Make named opaque types an experimental feature

Author: DougGregor

include/swift/Basic/Features.def

@@ -85,6 +85,7 @@ SUPPRESSIBLE_LANGUAGE_FEATURE(NoAsyncAvailability, 340, "@available(*, noasync)"
 
 EXPERIMENTAL_FEATURE(StaticAssert)
 EXPERIMENTAL_FEATURE(VariadicGenerics)
+EXPERIMENTAL_FEATURE(NamedOpaqueTypes)
 
 #undef EXPERIMENTAL_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

include/swift/Basic/LangOptions.h

@@ -317,10 +317,6 @@ namespace swift {
     /// Enable experimental concurrency model.
     bool EnableExperimentalConcurrency = false;
 
-    /// Enable experimental support for named opaque result types, e.g.
-    /// `func f() -> <T> T`.
-    bool EnableExperimentalNamedOpaqueTypes = false;
-
     /// Enable support for implicitly opening existential argument types
     /// in calls to generic functions.
     bool EnableOpenedExistentialTypes = false;

lib/AST/ASTPrinter.cpp

@@ -3003,6 +3003,10 @@ static bool usesFeatureVariadicGenerics(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureNamedOpaqueTypes(Decl *decl) {
+  return false;
+}
+
 static void
 suppressingFeatureNoAsyncAvailability(PrintOptions &options,
                                       llvm::function_ref<void()> action) {

lib/Frontend/CompilerInvocation.cpp

@@ -450,9 +450,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.EnableExperimentalConcurrency |=
     Args.hasArg(OPT_enable_experimental_concurrency);
 
-  Opts.EnableExperimentalNamedOpaqueTypes |=
-      Args.hasArg(OPT_enable_experimental_named_opaque_types);
-
   Opts.EnableOpenedExistentialTypes =
     Args.hasFlag(OPT_enable_experimental_opened_existential_types,
                  OPT_disable_experimental_opened_existential_types,
@@ -663,6 +660,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.Features.insert(Feature::VariadicGenerics);
   if (Args.hasArg(OPT_enable_experimental_static_assert))
     Opts.Features.insert(Feature::StaticAssert);
+  if (Args.hasArg(OPT_enable_experimental_associated_type_inference))
+    Opts.Features.insert(Feature::NamedOpaqueTypes);
 
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
 

lib/Parse/ParseType.cpp

@@ -564,7 +564,7 @@ ParserResult<TypeRepr> Parser::parseType(
 
 ParserResult<TypeRepr> Parser::parseTypeWithOpaqueParams(Diag<> MessageID) {
   GenericParamList *genericParams = nullptr;
-  if (Context.LangOpts.EnableExperimentalNamedOpaqueTypes) {
+  if (Context.LangOpts.hasFeature(Feature::NamedOpaqueTypes)) {
     auto result = maybeParseGenericParams();
     genericParams = result.getPtrOrNull();
     if (result.hasCodeCompletion())

tools/swift-ide-test/swift-ide-test.cpp

@@ -4299,7 +4299,7 @@ int main(int argc, char *argv[]) {
     InitInvok.getLangOptions().DisableImplicitStringProcessingModuleImport = true;
   }
   if (options::EnableExperimentalNamedOpaqueTypes) {
-    InitInvok.getLangOptions().EnableExperimentalNamedOpaqueTypes = true;
+    InitInvok.getLangOptions().Features.insert(Feature::NamedOpaqueTypes);
   }
   if (options::EnableExperimentalStringProcessing) {
     InitInvok.getLangOptions().EnableExperimentalStringProcessing = true;