[AST] Drop ResultBuilderASTTransform feature flag

Author: xedin

include/swift/Basic/Features.def

@@ -84,7 +84,6 @@ LANGUAGE_FEATURE(BuiltinCopy, 0, "Builtin.copy()", true)
 LANGUAGE_FEATURE(BuiltinStackAlloc, 0, "Builtin.stackAlloc", true)
 LANGUAGE_FEATURE(BuiltinTaskRunInline, 0, "Builtin.taskRunInline", true)
 LANGUAGE_FEATURE(BuiltinUnprotectedAddressOf, 0, "Builtin.unprotectedAddressOf", true)
-LANGUAGE_FEATURE(ResultBuilderASTTransform, 0, "result builders as AST transform", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(SpecializeAttributeWithAvailability, 0, "@_specialize attribute with availability", true)
 LANGUAGE_FEATURE(BuiltinAssumeAlignment, 0, "Builtin.assumeAlignment", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(UnsafeInheritExecutor, 0, "@_unsafeInheritExecutor", true)

lib/AST/ASTPrinter.cpp

@@ -3124,10 +3124,6 @@ static bool usesFeatureOneWayClosureParameters(Decl *decl) {
   return false;
 }
 
-static bool usesFeatureResultBuilderASTTransform(Decl *decl) {
-  return false;
-}
-
 static bool usesFeatureTypeWitnessSystemInference(Decl *decl) {
   return false;
 }

lib/Frontend/CompilerInvocation.cpp

@@ -708,8 +708,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   if (Args.hasArg(OPT_enable_experimental_opaque_type_erasure))
     Opts.Features.insert(Feature::OpaqueTypeErasure);
 
-  Opts.Features.insert(Feature::ResultBuilderASTTransform);
-
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
 
   Opts.EnableSwift3ObjCInference =

lib/Sema/BuilderTransform.cpp

@@ -2469,7 +2469,9 @@ ConstraintSystem::matchResultBuilder(AnyFunctionRef fn, Type builderType,
     return None;
   }
 
-  if (Context.LangOpts.hasFeature(Feature::ResultBuilderASTTransform)) {
+  auto disableASTTransform = [&](NominalTypeDecl *builder) { return false; };
+
+  if (!disableASTTransform(builder)) {
     auto transformedBody = getBuilderTransformedBody(fn, builder);
     // If this builder transform has not yet been applied to this function,
     // let's do it and cache the result.

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

@@ -4395,8 +4395,6 @@ int main(int argc, char *argv[]) {
     options::ImportObjCHeader;
   InitInvok.getClangImporterOptions().BridgingHeader =
     options::ImportObjCHeader;
-  InitInvok.getLangOptions().Features.insert(
-      Feature::ResultBuilderASTTransform);
   InitInvok.getLangOptions().EnableAccessControl =
     !options::DisableAccessControl;
   InitInvok.getLangOptions().EnableSwift3ObjCInference =