Add experimental feature flag for Implement 'some'

Author: angela-laar

include/swift/Basic/Features.def

@@ -138,6 +138,9 @@ EXPERIMENTAL_FEATURE(ParserValidation)
 /// Swift Swift parser.
 EXPERIMENTAL_FEATURE(ParserSequenceFolding)
 
+/// Enables implicit some while also enabling existential `any`
+EXPERIMENTAL_FEATURE(ImplicitSome)
+
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

include/swift/Option/FrontendOptions.td

@@ -579,6 +579,10 @@ def enable_experimental_associated_type_inference :
   Flag<["-"], "enable-experimental-associated-type-inference">,
   HelpText<"Enable experimental associated type inference via type witness systems">;
 
+def enable_experimental_implicit_some :
+  Flag<["-"], "enable-experimental-implicit-some">,
+  HelpText<"Enable experimental implicit some">;
+
 def disable_availability_checking : Flag<["-"],
   "disable-availability-checking">,
   HelpText<"Disable checking for potentially unavailable APIs">;

lib/AST/ASTPrinter.cpp

@@ -3045,6 +3045,10 @@ static bool usesFeatureExistentialAny(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureImplicitSome(Decl *decl) {
+  return false;
+}
+
 static bool usesFeatureForwardTrailingClosures(Decl *decl) {
   return false;
 }

lib/Frontend/CompilerInvocation.cpp

@@ -684,9 +684,12 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.Features.insert(Feature::ForwardModeDifferentiation);
   if (Args.hasArg(OPT_enable_experimental_additive_arithmetic_derivation))
     Opts.Features.insert(Feature::AdditiveArithmeticDerivedConformances);
-  
   if (Args.hasArg(OPT_enable_experimental_opaque_type_erasure))
     Opts.Features.insert(Feature::OpaqueTypeErasure);
+  if (Args.hasArg(OPT_enable_experimental_variadic_generics)){
+      Opts.Features.insert(Feature::ImplicitSome);
+      Opts.Features.insert(Feature::ExistentialAny);
+  }
 
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);