Fix an issue where add_field_formal_parameter would attempt to access the null name offset of a synthetic value.

Bug: #61853
Change-Id: Ic308b5baffcc9ef93dbe3aacbaefd53fdf408f5d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/457940
Reviewed-by: Konstantin Shcheglov <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: fshcheglov

pkg/analysis_server/lib/src/services/correction/dart/add_field_formal_parameters.dart

@@ -9,6 +9,7 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/error_verifier.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
 import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
+import 'package:collection/collection.dart';
 
 /// The boolean value indicates whether the field is required.
 /// The string value is the field/parameter name.
@@ -49,11 +50,16 @@ class AddFieldFormalParameters extends ResolvedCorrectionProducer {
     }
 
     // Compute uninitialized final fields.
-    var fields = ErrorVerifier.computeNotInitializedFields(constructor);
-    fields.retainWhere((FieldElement field) => field.isFinal);
-    fields.sort(
-      (a, b) => a.firstFragment.nameOffset! - b.firstFragment.nameOffset!,
-    );
+    var fields = ErrorVerifier.computeNotInitializedFields(constructor)
+        .where((field) => field.isFinal)
+        .map((field) {
+          var nameOffset = field.firstFragment.nameOffset;
+          return nameOffset != null ? (field, nameOffset) : null;
+        })
+        .nonNulls
+        .sortedBy((pair) => pair.$2)
+        .map((pair) => pair.$1)
+        .toList();
 
     // Prepare the last required parameter.
     FormalParameter? lastRequiredParameter;

pkg/analysis_server/test/src/services/correction/fix/add_field_formal_parameters_test.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/src/services/correction/fix.dart';
+import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
 import 'package:linter/src/lint_names.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
@@ -370,4 +371,24 @@ class Test {
 }
 ''');
   }
+
+  Future<void> test_synthetic_field() async {
+    await resolveTestCode('''
+class Test {
+  final int foo,;
+  Test();
+}
+''');
+    await assertHasFix(
+      '''
+class Test {
+  final int foo,;
+  Test(this.foo);
+}
+''',
+      filter: (diagnostic) =>
+          diagnostic.diagnosticCode ==
+          CompileTimeErrorCode.finalNotInitializedConstructor1,
+    );
+  }
 }