Compile time error if name is used before variable is declared

tests/language/ref_before_declaration_test.dart

+// Copyright (c) 2013, 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.
+
+// Test compile-time errors for illegal variable declarations if the name
+// has been referenced before the variable is declared.
+
+import 'dart:math' as math;
+
+use(value) => value;
+
+var x = 0;
+final y = 0;
+
+class C {
+  var f;
+  C() : f = 'How do you spell PTSD?';
+
+  void test1() {
+        use(f);  // Refers to instance field f.
+    var f = 'A shut mouth gathers no foot.';  /// 00: compile-time error
+  }
+
+  void test2() {
+        void localFunc() {
+      use(f);  // Refers to instance field f.
+        }
+
+    var f = 'When chemists die, they barium.';  /// 01: compile-time error
+    if (true) {
+      var f = 1; // ok, shadows outer f and instance field f.
+    }
+  }
+
+  void test3() {
+    if (true) {
+      use(x);  // Refers to top-level x.
+      use(y);  // Refers to top-level y.
+    }
+    final x = "I have not yet begun to procrastinate.";  /// 02: compile-time error
+    const y = "Honk if you like peace and quiet!";  /// 03: compile-time error
+  }
+
+  test() {
+    test1();
+    test2();
+    test3();
+  }
+}
+
+void testTypeRef() {
+  String s = 'Can vegetarians eat animal crackers?';
+  var String = "I distinctly remember forgetting that.";  /// 04: compile-time error
+}
+
+void testLibPrefix() {
+  var pie = math.PI;
+  final math = 0;  /// 05: compile-time error
+}
+
+
+void noErrorsExpected() {
+  use(x);
+  for (var x = 0; x < 10; x++) use(x);
+  for (var i = 0; i < 10; i++) var x = 0;
+  if (true) var x = 0;
+  while (false) var x = 0;
+  try { throw "ball"; } catch (x) { use(x); }
+  switch (x) {
+     case 0: var x = 'Does fuzzy logic tickle?';
+  }
+  var int = 007;
+}
+
+void main() {
+  var c = new C();
+  c.test();
+  testTypeRef();
+  testLibPrefix();
+  noErrorsExpected();
+}