Fix --swiftcopt being passed to module interface compiles

swift/toolchains/config/compile_config.bzl

@@ -1421,7 +1421,6 @@ def compile_action_configs(
         action_configs.append(
             ActionConfigInfo(
                 actions = all_compile_action_names() + [
-                    SWIFT_ACTION_COMPILE_MODULE_INTERFACE,
                     SWIFT_ACTION_DUMP_AST,
                     SWIFT_ACTION_PRECOMPILE_C_MODULE,
                 ],

test/fixtures/module_interface/BUILD

@@ -1,5 +1,6 @@
 load("//swift:swift_binary.bzl", "swift_binary")
 load("//swift:swift_import.bzl", "swift_import")
+load("//test:transitions.bzl", "transition_binary")
 load("//test/fixtures:common.bzl", "FIXTURE_TAGS")
 
 package(
@@ -56,3 +57,21 @@ swift_import(
     swiftinterface = "//test/fixtures/module_interface/library:toy_outputs/ToyModule.swiftinterface",
     tags = FIXTURE_TAGS,
 )
+
+swift_import(
+    name = "toy_module_interface",
+    module_name = "ToyModule",
+    swiftinterface = "//test/fixtures/module_interface/library:toy_interface/ToyModule.swiftinterface",
+    tags = FIXTURE_TAGS,
+)
+
+transition_binary(
+    name = "toy_module_interface_with_driver_flags",
+    swiftcopts = [
+        "-Xfrontend",
+        "-disable-availability-checking",
+        "-j1",
+    ],
+    tags = FIXTURE_TAGS,
+    target = ":toy_module_interface",
+)

test/fixtures/module_interface/library/BUILD

@@ -61,6 +61,13 @@ swift_library_artifact_collector(
     target_compatible_with = ["@platforms//os:macos"],
 )
 
+swift_library_artifact_collector(
+    name = "toy_module_interface_artifact_collector",
+    swiftinterface = "toy_interface/ToyModule.swiftinterface",
+    tags = FIXTURE_TAGS,
+    target = ":toy_module_library",
+)
+
 swift_library(
     name = "toy_module_library_without_library_evolution",
     srcs = ["ToyModule.swift"],

test/module_interface_tests.bzl

@@ -67,6 +67,22 @@ def module_interface_test_suite(name, tags = []):
     """
     all_tags = [name] + tags
 
+    build_test(
+        name = "{}_interface_only".format(name),
+        targets = [
+            "//test/fixtures/module_interface:toy_module_interface",
+        ],
+        tags = all_tags,
+    )
+
+    build_test(
+        name = "{}_swiftcopt_driver_flags".format(name),
+        targets = [
+            "//test/fixtures/module_interface:toy_module_interface_with_driver_flags",
+        ],
+        tags = all_tags,
+    )
+
     # Verify that a `swift_binary` builds properly when depending on a
     # `swift_import` target that references a `.swiftinterface` file.
     build_test(

test/transitions.bzl

@@ -11,6 +11,7 @@ _HOST_FEATURES = "//command_line_option:host_features"
 _IOS_MINIMUM_OS = "//command_line_option:ios_minimum_os"
 _MACOS_MINIMUM_OS = "//command_line_option:macos_minimum_os"
 _PLATFORMS = "//command_line_option:platforms"
+_SWIFTCOPTS = str(Label("//swift:copt"))
 _TVOS_MINIMUM_OS = "//command_line_option:tvos_minimum_os"
 
 _TRANSITION_OPTIONS = [
@@ -21,6 +22,7 @@ _TRANSITION_OPTIONS = [
     _IOS_MINIMUM_OS,
     _MACOS_MINIMUM_OS,
     _PLATFORMS,
+    _SWIFTCOPTS,
     _TVOS_MINIMUM_OS,
 ]
 
@@ -33,6 +35,7 @@ def _transition_impl(settings, attr):
         _IOS_MINIMUM_OS: attr.ios_minimum_os or settings[_IOS_MINIMUM_OS],
         _MACOS_MINIMUM_OS: attr.macos_minimum_os or attr.minimum_os or settings[_MACOS_MINIMUM_OS],
         _PLATFORMS: [attr.platform] if attr.platform else settings[_PLATFORMS],
+        _SWIFTCOPTS: settings[_SWIFTCOPTS] + attr.swiftcopts,
         _TVOS_MINIMUM_OS: attr.tvos_minimum_os or settings[_TVOS_MINIMUM_OS],
     }
 
@@ -66,6 +69,9 @@ _TRANSITION_ATTRS = {
     "platform": attr.string(
         doc = "Optional target platform label (e.g. `@apple_support//platforms:macos_x86_64`).",
     ),
+    "swiftcopts": attr.string_list(
+        doc = "Swift compiler flags appended to `//swift:copt` for the transitioned target.",
+    ),
     "transitive_features": attr.string_list(
         doc = "Feature strings appended to `//command_line_option:features` and `//command_line_option:host_features`.",
     ),

tools/worker/swift_runner.cc

@@ -50,12 +50,20 @@ namespace {
 using namespace bazel_rules_swift;
 
 // Creates a temporary file and writes the given arguments to it, one per line.
+// A leading -frontend is passed outside the response file by
+// ArgsWithResponseFile because some swift-driver versions select the invocation
+// mode before expanding response files.
 static std::unique_ptr<TempFile> WriteResponseFile(
     const std::vector<std::string>& args) {
   auto response_file = TempFile::Create("swiftc_params.XXXXXX");
   std::ofstream response_file_stream(response_file->GetPath());
 
-  for (const auto& arg : args) {
+  auto it = args.begin();
+  if (it != args.end() && *it == "-frontend") {
+    ++it;
+  }
+  for (; it != args.end(); ++it) {
+    const auto& arg = *it;
     // When Clang/Swift write out a response file to communicate from driver to
     // frontend, they just quote every argument to be safe; we duplicate that
     // instead of trying to be "smarter" and only quoting when necessary.
@@ -379,6 +387,17 @@ bool SupportsResponseFileInvocation(const std::vector<std::string>& args) {
   return args.empty() || args.front() != "-modulewrap";
 }
 
+std::vector<std::string> ArgsWithResponseFile(
+    const std::vector<std::string>& tool_args,
+    const std::vector<std::string>& args, const TempFile& response_file) {
+  std::vector<std::string> spawn_args(tool_args);
+  if (!args.empty() && args.front() == "-frontend") {
+    spawn_args.push_back(args.front());
+  }
+  spawn_args.push_back("@" + response_file.GetPath());
+  return spawn_args;
+}
+
 // Spawns an executable, constructing the command line by writing `args` to a
 // response file when the Swift invocation mode supports it and concatenating
 // that after `tool_args` (which are passed outside the response file).
@@ -389,22 +408,14 @@ int SpawnJob(const std::vector<std::string>& tool_args,
   std::vector<std::string> spawn_args(tool_args);
   if (SupportsResponseFileInvocation(args)) {
     auto response_file = WriteResponseFile(args);
-    spawn_args.push_back("@" + response_file->GetPath());
+    spawn_args = ArgsWithResponseFile(tool_args, args, *response_file);
     return RunSubProcess(spawn_args, env, stderr_stream, stdout_to_stderr);
   }
 
   spawn_args.insert(spawn_args.end(), args.begin(), args.end());
   return RunSubProcess(spawn_args, env, stderr_stream, stdout_to_stderr);
 }
 
-std::vector<std::string> ArgsWithResponseFile(
-    const std::vector<std::string>& tool_args,
-    const std::vector<std::string>& args, const TempFile& response_file) {
-  std::vector<std::string> spawn_args(tool_args);
-  spawn_args.push_back("@" + response_file.GetPath());
-  return spawn_args;
-}
-
 std::vector<std::string> FullArgsForDisplay(
     const std::vector<std::string>& tool_args,
     const std::vector<std::string>& args) {