Don't infer 'dynamic' on accessors in extensions of ObjC classes.

Instead, propagate the decision from the associated storage decl (var
or subscript), using the mechanisms that are already in place.

rdar://problem/29741743

Author: jrose-apple

lib/Sema/TypeCheckDecl.cpp

@@ -2227,6 +2227,12 @@ static void inferDynamic(ASTContext &ctx, ValueDecl *D) {
     if (VD->isLet() && !isNSManaged) return;
   }
 
+  // Accessors should not infer 'dynamic' on their own; they can get it from
+  // their storage decls.
+  if (auto FD = dyn_cast<FuncDecl>(D))
+    if (FD->isAccessor())
+      return;
+
   // The presence of 'final' on a class prevents 'dynamic'.
   auto classDecl = D->getDeclContext()->getAsClassOrClassExtensionContext();
   if (!classDecl) return;
@@ -3810,6 +3816,9 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       if (isObjC && !TC.isRepresentableInObjC(SD, *isObjC))
         isObjC = None;
       markAsObjC(TC, SD, isObjC);
+
+      // Infer 'dynamic' before touching accessors.
+      inferDynamic(TC.Context, SD);
     }
 
     if (SD->hasAccessorFunctions())
@@ -3838,8 +3847,6 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       synthesizeSetterForMutableAddressedStorage(SD, TC);
     }
 
-    inferDynamic(TC.Context, SD);
-
     TC.checkDeclAttributes(SD);
   }
 
@@ -7015,6 +7022,7 @@ void TypeChecker::validateDecl(ValueDecl *D) {
 
         markAsObjC(*this, VD, isObjC);
 
+        // Infer 'dynamic' before touching accessors.
         inferDynamic(Context, VD);
 
         // If this variable is a class member, mark it final if the

test/attr/attr_dynamic_infer.swift

@@ -54,3 +54,28 @@ extension Sub {
   override func baseFoo() {
   }
 }
+
+
+@objc class FinalTests {}
+
+extension FinalTests {
+  // CHECK:  @objc final func foo
+  final func foo() { }
+
+  // CHECK: @objc final var prop: Super
+  final var prop: Super {
+    // CHECK: @objc final get
+    get { return Super() }
+    // CHECK: @objc final set
+    set { }
+  }
+
+  // CHECK: @objc final subscript(sup: Super) -> Super
+  final subscript(sup: Super) -> Super {
+    // CHECK: @objc final get
+    get { return sup }
+    // CHECK: @objc final set
+    set { }
+  }
+}
+