Add experimental feature for one-way closure parameters

Author: DougGregor

include/swift/Basic/Features.def

@@ -88,6 +88,7 @@ EXPERIMENTAL_FEATURE(VariadicGenerics)
 EXPERIMENTAL_FEATURE(NamedOpaqueTypes)
 EXPERIMENTAL_FEATURE(FlowSensitiveConcurrencyCaptures)
 EXPERIMENTAL_FEATURE(MoveOnly)
+EXPERIMENTAL_FEATURE(OneWayClosureParameters)
 
 #undef EXPERIMENTAL_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

include/swift/Basic/LangOptions.h

@@ -721,10 +721,6 @@ namespace swift {
     /// Disable constraint system performance hacks.
     bool DisableConstraintSolverPerformanceHacks = false;
 
-    /// Enable experimental support for one-way constraints for the
-    /// parameters of closures.
-    bool EnableOneWayClosureParameters = false;
-
     /// See \ref FrontendOptions.PrintFullConvention
     bool PrintFullConvention = false;
   };

lib/AST/ASTPrinter.cpp

@@ -3015,6 +3015,10 @@ static bool usesFeatureMoveOnly(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureOneWayClosureParameters(Decl *decl) {
+  return false;
+}
+
 static void
 suppressingFeatureNoAsyncAvailability(PrintOptions &options,
                                       llvm::function_ref<void()> action) {

lib/Frontend/CompilerInvocation.cpp

@@ -661,6 +661,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     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);
 
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
 
@@ -1111,9 +1113,6 @@ static bool ParseTypeCheckerArgs(TypeCheckerOptions &Opts, ArgList &Args,
   // Always enable operator designated types for the standard library.
   Opts.EnableOperatorDesignatedTypes |= FrontendOpts.ParseStdlib;
 
-  Opts.EnableOneWayClosureParameters |=
-      Args.hasArg(OPT_experimental_one_way_closure_params);
-
   Opts.PrintFullConvention |=
       Args.hasArg(OPT_experimental_print_full_convention);
 

lib/Sema/CSSimplify.cpp

@@ -9874,7 +9874,7 @@ bool ConstraintSystem::resolveClosure(TypeVariableType *typeVar,
   // type as seen in the body of the closure and the external parameter
   // type.
   bool oneWayConstraints =
-    getASTContext().TypeCheckerOpts.EnableOneWayClosureParameters ||
+    getASTContext().LangOpts.hasFeature(Feature::OneWayClosureParameters) ||
     resultBuilderType;
 
   auto *paramList = closure->getParameters();