Report unused function type aliases.

pkg/analyzer/lib/src/generated/resolver.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;
 
 import "dart:math" as math;
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/utilities_collection.dart';
@@ skipping 4550 matching lines @@
     }
     if (identical(element, _enclosingExec)) {
       return;
     }
     // ignore places where the element is not actually used
     if (node.parent is TypeName) {
       AstNode parent2 = node.parent.parent;
       if (parent2 is IsExpression) {
         return;
       }
-      if (parent2 is VariableDeclarationList) {
+      // We need to instantiate/extend/implement a class to actually use it.
+      // OTOH, function type aliases are used to define closure structures.
+      if (parent2 is VariableDeclarationList && element is ClassElement) {
         return;
       }
     }
     // OK
     usedElements.addElement(element);
   }
 
   static bool _isReadIdentifier(SimpleIdentifier node) {
     // not reading at all
     if (!node.inGetterContext()) {
@@ skipping 10318 matching lines @@
     if (!_isUsedElement(element)) {
       _reportErrorForElement(HintCode.UNUSED_ELEMENT, element, [
         element.kind.displayName,
         element.displayName
       ]);
     }
     super.visitFunctionElement(element);
   }
 
   @override
+  visitFunctionTypeAliasElement(FunctionTypeAliasElement element) {
+    if (!_isUsedElement(element)) {
+      _reportErrorForElement(HintCode.UNUSED_ELEMENT, element, [
+        element.kind.displayName,
+        element.displayName
+      ]);
+    }
+    super.visitFunctionTypeAliasElement(element);
+  }
+
+  @override
   visitLocalVariableElement(LocalVariableElement element) {
     if (!_isUsedElement(element) && !_isNamedUnderscore(element)) {
       HintCode errorCode;
       if (_usedElements.isCatchException(element)) {
         errorCode = HintCode.UNUSED_CATCH_CLAUSE;
       } else if (_usedElements.isCatchStackTrace(element)) {
         errorCode = HintCode.UNUSED_CATCH_STACK;
       } else {
         errorCode = HintCode.UNUSED_LOCAL_VARIABLE;
       }
@@ skipping 485 matching lines @@
     nonFields.add(node);
     return null;
   }
 
   @override
   Object visitNode(AstNode node) => node.accept(TypeResolverVisitor_this);
 
   @override
   Object visitWithClause(WithClause node) => null;
 }