Use newer split module flag with Swift 5.4

Uses the newer `-experimental-skip-non-inlinable-function-bodies-without-types` which was introduced here: swiftlang/swift#34612. This should improve LLDB usage in some cases.

When using WMO, it has two downsides in Swift 5.5, both introduced by swiftlang/swift#38939:
- The swiftmodules will have swiftdeps info embedded in them, which is only needed for incremental compilation
- Interface hashing is enabled, which again is only needed for incremental compilation

This is because the swift compiler only expects `-experimental-skip-non-inlinable-function-bodies-without-types` to be used with the new `emit-module-separately` incremental build.

Author: brentleyjones

swift/internal/compiling.bzl

@@ -42,6 +42,7 @@ load(
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
     "SWIFT_FEATURE_ENABLE_LIBRARY_EVOLUTION",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
+    "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES",
     "SWIFT_FEATURE_ENABLE_TESTING",
     "SWIFT_FEATURE_FASTBUILD",
     "SWIFT_FEATURE_FULL_DEBUG_INFO",
@@ -849,6 +850,16 @@ def compile_action_configs(
                 ),
             ],
             features = [SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES],
+            not_features = [SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES],
+        ),
+        swift_toolchain_config.action_config(
+            actions = [swift_action_names.DERIVE_FILES],
+            configurators = [
+                swift_toolchain_config.add_arg(
+                    "-experimental-skip-non-inlinable-function-bodies-without-types",
+                ),
+            ],
+            features = [SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES],
         ),
         swift_toolchain_config.action_config(
             actions = [swift_action_names.COMPILE],

swift/internal/feature_names.bzl

@@ -254,9 +254,14 @@ SWIFT_FEATURE_GENERATE_FROM_RAW_PROTO_FILES = "swift.generate_from_raw_proto_fil
 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
+# files generation. This requires Swift 5.2.
 SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES = "swift.skip_function_bodies_for_derived_files"
 
+# If enabled the skip function bodies without types frontend flag is passed when
+# using derived files generation. This takes precedence over
+# swift.skip_function_bodies_for_derived_files. This requires Swift 5.4.
+SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES = "swift.skip_function_bodies_without_types_for_derived_files"
+
 # If enabled remap the absolute path to Xcode in debug info. When used with
 # swift.coverage_prefix_map also remap the path in coverage data.
 SWIFT_FEATURE_REMAP_XCODE_PATH = "swift.remap_xcode_path"

swift/internal/swift_autoconfiguration.bzl

@@ -29,6 +29,7 @@ load(
     "SWIFT_FEATURE_DEBUG_PREFIX_MAP",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
+    "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES",
     "SWIFT_FEATURE_MODULE_MAP_NO_PRIVATE_HEADERS",
     "SWIFT_FEATURE_SUPPORTS_PRIVATE_DEPS",
     "SWIFT_FEATURE_USE_RESPONSE_FILES",
@@ -84,6 +85,15 @@ def _check_skip_function_bodies(repository_ctx, swiftc_path, temp_dir):
         "-experimental-skip-non-inlinable-function-bodies",
     )
 
+def _check_skip_function_bodies_without_types(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-without-types",
+    )
+
 def _check_debug_prefix_map(repository_ctx, swiftc_path, temp_dir):
     """Returns True if `swiftc` supports debug prefix mapping."""
     return _swift_succeeds(
@@ -197,6 +207,7 @@ _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_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES: _check_skip_function_bodies_without_types,
     SWIFT_FEATURE_SUPPORTS_PRIVATE_DEPS: _check_supports_private_deps,
     SWIFT_FEATURE_USE_RESPONSE_FILES: _check_use_response_files,
 }

swift/internal/xcode_swift_toolchain.bzl

@@ -36,6 +36,7 @@ load(
     "SWIFT_FEATURE_DEBUG_PREFIX_MAP",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
+    "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES",
     "SWIFT_FEATURE_MODULE_MAP_HOME_IS_CWD",
     "SWIFT_FEATURE_MODULE_MAP_NO_PRIVATE_HEADERS",
     "SWIFT_FEATURE_REMAP_XCODE_PATH",
@@ -711,6 +712,7 @@ def _xcode_swift_toolchain_impl(ctx):
 
     # Xcode 12.5 implies Swift 5.4.
     if _is_xcode_at_least_version(xcode_config, "12.5"):
+        requested_features.append(SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES)
         requested_features.append(SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG)
 
     env = _xcode_env(platform = platform, xcode_config = xcode_config)

test/split_derived_files_tests.bzl

@@ -278,6 +278,7 @@ def split_derived_files_test_suite(name = "split_derived_files"):
         mnemonic = "SwiftCompile",
         not_expected_argv = [
             "-experimental-skip-non-inlinable-function-bodies",
+            "-experimental-skip-non-inlinable-function-bodies-without-types",
         ],
         tags = [name],
         target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",
@@ -286,11 +287,12 @@ def split_derived_files_test_suite(name = "split_derived_files"):
     split_swiftmodule_skip_function_bodies_test(
         name = "{}_skip_function_bodies".format(name),
         expected_argv = [
-            "-experimental-skip-non-inlinable-function-bodies",
+            "-experimental-skip-non-inlinable-function-bodies-without-types",
         ],
         mnemonic = "SwiftDeriveFiles",
         not_expected_argv = [
             "-emit-object",
+            "-experimental-skip-non-inlinable-function-bodies",
         ],
         tags = [name],
         target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",