[SourceKit] Mark overridable declarations as dynamic

lib/IDE/IDERequests.cpp

@@ -158,6 +158,13 @@ bool CursorInfoResolver::tryResolve(ValueDecl *D, TypeDecl *CtorTyRef,
       IsDynamic = true;
       ide::getReceiverType(BaseE, ReceiverTypes);
     }
+  } else if (ExprStack.empty() && isDeclOverridable(D)) {
+    // We aren't in a call (otherwise we would have an expression stack wouldn't
+    // be empty), so we're at the declaration of an overridable declaration.
+    // Mark the declaration as dynamic so that jump-to-definition can offer to
+    // jump to any declaration that overrides this declaration.
+    IsDynamic = true;
+    ReceiverTypes.push_back(D->getDeclContext()->getSelfNominalTypeDecl());
   }
 
   if (Data)

test/SourceKit/CursorInfo/cursor_of_protocol_requirement_is_dynamic.swift

@@ -0,0 +1,17 @@
+protocol MyProto {
+  // RUN: %sourcekitd-test -req=cursor -pos=%(line + 1):9 %s -- %s | %FileCheck %s
+  func foo()
+}
+
+// CHECK: DYNAMIC
+// CHECK: RECEIVERS BEGIN
+// CHECK: s:41cursor_of_protocol_requirement_is_dynamic7MyProtoP
+// CHECK: RECEIVERS END
+
+class ClassA: MyProto {
+  func foo() {}
+}
+
+class ClassB: MyProto {
+  func foo() {}
+}