Weird errors with dart2js and checked mode with functions and Object arguments

[kevmoo]

With dart2js & checked mode, I get the following exception when running the code at the bottom:

Uncaught Error: type 'constructor' is not a subtype of type '(($int, String) -> void) -> void'
    at Object.wrapException (js_helper.dart:1730)
    at RuntimeFunctionType._check$2 (js_helper.dart:3538)
    at RuntimeFunctionType._assertCheck$1 (js_helper.dart:3521)
    at Object.main (game_web.dart:3)
    at iterable.dart:276
    at init.currentScript (iterable.dart:276)
    at iterable.dart:276
    at iterable.dart:276
wrapException @ js_helper.dart:1730
_check$2 @ js_helper.dart:3538
_assertCheck$1 @ js_helper.dart:3521
main @ game_web.dart:3
(anonymous) @ iterable.dart:276
init.currentScript @ iterable.dart:276
(anonymous) @ iterable.dart:276
(anonymous) @ iterable.dart:276

void main() {
  doWeird(oneArgFunc);
  print('works');
  doWeird(oneArgFuncWeird);
  print("don't get here");
}

oneArgFunc(arg) => null;

oneArgFuncWeird(Object arg) => null;

doWeird(OnHijackCallback callback) => null;

typedef void OnHijackCallback(HijackCallback callback);

typedef void HijackCallback(int stream, String sink);

CC @rakudrama

[kevmoo]

Currently this is breaking pkg/shelf tests when run w/ dart2js.

[kevmoo]

FYI @sigmundch – this breaks with the latest pkg/test expectAsyncN methods – I'm guessing we'll see a LOT of folks hit this.

[kevmoo]

Recent changes to make pkg/test strong-mode clean have raised this issue.

[sigmundch]

So it appears the issue was that we weren't checking that functions are subtypes of object. This doesn't come up that often because the compiler optimizes away checks like is Object, so you need these nested scenarios to reproduce it.

Note that you can also see this issue without check mode by doing is checks on typedefs. For example:

typedef void T(void callback());
void m(Object arg) {}
main() => print('${m is T}');

incorrectly prints false.

CL https://codereview.chromium.org/2599073002/ is out for review