Illegal argument in isolate message : (object is a regular Dart Instance)" - Dart 1.22-dev.5 breaks pkg/test

[kevmoo]

See https://travis-ci.org/dart-lang/shelf/jobs/188931055#L690

"Failed to load "test/message_change_test.dart": Invalid argument(s): Illegal argument in isolate message : (object is a regular Dart Instance)"

Digging in a bit, but this seems gnarly/bad/etc

Reproduction:

• Sync down https://github.com/dart-lang/shelf
• cd into shelf
• pub get
• pub run test

[lrhn]

If it appeared when I made platform library methods generic, maybe (just guessing) there could be a problem of a generic method tear-off no longer being considered compile-time constant and sendable over send-ports. Or maybe it's completely unrelated.

[kevmoo]

I just tried to JSON-encode the message – and it worked.

So I'm thinking it just something weird...please hold...

[kevmoo]

After digging and bisecting, @lrhn it did turn out that 4459427 was the culprit

[lrhn]

Since the syntax change from comment-based-generics to real generic syntax shouldn't affect semantics of the VM at all, this is a VM bug.
The error message comes from some object not being sendable through a SendPort (or equivalently, as the initial parameter to an isolate spawn), and since it used to work, it must be some new object that has changed to no longer be sendable.
I'm guessing it's a closure of some sort, that didn't use to be a closure - you can send top-level/static functions to similar isolates, but not closures that capture part of their environment, so maybe a top-level generic function now thinks it's a closure because it contains the type variable. But that's just a guess based on what was actually changed, I have no actual idea what the problem is :)

Looking just at the travis output, the problem might be a message sent by the test framework to an isolate that is loading the test.

[lrhn]

I've tried adding some debug prints just before the error is thrown in the VM (raw_object_snapshot.cc line 122) and the error appears because the test:

if (writer->can_send_any_object() ||
    writer->AllowObjectsInDartLibrary(ptr()->library_)) {

fails both tests with the library URI being package:test/src/backend/group_entry.dart. That's slightly surprising because the only thing in the library is an abstract class, so whatever object is being sent, it's not originally from that library.

The errors seems to come from the test package itself, or maybe pub, but the files that fail are test files, so probably it's test.
If I run a test directly, it works, when running through pub run test, it fails.
Which is curious, because it only creates isolates using spawnUri, which only accept JSON-like data as arguments + send-ports, and the only argument to the isolate spawn is a send-port.

(One example of failing is the convert package, which is what I'm debugging on).
I hope this helps somebody.

[a-siva]

why doesn't 'pub --trace run test' produce any trace of what dart command is being run. Pretty unhelpful diagnostics from pub, how does one get at the actual dart command being run by pub?