fix: support tear-off methods for check-unnecessary-nullable

Author: incendial

CHANGELOG.md

@@ -11,6 +11,7 @@
 * fix: ignore method invocations in a variable declaration for [`prefer-moving-to-variable`](https://dartcodemetrics.dev/docs/rules/common/prefer-moving-to-variable).
 * feat: add `allow-initialized` option to [`avoid-late-keyword`](https://dartcodemetrics.dev/docs/rules/common/avoid-late-keyword).
 * feat: add `ignored-types` option to [`avoid-late-keyword`](https://dartcodemetrics.dev/docs/rules/common/avoid-late-keyword).
+* fix: support tear-off methods for `check-unnecessary-nullable`.
 
 ## 5.4.0
 

lib/src/analyzers/unnecessary_nullable_analyzer/invocations_visitor.dart

@@ -3,6 +3,7 @@
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/type.dart';
 
 import 'models/invocations_usage.dart';
 
@@ -20,6 +21,15 @@ class InvocationsVisitor extends RecursiveAstVisitor<void> {
     }
   }
 
+  @override
+  void visitPrefixedIdentifier(PrefixedIdentifier node) {
+    super.visitPrefixedIdentifier(node);
+
+    if (node.identifier.staticType is FunctionType) {
+      _recordUsedElement(node.identifier.staticElement, null);
+    }
+  }
+
   @override
   void visitMethodInvocation(MethodInvocation node) {
     super.visitMethodInvocation(node);
@@ -42,7 +52,7 @@ class InvocationsVisitor extends RecursiveAstVisitor<void> {
   }
 
   /// Records use of a not prefixed [element].
-  void _recordUsedElement(Element? element, ArgumentList arguments) {
+  void _recordUsedElement(Element? element, ArgumentList? arguments) {
     if (element == null) {
       return;
     }
@@ -52,6 +62,7 @@ class InvocationsVisitor extends RecursiveAstVisitor<void> {
       return;
     }
     // Remember the element.
-    invocationsUsages.addElementUsage(element, {arguments});
+    final usedArguments = arguments == null ? null : {arguments};
+    invocationsUsages.addElementUsage(element, usedArguments);
   }
 }

lib/src/analyzers/unnecessary_nullable_analyzer/models/invocations_usage.dart

@@ -5,14 +5,20 @@ import 'package:analyzer/dart/element/element.dart';
 /// elements.
 class InvocationsUsage {
   /// The set of referenced top-level elements.
-  final Map<Element, Set<ArgumentList>> elements = {};
+  final Map<Element, Set<ArgumentList>?> elements = {};
 
   final Set<String> exports = {};
 
-  void addElementUsage(Element element, Set<ArgumentList> expressions) {
+  void addElementUsage(Element element, Set<ArgumentList>? expressions) {
     elements.update(
       element,
-      (value) => value..addAll(expressions),
+      (value) {
+        if (expressions == null || value == null) {
+          return null;
+        }
+
+        return value..addAll(expressions);
+      },
       ifAbsent: () => expressions,
     );
   }

test/resources/unnecessary_nullable_analyzer/nullable_method_parameters.dart

@@ -22,4 +22,6 @@ class ClassWithMethods {
 
   // ignore: unnecessary-nullable
   void ignoredAlwaysNonNullable(String? anotherValue) {}
+
+  void tearOff(String? anotherValue) {}
 }

test/resources/unnecessary_nullable_analyzer/nullable_widget_key_parameters.dart

@@ -1,5 +1,5 @@
 class MyWidget extends StatelessWidget {
-  const MyWidget(Key? key) : super(key);
+  const MyWidget(super.key);
 }
 
 class Widget {
@@ -9,9 +9,15 @@ class Widget {
 }
 
 class StatelessWidget extends Widget {
-  const StatelessWidget(Key? key) : super(key);
+  const StatelessWidget(super.key);
 }
 
 class Key {}
 
 class GlobalKey extends Key {}
+
+class AnotherWidget extends Widget {
+  final void Function(String?) onSubmit;
+
+  const AnotherWidget({required this.onSubmit}) : super(null);
+}

test/resources/unnecessary_nullable_analyzer/unnecessary_nullable_example.dart

@@ -13,7 +13,8 @@ void main() {
 
   withMethods
     ..someMethod(null)
-    ..someMethod('value');
+    ..someMethod('value')
+    ..tearOff('str');
 
   withMethods.alwaysNonNullable('anotherValue');
   withMethods.ignoredAlwaysNonNullable('anotherValue');
@@ -44,6 +45,8 @@ void main() {
   multipleParametersWithOptional('name', 1, 'secondName');
 
   MyWidget(GlobalKey());
+
+  AnotherWidget(onSubmit: withMethods.tearOff);
 }
 
 class _Test {