Merge pull request #40 from n-bernat/task/avoid-returning-widget-lint

Add avoid_returning_widgets lint

example/analysis_options.yaml

@@ -15,3 +15,4 @@ custom_lint:
     - avoid_non_null_assertion
     - avoid_late_keyword
     - avoid_global_state
+    - avoid_returning_widgets

example/pubspec.yaml

@@ -5,6 +5,10 @@ publish_to: none
 environment:
   sdk: '>=3.0.0 <4.0.0'
 
+dependencies:
+  flutter:
+    sdk: flutter
+
 dev_dependencies:
   custom_lint: ^0.5.0
   solid_lints:

example/test/avoid_returning_widget_test.dart

@@ -0,0 +1,31 @@
+// ignore_for_file: unused_element
+
+/// Check returning a widget fail
+/// `avoid_returning_widgets`
+
+import 'package:flutter/widgets.dart';
+
+// expect_lint: avoid_returning_widgets
+Widget avoidReturningWidgets() => const SizedBox();
+
+class MyWidget extends StatelessWidget {
+  const MyWidget({super.key});
+
+  // expect_lint: avoid_returning_widgets
+  Widget _test1() => const SizedBox();
+
+  // expect_lint: avoid_returning_widgets
+  Widget _test2() {
+    return const SizedBox(
+      child: SizedBox(),
+    );
+  }
+
+  // expect_lint: avoid_returning_widgets
+  Widget get _test3 => const SizedBox();
+
+  @override
+  Widget build(BuildContext context) {
+    return const SizedBox();
+  }
+}

lib/lints/avoid_returning_widgets/avoid_returning_widgets_rule.dart

@@ -0,0 +1,35 @@
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/error/listener.dart';
+import 'package:custom_lint_builder/custom_lint_builder.dart';
+import 'package:solid_lints/utils/types_utils.dart';
+
+/// A rule which forbids returning widgets from functions and methods.
+class AvoidReturningWidgetsRule extends DartLintRule {
+  /// The [LintCode] of this lint rule that represents
+  /// the error whether we return a widget.
+  static const lintName = 'avoid_returning_widgets';
+
+  /// Creates a new instance of [AvoidReturningWidgetsRule].
+  const AvoidReturningWidgetsRule({required super.code});
+
+  @override
+  void run(
+    CustomLintResolver resolver,
+    ErrorReporter reporter,
+    CustomLintContext context,
+  ) {
+    context.registry.addDeclaration((node) {
+      final isWidgetReturned = switch (node) {
+        FunctionDeclaration(returnType: TypeAnnotation(:final type?)) ||
+        MethodDeclaration(returnType: TypeAnnotation(:final type?)) =>
+          hasWidgetType(type),
+        _ => false,
+      };
+
+      // `build` methods return widgets by nature
+      if (isWidgetReturned && node.declaredElement?.name != "build") {
+        reporter.reportErrorForNode(code, node);
+      }
+    });
+  }
+}

lib/solid_lints.dart

@@ -4,6 +4,7 @@ import 'package:custom_lint_builder/custom_lint_builder.dart';
 import 'package:solid_lints/lints/avoid_global_state/avoid_global_state_rule.dart';
 import 'package:solid_lints/lints/avoid_late_keyword/avoid_late_keyword_rule.dart';
 import 'package:solid_lints/lints/avoid_non_null_assertion/avoid_non_null_assertion_rule.dart';
+import 'package:solid_lints/lints/avoid_returning_widgets/avoid_returning_widgets_rule.dart';
 import 'package:solid_lints/lints/cyclomatic_complexity/cyclomatic_complexity_metric.dart';
 import 'package:solid_lints/lints/cyclomatic_complexity/models/cyclomatic_complexity_parameters.dart';
 import 'package:solid_lints/lints/function_lines_of_code/function_lines_of_code_metric.dart';
@@ -96,6 +97,20 @@ class _SolidLints extends PluginBase {
       rules.add(AvoidGlobalStateRule(code: avoidGlobalState.lintCode));
     }
 
+    final avoidReturningWidgets = MetricRule(
+      configs: configs,
+      name: AvoidReturningWidgetsRule.lintName,
+      problemMessage: (_) => ''
+          'Returning a widget from a function is considered an anti-pattern. '
+          'Extract your widget to a separate class.',
+    );
+
+    if (avoidReturningWidgets.enabled) {
+      rules.add(
+        AvoidReturningWidgetsRule(code: avoidReturningWidgets.lintCode),
+      );
+    }
+
     return rules;
   }
 }

lib/utils/types_utils.dart

@@ -0,0 +1,150 @@
+// MIT License
+//
+// Copyright (c) 2020-2021 Dart Code Checker team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+// ignore_for_file: public_member_api_docs
+
+import 'package:analyzer/dart/element/type.dart';
+
+bool hasWidgetType(DartType type) =>
+    (isWidgetOrSubclass(type) ||
+        _isIterable(type) ||
+        _isList(type) ||
+        _isFuture(type)) &&
+    !(_isMultiProvider(type) ||
+        _isSubclassOfInheritedProvider(type) ||
+        _isIterableInheritedProvider(type) ||
+        _isListInheritedProvider(type) ||
+        _isFutureInheritedProvider(type));
+
+bool isWidgetOrSubclass(DartType? type) =>
+    _isWidget(type) || _isSubclassOfWidget(type);
+
+bool isRenderObjectOrSubclass(DartType? type) =>
+    _isRenderObject(type) || _isSubclassOfRenderObject(type);
+
+bool isRenderObjectWidgetOrSubclass(DartType? type) =>
+    _isRenderObjectWidget(type) || _isSubclassOfRenderObjectWidget(type);
+
+bool isRenderObjectElementOrSubclass(DartType? type) =>
+    _isRenderObjectElement(type) || _isSubclassOfRenderObjectElement(type);
+
+bool isWidgetStateOrSubclass(DartType? type) =>
+    _isWidgetState(type) || _isSubclassOfWidgetState(type);
+
+bool isSubclassOfListenable(DartType? type) =>
+    type is InterfaceType && type.allSupertypes.any(_isListenable);
+
+bool isListViewWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'ListView';
+
+bool isSingleChildScrollViewWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'SingleChildScrollView';
+
+bool isColumnWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'Column';
+
+bool isRowWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'Row';
+
+bool isPaddingWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'Padding';
+
+bool isBuildContext(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'BuildContext';
+
+bool isGameWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'GameWidget';
+
+bool _isWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'Widget';
+
+bool _isSubclassOfWidget(DartType? type) =>
+    type is InterfaceType && type.allSupertypes.any(_isWidget);
+
+// ignore: deprecated_member_use
+bool _isWidgetState(DartType? type) => type?.element2?.displayName == 'State';
+
+bool _isSubclassOfWidgetState(DartType? type) =>
+    type is InterfaceType && type.allSupertypes.any(_isWidgetState);
+
+bool _isIterable(DartType type) =>
+    type.isDartCoreIterable &&
+    type is InterfaceType &&
+    isWidgetOrSubclass(type.typeArguments.firstOrNull);
+
+bool _isList(DartType type) =>
+    type.isDartCoreList &&
+    type is InterfaceType &&
+    isWidgetOrSubclass(type.typeArguments.firstOrNull);
+
+bool _isFuture(DartType type) =>
+    type.isDartAsyncFuture &&
+    type is InterfaceType &&
+    isWidgetOrSubclass(type.typeArguments.firstOrNull);
+
+bool _isListenable(DartType type) =>
+    type.getDisplayString(withNullability: false) == 'Listenable';
+
+bool _isRenderObject(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'RenderObject';
+
+bool _isSubclassOfRenderObject(DartType? type) =>
+    type is InterfaceType && type.allSupertypes.any(_isRenderObject);
+
+bool _isRenderObjectWidget(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'RenderObjectWidget';
+
+bool _isSubclassOfRenderObjectWidget(DartType? type) =>
+    type is InterfaceType && type.allSupertypes.any(_isRenderObjectWidget);
+
+bool _isRenderObjectElement(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'RenderObjectElement';
+
+bool _isSubclassOfRenderObjectElement(DartType? type) =>
+    type is InterfaceType && type.allSupertypes.any(_isRenderObjectElement);
+
+bool _isMultiProvider(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'MultiProvider';
+
+bool _isSubclassOfInheritedProvider(DartType? type) =>
+    type is InterfaceType && type.allSupertypes.any(_isInheritedProvider);
+
+bool _isInheritedProvider(DartType? type) =>
+    type != null &&
+    type
+        .getDisplayString(withNullability: false)
+        .startsWith('InheritedProvider<');
+
+bool _isIterableInheritedProvider(DartType type) =>
+    type.isDartCoreIterable &&
+    type is InterfaceType &&
+    _isSubclassOfInheritedProvider(type.typeArguments.firstOrNull);
+
+bool _isListInheritedProvider(DartType type) =>
+    type.isDartCoreList &&
+    type is InterfaceType &&
+    _isSubclassOfInheritedProvider(type.typeArguments.firstOrNull);
+
+bool _isFutureInheritedProvider(DartType type) =>
+    type.isDartAsyncFuture &&
+    type is InterfaceType &&
+    _isSubclassOfInheritedProvider(type.typeArguments.firstOrNull);