feat: ignore Flutter builder functions in "prefer-extracting-callbacks" rule (#469)

* feat: ignore Flutter builder functions in "prefer-extracting-callbacks" rule

* fix: address code review comment

Author: Roman Petrov

CHANGELOG.md

@@ -5,6 +5,7 @@
 * feat: Add static code diagnostic `prefer-const-border-radius`.
 * Improve static code diagnostic `prefer-extracting-callbacks`, don't trigger on empty function blocks.
 * Improve unused files check, add support for `vm:entry-point` annotation.
+* feat: ignore Flutter builder functions in `prefer-extracting-callbacks` rule.
 
 ## 4.3.3
 

doc/rules/prefer-extracting-callbacks.md

@@ -13,8 +13,9 @@ Warns about inline callbacks in a widget tree and suggests to extract them to wi
 **NOTE** the rule will not trigger on: 
  - arrow functions like `onPressed: () => _handler(...)` in order to cover cases when a callback needs a variable from the outside;
  - empty blocks.
+ - Flutter specific: arguments with functions returning `Widget` type (or its subclass) and with first parameter of type `BuildContext`. "Builder" functions is a common pattern in Flutter, for example, [IndexedWidgetBuilder typedef](https://api.flutter.dev/flutter/widgets/IndexedWidgetBuilder.html) is used in [ListView.builder](https://api.flutter.dev/flutter/widgets/ListView/ListView.builder.html).
 
-Use `ignored-named-arguments` configuration, if you want to ignore specific named parameters (`builder` argument is ignored by default).
+Use `ignored-named-arguments` configuration, if you want to ignore specific named parameters.
 
 ### Config example
 

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

@@ -22,6 +22,9 @@ bool isPaddingWidget(DartType? type) =>
 bool _isWidget(DartType? type) =>
     type?.getDisplayString(withNullability: false) == 'Widget';
 
+bool isBuildContext(DartType? type) =>
+    type?.getDisplayString(withNullability: false) == 'BuildContext';
+
 bool _isSubclassOfWidget(DartType? type) =>
     type is InterfaceType && type.allSupertypes.any(_isWidget);
 

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

@@ -40,7 +40,8 @@ class _InstanceCreationVisitor extends RecursiveAstVisitor<void> {
 
       if (_isNotIgnored(argument) &&
           expression is FunctionExpression &&
-          _hasNotEmptyBlockBody(expression)) {
+          _hasNotEmptyBlockBody(expression) &&
+          !_isFlutterBuilder(expression)) {
         _expressions.add(argument);
       }
     }
@@ -55,8 +56,19 @@ class _InstanceCreationVisitor extends RecursiveAstVisitor<void> {
     return body.block.statements.isNotEmpty;
   }
 
+  bool _isFlutterBuilder(FunctionExpression expression) {
+    if (!isWidgetOrSubclass(expression.declaredElement?.returnType)) {
+      return false;
+    }
+
+    final formalParameters = expression.parameters?.parameters;
+
+    return formalParameters == null ||
+        formalParameters.isNotEmpty &&
+            isBuildContext(formalParameters.first.declaredElement?.type);
+  }
+
   bool _isNotIgnored(Expression argument) =>
       argument is! NamedExpression ||
-      (argument.name.label.name != 'builder' &&
-          !_ignoredArguments.contains(argument.name.label.name));
+      !_ignoredArguments.contains(argument.name.label.name);
 }

test/analyzers/lint_analyzer/rules/rules_list/prefer_extracting_callbacks/examples/example.dart

@@ -56,7 +56,13 @@ class MyAnotherWidget extends StatelessWidget {
         return null;
       },
       child: Container(),
-      builder: () {
+      builder: (context) {
+        return null;
+      },
+      anotherBuilder: (context, index) {
+        return null;
+      },
+      myOtherWidgetBuilder: (context) {
         return null;
       },
     );
@@ -86,6 +92,8 @@ class Widget {}
 
 class StatelessWidget extends Widget {}
 
+class BuildContext {}
+
 class Container extends Widget {
   final Widget? child;
 
@@ -95,12 +103,16 @@ class Container extends Widget {
 class TextButton {
   final Widget child;
   final void Function()? onPressed;
-  final void Function()? builder;
+  final Widget Function(BuildContext)? builder;
+  final Widget Function(BuildContext, int)? anotherBuilder;
+  final MyOtherWidget Function(BuildContext, int)? myOtherWidgetBuilder;
 
   const TextButton({
     required this.child,
     required this.onPressed,
     this.builder,
+    this.anotherBuilder,
+    this.myOtherWidgetBuilder,
   });
 }