Thin and C functions conform to ConcurrentValue

Author: DougGregor

lib/Sema/TypeCheckConcurrency.cpp

@@ -768,7 +768,20 @@ static bool isConcurrentValueType(const DeclContext *dc, Type type) {
 
     bool visitFunctionType(FunctionType *type) {
       // Concurrent function types meet the requirements.
-      return type->isConcurrent();
+      if (type->isConcurrent())
+        return true;
+
+      // C and thin function types meeting the requirements because they
+      // cannot have captures.
+      switch (type->getExtInfo().getRepresentation()) {
+      case FunctionTypeRepresentation::Block:
+      case FunctionTypeRepresentation::Swift:
+        return false;
+
+      case FunctionTypeRepresentation::CFunctionPointer:
+      case FunctionTypeRepresentation::Thin:
+        return true;
+      }
     }
 
     bool visitProtocolCompositionType(ProtocolCompositionType *type) {

test/Concurrency/concurrent_value_inference.swift

@@ -80,10 +80,16 @@ public enum PublicEnum {
   case some
 }
 
+struct HasFunctions {
+  var tfp: @convention(thin) () -> Void
+  var cfp: @convention(c) () -> Void
+}
+
 func testCV(
   c1: C1, c2: C2, s1: S1, e1: E1, e2: E2, gs1: GS1<Int>, gs2: GS2<Int>,
   bc: Bitcode, ps: PublicStruct, pe: PublicEnum,
-  fps: FrozenPublicStruct, fpe: FrozenPublicEnum
+  fps: FrozenPublicStruct, fpe: FrozenPublicEnum,
+  hf: HasFunctions
 ) {
   acceptCV(c1) // expected-error{{'C1' conform to 'ConcurrentValue'}}
   acceptCV(c2)
@@ -103,4 +109,7 @@ func testCV(
   // Public is okay when also @frozen.
   acceptCV(fps)
   acceptCV(fpe)
+
+  // Thin and C function types are ConcurrentValue.
+  acceptCV(hf)
 }