Fixes #3029. Add more tests for constants (#3045)

Language/Expressions/Constants/no_other_constant_expressions_t01.dart

@@ -0,0 +1,32 @@
+// 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 There are no other constant expressions.
+///
+/// @description Checks that a null-check operator cannot be used in a constant
+/// expression.
+/// @author sgrekhov22@gmail.com
+/// @issue 59800
+
+const one = 1!;
+//           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+const int? two = 2;
+const int nonNullableTwo = two!;
+//                            ^
+// [analyzer] unspecified
+// [cfe] unspecified
+const int three = 1 + two!;
+//                       ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(one);
+  print(two);
+  print(nonNullableTwo);
+  print(three);
+}

Language/Expressions/Constants/string_length_t04.dart

@@ -0,0 +1,42 @@
+// 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 The potentially constant expressions and constant expressions are
+/// the following:
+/// ...
+/// • An expression of the form `e.length` is potentially constant if `e` is a
+///   potentially constant expression. It is further constant if `e` is a
+///   constant expression that evaluates to an instance of [String], such that
+///   `length` denotes an instance getter invocation.
+///
+/// @description Checks that it is a compile-time error to use a null-aware
+/// operator `?.` in a constant `String.length` expression.
+/// @author sgrekhov22@gmail.com
+/// @issue 59904
+
+const c1 = "x"?.length;
+//            ^^
+// [analyzer] unspecified
+// [cfe] unspecified
+const String? one = "1";
+const int? c2 = one?.length;
+//                 ^^
+// [analyzer] unspecified
+// [cfe] unspecified
+const String? three = null;
+const int? c3 = three?.length;
+//                   ^^
+// [analyzer] unspecified
+// [cfe] unspecified
+const int? c4 = three == null ? null : three?.length;
+//                                          ^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(c1);
+  print(c2);
+  print(c3);
+  print(c4);
+}

Language/Expressions/Constants/string_length_t05.dart

@@ -0,0 +1,30 @@
+// 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 The potentially constant expressions and constant expressions are
+/// the following:
+/// ...
+/// • An expression of the form `e.length` is potentially constant if `e` is a
+///   potentially constant expression. It is further constant if `e` is a
+///   constant expression that evaluates to an instance of [String], such that
+///   `length` denotes an instance getter invocation.
+///
+/// @description Checks that it is a compile-time error to use a cascade member
+/// access in a constant `String.length` expression.
+/// @author sgrekhov22@gmail.com
+
+const c1 = "x"..length;
+//            ^^
+// [analyzer] unspecified
+// [cfe] unspecified
+const String one = "1";
+const c2 = one..length;
+//            ^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(c1);
+  print(c2);
+}