feat: support superscope search in later initializer.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -2040,6 +2040,34 @@ class BodyBuilder extends ScopeListener<JumpTarget>
       declaration = classBuilder.origin
           .findStaticBuilder(name, charOffset, uri, libraryBuilder);
     }
+    if (declaration == null && inFieldInitializer && inLateFieldInitializer) {
+      TypeBuilder superClassType = classBuilder.supertypeBuilder;
+      while (superClassType != null) {
+        ClassBuilder superClass;
+        if (superClassType is NamedTypeBuilder) {
+          TypeDeclarationBuilder decl = superClassType.declaration;
+          TypeAliasBuilder aliasBuilder; // Non-null if a type alias is use.
+          if (decl is TypeAliasBuilder) {
+            aliasBuilder = decl;
+            decl = aliasBuilder.unaliasDeclaration(superClassType.arguments);
+          }
+          if (decl is ClassBuilder) {
+            superClass = decl;
+          }
+        }
+
+        declaration = superClass?.scope?.lookup(
+          name,
+          superClass?.charOffset,
+          superClass?.fileUri,
+        );
+
+        superClassType = superClass?.supertypeBuilder;
+        if (declaration != null) {
+          break;
+        }
+      }
+    }
     if (declaration != null &&
         declaration.isDeclarationInstanceMember &&
         (inFieldInitializer && !inLateFieldInitializer) &&

pkg/front_end/lib/src/fasta/kernel/implicit_field_type.dart

@@ -4,7 +4,7 @@
 
 library fasta.implicit_type;
 
-import 'package:_fe_analyzer_shared/src/scanner/token.dart' show Token;
+import 'package:_fe_analyzer_shared/src/scanner/token.dart' show Token, TokenClass;
 
 import 'package:kernel/ast.dart' hide MapEntry;
 
@@ -140,6 +140,7 @@ class _ImplicitFieldTypeRoot extends ImplicitFieldType {
       bodyBuilder.constantContext = fieldBuilder.isConst
           ? ConstantContext.inferred
           : ConstantContext.none;
+      bodyBuilder.beginFieldInitializer(initializerToken);
       Expression initializer =
           bodyBuilder.parseFieldInitializer(initializerToken);
       initializerToken = null;

pkg/front_end/testcases/late_lowering/late_final_local_with_initializer.dart

@@ -2,6 +2,18 @@
 // 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.
 
+class B {
+  final int x;
+
+  B(this.x);
+}
+
+class C extends B {
+  late final y = x + 1;
+
+  C(int x) : super(x);
+}
+
 main() {
   int? lateLocalInit;
   int initLateLocal(int value) {
@@ -30,6 +42,7 @@ main() {
   local<int?>(null);
   local<int?>(42);
   local<int>(42);
+  expect(2, C(1).y);
 }
 
 expect(expected, actual) {