Sema: Fix assertion failure when overriding a dynamic method with a final method

Fixes <https://bugs.swift.org/browse/SR-5924>, <rdar://problem/34497670>.

Author: slavapestov

lib/Sema/TypeCheckDecl.cpp

@@ -6235,6 +6235,10 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     }
 
     void visitDynamicAttr(DynamicAttr *attr) {
+      // Final overrides are not dynamic.
+      if (Override->isFinal())
+        return;
+
       makeDynamic(TC.Context, Override);
     }
 

test/SILGen/vtables_objc.swift

@@ -9,13 +9,50 @@ import gizmo
 class Hoozit : Gizmo {
   // Overrides Gizmo.frob
   override func frob() {}
+
   // Overrides Gizmo.funge
   override func funge() {}
 
+  // Overrides Gizmo.foo
+  final override func foo() {}
+
   func anse() {}
   func incorrige() {}
 }
 
+// CHECK-LABEL: sil hidden @_T012vtables_objc10callHoozityAA0D0CF : $@convention(thin) (@owned Hoozit) -> ()
+func callHoozit(_ h: Hoozit) {
+  // CHECK: class_method [volatile] {{.*}} : $Hoozit, #Hoozit.frob!1.foreign
+  h.frob()
+  // CHECK: function_ref @_T012vtables_objc6HoozitC3fooyyF
+  h.foo()
+  // CHECK: class_method {{.*}} : $Hoozit, #Hoozit.anse!1
+  h.anse()
+  // CHECK: return
+}
+
+class Wotsit : Hoozit {
+  // Overrides Gizmo.funge
+  override func funge() {}
+
+  // Overrides Hoozit.incorrige
+  override func incorrige() {}
+
+  // Overrides Gizmo.frob
+  final override func frob() {}
+}
+
+// CHECK-LABEL: sil hidden @_T012vtables_objc10callWotsityAA0D0CF : $@convention(thin) (@owned Wotsit) -> ()
+func callWotsit(_ w: Wotsit) {
+  // CHECK: class_method [volatile] {{.*}} : $Wotsit, #Wotsit.funge!1.foreign
+  w.funge()
+  // CHECK: class_method {{.*}} : $Wotsit, #Wotsit.incorrige!1
+  w.incorrige()
+  // CHECK: function_ref @_T012vtables_objc6WotsitC4frobyyF
+  w.frob()
+  // CHECK: return
+}
+
 // Entries only exist for native Swift methods
 
 // CHECK: sil_vtable Hoozit {
@@ -26,11 +63,6 @@ class Hoozit : Gizmo {
 // CHECK-NEXT:   #Hoozit.deinit!deallocator: _T012vtables_objc6HoozitCfD
 // CHECK-NEXT: }
 
-class Wotsit : Hoozit {
-  override func funge() {}
-  override func incorrige() {}
-}
-
 // CHECK: sil_vtable Wotsit {
 // CHECK-NEXT:   #Hoozit.anse!1: {{.*}} : _T012vtables_objc6HoozitC4anse{{[_0-9a-zA-Z]*}}F
 // CHECK-NEXT:   #Hoozit.incorrige!1: {{.*}} : _T012vtables_objc6WotsitC9incorrige{{[_0-9a-zA-Z]*}}F