Handle toString on DOM types

pkg/dev_compiler/tool/input_sdk/private/js_helper.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.
 
 library dart._js_helper;
 
 import 'dart:collection';
 
 import 'dart:_debugger' show stackTraceMapper;
 
@@ skipping 167 matching lines @@
       return _parseDoubleError(source, handleError);
     }
     return result;
   }
 
   /** [: r"$".codeUnitAt(0) :] */
   static const int DOLLAR_CHAR_VALUE = 36;
 
   /// Returns the type of [object] as a string (including type arguments).
   ///
   /// In minified mode, uses the unminified names if available.

[Jennifer Messerly, 2017/06/23 18:27:11]

not related to your change, but this comment seems obsolete?

[vsm, 2017/06/26 20:29:24]

deleted

   static String objectTypeName(Object object) {

[Jennifer Messerly, 2017/06/23 18:27:11]

is this function used?

[vsm, 2017/06/26 20:29:24]

deleted

     return getRuntimeType(object).toString();
   }
 
   /// In minified mode, uses the unminified names if available.

[Jennifer Messerly, 2017/06/23 18:27:11]

this one too

[vsm, 2017/06/26 20:29:24]

deleted

   static String objectToString(Object object) {
-    // String name = objectTypeName(object);
-    String name = JS('String', 'dart.typeName(dart.getReifiedType(#))', object);
-    return "Instance of '$name'";
+    bool nativeType = JS('bool', 'typeof # == "object" && !(# instanceof #)',

[Jennifer Messerly, 2017/06/23 18:27:11]

the normal way to check this is `getExtensionType`. Here's how dart.toString is
defined:

  var extension = getExtensionType(obj);
  if (extension != null) {
    return JS('String', '#[dartx.toString]()', obj);
  }

... this is used for all Object members. Should we change the pattern?

... also should we change dart.toString somehow? It seems like this code here
suggests we never want to fall back to Dart's Object.toString for native types
(unless the class defines it). So we're kinda dispatching to darx.toString, but
then we end up here and have to check again if we're a native type.

Instead, we could make sure native types don't get hooked up to dart:core
Object.toString in the first place. I'm not 100% sure how that happens without
poking around but it seems worth investigating?

[vsm, 2017/06/26 20:29:24]

Ahh, all our extension types (i think) extend Interceptor.  Moved the logic
there (see added-to-cl file).  If an extension defines its own toString, that
should be called.  Otherwise, Interceptor.toString should forward to JS before
we ever get here.

+        object, object, Object);
+    if (nativeType) {

[Jennifer Messerly, 2017/06/23 18:27:11]

very minor suggestion: if you put the conditional up here, I think it skips the
null check.

[vsm, 2017/06/26 20:29:24]

We already inferred nativeType as non-nullable.  Would have to define it as:

bool nativeType = JS('bool|Null', ....);

to allow null.   But killed the code anyway.  :-)

+      // Forward DOM types and other JS objects to their native toString method.
+      return JS('String', '#.toString()', object);
+    } else {
+      // Otherwise, fall back on default Object implemation.
+      String name =
+          JS('String', 'dart.typeName(dart.getReifiedType(#))', object);

[Jennifer Messerly, 2017/06/23 18:27:11]

can this just call `typeName(getReifiedType(object))` ... I don't think there's
anything special about dispatching through JS.

[vsm, 2017/06/26 20:29:24]

I was going to say we have no way to import our runtime - but it works!  Not
sure why I thought it didn't/wouldn't work.  :-)

+      return "Instance of '$name'";
+    }
   }
 
   static int dateNow() => JS('int', r'Date.now()');
 
   static void initTicker() {
     if (timerFrequency != null) return;
     // Start with low-resolution. We overwrite the fields if we find better.
     timerFrequency = 1000;
     timerTicks = dateNow;
     if (JS('bool', 'typeof window == "undefined"')) return;
@@ skipping 715 matching lines @@
   // we have no way of telling the compiler yet, so it will generate an extra
   // layer of indirection that wraps the SyncIterator.
   _jsIterator() => JS('', '#(...#)', _generator, _args);
 
   Iterator<E> get iterator => new SyncIterator<E>(_jsIterator());
 }
 
 class BooleanConversionAssertionError extends AssertionError {
   toString() => 'Failed assertion: boolean expression must not be null';
 }