#1401. Add additional tests for shared case scoping

LanguageFeatures/Patterns/shared_case_scope_A01_t05.dart

@@ -0,0 +1,88 @@
+// 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 In a switch statement, multiple cases may share the same body.
+/// ...
+/// We specify how this behaves by creating a new shared case scope that
+/// contains all variables from all of the cases and then report errors from
+/// invalid uses of them. The shared case scope s of a body used by a set of
+/// cases with pattern variable sets vs (where default cases and labels have
+/// empty pattern variable sets) is:
+///
+/// 1. Create a new empty scope s whose enclosing scope is the scope surrounding
+///   the switch statement or expression.
+///
+/// 2. For each name n appearing as a variable name in any of the pattern
+///   variable sets in vs:
+///
+/// i. If n is defined in every pattern variable set in vs and has the same type
+///   and finality, then introduce n into s with the same type and finality.
+///   This is a shared variable and is available for use in the body.
+///
+///   If any of the corresponding variables in vs are promoted, calculate the
+///   promoted type of the variable in s based on all of the promoted types of n
+///   in the cases in the same way that promotions are merged at join points.
+///
+/// ii. Else n is not consistently defined by all cases and thus isn't safe to
+///   use in the body. Introduce a new variable n into s with unspecified type
+///   and finality.
+///
+/// 3. Compile the body in s. It is a compile-time error if any identifier in
+///   the body resolves to a variable in s that isn't shared.
+///
+/// @description Checks that it is a compile-time error if any identifier in the
+/// body resolves to a variable in s that isn't shared. Test the case when there
+/// is a variable with the same name outside of the switch.
+/// @author sgrekhov22@gmail.com
+
+main() {
+  int n = 1;
+  int x = 2;
+
+  switch (n) {
+    case int x when 1 > 2:
+    case num when 1 > 2:
+      print(x);
+//          ^
+// [analyzer] unspecified
+// [cfe] unspecified
+    case _:
+      print(x);
+  }
+
+  switch (n) {
+    case int x when 1 > 2:
+    case _ when 1 > 2:
+      print(x);
+//          ^
+// [analyzer] unspecified
+// [cfe] unspecified
+    default:
+      print(x);
+  }
+
+  switch (n) {
+    case int x when 1 > 2:
+    case num when 1 > 2:
+      print(x);
+//          ^
+// [analyzer] unspecified
+// [cfe] unspecified
+    label:
+    case _:
+      print(x);
+  }
+
+  switch (n) {
+    label:
+    case int x when 1 > 2:
+    case _ when 1 > 2:
+      print(x);
+//          ^
+// [analyzer] unspecified
+// [cfe] unspecified
+    default:
+      print(x);
+  }
+}