Check boolean conversion in checked mode.

lib/compiler/implementation/lib/js_helper.dart

 // Copyright (c) 2012, 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.
 
 #library('dart:_js_helper');
 
 #import('coreimpl.dart');
 
 #source('constant_map.dart');
 #source('native_helper.dart');
@@ skipping 959 matching lines @@
   // TODO(ngeoffray): Make the object a top-level field to avoid
   // allocating a new object every single time.
   return (res == null) ? JS('var', '{}') : res;
 }
 
 /**
  * The following methods are called by the runtime to implement
  * checked mode and casts. We specialize each primitive type (eg int, bool), and
  * use the compiler's convention to do is-checks on regular objects.
  */
+boolConversionCheck(value) {
+  boolTypeCheck(value);

[kasperl, 2012/09/13 10:34:19]

Wouldn't it be more logical to just check that value is bool here? What kind of
error is this boolean conversion supposed to give if the value isn't a bool?
Right now, you either get a type error or an assertion error which seems a bit
weird.

[ngeoffray, 2012/09/13 10:52:32]

As discussed, this method is implementing what the spec says: type check and
then assert it's not null. I kept the code as-is.

+  assert(value != null);
+  return value;
+}
+
 stringTypeCheck(value) {
   if (value === null) return value;
   if (value is String) return value;
   throw new TypeErrorImplementation('$value does not implement String');
 }
 
 stringTypeCast(value) {
   if (value is String || value === null) return value;
   // TODO(lrn): When reified types are available, pass value.class and String.
   throw new CastExceptionImplementation(
@@ skipping 263 matching lines @@
 class FallThroughErrorImplementation implements FallThroughError {
   const FallThroughErrorImplementation();
   String toString() => "Switch case fall-through.";
 }
 
 /**
  * Helper function for implementing asserts. The compiler treats this specially.
  */
 void assert(condition) {
   if (condition is Function) condition = condition();
-  if (!condition) throw new AssertionError();
+  if (condition is !bool) {
+    throw new TypeErrorImplementation('$condition does not implement bool');
+  }
+  // Compare to true to avoid boolean conversion check in checked
+  // mode.
+  if (condition !== true) throw new AssertionError();
 }
 
 /**
  * Called by generated code when a method that must be statically
  * resolved cannot be found.
  */
 void throwNoSuchMethod(obj, name, arguments) {
   throw new NoSuchMethodError(obj, name, arguments);
 }
 
 /**
  * Called by generated code when a static field's initializer references the
  * field that is currently being initialized.
  */
 void throwCyclicInit(String staticName) {
   throw new RuntimeError("Cyclic initialization for static $staticName");
 }