Print useful message when worker threads cannot be used due to Node.js flags

[novemberborn]

See discussion in #3015. Certain Node.js flags stop worker threads from working. We should recognize that error (ERR_WORKER_INVALID_EXEC_ARGV) and print a useful error message so users know to disable worker threads in AVA.

[oantoro]

Since the error is initiated by worker_threads.Worker() in

ava/lib/fork.js

Line 24 in ada1a4f

worker = new Worker(workerPath, {

I think the main process has to stop forking worker for the rest of the test files and then print appropriate error message, otherwise we will get aggregated error with same error messages.
But I am afraid, by changing stopOnError to true in

ava/lib/api.js

Line 302 in ada1a4f

}, {concurrency, stopOnError: false});

will change the behavior completely.

Second approach: Check if the error is ERR_WORKER_INVALID_EXEC_ARGV in

ava/lib/api.js

Line 309 in ada1a4f

for (const error_ of error.errors) {

and then add warnWorkerThreadError: true property to the emitted internal-error event, so the reporter can display a warning message.

What's your opinion?

[novemberborn]

We could also check whether worker threads are enabled (in AVA's config) and then create a worker. If that fails with a recognized error we don't run the tests at all.

The worker can be created with the eval option and an empty script, so that we don't have to actually run anything.

[novemberborn]

See also #3207.