[CFE] Fix crash if trying to compile extension with missing on

Change-Id: I2c0dd97faba95d97d88452ae29421c7f85a7714f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/394481
Commit-Queue: Jens Johansen <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: jensjoha

pkg/front_end/lib/src/source/builder_factory.dart

@@ -123,7 +123,7 @@ abstract class BuilderFactory {
   void beginExtensionDeclaration(String? name, int charOffset,
       List<NominalParameterBuilder>? typeParameters);
 
-  void beginExtensionBody(TypeBuilder? extensionThisType);
+  void beginExtensionBody(TypeBuilder extensionThisType);
 
   void endExtensionDeclaration(String? name);
 

pkg/front_end/lib/src/source/outline_builder.dart

@@ -1110,11 +1110,14 @@ class OutlineBuilder extends StackListenerImpl {
         assert(checkState(token, [
           unionOfKinds([ValueKinds.ParserRecovery, ValueKinds.TypeBuilder])
         ]));
-
         Object? extensionThisType = peek();
-        // TODO(johnniwinther): Supply an invalid type as the extension on type.
-        _builderFactory.beginExtensionBody(
-            extensionThisType is TypeBuilder ? extensionThisType : null);
+        _builderFactory.beginExtensionBody(extensionThisType is TypeBuilder
+            ? extensionThisType
+            : new InvalidTypeBuilderImpl(
+                uri,
+                extensionThisType is ParserRecovery
+                    ? extensionThisType.charOffset
+                    : TreeNode.noOffset));
         break;
       case DeclarationKind.ExtensionType:
         declarationContext = DeclarationContext.ExtensionTypeBody;

pkg/front_end/testcases/regress/extension_on_missing.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+extension bar {
+  get foo { }
+}

pkg/front_end/testcases/regress/extension_on_missing.dart.strong.expect

@@ -0,0 +1,18 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:11: Error: Expected 'on' after this.
+// extension bar {
+//           ^^^
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:15: Error: Expected a type, but got '{'.
+// extension bar {
+//               ^
+//
+import self as self;
+
+extension bar on invalid-type {
+  get foo = self::bar|get#foo;
+}
+static extension-member method bar|get#foo(lowered final invalid-type #this) → dynamic {}

pkg/front_end/testcases/regress/extension_on_missing.dart.strong.modular.expect

@@ -0,0 +1,18 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:11: Error: Expected 'on' after this.
+// extension bar {
+//           ^^^
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:15: Error: Expected a type, but got '{'.
+// extension bar {
+//               ^
+//
+import self as self;
+
+extension bar on invalid-type {
+  get foo = self::bar|get#foo;
+}
+static extension-member method bar|get#foo(lowered final invalid-type #this) → dynamic {}

pkg/front_end/testcases/regress/extension_on_missing.dart.strong.outline.expect

@@ -0,0 +1,19 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:11: Error: Expected 'on' after this.
+// extension bar {
+//           ^^^
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:15: Error: Expected a type, but got '{'.
+// extension bar {
+//               ^
+//
+import self as self;
+
+extension bar on invalid-type {
+  get foo = self::bar|get#foo;
+}
+static extension-member method bar|get#foo(lowered final invalid-type #this) → dynamic
+  ;

pkg/front_end/testcases/regress/extension_on_missing.dart.strong.transformed.expect

@@ -0,0 +1,18 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:11: Error: Expected 'on' after this.
+// extension bar {
+//           ^^^
+//
+// pkg/front_end/testcases/regress/extension_on_missing.dart:5:15: Error: Expected a type, but got '{'.
+// extension bar {
+//               ^
+//
+import self as self;
+
+extension bar on invalid-type {
+  get foo = self::bar|get#foo;
+}
+static extension-member method bar|get#foo(lowered final invalid-type #this) → dynamic {}

pkg/front_end/testcases/regress/extension_on_missing.dart.textual_outline.expect

@@ -0,0 +1,3 @@
+extension bar on{
+  get foo {}
+}

pkg/front_end/testcases/regress/extension_on_missing.dart.textual_outline_modelled.expect

@@ -0,0 +1,3 @@
+extension bar on{
+  get foo {}
+}