Add a new flag to disable round trip through the new Swift parser

Author: meg-gupta

include/swift/Option/FrontendOptions.td

@@ -1310,4 +1310,9 @@ def platform_c_calling_convention :
 def platform_c_calling_convention_EQ :
     Joined<["-"], "experimental-platform-c-calling-convention=">,
     Alias<platform_c_calling_convention>;
+
+def disable_experimental_parser_round_trip : Flag<["-"],
+  "disable-experimental-parser-round-trip">,
+  HelpText<"Disable round trip through the new swift parser">;
+
 } // end let Flags = [FrontendOption, NoDriverOption, HelpHidden]

lib/Basic/LangOptions.cpp

@@ -33,10 +33,6 @@ using namespace swift;
 
 LangOptions::LangOptions() {
   // Note: Introduce default-on language options here.
-#ifndef NDEBUG
-  Features.insert(Feature::ParserRoundTrip);
-  Features.insert(Feature::ParserValidation);
-#endif
   // Enable any playground options that are enabled by default.
 #define PLAYGROUND_OPTION(OptionName, Description, DefaultOn, HighPerfOn) \
   if (DefaultOn) \

lib/Frontend/CompilerInvocation.cpp

@@ -1402,6 +1402,16 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
+#ifndef NDEBUG
+  /// Enable round trip parsing via the new swift parser unless it is disabled
+  /// explicitly. The new Swift parser can have mismatches with C++ parser -
+  /// rdar://118013482 Use this flag to disable round trip through the new
+  /// Swift parser for such cases.
+  if (!Args.hasArg(OPT_disable_experimental_parser_round_trip)) {
+    Opts.Features.insert(Feature::ParserRoundTrip);
+    Opts.Features.insert(Feature::ParserValidation);
+  }
+#endif
   return HadError || UnsupportedOS || UnsupportedArch;
 }
 

test/Parse/result_depends_on.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift  -enable-builtin-module -enable-experimental-feature NonEscapableTypes
+// RUN: %target-typecheck-verify-swift  -enable-builtin-module -enable-experimental-feature NonEscapableTypes -disable-experimental-parser-round-trip
 // REQUIRES: asserts
 
 import Builtin
@@ -19,9 +19,7 @@ func testMultipleTypeSpecifier(x : _resultDependsOn Klass, y : _resultDependsOn
   return (Builtin.unsafeCastToNativeObject(x), Builtin.unsafeCastToNativeObject(x))
 }
 
-/*
-rdar://118125715 (Combining parameter modifiers doesn't work in the new swift parser)
+// rdar://118125715 (Combining parameter modifiers doesn't work in the new swift parser)
 func testTypeSpecifierBorrowing(x : borrowing _resultDependsOn Klass) -> Builtin.NativeObject {
-  return Builtin.unsafeCastToNativeObject(x)
+  return Builtin.unsafeCastToNativeObject(copy x)
 }
-*/