Check for the type of the the spawned function.

runtime/lib/isolate_patch.dart

 // Copyright (c) 2012, 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.
 
 import "dart:collection" show HashMap;
 import "dart:_internal";
 
 @patch class ReceivePort {
   @patch factory ReceivePort() = _ReceivePortImpl;
 
@@ skipping 292 matching lines @@
       (VMLibraryHooks.packageConfigUriFuture != null) &&
       (VMLibraryHooks.resolvePackageUriFuture != null);
 
   @patch static Future<Isolate> spawn(
       void entryPoint(message), var message,
       {bool paused: false, bool errorsAreFatal,
        SendPort onExit, SendPort onError}) async {
     // `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();
 
       // We do not inherit the package root or package config settings
       // from the parent isolate, instead we use the values that were
       // set on the command line.
       var packageRoot = VMLibraryHooks.packageRootString;
       var packageConfig = VMLibraryHooks.packageConfigString;
       var script = VMLibraryHooks.platformScript;
       if (script == null) {
@@ skipping 250 matching lines @@
     try {
       return Uri.parse(_getCurrentRootUriStr());
     } catch (e, s) {
       return null;
     }
   }
 
   static String _getCurrentRootUriStr()
       native "Isolate_getCurrentRootUriStr";
 }