Make value range analysis tolerate erroneous length expressions.

tests/compiler/dart2js_extra/21166_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file

[floitsch, 2015/02/18 13:52:47]

I prefer if it is in the language tests.

Give the test a "correct" name, and mention the bug only in the comments (as you
do now).

+// 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.
+
+// Regression test for http://dartbug.com/21166/
+// Fails when compiling with --checked.

[floitsch, 2015/02/18 13:52:47]

Shouldn't fail.

+
+var a = [];
+
+void doStuff() {
+  if (a.length) { // This triggers a TypeConversion to bool in checked mode.
+    var element = a[0]; // This triggers a bounds check but a.length will have
+    a.remove(element);  // type [empty].
+  }
+}
+
+main() {
+  a.add(1);
+  a.add(2);
+  try {
+    doStuff(); // This is expected to fail but not crash the compiler.

[floitsch, 2015/02/18 13:52:47]

Check your operations.

+  } catch (_) {}

[floitsch, 2015/02/18 13:52:47]

Make sure this is a TypeError.

+}
+
+