Fix TypeChecker.isSuperTypeOf throws on null value

fixes #229

Author: charlescyt

packages/custom_lint_builder/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## Unreleased patch
 
 - Upgrade analyzer to support 6.4.0
+- Fix null exception when using `TypeChecker.isSuperTypeOf` (thanks to @charlescyt)
 
 ## 0.6.1 - 2024-02-14
 

packages/custom_lint_core/CHANGELOG.md

@@ -1,3 +1,7 @@
+## Unreleased patch
+
+- Fix null exception when using `TypeChecker.isSuperTypeOf` (thanks to @charlescyt)
+
 ## 0.6.1 - 2024-02-14
 
 - Exported `NodeLintRegistry`

packages/custom_lint_core/lib/src/type_checker.dart

@@ -221,7 +221,11 @@ abstract class TypeChecker {
   ///
   /// This only takes into account the *extends* hierarchy. If you wish
   /// to check mixins and interfaces, use [isAssignableFromType].
-  bool isSuperTypeOf(DartType staticType) => isSuperOf(staticType.element!);
+  // TODO changelog patch: Fixed a bug where isSuperTypeOf throws if the element is null (thanks to @charlescyt)
+  bool isSuperTypeOf(DartType staticType) {
+    final element = staticType.element;
+    return element != null && isSuperOf(element);
+  }
 }
 
 // Checks a static type against another static type;

packages/custom_lint_core/test/type_checker_test.dart

@@ -34,6 +34,32 @@ void main() {
     );
   });
 
+  test('Can call isSuperTypeOf in DartTypes with no element', () async {
+    final file = writeToTemporaryFile(r'''
+void fn((int, String) record) {
+  final first = record.$1;
+}
+''');
+
+    final unit = await resolveFile2(path: file.path);
+    unit as ResolvedUnitResult;
+
+    const checker = TypeChecker.fromName('record');
+
+    late final PropertyAccess propertyAccessNode;
+    unit.unit.accept(
+      _PropertyAccessVisitor((node) {
+        propertyAccessNode = node;
+      }),
+    );
+
+    expect(propertyAccessNode.realTarget.staticType!.element, isNull);
+    expect(
+      checker.isExactlyType(propertyAccessNode.realTarget.staticType!),
+      isFalse,
+    );
+  });
+
   group('TypeChecker.fromPackage', () {
     test('matches a type from a package', () async {
       final tempDir = Directory.systemTemp.createTempSync();
@@ -109,3 +135,15 @@ class _MethodInvocationVisitor extends RecursiveAstVisitor<void> {
     super.visitMethodInvocation(node);
   }
 }
+
+class _PropertyAccessVisitor extends RecursiveAstVisitor<void> {
+  _PropertyAccessVisitor(this.onPropertyAccess);
+
+  final void Function(PropertyAccess node) onPropertyAccess;
+
+  @override
+  void visitPropertyAccess(PropertyAccess node) {
+    onPropertyAccess(node);
+    super.visitPropertyAccess(node);
+  }
+}