fix: correctly handle FunctionExpressions for avoid-redundant-async (#1124)

* fix: correctly handle FunctionExpressions for avoid-redundant-async

* chore: update example

Author: incendial

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* fix: correctly handle FunctionExpressions for [`avoid-redundant-async`](https://dartcodemetrics.dev/docs/rules/common/avoid-redundant-async).
 * feat: support ignoring nesting for [`prefer-conditional-expressions`](https://dartcodemetrics.dev/docs/rules/common/prefer-conditional-expressions).
 * fix: ignore Providers for ['avoid-returning-widgets'](https://dartcodemetrics.dev/docs/rules/common/avoid-returning-widgets).
 * feat: add [`use-setstate-synchronously`](https://dartcodemetrics.dev/docs/rules/flutter/use-setstate-synchronously).

lib/src/analyzers/lint_analyzer/rules/rules_list/avoid_redundant_async/avoid_redundant_async_rule.dart

@@ -35,13 +35,15 @@ class AvoidRedundantAsyncRule extends CommonRule {
 
     source.unit.visitChildren(visitor);
 
-    return visitor.declarations.map((declaration) => createIssue(
-          rule: this,
-          location: nodeLocation(
-            node: declaration,
-            source: source,
-          ),
-          message: _warningMessage,
-        ));
+    return visitor.nodes.map(
+      (node) => createIssue(
+        rule: this,
+        location: nodeLocation(
+          node: node,
+          source: source,
+        ),
+        message: _warningMessage,
+      ),
+    );
   }
 }

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

@@ -1,9 +1,9 @@
 part of 'avoid_redundant_async_rule.dart';
 
 class _Visitor extends RecursiveAstVisitor<void> {
-  final _declarations = <Declaration>[];
+  final _nodes = <AstNode>[];
 
-  Iterable<Declaration> get declarations => _declarations;
+  Iterable<AstNode> get nodes => _nodes;
 
   @override
   void visitMethodDeclaration(MethodDeclaration node) {
@@ -15,16 +15,16 @@ class _Visitor extends RecursiveAstVisitor<void> {
     );
 
     if (!isOverride && _hasRedundantAsync(node.body)) {
-      _declarations.add(node);
+      _nodes.add(node);
     }
   }
 
   @override
-  void visitFunctionDeclaration(FunctionDeclaration node) {
-    super.visitFunctionDeclaration(node);
+  void visitFunctionExpression(FunctionExpression node) {
+    super.visitFunctionExpression(node);
 
-    if (_hasRedundantAsync(node.functionExpression.body)) {
-      _declarations.add(node);
+    if (_hasRedundantAsync(node.body)) {
+      _nodes.add(node);
     }
   }
 

test/src/analyzers/lint_analyzer/rules/rules_list/avoid_redundant_async/avoid_redundant_async_rule_test.dart

@@ -25,17 +25,21 @@ void main() {
 
       RuleTestHelper.verifyIssues(
         issues: issues,
-        startLines: [12, 22],
-        startColumns: [1, 3],
+        startLines: [12, 22, 59, 60],
+        startColumns: [26, 3, 5, 22],
         locationTexts: [
-          'Future<int> fastestBranch(Future<int> left, Future<int> right) async {\n'
+          '(Future<int> left, Future<int> right) async {\n'
               '  return Future.any([left, right]);\n'
               '}',
           "Future<String> anotherAsyncMethod() async => Future.value('value');",
+          '() async => instance.someAsyncMethod()',
+          '() async => instance.someAsyncMethod()',
         ],
         messages: [
           "'async' keyword is redundant, consider removing it.",
           "'async' keyword is redundant, consider removing it.",
+          "'async' keyword is redundant, consider removing it.",
+          "'async' keyword is redundant, consider removing it.",
         ],
       );
     });

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

@@ -44,3 +44,19 @@ class SomeClass {
     }
   }
 }
+
+class WithFunctionField {
+  final Function(void) onSelected;
+  final Function(void) onSelectedNamed;
+
+  const WithFunctionField(this.onSelected, {required this.onSelectedNamed});
+}
+
+void main() {
+  final instance = SomeClass();
+
+  WithFunctionField(
+    () async => instance.someAsyncMethod(), // LINT
+    onSelectedNamed: () async => instance.someAsyncMethod(), // LINT
+  );
+}