Issue 23190. Type check with a function type alias is its usage.

pkg/analyzer/test/generated/resolver_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library engine.resolver_test;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 3511 matching lines @@
 _f(int p) {
   _f(p - 1);
 }
 main() {
 }''');
     resolve(source);
     assertErrors(source, [HintCode.UNUSED_ELEMENT]);
     verify([source]);
   }
 
+  void test_unusedElement_functionTypeAlias_isUsed_isExpression() {
+    enableUnusedElement = true;
+    Source source = addSource(r'''
+typedef _F(a, b);
+main(f) {
+  if (f is _F) {
+    print('F');
+  }
+}''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   void test_unusedElement_functionTypeAlias_isUsed_reference() {
     enableUnusedElement = true;
     Source source = addSource(r'''
 typedef _F(a, b);
 main(_F f) {
 }''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
@@ skipping 10162 matching lines @@
         // check propagated type
         FunctionType propagatedType = node.propagatedType as FunctionType;
         expect(propagatedType.returnType, test.typeProvider.stringType);
       } on AnalysisException catch (e, stackTrace) {
         thrownException[0] = new CaughtException(e, stackTrace);
       }
     }
     return null;
   }
 }