Updated dart lint rules

analysis_options.yaml

-# https://www.dartlang.org/guides/language/analysis-options
+# Specify analysis options.
+#
+# Until there are meta linter rules, each desired lint must be explicitly enabled.
+# See: https://github.com/dart-lang/linter/issues/288
+#
+# For a list of lints, see: http://dart-lang.github.io/linter/lints/
+# See the configuration guide for more
+# https://github.com/dart-lang/sdk/tree/master/pkg/analyzer#configuring-the-analyzer
+#
+# There are four similar analysis options files in the flutter repos:
+#   - analysis_options.yaml (this file)
+#   - packages/flutter/lib/analysis_options_user.yaml
+#   - https://github.com/flutter/plugins/blob/master/analysis_options.yaml
+#   - https://github.com/flutter/engine/blob/master/analysis_options.yaml
+#
+# This file contains the analysis options used by Flutter tools, such as IntelliJ,
+# Android Studio, and the `flutter analyze` command.
+#
+# The flutter/plugins repo contains a copy of this file, which should be kept
+# in sync with this file.
+
 analyzer:
 analyzer:
-  strong-mode: true
+  language:
+    enableSuperMixins: true
+  strong-mode:
+    implicit-dynamic: false
+  errors:
+    # treat missing required parameters as a warning (not a hint)
+    missing_required_param: warning
+    # treat missing returns as a warning (not a hint)
+    missing_return: warning
+    # allow having TODOs in the code
+    todo: ignore
+  exclude:
+    - 'bin/cache/**'
+    # the following two are relative to the stocks example and the flutter package respectively
+    # see https://github.com/dart-lang/sdk/issues/28463
+    - 'lib/i18n/stock_messages_*.dart'
+    - 'lib/src/http/**'
 
 
-# Source of linter options:
-# http://dart-lang.github.io/linter/lints/options/options.html
 linter:
 linter:
   rules:
   rules:
+    # these rules are documented on and in the same order as
+    # the Dart Lint rules page to make maintenance easier
+    # https://github.com/dart-lang/linter/blob/master/example/all.yaml
     - always_declare_return_types
     - always_declare_return_types
-    - camel_case_types
-    - empty_constructor_bodies
+    - always_put_control_body_on_new_line
+    # - always_put_required_named_parameters_first # we prefer having parameters in the same order as fields https://github.com/flutter/flutter/issues/10219
+    - always_require_non_null_named_parameters
+    - always_specify_types
     - annotate_overrides
     - annotate_overrides
+    # - avoid_annotating_with_dynamic # conflicts with always_specify_types
+    - avoid_as
+    # - avoid_bool_literals_in_conditional_expressions # not yet tested
+    # - avoid_catches_without_on_clauses # we do this commonly
+    # - avoid_catching_errors # we do this commonly
+    - avoid_classes_with_only_static_members
+    # - avoid_double_and_int_checks # only useful when targeting JS runtime
+    - avoid_empty_else
+    - avoid_field_initializers_in_const_classes
+    - avoid_function_literals_in_foreach_calls
     - avoid_init_to_null
     - avoid_init_to_null
-    - constant_identifier_names
-    - one_member_abstracts
+    # - avoid_js_rounded_ints # only useful when targeting JS runtime
+    - avoid_null_checks_in_equality_operators
+    # - avoid_positional_boolean_parameters # not yet tested
+    # - avoid_private_typedef_functions # we prefer having typedef (discussion in https://github.com/flutter/flutter/pull/16356)
+    - avoid_relative_lib_imports
+    - avoid_renaming_method_parameters
+    - avoid_return_types_on_setters
+    # - avoid_returning_null # we do this commonly
+    # - avoid_returning_this # https://github.com/dart-lang/linter/issues/842
+    # - avoid_setters_without_getters # not yet tested
+    # - avoid_single_cascade_in_expression_statements # not yet tested
+    - avoid_slow_async_io
+    # - avoid_types_as_parameter_names # https://github.com/dart-lang/linter/pull/954/files
+    # - avoid_types_on_closure_parameters # conflicts with always_specify_types
+    # - avoid_unused_constructor_parameters # https://github.com/dart-lang/linter/pull/847
+    - await_only_futures
+    - camel_case_types
+    - cancel_subscriptions
+    # - cascade_invocations # not yet tested
+    # - close_sinks # https://github.com/flutter/flutter/issues/5789
+    # - comment_references # blocked on https://github.com/dart-lang/dartdoc/issues/1153
+    # - constant_identifier_names # https://github.com/dart-lang/linter/issues/204
+    - control_flow_in_finally
+    - directives_ordering
+    - empty_catches
+    - empty_constructor_bodies
+    - empty_statements
+    - hash_and_equals
+    - implementation_imports
+    # - invariant_booleans # https://github.com/flutter/flutter/issues/5790
+    - iterable_contains_unrelated_type
+    # - join_return_with_assignment # not yet tested
+    - library_names
+    - library_prefixes
+    - list_remove_unrelated_type
+    # - literal_only_boolean_expressions # https://github.com/flutter/flutter/issues/5791
+    - no_adjacent_strings_in_list
+    - no_duplicate_case_values
+    - non_constant_identifier_names
+    # - omit_local_variable_types # opposite of always_specify_types
+    # - one_member_abstracts # too many false positives
+    # - only_throw_errors # https://github.com/flutter/flutter/issues/5792
+    - overridden_fields
+    - package_api_docs
+    - package_names
+    - package_prefixed_library_names
+    # - parameter_assignments # we do this commonly
+    - prefer_adjacent_string_concatenation
+    - prefer_asserts_in_initializer_lists
+    - prefer_bool_in_asserts
+    - prefer_collection_literals
+    - prefer_conditional_assignment
+    - prefer_const_constructors
+    - prefer_const_constructors_in_immutables
+    - prefer_const_declarations
+    - prefer_const_literals_to_create_immutables
+    # - prefer_constructors_over_static_methods # not yet tested
+    - prefer_contains
+    - prefer_equal_for_default_values
+    # - prefer_expression_function_bodies # conflicts with https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#consider-using--for-short-functions-and-methods
+    - prefer_final_fields
+    - prefer_final_locals
+    - prefer_foreach
+    # - prefer_function_declarations_over_variables # not yet tested
+    - prefer_initializing_formals
+    # - prefer_interpolation_to_compose_strings # not yet tested
+    # - prefer_iterable_whereType # https://github.com/dart-lang/sdk/issues/32463
+    - prefer_is_empty
+    - prefer_is_not_empty
+    - prefer_single_quotes
+    - prefer_typing_uninitialized_variables
+    - recursive_getters
     - slash_for_doc_comments
     - slash_for_doc_comments
     - sort_constructors_first
     - sort_constructors_first
+    - sort_unnamed_constructors_first
+    - super_goes_last
+    - test_types_in_equals
+    - throw_in_finally
+    # - type_annotate_public_apis # subset of always_specify_types
+    - type_init_formals
+    # - unawaited_futures # https://github.com/flutter/flutter/issues/5793
     - unnecessary_brace_in_string_interps
     - unnecessary_brace_in_string_interps
+    # - unnecessary_const
+    - unnecessary_getters_setters
+    # - unnecessary_lambdas # https://github.com/dart-lang/linter/issues/498
+    - unnecessary_null_aware_assignments
+    - unnecessary_null_in_if_null_operators
+    - unnecessary_overrides
+    - unnecessary_parenthesis
+    # - unnecessary_statements # not yet tested
+    - unnecessary_this
+    - unrelated_type_equality_checks
+    - use_rethrow_when_possible
+    # - use_setters_to_change_properties # not yet tested
+    # - use_string_buffers # https://github.com/dart-lang/linter/pull/664
+    # - use_to_and_as_if_applicable # has false positives, so we prefer to catch this by code-review
+    - valid_regexps
+    # - void_checks # not yet tested

example/lib/main.dart

-import 'package:flutter/material.dart';
 import 'dart:async';
 import 'dart:async';
 
 
+import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/services.dart';
 import 'package:permission_handler/permission_enums.dart';
 import 'package:permission_handler/permission_enums.dart';
 import 'package:permission_handler/permission_handler.dart';
 import 'package:permission_handler/permission_handler.dart';
@@ -31,12 +31,12 @@ class _MyAppState extends State<MyApp> {
           .checkPermissionStatus(PermissionGroup.calendar);
           .checkPermissionStatus(PermissionGroup.calendar);
 
 
       if (permissionStatus != PermissionStatus.granted) {
       if (permissionStatus != PermissionStatus.granted) {
-        final shouldShowRationale = await PermissionHandler
+        final bool shouldShowRationale = await PermissionHandler
             .shouldShowRequestPermissionRationale(PermissionGroup.calendar);
             .shouldShowRequestPermissionRationale(PermissionGroup.calendar);
 
 
         if (shouldShowRationale) {
         if (shouldShowRationale) {
-          var permissions = await PermissionHandler
-              .requestPermissions([PermissionGroup.calendar]);
+          final Map<PermissionGroup, PermissionStatus> permissions = await PermissionHandler
+              .requestPermissions(<PermissionGroup>[PermissionGroup.calendar]);
           if (permissions.containsKey(PermissionGroup.calendar)) {
           if (permissions.containsKey(PermissionGroup.calendar)) {
             permissionStatus = permissions[PermissionGroup.calendar];
             permissionStatus = permissions[PermissionGroup.calendar];
           }
           }
@@ -49,7 +49,9 @@ class _MyAppState extends State<MyApp> {
     // If the widget was removed from the tree while the asynchronous platform
     // If the widget was removed from the tree while the asynchronous platform
     // message was in flight, we want to discard the reply rather than calling
     // message was in flight, we want to discard the reply rather than calling
     // setState to update our non-existent appearance.
     // setState to update our non-existent appearance.
-    if (!mounted) return;
+    if (!mounted) {
+      return;
+    }
 
 
     setState(() {
     setState(() {
       _permissionStatus = permissionStatus.toString();
       _permissionStatus = permissionStatus.toString();
@@ -68,7 +70,7 @@ class _MyAppState extends State<MyApp> {
             children: <Widget>[
             children: <Widget>[
               new Text('Running on: $_permissionStatus\n'),
               new Text('Running on: $_permissionStatus\n'),
               new RaisedButton(
               new RaisedButton(
-                child: new Text("Open settings"),
+                child: const Text('Open settings'),
                 onPressed: () async =>
                 onPressed: () async =>
                     await PermissionHandler.openAppSettings(),
                     await PermissionHandler.openAppSettings(),
               ),
               ),

lib/permission_handler.dart

@@ -12,7 +12,7 @@ class PermissionHandler {
   /// Returns a [Future] containing the current permission status for the supplied [PermissionGroup].
   /// Returns a [Future] containing the current permission status for the supplied [PermissionGroup].
   static Future<PermissionStatus> checkPermissionStatus(
   static Future<PermissionStatus> checkPermissionStatus(
       PermissionGroup permission) async {
       PermissionGroup permission) async {
-    final status = await _channel.invokeMethod(
+    final dynamic status = await _channel.invokeMethod(
         'checkPermissionStatus', Codec.encodePermissionGroup(permission));
         'checkPermissionStatus', Codec.encodePermissionGroup(permission));
 
 
     return Codec.decodePermissionStatus(status);
     return Codec.decodePermissionStatus(status);
@@ -21,16 +21,18 @@ class PermissionHandler {
   /// Open the App settings page.
   /// Open the App settings page.
   ///
   ///
   /// Returns [true] if the app settings page could be opened, otherwise [false] is returned.
   /// Returns [true] if the app settings page could be opened, otherwise [false] is returned.
-  static Future<bool> openAppSettings() async =>
-      await _channel.invokeMethod("openAppSettings");
+  static Future<bool> openAppSettings() async {
+      final bool hasOpened = await _channel.invokeMethod('openAppSettings');
+      return hasOpened;
+  }
 
 
   /// Request the user for access to the supplied list of permissiongroups.
   /// Request the user for access to the supplied list of permissiongroups.
   ///
   ///
   /// Returns a [Map] containing the status per requested permissiongroup.
   /// Returns a [Map] containing the status per requested permissiongroup.
   static Future<Map<PermissionGroup, PermissionStatus>> requestPermissions(
   static Future<Map<PermissionGroup, PermissionStatus>> requestPermissions(
       List<PermissionGroup> permissions) async {
       List<PermissionGroup> permissions) async {
-    final jsonData = Codec.encodePermissionGroups(permissions);
-    final status = await _channel.invokeMethod('requestPermissions', jsonData);
+    final String jsonData = Codec.encodePermissionGroups(permissions);
+    final dynamic status = await _channel.invokeMethod('requestPermissions', jsonData);
 
 
     return Codec.decodePermissionRequestResult(status);
     return Codec.decodePermissionRequestResult(status);
   }
   }
@@ -40,7 +42,10 @@ class PermissionHandler {
   /// This method is only implemented on Android, calling this on iOS always
   /// This method is only implemented on Android, calling this on iOS always
   /// returns [false].
   /// returns [false].
   static Future<bool> shouldShowRequestPermissionRationale(
   static Future<bool> shouldShowRequestPermissionRationale(
-          PermissionGroup permission) async =>
-      await _channel.invokeMethod('shouldShowRequestPermissionRationale',
+          PermissionGroup permission) async {
+    final bool shouldShowRationale = await _channel.invokeMethod('shouldShowRequestPermissionRationale',
           Codec.encodePermissionGroup(permission));
           Codec.encodePermissionGroup(permission));
+    
+    return shouldShowRationale;
+  }
 }
 }

lib/utils/codec.dart

@@ -4,22 +4,22 @@ import 'package:permission_handler/permission_enums.dart';
 
 
 class Codec {
 class Codec {
   static PermissionStatus decodePermissionStatus(dynamic value) {
   static PermissionStatus decodePermissionStatus(dynamic value) {
-    final permission = json.decode(value);
+    final dynamic permission = json.decode(value.toString());
 
 
     return PermissionStatus.values
     return PermissionStatus.values
-        .firstWhere((e) => e.toString().split('.').last == permission);
+        .firstWhere((PermissionStatus e) => e.toString().split('.').last == permission);
   }
   }
 
 
   static Map<PermissionGroup, PermissionStatus> decodePermissionRequestResult(
   static Map<PermissionGroup, PermissionStatus> decodePermissionRequestResult(
       dynamic value) {
       dynamic value) {
-    final jsonObject = json.decode(value);
+    final dynamic jsonObject = json.decode(value.toString());
 
 
-    final permissionResults = Map<PermissionGroup, PermissionStatus>();
-    jsonObject.forEach((key, value) {
-      final permissionGroup = PermissionGroup.values
-          .firstWhere((e) => e.toString().split('.').last == key.toString());
-      final permissionStatus = PermissionStatus.values
-          .firstWhere((e) => e.toString().split('.').last == value.toString());
+    final Map<PermissionGroup, PermissionStatus> permissionResults = <PermissionGroup, PermissionStatus>{};
+    jsonObject.forEach((PermissionGroup key, PermissionStatus value) {
+      final PermissionGroup permissionGroup = PermissionGroup.values
+          .firstWhere((PermissionGroup e) => e.toString().split('.').last == key.toString());
+      final PermissionStatus permissionStatus = PermissionStatus.values
+          .firstWhere((PermissionStatus e) => e.toString().split('.').last == value.toString());
 
 
       permissionResults[permissionGroup] = permissionStatus;
       permissionResults[permissionGroup] = permissionStatus;
     });
     });
@@ -31,7 +31,7 @@ class Codec {
       json.encode(_encodeEnum(permissionGroup));
       json.encode(_encodeEnum(permissionGroup));
 
 
   static String encodePermissionGroups(List<PermissionGroup> permissions) =>
   static String encodePermissionGroups(List<PermissionGroup> permissions) =>
-      json.encode(permissions.map((p) => _encodeEnum(p)).toList());
+      json.encode(permissions.map((PermissionGroup p) => _encodeEnum(p)).toList());
 
 
   static String _encodeEnum(dynamic value) {
   static String _encodeEnum(dynamic value) {
     return value.toString().split('.').last;
     return value.toString().split('.').last;