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Use -fsystem-module if the compiler is new enough to support it (Xcode 12.5/Swift 5.4 or higher). #626

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merged 1 commit into from
May 28, 2021
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Use -fsystem-module if the compiler is new enough to support it (Xcode 12.5/Swift 5.4 or higher). #626

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28 changes: 21 additions & 7 deletions swift/internal/compiling.bzl
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Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,7 @@ load(
"SWIFT_FEATURE_OPT_USES_WMO",
"SWIFT_FEATURE_SPLIT_DERIVED_FILES_GENERATION",
"SWIFT_FEATURE_SUPPORTS_LIBRARY_EVOLUTION",
"SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG",
"SWIFT_FEATURE_SYSTEM_MODULE",
"SWIFT_FEATURE_USE_C_MODULES",
"SWIFT_FEATURE_USE_GLOBAL_MODULE_CACHE",
Expand Down Expand Up @@ -603,20 +604,33 @@ def compile_action_configs(
swift_toolchain_config.action_config(
actions = [swift_action_names.PRECOMPILE_C_MODULE],
configurators = [
# TODO(b/165649949): ClangImporter doesn't currently handle the
# IsSystem bit correctly for the input file, which causes the
# module map to be treated as a user input. To work around this
# for now, we disable all diagnostics when compiling the
# explicit module for system modules, since they're not useful
# anyway; this is "close enough" to compiling it as a system
# module for the purposes of avoiding noise in the build logs.
# Before Swift 5.4, ClangImporter doesn't currently handle the
# IsSystem bit correctly for the input file and ignores the
# `-fsystem-module` flag, which causes the module map to be
# treated as a user input. We can work around this by disabling
# diagnostics for system modules. However, this also disables
# behavior in ClangImporter that causes system APIs that use
# `UInt` to be imported to use `Int` instead. The only solution
# here is to use Xcode 12.5 or higher.
swift_toolchain_config.add_arg("-Xcc", "-w"),
swift_toolchain_config.add_arg(
"-Xcc",
"-Wno-nullability-declspec",
),
],
features = [SWIFT_FEATURE_SYSTEM_MODULE],
not_features = [SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG],
),
swift_toolchain_config.action_config(
actions = [swift_action_names.PRECOMPILE_C_MODULE],
configurators = [
swift_toolchain_config.add_arg("-Xcc", "-Xclang"),
swift_toolchain_config.add_arg("-Xcc", "-fsystem-module"),
],
features = [
SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG,
SWIFT_FEATURE_SYSTEM_MODULE,
],
),
]

Expand Down
8 changes: 8 additions & 0 deletions swift/internal/feature_names.bzl
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Expand Up @@ -71,6 +71,14 @@ SWIFT_FEATURE_LAYERING_CHECK = "swift.layering_check"
# If enabled, the C or Objective-C target should be compiled as a system module.
SWIFT_FEATURE_SYSTEM_MODULE = "swift.system_module"

# If enabled, the `-Xcc -fsystem-module` flag will be passed when compiling a
# system C/Objective-C module (with feature `swift.system_module`) because the
# compiler is new enough to honor it correctly. If disabled, we attempt to mimic
# this by disabling certain warnings; however, this unfortunately causes `UInt`
# APIs to be imported by ClangImporter as `UInt` instead of `Int` because
# ClangImporter doesn't recognize them as true system modules.
Comment on lines +74 to +79
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That took me so long to figure out 😅

SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG = "swift.supports_system_module_flag"

# If enabled, Swift compilation actions will use batch mode by passing
# `-enable-batch-mode` to `swiftc`. This is a new compilation mode as of
# Swift 4.2 that is intended to speed up non-incremental non-WMO builds by
Expand Down
5 changes: 5 additions & 0 deletions swift/internal/xcode_swift_toolchain.bzl
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@ load(
"SWIFT_FEATURE_REMAP_XCODE_PATH",
"SWIFT_FEATURE_SUPPORTS_LIBRARY_EVOLUTION",
"SWIFT_FEATURE_SUPPORTS_PRIVATE_DEPS",
"SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG",
"SWIFT_FEATURE_USE_RESPONSE_FILES",
)
load(":features.bzl", "features_for_build_modes")
Expand Down Expand Up @@ -732,6 +733,10 @@ def _xcode_swift_toolchain_impl(ctx):
if _is_xcode_at_least_version(xcode_config, "11.4"):
requested_features.append(SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES)

# Xcode 12.5 implies Swift 5.4.
if _is_xcode_at_least_version(xcode_config, "12.5"):
requested_features.append(SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG)

env = _xcode_env(platform = platform, xcode_config = xcode_config)
execution_requirements = xcode_config.execution_info()
generated_header_rewriter = ctx.executable.generated_header_rewriter
Expand Down