Introduce feature to register a separate action to generate swift derived files

swift/internal/actions.bzl

@@ -37,6 +37,10 @@ swift_action_names = struct(
     # Precompiles an explicit module for a C/Objective-C module map and its
     # headers, emitting a `.pcm` file.
     PRECOMPILE_C_MODULE = "SwiftPrecompileCModule",
+
+    # Produces files that are usually fallout of the compilation such as
+    # .swiftmodule, -Swift.h and more.
+    DERIVE_FILES = "SwiftDeriveFiles",
 )
 
 def _apply_configurator(configurator, prerequisites, args):

swift/internal/feature_names.bzl

@@ -227,3 +227,12 @@ SWIFT_FEATURE_NO_EMBED_DEBUG_MODULE = "swift.no_embed_debug_module"
 # files where the protoc command line might not be crafted correctly, so it
 # remains opt in.
 SWIFT_FEATURE_GENERATE_FROM_RAW_PROTO_FILES = "swift.generate_from_raw_proto_files"
+
+# If enabled and whole module optimisation is being used, the `*.swiftdoc`,
+# `*.swiftmodule` and `*-Swift.h` are generated with a separate action
+# rather than as part of the compilation.
+SWIFT_FEATURE_SPLIT_DERIVED_FILES_GENERATION = "swift.split_derived_files_generation"
+
+# If enabled the skip function bodies frontend flag is passed when using derived
+# files generation. This requires Swift 5.2
+SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES = "swift.skip_function_bodies_for_derived_files"

swift/internal/swift_autoconfiguration.bzl

@@ -28,6 +28,7 @@ load(
     "@build_bazel_rules_swift//swift/internal:feature_names.bzl",
     "SWIFT_FEATURE_DEBUG_PREFIX_MAP",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
+    "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
     "SWIFT_FEATURE_IMPLICIT_MODULES",
     "SWIFT_FEATURE_MODULE_MAP_NO_PRIVATE_HEADERS",
     "SWIFT_FEATURE_SUPPORTS_PRIVATE_DEPS",
@@ -75,6 +76,15 @@ def _check_enable_batch_mode(repository_ctx, swiftc_path, temp_dir):
         "-enable-batch-mode",
     )
 
+def _check_skip_function_bodies(repository_ctx, swiftc_path, temp_dir):
+    """Returns True if `swiftc` supports skip function bodies."""
+    return _swift_succeeds(
+        repository_ctx,
+        swiftc_path,
+        "-version",
+        "-experimental-skip-non-inlinable-function-bodies",
+    )
+
 def _check_debug_prefix_map(repository_ctx, swiftc_path, temp_dir):
     """Returns True if `swiftc` supports debug prefix mapping."""
     return _swift_succeeds(
@@ -187,6 +197,7 @@ def _compute_feature_values(repository_ctx, swiftc_path):
 _FEATURE_CHECKS = {
     SWIFT_FEATURE_DEBUG_PREFIX_MAP: _check_debug_prefix_map,
     SWIFT_FEATURE_ENABLE_BATCH_MODE: _check_enable_batch_mode,
+    SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES: _check_skip_function_bodies,
     SWIFT_FEATURE_SUPPORTS_PRIVATE_DEPS: _check_supports_private_deps,
     SWIFT_FEATURE_USE_RESPONSE_FILES: _check_use_response_files,
 }

swift/internal/swift_toolchain.bzl

@@ -59,6 +59,15 @@ def _all_tool_configs(
     """
     _swift_driver_tool_config = swift_toolchain_config.driver_tool_config
 
+    compile_tool_config = _swift_driver_tool_config(
+        driver_mode = "swiftc",
+        swift_executable = swift_executable,
+        toolchain_root = toolchain_root,
+        use_param_file = use_param_file,
+        worker_mode = "persistent",
+        additional_tools = additional_tools,
+    )
+
     return {
         swift_action_names.AUTOLINK_EXTRACT: _swift_driver_tool_config(
             driver_mode = "swift-autolink-extract",
@@ -67,14 +76,8 @@ def _all_tool_configs(
             worker_mode = "wrap",
             additional_tools = additional_tools,
         ),
-        swift_action_names.COMPILE: _swift_driver_tool_config(
-            driver_mode = "swiftc",
-            swift_executable = swift_executable,
-            toolchain_root = toolchain_root,
-            use_param_file = use_param_file,
-            worker_mode = "persistent",
-            additional_tools = additional_tools,
-        ),
+        swift_action_names.COMPILE: compile_tool_config,
+        swift_action_names.DERIVE_FILES: compile_tool_config,
         swift_action_names.MODULEWRAP: _swift_driver_tool_config(
             # This must come first after the driver name.
             args = ["-modulewrap"],

swift/internal/xcode_swift_toolchain.bzl

@@ -34,6 +34,7 @@ load(
     "SWIFT_FEATURE_BUNDLED_XCTESTS",
     "SWIFT_FEATURE_DEBUG_PREFIX_MAP",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
+    "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
     "SWIFT_FEATURE_MODULE_MAP_HOME_IS_CWD",
     "SWIFT_FEATURE_MODULE_MAP_NO_PRIVATE_HEADERS",
     "SWIFT_FEATURE_SUPPORTS_LIBRARY_EVOLUTION",
@@ -287,6 +288,7 @@ def _all_action_configs(
         swift_toolchain_config.action_config(
             actions = [
                 swift_action_names.COMPILE,
+                swift_action_names.DERIVE_FILES,
                 swift_action_names.PRECOMPILE_C_MODULE,
             ],
             configurators = [
@@ -317,6 +319,7 @@ def _all_action_configs(
         swift_toolchain_config.action_config(
             actions = [
                 swift_action_names.COMPILE,
+                swift_action_names.DERIVE_FILES,
                 swift_action_names.PRECOMPILE_C_MODULE,
             ],
             configurators = [swift_toolchain_config.add_arg("-embed-bitcode")],
@@ -325,6 +328,7 @@ def _all_action_configs(
         swift_toolchain_config.action_config(
             actions = [
                 swift_action_names.COMPILE,
+                swift_action_names.DERIVE_FILES,
                 swift_action_names.PRECOMPILE_C_MODULE,
             ],
             configurators = [
@@ -342,6 +346,7 @@ def _all_action_configs(
             swift_toolchain_config.action_config(
                 actions = [
                     swift_action_names.COMPILE,
+                    swift_action_names.DERIVE_FILES,
                     swift_action_names.PRECOMPILE_C_MODULE,
                 ],
                 configurators = [
@@ -389,16 +394,19 @@ def _all_tool_configs(
         env = dict(env)
         env["TOOLCHAINS"] = custom_toolchain
 
+    tool_config = swift_toolchain_config.driver_tool_config(
+        driver_mode = "swiftc",
+        env = env,
+        execution_requirements = execution_requirements,
+        swift_executable = swift_executable,
+        toolchain_root = toolchain_root,
+        use_param_file = use_param_file,
+        worker_mode = "persistent",
+    )
+
     tool_configs = {
-        swift_action_names.COMPILE: swift_toolchain_config.driver_tool_config(
-            driver_mode = "swiftc",
-            env = env,
-            execution_requirements = execution_requirements,
-            swift_executable = swift_executable,
-            toolchain_root = toolchain_root,
-            use_param_file = use_param_file,
-            worker_mode = "persistent",
-        ),
+        swift_action_names.COMPILE: tool_config,
+        swift_action_names.DERIVE_FILES: tool_config,
     }
 
     # Xcode 12.0 implies Swift 5.3.
@@ -594,6 +602,10 @@ def _xcode_swift_toolchain_impl(ctx):
         requested_features.append(SWIFT_FEATURE_SUPPORTS_LIBRARY_EVOLUTION)
         requested_features.append(SWIFT_FEATURE_SUPPORTS_PRIVATE_DEPS)
 
+    # Xcode 11.4 implies Swift 5.2.
+    if _is_xcode_at_least_version(xcode_config, "11.4"):
+        requested_features.append(SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES)
+
     command_line_copts = _command_line_objc_copts(
         ctx.var["COMPILATION_MODE"],
         ctx.fragments.objc,

test/BUILD

@@ -4,6 +4,7 @@ load(":coverage_settings_tests.bzl", "coverage_settings_test_suite")
 load(":generated_header_tests.bzl", "generated_header_test_suite")
 load(":private_deps_tests.bzl", "private_deps_test_suite")
 load(":swift_through_non_swift_tests.bzl", "swift_through_non_swift_test_suite")
+load(":split_derived_files_tests.bzl", "split_derived_files_test_suite")
 
 licenses(["notice"])
 
@@ -17,6 +18,8 @@ private_deps_test_suite()
 
 swift_through_non_swift_test_suite()
 
+split_derived_files_test_suite()
+
 test_suite(
     name = "all_tests",
 )