[ModuleInterface] Add mechanism to exclude experimental flags from th…

include/swift/Basic/Feature.h

@@ -66,6 +66,10 @@ llvm::Optional<Feature> getExperimentalFeature(llvm::StringRef name);
 /// \c None if it does not have such a version.
 llvm::Optional<unsigned> getFeatureLanguageVersion(Feature feature);
 
+/// Determine whether this feature should be included in the
+/// module interface
+bool includeInModuleInterface(Feature feature);
+
 }
 
 #endif // SWIFT_BASIC_FEATURES_H

include/swift/Basic/Features.def

@@ -62,6 +62,11 @@
                       langOpts.hasFeature(#FeatureName))
 #endif
 
+#ifndef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
+#  define EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE(FeatureName, AvailableInProd) \
+     EXPERIMENTAL_FEATURE(FeatureName, AvailableInProd)
+#endif
+
 LANGUAGE_FEATURE(AsyncAwait, 296, "async/await", true)
 LANGUAGE_FEATURE(EffectfulProp, 310, "Effectful properties", true)
 LANGUAGE_FEATURE(MarkerProtocol, 0, "@_marker protocol", true)
@@ -134,8 +139,8 @@ EXPERIMENTAL_FEATURE(ModuleInterfaceExportAs, true)
 EXPERIMENTAL_FEATURE(AccessLevelOnImport, true)
 
 /// Whether to enable experimental layout string value witnesses
-EXPERIMENTAL_FEATURE(LayoutStringValueWitnesses, true)
-EXPERIMENTAL_FEATURE(LayoutStringValueWitnessesInstantiation, true)
+EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE(LayoutStringValueWitnesses, true)
+EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE(LayoutStringValueWitnessesInstantiation, true)
 
 /// Whether to enable experimental differentiable programming features:
 /// `@differentiable` declaration attribute, etc.
@@ -196,6 +201,7 @@ EXPERIMENTAL_FEATURE(ReferenceBindings, false)
 /// Enable the explicit 'import Builtin' and allow Builtin usage.
 EXPERIMENTAL_FEATURE(BuiltinModule, true)
 
+#undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

lib/Basic/LangOptions.cpp

@@ -489,7 +489,7 @@ bool swift::isFeatureAvailableInProduction(Feature feature) {
   switch (feature) {
 #define LANGUAGE_FEATURE(FeatureName, SENumber, Description, Option)  \
   case Feature::FeatureName: return true;
-#define EXPERIMENTAL_FEATURE(FeatureName, AvailableInProd)            \
+#define EXPERIMENTAL_FEATURE(FeatureName, AvailableInProd) \
   case Feature::FeatureName: return AvailableInProd;
 #include "swift/Basic/Features.def"
   }
@@ -508,7 +508,7 @@ llvm::Optional<Feature> swift::getUpcomingFeature(llvm::StringRef name) {
 llvm::Optional<Feature> swift::getExperimentalFeature(llvm::StringRef name) {
   return llvm::StringSwitch<Optional<Feature>>(name)
 #define LANGUAGE_FEATURE(FeatureName, SENumber, Description, Option)
-#define EXPERIMENTAL_FEATURE(FeatureName, AvailableInProd)                  \
+#define EXPERIMENTAL_FEATURE(FeatureName, AvailableInProd) \
                    .Case(#FeatureName, Feature::FeatureName)
 #include "swift/Basic/Features.def"
                    .Default(None);
@@ -524,6 +524,17 @@ llvm::Optional<unsigned> swift::getFeatureLanguageVersion(Feature feature) {
   }
 }
 
+bool swift::includeInModuleInterface(Feature feature) {
+  switch (feature) {
+#define LANGUAGE_FEATURE(FeatureName, SENumber, Description, Option)  \
+  case Feature::FeatureName: return true;
+#define EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE(FeatureName, AvailableInProd) \
+  case Feature::FeatureName: return false;
+#include "swift/Basic/Features.def"
+  }
+  llvm_unreachable("covered switch");
+}
+
 DiagnosticBehavior LangOptions::getAccessNoteFailureLimit() const {
   switch (AccessNoteBehavior) {
   case AccessNoteDiagnosticBehavior::Ignore:

lib/Frontend/CompilerInvocation.cpp

@@ -417,6 +417,19 @@ static void ParseModuleInterfaceArgs(ModuleInterfaceOptions &Opts,
   }
 }
 
+/// Checks if an arg is generally allowed to be included
+/// in a module interface
+static bool ShouldIncludeModuleInterfaceArg(const Arg *A) {
+  if (!A->getOption().matches(options::OPT_enable_experimental_feature))
+    return true;
+
+  if (auto feature = getExperimentalFeature(A->getValue())) {
+    return swift::includeInModuleInterface(*feature);
+  }
+
+  return true;
+}
+
 /// Save a copy of any flags marked as ModuleInterfaceOption, if running
 /// in a mode that is going to emit a .swiftinterface file.
 static void SaveModuleInterfaceArgs(ModuleInterfaceOptions &Opts,
@@ -428,6 +441,9 @@ static void SaveModuleInterfaceArgs(ModuleInterfaceOptions &Opts,
   ArgStringList RenderedArgsIgnorable;
   ArgStringList RenderedArgsIgnorablePrivate;
   for (auto A : Args) {
+    if (!ShouldIncludeModuleInterfaceArg(A))
+      continue;
+
     if (A->getOption().hasFlag(options::ModuleInterfaceOptionIgnorablePrivate)) {
       A->render(Args, RenderedArgsIgnorablePrivate);
     } else if (A->getOption().hasFlag(options::ModuleInterfaceOptionIgnorable)) {

test/ModuleInterface/option-filtering.swift

@@ -0,0 +1,10 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -enable-library-evolution -emit-module-interface-path %t.swiftinterface -module-name t %s -target-min-inlining-version 42 -emit-module -o /dev/null -O -enable-experimental-feature LayoutStringValueWitnesses -enable-experimental-feature LayoutStringValueWitnessesInstantiation
+// RUN: %FileCheck %s < %t.swiftinterface -check-prefix=CHECK-SWIFTINTERFACE
+//
+// CHECK-SWIFTINTERFACE: swift-module-flags-ignorable:
+// CHECK-SWIFTINTERFACE-NOT: -enable-experimental-feature LayoutStringValueWitnesses
+// CHECK-SWIFTINTERFACE-NOT: -enable-experimental-feature LayoutStringValueWitnessesInstantiation
+
+public func foo() { }