feat: add static code diagnostic avoid-use-expanded-as-spacer (#903)

* feat: add static code diagnostic [`avoid-use-expanded-as-spacer`](https://dartcodemetrics.dev/docs/rules/flutter/avoid-use-expanded-as-spacer).

* feat: fix test

* feat: review changes

Co-authored-by: Dmitry Krutskikh <dmitry.krutskikh@gmail.com>

Author: vlkonoshenko

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* feat: add static code diagnostic [`avoid-use-expanded-as-spacer`](https://dartcodemetrics.dev/docs/rules/flutter/avoid-use-expanded-as-spacer).
 * chore: restrict `analyzer` version to `>=2.7.0 <4.3.0`.
 
 ## 4.16.0

lib/src/analyzers/lint_analyzer/rules/rules_factory.dart

@@ -4,6 +4,7 @@ import 'rules_list/avoid_banned_imports/avoid_banned_imports_rule.dart';
 import 'rules_list/avoid_border_all/avoid_border_all_rule.dart';
 import 'rules_list/avoid_collection_methods_with_unrelated_types/avoid_collection_methods_with_unrelated_types_rule.dart';
 import 'rules_list/avoid_dynamic/avoid_dynamic_rule.dart';
+import 'rules_list/avoid_expanded_as_spacer/avoid_expanded_as_spacer_rule.dart';
 import 'rules_list/avoid_global_state/avoid_global_state_rule.dart';
 import 'rules_list/avoid_ignoring_return_values/avoid_ignoring_return_values_rule.dart';
 import 'rules_list/avoid_late_keyword/avoid_late_keyword_rule.dart';
@@ -89,6 +90,8 @@ final _implementedRules = <String, Rule Function(Map<String, Object>)>{
       AvoidUnusedParametersRule(config),
   AvoidWrappingInPaddingRule.ruleId: (config) =>
       AvoidWrappingInPaddingRule(config),
+  AvoidExpandedAsSpacerRule.ruleId: (config) =>
+      AvoidExpandedAsSpacerRule(config),
   BanNameRule.ruleId: (config) => BanNameRule(config),
   BinaryExpressionOperandOrderRule.ruleId: (config) =>
       BinaryExpressionOperandOrderRule(config),

lib/src/analyzers/lint_analyzer/rules/rules_list/avoid_expanded_as_spacer/avoid_expanded_as_spacer_rule.dart

@@ -0,0 +1,47 @@
+// ignore_for_file: public_member_api_docs
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+
+import '../../../../../utils/node_utils.dart';
+import '../../../lint_utils.dart';
+import '../../../models/internal_resolved_unit_result.dart';
+import '../../../models/issue.dart';
+import '../../../models/replacement.dart';
+import '../../../models/severity.dart';
+import '../../models/flutter_rule.dart';
+import '../../rule_utils.dart';
+
+part 'visitor.dart';
+
+class AvoidExpandedAsSpacerRule extends FlutterRule {
+  static const ruleId = 'avoid-expanded-as-spacer';
+  static const _issueMessage =
+      'Prefer using Spacer widget instead of Expanded.';
+  static const _replaceComment = 'Replace with Spacer widget.';
+
+  AvoidExpandedAsSpacerRule([Map<String, Object> config = const {}])
+      : super(
+          id: ruleId,
+          severity: readSeverity(config, Severity.style),
+          excludes: readExcludes(config),
+        );
+
+  @override
+  Iterable<Issue> check(InternalResolvedUnitResult source) {
+    final visitor = _Visitor();
+    source.unit.visitChildren(visitor);
+
+    return visitor.expressions
+        .map((expression) => createIssue(
+              rule: this,
+              location: nodeLocation(node: expression, source: source),
+              message: _issueMessage,
+              replacement: const Replacement(
+                comment: _replaceComment,
+                replacement: 'const Spacer()',
+              ),
+            ))
+        .toList(growable: false);
+  }
+}

lib/src/analyzers/lint_analyzer/rules/rules_list/avoid_expanded_as_spacer/visitor.dart

@@ -0,0 +1,43 @@
+part of 'avoid_expanded_as_spacer_rule.dart';
+
+const _expandedClassName = 'Expanded';
+const _containerClassName = 'Container';
+const _sizeBoxClassName = 'SizeBox';
+
+class _Visitor extends RecursiveAstVisitor<void> {
+  final _expressions = <InstanceCreationExpression>[];
+
+  Iterable<InstanceCreationExpression> get expressions => _expressions;
+
+  @override
+  void visitInstanceCreationExpression(InstanceCreationExpression expression) {
+    super.visitInstanceCreationExpression(expression);
+
+    final arguments = expression.argumentList.arguments;
+    final isExpanded = expression.staticType?.getDisplayString(
+          withNullability: true,
+        ) ==
+        _expandedClassName;
+
+    final hasOneArgument = arguments.length == 1;
+
+    if (isExpanded && hasOneArgument) {
+      final expandedChild = arguments.first as NamedExpression;
+
+      final childName = expandedChild.staticType?.getDisplayString(
+        withNullability: true,
+      );
+
+      final child = expandedChild.expression;
+      if (child is InstanceCreationExpression) {
+        final hasNoArgument = child.argumentList.arguments.isEmpty;
+
+        if (hasNoArgument &&
+            (childName == _containerClassName ||
+                childName == _sizeBoxClassName)) {
+          _expressions.add(expression);
+        }
+      }
+    }
+  }
+}

test/src/analyzers/lint_analyzer/rules/rules_list/avoid_expanded_as_spacer/avoid_expanded_as_spacer_rule_test.dart

@@ -0,0 +1,49 @@
+import 'package:dart_code_metrics/src/analyzers/lint_analyzer/models/severity.dart';
+import 'package:dart_code_metrics/src/analyzers/lint_analyzer/rules/rules_list/avoid_expanded_as_spacer/avoid_expanded_as_spacer_rule.dart';
+import 'package:test/test.dart';
+
+import '../../../../../helpers/rule_test_helper.dart';
+
+const _examplePath = 'avoid_expanded_as_spacer/examples/example.dart';
+
+void main() {
+  group('AvoidExpandedAsSpacerRule', () {
+    test('initialization', () async {
+      final unit = await RuleTestHelper.resolveFromFile(_examplePath);
+      final issues = AvoidExpandedAsSpacerRule().check(unit);
+
+      RuleTestHelper.verifyInitialization(
+        issues: issues,
+        ruleId: 'avoid-expanded-as-spacer',
+        severity: Severity.style,
+      );
+    });
+
+    test('reports about found issues', () async {
+      final unit = await RuleTestHelper.resolveFromFile(_examplePath);
+      final issues = AvoidExpandedAsSpacerRule().check(unit);
+
+      RuleTestHelper.verifyIssues(
+        issues: issues,
+        startLines: [3, 4],
+        startColumns: [9, 9],
+        locationTexts: [
+          'Expanded(child: Container())',
+          'Expanded(child: SizeBox())',
+        ],
+        replacementComments: [
+          'Replace with Spacer widget.',
+          'Replace with Spacer widget.',
+        ],
+        messages: [
+          'Prefer using Spacer widget instead of Expanded.',
+          'Prefer using Spacer widget instead of Expanded.',
+        ],
+        replacements: [
+          'const Spacer()',
+          'const Spacer()',
+        ],
+      );
+    });
+  });
+}

test/src/analyzers/lint_analyzer/rules/rules_list/avoid_expanded_as_spacer/examples/example.dart

@@ -0,0 +1,48 @@
+class MyWidget extends StatelessWidget {
+  Widget build(BuildContext context) => Column(children: [
+        Expanded(child: Container()), // LINT
+        Expanded(child: SizeBox()), // LINT
+        Expanded(child: foo()),
+        Expanded(child: SizeBox(child: Container())),
+        Expanded(child: Container(child: SizeBox())),
+        Spacer(),
+      ]);
+}
+
+Widget foo() => SizeBox();
+
+class Container extends Widget {
+  final Widget? child;
+
+  const Container({this.child});
+}
+
+class Expanded extends Widget {
+  final Widget? child;
+
+  const Expanded({this.child});
+}
+
+class SizeBox extends Widget {
+  final Widget? child;
+
+  const SizeBox({this.child});
+}
+
+class Spacer extends Widget {
+  const Spacer();
+}
+
+class Column extends Widget {
+  final List<Widget> children;
+
+  Column({required this.children});
+}
+
+class StatelessWidget extends Widget {}
+
+class Widget {
+  const Widget();
+}
+
+class BuildContext {}

website/docs/rules/flutter/avoid-use-expanded-as-spacer.md

@@ -0,0 +1,39 @@
+# Avoid use Expanded widget instead of Spacer
+
+## Rule id {#rule-id}
+
+avoid-use-expanded-as-spacer
+
+## Severity {#severity}
+
+Style
+
+## Description {#description}
+
+The rule detects Expanded widgets that contain empty SizedBox/Container and proposes to replace them with the Spacer widget.
+
+### Example {#example}
+
+Bad:
+
+```dart
+Column(
+    children: [
+        Container(),
+        const Expanded(child: SizedBox()),
+        Container(),
+    ]
+)
+```
+
+Good:
+
+```dart
+Column(
+    children: [
+        Container(),
+        const Spacer(),
+        Container(),
+    ]
+)
+```

website/docs/rules/overview.md

@@ -189,6 +189,10 @@ Rules configuration is [described here](../getting-started/configuration#configu
 
     Warns when a widget is wrapped in a Padding widget but has a padding settings by itself.
 
+- [avoid-use-expanded-as-spacer](./flutter/avoid-use-expanded-as-spacer.md)   ![Has auto-fix](https://img.shields.io/badge/-has%20auto--fix-success)
+
+    Avoid using Expanded widget as Spacer.
+
 - [prefer-const-border-radius](./flutter/prefer-const-border-radius.md)   ![Has auto-fix](https://img.shields.io/badge/-has%20auto--fix-success)
 
     Warns when used non const border radius.