags = ["-fmodule-map-file=%{cpp_module_header_map_files}"],
+                    ),
+                ],
+            ),
+        ],
+        enabled = True,
+    )
+
     no_dotd_file_feature = feature(name = "no_dotd_file")
 
     skip_virtual_includes_feature = feature(name = "skip_virtual_includes")
@@ -1883,6 +1901,7 @@ def _impl(ctx):
             cpp_modules_feature,
             cpp_module_modmap_file_feature,
             cpp20_module_compile_flags_feature,
+            cpp_module_header_map_files_feature,
             dependency_file_feature,
             serialized_diagnostics_file_feature,
             random_seed_feature,