Enable is and as checks on non-ground types

lib/runtime/_operations.js

Index: lib/runtime/_operations.js
diff --git a/lib/runtime/_operations.js b/lib/runtime/_operations.js
index 1d3997d06e5e16f62c869ce4e210b1755048615f..b6085e9a38059e8007e32718e5d072e3171dd8ba 100644
--- a/lib/runtime/_operations.js
+++ b/lib/runtime/_operations.js
@@ -191,26 +191,46 @@ dart_library.library('dart_runtime/_operations', null, /* Imports */[
     return false;
   }
 
-  function instanceOf(obj, type) {
+  function strongInstanceOf(obj, type) {
     return types.isSubtype(rtti.realRuntimeType(obj), type);
   }
-  exports.instanceOf = instanceOf;
+  exports.strongInstanceOf = strongInstanceOf;
 
   function instanceOfOrNull(obj, type) {
-    if ((obj == null) || instanceOf(obj, type)) return true;
-    let actual = rtti.realRuntimeType(obj);
-    if (_ignoreTypeFailure(actual, type)) return true;
+    if ((obj == null) || strongInstanceOf(obj, type)) return true;
     return false;
   }
-  exports.instanceOfOrNull = instanceOfOrNull;
+
+  function instanceOf(obj, type) {
+    if (strongInstanceOf(obj, type)) return true;
+    // TODO(vsm): This is perhaps too eager to throw a StrongModeError?
+    // It will throw on <int>[] is List<String>.
+    // TODO(vsm): We can statically detect many cases where this
+    // check is unnecessary.
+    if (types.isGroundType(type)) return false;
+    let actual = rtti.realRuntimeType(obj);
+    dart_utils.throwStrongModeError('Strong mode cast failure from ' +

[Leaf, 2015/08/18 23:31:11]

Calling this a "cast failure" is a bit misleading, I think.  Maybe call it an
"is check failure", and say something like "types.typeName(actual) is not an
instance of types.typeName(type)"?

+      types.typeName(actual) + ' to ' + types.typeName(type));
+  }
+  exports.instanceOf = instanceOf;
 
   function cast(obj, type) {
     // TODO(vsm): handle non-nullable types
-    if (obj == null) return obj;
+    if (instanceOfOrNull(obj, type)) return obj;
     let actual = rtti.realRuntimeType(obj);
-    if (types.isSubtype(actual, type)) return obj;
-    if (_ignoreTypeFailure(actual, type)) return obj;
-    errors.throwCastError(actual, type);
+    if (_ignoreTypeFailure(actual, type)) {
+      // TODO(vsm): track why this is happening in our async / await tests.
+      if (types.isGroundType(type)) {
+        console.error('Should not ignore cast failure from ' +
+          types.typeName(actual) + ' to ' + types.typeName(type));
+      }
+      return obj;
+    }
+    if (types.isGroundType(type)) {
+      errors.throwCastError(actual, type);
+    }
+    dart_utils.throwStrongModeError('Strong mode cast failure from ' +
+      types.typeName(actual) + ' to ' + types.typeName(type));
   }
   exports.cast = cast;
 
@@ -230,8 +250,7 @@ dart_library.library('dart_runtime/_operations', null, /* Imports */[
 
   /** Checks that `x` is not null or undefined. */
   function notNull(x) {
-    // TODO(leafp): This is probably not the right error to throw.
-    if (x == null) throwError('expected not-null value');
+    if (x == null) errors.throwNullValueError();
     return x;
   }
   exports.notNull = notNull;