[CFE] Fix crash in finalize export for extension types

The used reference wasn't registered where we look it up when finalizing
exports which caused a crash.

Fixes #60236

Change-Id: Id8807d1a53fa433806061a08b904d2cc2ef3e2fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/432640
Commit-Queue: Jens Johansen <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: jensjoha

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

@@ -2428,6 +2428,10 @@ _AddBuilder _createExtensionTypeBuilder(ExtensionTypeFragment fragment,
           fragment: fragment,
           indexedContainer: indexedContainer,
           representationFieldFragment: representationFieldFragment);
+  if (indexedContainer?.reference != null) {
+    loader.buildersCreatedWithReferences[indexedContainer!.reference] =
+        extensionTypeDeclarationBuilder;
+  }
   return new _AddBuilder(
       fragment.name, extensionTypeDeclarationBuilder, fragment.uriOffset,
       inPatch: fragment.enclosingCompilationUnit.isPatch);

pkg/front_end/testcases/incremental/finalize_exports_with_extension_types.yaml

@@ -0,0 +1,28 @@
+# Copyright (c) 2025, 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.
+
+# Reproduce a crash in ExtensionTypeDeclaration.enclosingLibrary
+# when finalizing exports.
+# Likely also whats seen in https://github.com/dart-lang/sdk/issues/60236.
+
+type: newworld
+worlds:
+  - entry:
+      - bar.dart
+    sources:
+      foo.dart: |
+        export 'bar.dart';
+      bar.dart: |
+        import 'foo.dart';
+        extension type Baz(String qux) {}
+    expectedLibraryCount: 2
+
+  - entry:
+      - bar.dart
+    worldType: updated
+    expectInitializeFromDill: false
+    invalidate:
+      - bar.dart
+    expectedLibraryCount: 2
+    advancedInvalidation: bodiesOnly # or something else?

pkg/front_end/testcases/incremental/finalize_exports_with_extension_types.yaml.world.1.expect

@@ -0,0 +1,23 @@
+main = <No Member>;
+library from "org-dartlang-test:///bar.dart" as bar {
+
+  import "org-dartlang-test:///foo.dart";
+
+  extension type Baz(dart.core::String qux) {
+    abstract extension-type-member representation-field get qux() → dart.core::String;
+    constructor • = bar::Baz|constructor#;
+    constructor tearoff • = bar::Baz|constructor#_#new#tearOff;
+  }
+  static extension-type-member method Baz|constructor#(dart.core::String qux) → bar::Baz% /* erasure=dart.core::String, declared=! */ {
+    lowered final bar::Baz% /* erasure=dart.core::String, declared=! */ #this = qux;
+    return #this;
+  }
+  static extension-type-member synthetic method Baz|constructor#_#new#tearOff(dart.core::String qux) → bar::Baz% /* erasure=dart.core::String, declared=! */
+    return bar::Baz|constructor#(qux);
+}
+library from "org-dartlang-test:///foo.dart" as foo {
+additionalExports = (bar::Baz)
+
+  export "org-dartlang-test:///bar.dart";
+
+}

pkg/front_end/testcases/incremental/finalize_exports_with_extension_types.yaml.world.2.expect

@@ -0,0 +1,23 @@
+main = <No Member>;
+library from "org-dartlang-test:///bar.dart" as bar {
+
+  import "org-dartlang-test:///foo.dart";
+
+  extension type Baz(dart.core::String qux) {
+    abstract extension-type-member representation-field get qux() → dart.core::String;
+    constructor • = bar::Baz|constructor#;
+    constructor tearoff • = bar::Baz|constructor#_#new#tearOff;
+  }
+  static extension-type-member method Baz|constructor#(dart.core::String qux) → bar::Baz% /* erasure=dart.core::String, declared=! */ {
+    lowered final bar::Baz% /* erasure=dart.core::String, declared=! */ #this = qux;
+    return #this;
+  }
+  static extension-type-member synthetic method Baz|constructor#_#new#tearOff(dart.core::String qux) → bar::Baz% /* erasure=dart.core::String, declared=! */
+    return bar::Baz|constructor#(qux);
+}
+library from "org-dartlang-test:///foo.dart" as foo {
+additionalExports = (bar::Baz)
+
+  export "org-dartlang-test:///bar.dart";
+
+}