Check for the type of the the spawned function.

runtime/lib/isolate_patch.dart

Index: runtime/lib/isolate_patch.dart
diff --git a/runtime/lib/isolate_patch.dart b/runtime/lib/isolate_patch.dart
index 7e4579a419072dd90df43b52fa71e1f8f12141e0..65565058acf186d1c343b230bd69f03494fe7380 100644
--- a/runtime/lib/isolate_patch.dart
+++ b/runtime/lib/isolate_patch.dart
@@ -310,6 +310,11 @@ void _startIsolate(SendPort parentPort,
     // `paused` isn't handled yet.
     RawReceivePort readyPort;
     try {
+      // Check for the type of `entryPoint` on the spawning isolate to make
+      // error-handling easier.
+      if (entryPoint is! _MainFunctionArgs) {

[Lasse Reichstein Nielsen, 2016/10/14 10:13:56]

_MainFunctionArgs is not really the correct type name for this - this is just an
unary function, not a "main function".
If we ever change _MainFunctionArgs to check that the first parameter has type
List<String>, this will stop working.

Maybe just rename the typedefs to _NullaryFunction, _UnaryFunction and
_BinaryFunction, then it's clear what they are checking and what they aren't
checking.

[floitsch, 2016/10/14 11:25:58]

Done.

+        throw new ArgumentError(entryPoint);
+      }
       // The VM will invoke [_startIsolate] with entryPoint as argument.
       readyPort = new RawReceivePort();