Add experimental feature for type witness system inference

Author: DougGregor

include/swift/Basic/Features.def

@@ -89,6 +89,7 @@ EXPERIMENTAL_FEATURE(NamedOpaqueTypes)
 EXPERIMENTAL_FEATURE(FlowSensitiveConcurrencyCaptures)
 EXPERIMENTAL_FEATURE(MoveOnly)
 EXPERIMENTAL_FEATURE(OneWayClosureParameters)
+EXPERIMENTAL_FEATURE(TypeWitnessSystemInference)
 
 #undef EXPERIMENTAL_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

include/swift/Basic/LangOptions.h

@@ -330,10 +330,6 @@ namespace swift {
     /// Enable inference of Sendable conformances for public types.
     bool EnableInferPublicSendable = false;
 
-    /// Enable experimental associated type inference using type witness
-    /// systems.
-    bool EnableExperimentalAssociatedTypeInference = false;
-
     /// Disable the implicit import of the _Concurrency module.
     bool DisableImplicitConcurrencyModuleImport =
         !SWIFT_IMPLICIT_CONCURRENCY_IMPORT;

lib/AST/ASTPrinter.cpp

@@ -3019,6 +3019,10 @@ static bool usesFeatureOneWayClosureParameters(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureTypeWitnessSystemInference(Decl *decl) {
+  return false;
+}
+
 static void
 suppressingFeatureNoAsyncAvailability(PrintOptions &options,
                                       llvm::function_ref<void()> action) {

lib/Frontend/CompilerInvocation.cpp

@@ -455,9 +455,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                  OPT_disable_experimental_opened_existential_types,
                  true);
 
-  Opts.EnableExperimentalAssociatedTypeInference |=
-      Args.hasArg(OPT_enable_experimental_associated_type_inference);
-
   Opts.EnableInferPublicSendable |=
     Args.hasFlag(OPT_enable_infer_public_concurrent_value,
                  OPT_disable_infer_public_concurrent_value,
@@ -655,14 +652,16 @@ 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))
+  if (Args.hasArg(OPT_enable_experimental_named_opaque_types))
     Opts.Features.insert(Feature::NamedOpaqueTypes);
   if (Args.hasArg(OPT_enable_experimental_flow_sensitive_concurrent_captures))
     Opts.Features.insert(Feature::FlowSensitiveConcurrencyCaptures);
   if (Args.hasArg(OPT_enable_experimental_move_only))
     Opts.Features.insert(Feature::MoveOnly);
   if (Args.hasArg(OPT_experimental_one_way_closure_params))
     Opts.Features.insert(Feature::OneWayClosureParameters);
+  if (Args.hasArg(OPT_enable_experimental_associated_type_inference))
+    Opts.Features.insert(Feature::TypeWitnessSystemInference);
 
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
 

lib/Sema/TypeCheckProtocolInference.cpp

@@ -1206,7 +1206,7 @@ AssociatedTypeDecl *AssociatedTypeInference::inferAbstractTypeWitnesses(
   // not resolve otherwise.
   llvm::SmallVector<AbstractTypeWitness, 2> abstractTypeWitnesses;
 
-  if (ctx.LangOpts.EnableExperimentalAssociatedTypeInference) {
+  if (ctx.LangOpts.hasFeature(Feature::TypeWitnessSystemInference)) {
     TypeWitnessSystem system(unresolvedAssocTypes);
     collectAbstractTypeWitnesses(system, unresolvedAssocTypes);