@literal support for extension types

See: https://github.com/dart-lang/sdk/issues/53434

Change-Id: I2668b74e2037176d0ac6e6da22300be29ba14d8d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/325444
Commit-Queue: Phil Quitslund <pquitslund@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer/lib/src/error/annotation_verifier.dart

@@ -197,6 +197,10 @@ class AnnotationVerifier {
   /// `@literal` annotation.
   void _checkLiteral(AstNode node) {
     var parent = node.parent;
+    // Primary constructor of an extension type declaration.
+    if (parent is ExtensionTypeDeclaration && parent.constKeyword != null) {
+      return;
+    }
     if (parent is! ConstructorDeclaration || parent.constKeyword == null) {
       _errorReporter
           .reportErrorForNode(WarningCode.INVALID_LITERAL_ANNOTATION, node, []);

pkg/analyzer/lib/src/error/best_practices_verifier.dart

@@ -1172,8 +1172,11 @@ class BestPracticesVerifier extends RecursiveAstVisitor<void> {
     if (constructor == null) {
       return;
     }
+    var enclosingElement = constructor.enclosingElement;
     if (!node.isConst &&
-        constructor.hasLiteral &&
+        (constructor.hasLiteral ||
+            (enclosingElement is ExtensionTypeElement &&
+                enclosingElement.hasLiteral)) &&
         _linterContext.canBeConst(node)) {
       // Echoing jwren's TODO from _checkForDeprecatedMemberUse:
       // TODO(jwren) We should modify ConstructorElement.getDisplayName(), or

pkg/analyzer/test/src/diagnostics/invalid_literal_annotation_test.dart

@@ -31,6 +31,24 @@ class A {
 ''');
   }
 
+  test_extensionType_constConstructor() async {
+    await assertNoErrorsInCode(r'''
+import 'package:meta/meta.dart';
+extension type const E(int i) {
+  @literal
+  const E.zero(): this(0);
+}
+''');
+  }
+
+  test_extensionType_primaryConstructor_const() async {
+    await assertNoErrorsInCode(r'''
+import 'package:meta/meta.dart';
+@literal
+extension type const E(int i) { }
+''');
+  }
+
   test_nonConstConstructor() async {
     await assertErrorsInCode(r'''
 import 'package:meta/meta.dart';

pkg/analyzer/test/src/diagnostics/non_const_call_to_literal_constructor_test.dart

@@ -42,6 +42,15 @@ const a = A();
 ''');
   }
 
+  test_constContextCreation_extensionType() async {
+    await assertNoErrorsInCode(r'''
+import 'package:meta/meta.dart';
+@literal
+extension type const E(int i) { }
+const e = E(1);
+''');
+  }
+
   test_constCreation() async {
     await assertNoErrorsInCode(r'''
 import 'package:meta/meta.dart';
@@ -53,6 +62,15 @@ const a = const A();
 ''');
   }
 
+  test_constCreation_extensionType() async {
+    await assertNoErrorsInCode(r'''
+import 'package:meta/meta.dart';
+@literal
+extension type const E(int i) { }
+const e = const E(1);
+''');
+  }
+
   test_namedConstructor() async {
     await assertErrorsInCode(r'''
 import 'package:meta/meta.dart';
@@ -102,4 +120,28 @@ var a = new A();
       error(WarningCode.NON_CONST_CALL_TO_LITERAL_CONSTRUCTOR_USING_NEW, 77, 7),
     ]);
   }
+
+  test_usingNew_extensionType() async {
+    await assertErrorsInCode(r'''
+import 'package:meta/meta.dart';
+extension type const E(int i) { 
+  @literal
+  const E.zero(): this(0);
+}
+E e = E.zero();
+''', [
+      error(WarningCode.NON_CONST_CALL_TO_LITERAL_CONSTRUCTOR, 112, 8),
+    ]);
+  }
+
+  test_usingNew_extensionType_primaryConstructor() async {
+    await assertErrorsInCode(r'''
+import 'package:meta/meta.dart';
+@literal
+extension type const E(int i) { }
+E e = E(1);
+''', [
+      error(WarningCode.NON_CONST_CALL_TO_LITERAL_CONSTRUCTOR, 82, 4),
+    ]);
+  }
 }