Diagnostic: dynamic replacement and replaced function's @objc attribute must match

rdar://48259565

Author: aschwaighofer

include/swift/AST/DiagnosticsSema.def

@@ -3921,6 +3921,10 @@ ERROR(dynamic_replacement_not_in_extension, none,
       "dynamicReplacement(for:) of %0 is not defined in an extension or at the file level", (DeclName))
 ERROR(dynamic_replacement_must_not_be_dynamic, none,
       "dynamicReplacement(for:) of %0 must not be dynamic itself", (DeclName))
+ERROR(dynamic_replacement_replaced_not_objc_dynamic, none,
+      "%0 is not marked @objc dynamic", (DeclName))
+ERROR(dynamic_replacement_replacement_not_objc_dynamic, none,
+      "%0 is marked @objc dynamic", (DeclName))
 
 //------------------------------------------------------------------------------
 // MARK: @available

lib/Sema/TypeCheckAttr.cpp

@@ -2229,7 +2229,23 @@ void TypeChecker::checkDynamicReplacementAttribute(ValueDecl *D) {
     if (auto *attr = replacements[index]
                          ->getAttrs()
                          .getAttribute<DynamicReplacementAttr>()) {
-      attr->setReplacedFunction(origs[index]);
+      auto *replacedFun = origs[index];
+      auto *replacement = replacements[index];
+      if (replacedFun->isObjC() && !replacement->isObjC()) {
+        diagnose(attr->getLocation(),
+                 diag::dynamic_replacement_replacement_not_objc_dynamic,
+                 attr->getReplacedFunctionName());
+        attr->setInvalid();
+        return;
+      }
+      if (!replacedFun->isObjC() && replacement->isObjC()) {
+        diagnose(attr->getLocation(),
+                 diag::dynamic_replacement_replaced_not_objc_dynamic,
+                 attr->getReplacedFunctionName());
+        attr->setInvalid();
+        return;
+      }
+      attr->setReplacedFunction(replacedFun);
       continue;
     }
     auto *newAttr = DynamicReplacementAttr::create(

test/attr/attr_objc_dynamic_replacement.swift

@@ -0,0 +1,22 @@
+// RUN: %target-typecheck-verify-swift -swift-version 5
+//
+// REQUIRES: objc_interop
+
+class Object {
+  @objc dynamic func method(){
+  }
+
+  dynamic func nativeMethod() {
+  }
+}
+
+extension Object {
+  @_dynamicReplacement(for: method()) // expected-error{{'method()' is marked @objc dynamic}}
+  func replacement() {
+  }
+
+  @_dynamicReplacement(for: nativeMethod()) // expected-error{{'nativeMethod()' is not marked @objc dynamic}}
+  @objc dynamic func replacement2() {
+  }
+
+}