Add feature for partially explicit modules

swift/internal/BUILD

@@ -45,6 +45,7 @@ bzl_library(
         ":debugging",
         ":derived_files",
         ":developer_dirs",
+        ":explicit_module_map_file",
         ":feature_names",
         ":features",
         ":providers",
@@ -388,6 +389,11 @@ bzl_library(
     ],
 )
 
+bzl_library(
+    name = "explicit_module_map_file",
+    srcs = ["explicit_module_map_file.bzl"],
+)
+
 bzl_library(
     name = "feature_names",
     srcs = ["feature_names.bzl"],

swift/internal/compiling.bzl

@@ -24,6 +24,7 @@ load(
     "run_toolchain_action",
     "swift_action_names",
 )
+load(":explicit_module_map_file.bzl", "write_explicit_swift_module_map_file")
 load(":derived_files.bzl", "derived_files")
 load(
     ":feature_names.bzl",
@@ -62,6 +63,7 @@ load(
     "SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG",
     "SWIFT_FEATURE_SYSTEM_MODULE",
     "SWIFT_FEATURE_USE_C_MODULES",
+    "SWIFT_FEATURE_USE_EXPLICIT_SWIFT_MODULE_MAP",
     "SWIFT_FEATURE_USE_GLOBAL_INDEX_STORE",
     "SWIFT_FEATURE_USE_GLOBAL_MODULE_CACHE",
     "SWIFT_FEATURE_USE_OLD_DRIVER",
@@ -875,7 +877,10 @@ def compile_action_configs(
                 swift_action_names.DUMP_AST,
             ],
             configurators = [_dependencies_swiftmodules_configurator],
-            not_features = [SWIFT_FEATURE_VFSOVERLAY],
+            not_features = [
+                [SWIFT_FEATURE_VFSOVERLAY],
+                [SWIFT_FEATURE_USE_EXPLICIT_SWIFT_MODULE_MAP],
+            ],
         ),
         swift_toolchain_config.action_config(
             actions = [
@@ -888,6 +893,17 @@ def compile_action_configs(
             ],
             features = [SWIFT_FEATURE_VFSOVERLAY],
         ),
+        swift_toolchain_config.action_config(
+            actions = [
+                swift_action_names.COMPILE,
+                swift_action_names.DERIVE_FILES,
+                swift_action_names.DUMP_AST,
+            ],
+            configurators = [
+                _explicit_swift_module_map_configurator,
+            ],
+            features = [SWIFT_FEATURE_USE_EXPLICIT_SWIFT_MODULE_MAP],
+        ),
     ])
 
     #### Search paths for framework dependencies
@@ -1620,6 +1636,21 @@ def _dependencies_swiftmodules_vfsoverlay_configurator(prerequisites, args):
         inputs = swiftmodules + [prerequisites.vfsoverlay_file],
     )
 
+def _explicit_swift_module_map_configurator(prerequisites, args):
+    """Adds the explicit Swift module map file to the command line."""
+    args.add_all(
+        [
+            "-explicit-swift-module-map-file",
+            prerequisites.explicit_swift_module_map_file,
+        ],
+        before_each = "-Xfrontend",
+    )
+    return swift_toolchain_config.config_result(
+        inputs = prerequisites.transitive_swiftmodules + [
+            prerequisites.explicit_swift_module_map_file,
+        ],
+    )
+
 def _module_name_configurator(prerequisites, args):
     """Adds the module name flag to the command line."""
     args.add("-module-name", prerequisites.module_name)
@@ -2081,11 +2112,32 @@ def compile(
     else:
         vfsoverlay_file = None
 
+    if is_feature_enabled(
+        feature_configuration = feature_configuration,
+        feature_name = SWIFT_FEATURE_USE_EXPLICIT_SWIFT_MODULE_MAP,
+    ):
+        if vfsoverlay_file:
+            fail("Cannot use both `swift.vfsoverlay` and `swift.use_explicit_swift_module_map` features at the same time.")
+
+        # Generate the JSON file that contains the manifest of Swift
+        # dependencies.
+        explicit_swift_module_map_file = actions.declare_file(
+            "{}.swift-explicit-module-map.json".format(target_name),
+        )
+        write_explicit_swift_module_map_file(
+            actions = actions,
+            explicit_swift_module_map_file = explicit_swift_module_map_file,
+            module_contexts = transitive_modules,
+        )
+    else:
+        explicit_swift_module_map_file = None
+
     prerequisites = struct(
         additional_inputs = additional_inputs,
         bin_dir = feature_configuration._bin_dir,
         cc_compilation_context = merged_providers.cc_info.compilation_context,
         defines = sets.to_list(defines_set),
+        explicit_swift_module_map_file = explicit_swift_module_map_file,
         developer_dirs = swift_toolchain.developer_dirs,
         genfiles_dir = feature_configuration._genfiles_dir,
         is_swift = True,

swift/internal/explicit_module_map_file.bzl

@@ -0,0 +1,50 @@
+# Copyright 2022 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Generates the JSON manifest used to pass Swift modules to the compiler."""
+
+def write_explicit_swift_module_map_file(
+        *,
+        actions,
+        explicit_swift_module_map_file,
+        module_contexts):
+    """Generates the JSON-formatted explicit module map file.
+
+    This file is a manifest that contains the path information for all the
+    Swift modules from dependencies that are needed to compile a particular
+    module.
+
+    Args:
+        actions: The object used to register actions.
+        explicit_swift_module_map_file: A `File` to which the generated JSON
+            will be written.
+        module_contexts: A list of module contexts that provide the Swift
+            dependencies for the compilation.
+    """
+    module_descriptions = []
+
+    for module_context in module_contexts:
+        if not module_context.swift:
+            continue
+
+        swift_context = module_context.swift
+        module_description = {"moduleName": module_context.name}
+        if swift_context.swiftmodule:
+            module_description["modulePath"] = swift_context.swiftmodule.path
+        module_descriptions.append(module_description)
+
+    actions.write(
+        content = json.encode(module_descriptions),
+        output = explicit_swift_module_map_file,
+    )

swift/internal/feature_names.bzl

@@ -166,6 +166,10 @@ SWIFT_FEATURE_REWRITE_GENERATED_HEADER = "swift.rewrite_generated_header"
 # them.
 SWIFT_FEATURE_USE_C_MODULES = "swift.use_c_modules"
 
+# If enabled, Swift modules for dependencies will be passed to the compiler
+# using a JSON file instead of `-I` search paths.
+SWIFT_FEATURE_USE_EXPLICIT_SWIFT_MODULE_MAP = "swift.use_explicit_swift_module_map"
+
 # If enabled, Swift compilation actions will use the same global Clang module
 # cache used by Objective-C compilation actions. This is disabled by default
 # because under some circumstances Clang module cache corruption can cause the

test/features_tests.bzl

@@ -38,6 +38,22 @@ file_prefix_xcode_remap_test = make_action_command_line_test_rule(
     },
 )
 
+vfsoverlay_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:features": [
+            "swift.vfsoverlay",
+        ],
+    },
+)
+
+explicit_swift_module_map_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:features": [
+            "swift.use_explicit_swift_module_map",
+        ],
+    },
+)
+
 def features_test_suite(name):
     """Test suite for various features.
 
@@ -47,13 +63,16 @@ def features_test_suite(name):
     default_test(
         name = "{}_default_test".format(name),
         tags = [name],
-        expected_argv = ["-emit-object"],
+        expected_argv = [
+            "-emit-object",
+            "-I$(BIN_DIR)/test/fixtures/basic",
+        ],
         not_expected_argv = [
             "-file-prefix-map",
             "-Xwrapped-swift=-file-prefix-pwd-is-dot",
         ],
         mnemonic = "SwiftCompile",
-        target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",
+        target_under_test = "@build_bazel_rules_swift//test/fixtures/basic:second",
     )
 
     file_prefix_map_test(
@@ -95,3 +114,33 @@ def features_test_suite(name):
         mnemonic = "SwiftCompile",
         target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",
     )
+
+    vfsoverlay_test(
+        name = "{}_vfsoverlay_test".format(name),
+        tags = [name],
+        expected_argv = [
+            "-Xfrontend -vfsoverlay$(BIN_DIR)/test/fixtures/basic/second.vfsoverlay.yaml",
+            "-I/__build_bazel_rules_swift/swiftmodules",
+        ],
+        not_expected_argv = [
+            "-I$(BIN_DIR)/test/fixtures/basic",
+            "-explicit-swift-module-map-file",
+        ],
+        mnemonic = "SwiftCompile",
+        target_under_test = "@build_bazel_rules_swift//test/fixtures/basic:second",
+    )
+
+    explicit_swift_module_map_test(
+        name = "{}_explicit_swift_module_map_test".format(name),
+        tags = [name],
+        expected_argv = [
+            "-Xfrontend -explicit-swift-module-map-file -Xfrontend $(BIN_DIR)/test/fixtures/basic/second.swift-explicit-module-map.json",
+        ],
+        not_expected_argv = [
+            "-I$(BIN_DIR)/test/fixtures/basic",
+            "-I/__build_bazel_rules_swift/swiftmodules",
+            "-Xfrontend -vfsoverlay$(BIN_DIR)/test/fixtures/basic/second.vfsoverlay.yaml",
+        ],
+        mnemonic = "SwiftCompile",
+        target_under_test = "@build_bazel_rules_swift//test/fixtures/basic:second",
+    )

test/fixtures/basic/BUILD

@@ -0,0 +1,21 @@
+load("//swift:swift.bzl", "swift_library")
+load("//test/fixtures:common.bzl", "FIXTURE_TAGS")
+
+package(
+    default_visibility = ["//test:__subpackages__"],
+)
+
+licenses(["notice"])
+
+swift_library(
+    name = "first",
+    srcs = ["first.swift"],
+    tags = FIXTURE_TAGS,
+)
+
+swift_library(
+    name = "second",
+    srcs = ["second.swift"],
+    tags = FIXTURE_TAGS,
+    deps = ["first"],
+)

test/fixtures/basic/first.swift

@@ -0,0 +1,3 @@
+public func foo() -> String {
+    return "foo"
+}

test/fixtures/basic/second.swift

@@ -0,0 +1,5 @@
+import first
+
+public func bar() -> String {
+    return foo()
+}

test/rules/action_command_line_test.bzl

@@ -77,7 +77,9 @@ def _action_command_line_test_impl(ctx):
     # end and look for arguments followed by a trailing space so that having
     # `-foo` in the expected list doesn't match `-foobar`, for example.
     concatenated_args = " ".join(action.argv) + " "
+    bin_dir = analysistest.target_bin_dir_path(env)
     for expected in ctx.attr.expected_argv:
+        expected = expected.replace("$(BIN_DIR)", bin_dir)
         if expected + " " not in concatenated_args and expected + "=" not in concatenated_args:
             unittest.fail(
                 env,
@@ -88,6 +90,7 @@ def _action_command_line_test_impl(ctx):
                 ),
             )
     for not_expected in ctx.attr.not_expected_argv:
+        not_expected = not_expected.replace("$(BIN_DIR)", bin_dir)
         if not_expected + " " in concatenated_args or not_expected + "=" in concatenated_args:
             unittest.fail(
                 env,