[Frontend] NFC: Add a flag to enable bridging of completion handlers to checked continuations

(cherry picked from commit b8fb94b)

Author: xedin

include/swift/Basic/LangOptions.h

@@ -389,6 +389,10 @@ namespace swift {
     bool DisableImplicitBacktracingModuleImport =
         !SWIFT_IMPLICIT_BACKTRACING_IMPORT;
 
+    // Whether to use checked continuations when making an async call from
+    // Swift into ObjC. If false, will use unchecked continuations instead.
+    bool UseCheckedAsyncObjCBridging = false;
+
     /// Should we check the target OSs of serialized modules to see that they're
     /// new enough?
     bool EnableTargetOSChecking = true;

include/swift/Option/FrontendOptions.td

@@ -364,6 +364,10 @@ def enable_experimental_async_top_level :
 // HIDDEN FLAGS
 let Flags = [FrontendOption, NoDriverOption, HelpHidden] in {
 
+def checked_async_objc_bridging : Joined<["-"], "checked-async-objc-bridging=">,
+  HelpText<"Control whether checked continuations are used when bridging "
+           "async calls from Swift to ObjC: 'on', 'off' ">;
+
 def debug_constraints : Flag<["-"], "debug-constraints">,
   HelpText<"Debug the constraint-based type checker">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -1326,6 +1326,21 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     HadError = true;
   }
 
+  if (auto A = Args.getLastArg(OPT_checked_async_objc_bridging)) {
+    auto value = llvm::StringSwitch<llvm::Optional<bool>>(A->getValue())
+                     .Case("off", false)
+                     .Case("on", true)
+                     .Default(llvm::None);
+
+    if (value) {
+      Opts.UseCheckedAsyncObjCBridging = *value;
+    } else {
+      Diags.diagnose(SourceLoc(), diag::error_invalid_arg_value,
+                     A->getAsString(Args), A->getValue());
+      HadError = true;
+    }
+  }
+
   return HadError || UnsupportedOS || UnsupportedArch;
 }
 

test/SILGen/objc_async.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-silgen -I %S/Inputs/custom-modules  -disable-availability-checking %s -verify | %FileCheck --check-prefix=CHECK --check-prefix=CHECK-%target-cpu %s
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-silgen -checked-async-objc-bridging=off -I %S/Inputs/custom-modules  -disable-availability-checking %s -verify | %FileCheck --check-prefix=CHECK --check-prefix=CHECK-%target-cpu %s
 // REQUIRES: concurrency
 // REQUIRES: objc_interop
 

test/SILGen/objc_effectful_properties.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-silgen -disable-availability-checking -I %S/Inputs/custom-modules %s -verify | %FileCheck --enable-var-scope --check-prefix=CHECK --check-prefix=CHECK-%target-cpu %s
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-silgen -checked-async-objc-bridging=off -disable-availability-checking -I %S/Inputs/custom-modules %s -verify | %FileCheck --enable-var-scope --check-prefix=CHECK --check-prefix=CHECK-%target-cpu %s
 // REQUIRES: concurrency
 // REQUIRES: objc_interop