#3030. Add tests constants tests for String.length (#3041)

Language/Classes/Constructors/Constant_Constructors/not_a_constant_in_initializer_list_t05.dart

@@ -0,0 +1,41 @@
+// 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.
+
+/// @assertion Any expression that appears within the initializer list of a
+/// constant constructor must be a potentially constant expression, or a
+/// compile-time error occurs.
+///
+/// A potentially constant expression is an expression E that would be a valid
+/// constant expression if all formal parameters of E's immediately enclosing
+/// constant constructor were treated as compile-time constants that were
+/// guaranteed to evaluate to an integer, boolean or string value as required
+/// by their immediately enclosing superexpression.
+///
+/// @description Checks that it is a compile-time error when a constant
+/// constructor's initializer list contains a use of a non-constant.
+/// @author sgrekhov22@gmail.com
+
+final String zero = "0";
+
+class C {
+  static final name = "name";
+  final int v;
+
+  const C.fromObject(Object o) : v = o.toString().length;
+//                                   ^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const C.fromGlobal() : v = zero.length;
+//                           ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const C.fromName() : v = name.length;
+//                         ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  print(C);
+}

Language/Classes/Constructors/Constant_Constructors/not_a_constant_in_initializer_list_t06.dart

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+// 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.
+
+/// @assertion Any expression that appears within the initializer list of a
+/// constant constructor must be a potentially constant expression, or a
+/// compile-time error occurs.
+///
+/// A potentially constant expression is an expression E that would be a valid
+/// constant expression if all formal parameters of E's immediately enclosing
+/// constant constructor were treated as compile-time constants that were
+/// guaranteed to evaluate to an integer, boolean or string value as required
+/// by their immediately enclosing superexpression.
+///
+/// @description Checks that it is not an error to use `String.length` in a
+/// constant constructor's initializer list if the string is a constant.
+/// @author sgrekhov22@gmail.com
+
+import '../../../../Utils/expect.dart';
+
+const String zero = "0";
+
+class C {
+  static const name = "name";
+  final int v;
+
+  const C() : v = "".length;
+  const C.fromString(String s) : v = s.length;
+  const C.fromGlobal() : v = zero.length;
+  const C.fromName() : v = name.length;
+}
+
+main() {
+  Expect.equals(0, const C().v);
+  Expect.equals(3, const C.fromString("123").v);
+  Expect.equals(1, const C.fromGlobal().v);
+  Expect.equals(4, const C.fromName().v);
+}