Better stack trace support

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 475 matching lines @@
   }
 
   static void setProperty(object, key, value) {
     if (object == null || object is bool || object is num || object is String) {
       throw argumentErrorValue(object);
     }
     JS('void', '#[#] = #', object, key, value);
   }
 
   static StackTrace extractStackTrace(Error error) {
-    return getTraceFromException(JS('', r'#.$thrownJsError', error));
+    return JS('StackTrace', 'dart.stackTrace(#)', error);

[Jennifer Messerly, 2017/05/05 23:59:15]

question ... i've seen this pattern too in dart:mirrors ... can we not just:

import 'dart:_runtime' as dart;

    return dart.stackTrace(error);

... as long as we're importing 'dart:_runtime' from our own private SDK code
(such as this file, or our mirrors patch) it should be fine to do that.

Bonus: better static checking of our SDK implementations :D

... last but not least I think `dart.stackTrace` is equivalent to
getTraceFromException, below

[vsm, 2017/05/08 17:07:44]

Oh nice - the typed call works!  

In this case though, calling getTraceFromException direct is the right call.

We should switch to typed calls though - we may also need better static typing
to avoid additional casts though (we're avoiding some since we trust JS).

   }
 }
 
 /**
  * Diagnoses an indexing error. Returns the ArgumentError or RangeError that
  * describes the problem.
  */
 @NoInline()
 Error diagnoseIndexError(indexable, index) {
   if (index is! int) return new ArgumentError.value(index, 'index');
@@ skipping 113 matching lines @@
 
 class UnknownJsTypeError extends Error {
   final String _message;
 
   UnknownJsTypeError(this._message);
 
   String toString() => _message.isEmpty ? 'Error' : 'Error: $_message';
 }
 
 /**
- * Called by generated code to fetch the stack trace from an
+ * Called by generated code to fetch the stack trace from a Dart
  * exception. Should never return null.
  */
-StackTrace getTraceFromException(exception) => new _StackTrace(exception);
+final _stackTrace = JS('', 'Symbol("_stackTrace")');
+StackTrace getTraceFromException(exception) {
+  var error = JS('', 'dart.recordJsError(#)', exception);

[Jennifer Messerly, 2017/05/05 23:59:15]

same as above, I don't think we need to use JS code to call this method

+  var trace = JS('StackTrace', '#[#]', error, _stackTrace);
+  if (trace != null) return trace;
+  trace = new _StackTrace(error);
+  JS('', '#[#] = #', error, _stackTrace, trace);
+  return trace;
+}
+
+//=> JS('StackTrace', 'dart.stackTrace(#)', exception);

[Jennifer Messerly, 2017/05/05 23:59:15]

remove this comment?

[vsm, 2017/05/08 17:07:44]

doh!

 
 class _StackTrace implements StackTrace {
   var _exception;
   String _trace;
 
   _StackTrace(this._exception);
 
   String toString() {
     if (_trace != null) return _trace;
 
@@ skipping 272 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';
 }