Fix hints and warnings.

pkg/analyzer/lib/src/generated/error_verifier.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 analyzer.src.generated.error_verifier;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2568 matching lines @@
           StaticWarningCode.ASSIGNMENT_TO_TYPE, expression);
     }
   }
 
   /**
    * Verifies that the class is not named `Function` and that it doesn't
    * extends/implements/mixes in `Function`.
    */
   void _checkForBadFunctionUse(ClassDeclaration node) {
     ExtendsClause extendsClause = node.extendsClause;
-    ImplementsClause implementsClause = node.implementsClause;
     WithClause withClause = node.withClause;
 
     if (node.name.name == "Function") {
       _errorReporter.reportErrorForNode(
           HintCode.DEPRECATED_FUNCTION_CLASS_DECLARATION, node.name);
     }
 
     if (extendsClause != null) {
       InterfaceType superclassType = _enclosingClass.supertype;
       ClassElement superclassElement = superclassType?.element;
@@ skipping 4478 matching lines @@
 class _InvocationCollector extends RecursiveAstVisitor {
   final List<String> superCalls = <String>[];
 
   @override
   visitMethodInvocation(MethodInvocation node) {
     if (node.target is SuperExpression) {
       superCalls.add(node.methodName.name);
     }
   }
 }