extension type support for prefer_const_constructors_in_immutables

Fixes: https://github.com/dart-lang/linter/issues/4720

Change-Id: Ia55289f53b6191e8511664cfa5b05ebcfe42ed6c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330180
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/linter/lib/src/rules/prefer_const_constructors_in_immutables.dart

@@ -58,6 +58,7 @@ class PreferConstConstructorsInImmutables extends LintRule {
       NodeLintRegistry registry, LinterContext context) {
     var visitor = _Visitor(this, context);
     registry.addConstructorDeclaration(this, visitor);
+    registry.addExtensionTypeDeclaration(this, visitor);
   }
 }
 
@@ -88,6 +89,16 @@ class _Visitor extends SimpleAstVisitor<void> {
     }
   }
 
+  @override
+  void visitExtensionTypeDeclaration(ExtensionTypeDeclaration node) {
+    if (node.constKeyword != null) return;
+    var element = node.declaredElement;
+    if (element == null) return;
+    if (element.hasImmutable) {
+      rule.reportLintForToken(node.name);
+    }
+  }
+
   bool _hasConstConstructorInvocation(ConstructorDeclaration node) {
     var declaredElement = node.declaredElement;
     if (declaredElement == null) {
@@ -107,6 +118,11 @@ class _Visitor extends SimpleAstVisitor<void> {
     if (redirectInvocation != null) {
       return redirectInvocation.staticElement?.isConst ?? false;
     }
+
+    if (clazz is ExtensionTypeElement) {
+      return clazz.primaryConstructor.isConst;
+    }
+
     // Constructor with implicit `super()` call.
     var unnamedSuperConstructor =
         clazz.supertype?.constructors.firstWhereOrNull((e) => e.name.isEmpty);

pkg/linter/test/rules/prefer_const_constructors_in_immutables_test.dart

@@ -83,6 +83,46 @@ class B extends A {
 ''');
   }
 
+  test_extensionType_constConstructor_named() async {
+    await assertNoDiagnostics(r'''
+import 'package:meta/meta.dart';
+@immutable
+extension type const E(int i) {
+  const E.e(this.i);
+}
+''');
+  }
+
+  test_extensionType_constConstructor_primary() async {
+    await assertNoDiagnostics(r'''
+import 'package:meta/meta.dart';
+@immutable
+extension type const E(int i) { }
+''');
+  }
+
+  test_extensionType_nonConstConstructor_named() async {
+    await assertDiagnostics(r'''
+import 'package:meta/meta.dart';
+@immutable
+extension type const E(int i) {
+  E.e(this.i);
+}
+''', [
+      lint(78, 1),
+    ]);
+  }
+
+  test_extensionType_nonConstConstructor_primary() async {
+    await assertDiagnostics(r'''
+import 'package:meta/meta.dart';
+@immutable
+extension type E(int i) { }
+''', [
+      lint(59, 1),
+    ]);
+  }
+
   test_immutable_constConstructor() async {
     await assertNoDiagnostics(r'''
 import 'package:meta/meta.dart';