Better stack trace support

pkg/dev_compiler/tool/input_sdk/private/js_helper.dart

Index: pkg/dev_compiler/tool/input_sdk/private/js_helper.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/js_helper.dart b/pkg/dev_compiler/tool/input_sdk/private/js_helper.dart
index 1cb146ddcc3931bb5737e64d69aaffd85c1060f0..6fc12bd7f1fbd2f4d6d304b39e8ebe3e8c77617a 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/js_helper.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/js_helper.dart
@@ -493,7 +493,7 @@ class Primitives {
   }
 
   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).

   }
 }
 
@@ -627,10 +627,20 @@ class UnknownJsTypeError extends Error {
 }
 
 /**
- * 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;