Frontend: Add -enable-resilient-objc-class-stubs command line flag

Author: slavapestov

include/swift/Basic/LangOptions.h

@@ -296,6 +296,11 @@ namespace swift {
     /// set to true.
     bool ExperimentalDependenciesIncludeIntrafileOnes = false;
 
+    /// Enable experimental support for emitting Objective-C resilient class
+    /// stubs. This is a language option since it also determines if we admit
+    /// @objc members in extensions of classes with resilient ancestry.
+    bool EnableObjCResilientClassStubs = false;
+
     /// Sets the target we are building for and updates platform conditions
     /// to match.
     ///

include/swift/Option/FrontendOptions.td

@@ -555,4 +555,8 @@ def type_info_dump_filter_EQ : Joined<["-"], "type-info-dump-filter=">,
   Flags<[FrontendOption]>,
   HelpText<"One of 'all', 'resilient' or 'fragile'">;
 
+def enable_objc_resilient_class_stubs : Flag<["-"], "enable-resilient-objc-class-stubs">,
+  HelpText<"Emit Objective-C resilient class stubs for classes with "
+           "resiliently-sized metadata">;
+
 } // end let Flags = [FrontendOption, NoDriverOption, HelpHidden]

lib/Frontend/CompilerInvocation.cpp

@@ -450,6 +450,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DisableConstraintSolverPerformanceHacks |=
       Args.hasArg(OPT_disable_constraint_solver_performance_hacks);
 
+  Opts.EnableObjCResilientClassStubs =
+      Args.hasArg(OPT_enable_objc_resilient_class_stubs);
+
   // Must be processed after any other language options that could affect
   // platform conditions.
   bool UnsupportedOS, UnsupportedArch;