Lint to prefer x.isNotEmpty vs. !x.isEmpty (#143).

lib/src/rules.dart

 // Copyright (c) 2015, 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 linter.src.rules;
 
 import 'dart:collection';
 
 import 'package:linter/src/config.dart';
 import 'package:linter/src/linter.dart';
 import 'package:linter/src/rules/always_declare_return_types.dart';
 import 'package:linter/src/rules/always_specify_types.dart';
 import 'package:linter/src/rules/camel_case_types.dart';
 import 'package:linter/src/rules/constant_identifier_names.dart';
 import 'package:linter/src/rules/empty_constructor_bodies.dart';
 import 'package:linter/src/rules/implementation_imports.dart';
 import 'package:linter/src/rules/library_names.dart';
 import 'package:linter/src/rules/library_prefixes.dart';
 import 'package:linter/src/rules/non_constant_identifier_names.dart';
 import 'package:linter/src/rules/one_member_abstracts.dart';
 import 'package:linter/src/rules/package_api_docs.dart';
 import 'package:linter/src/rules/package_prefixed_library_names.dart';
+import 'package:linter/src/rules/prefer_is_not_empty.dart';
 import 'package:linter/src/rules/pub/package_names.dart';
 import 'package:linter/src/rules/slash_for_doc_comments.dart';
 import 'package:linter/src/rules/super_goes_last.dart';
 import 'package:linter/src/rules/type_init_formals.dart';
 import 'package:linter/src/rules/unnecessary_brace_in_string_interp.dart';
 import 'package:linter/src/rules/unnecessary_getters_setters.dart';
 
 final Registry ruleRegistry = new Registry()
   ..register(new AlwaysDeclareReturnTypes())
   ..register(new AlwaysSpecifyTypes())
   ..register(new CamelCaseTypes())
   ..register(new ConstantIdentifierNames())
   ..register(new EmptyConstructorBodies())
   ..register(new ImplementationImports())
   ..register(new LibraryNames())
   ..register(new LibraryPrefixes())
   ..register(new NonConstantIdentifierNames())
+  ..register(new PreferIsNotEmpty())
   ..register(new OneMemberAbstracts())
   ..register(new PackageApiDocs())
   ..register(new PackagePrefixedLibraryNames())
   ..register(new PubPackageNames())
   ..register(new SlashForDocComments())
   ..register(new SuperGoesLast())
   ..register(new TypeInitFormals())
   ..register(new UnnecessaryBraceInStringInterp())
   // Disabled pending fix: https://github.com/dart-lang/linter/issues/35
   //..register(new UnnecessaryGetters())
@@ skipping 18 matching lines @@
   /// enables `my_rule`.
   /// 
   /// Unspecified rules are treated as disabled by default.
   Iterable<LintRule> enabled(LintConfig config) => rules
       .where((rule) => config.ruleConfigs.any((rc) => rc.enables(rule.name)));
 
   void register(LintRule rule) {
     _ruleMap[rule.name] = rule;
   }
 }