[Ftr] Block until termination of long-running processes

[l3nz]

Is your feature request related to a problem? Please describe.

A number of people have a need to keep the JVM/JS up for a while (se e.g. #66 #83) after the cli run command stops.

Describe the solution you'd like

Your main function that implements the subcommand should return:

• an integer return status, as it does today, or
• a promise of an integer, or
• a core-async channel (if it's available) that will return an integer

In the last two cases, wait until the promise is fulfilled or the channel has some data, and run System.exit with the value read from there.

Describe alternatives you've considered

I do not like the idea of having core.async as a mandatory dependency as I would only use core features.

Not sure how and if this works in JS - Clojure promises don't work, it has its own js/Promise so the best pattern would likely be core.async.

[l3nz]

In CLJS, we might require https://www.blog.nodrama.io/clojurescript-chaining-js-promises-previous-value/

[l3nz]

As a simpler alternative, we might require https://cljdoc.org/d/funcool/promesa/4.0.2/doc/user-guide for CLJS.

[rgm]

I'm perfectly fine with the core.async dep. Maybe it could be a soft-dependency and only really needed if you actually want the long-running behaviour we're discussing. Probably mucks up the code with a bunch of does-async-namespace-exist introspection though.

An alternative for JS off the top of my head could be similar to a pattern you see in older pre-promise test runners. Since we don't worry about arity (ugh), the signature of the :runs fn could be function (options, done) { doLongRunningStuff(done); } with clj-matic providing the done function. The long-running fn eventually invokes done(int) to return control to clj-matic and exit. Because of JS's arity quirk, it's invisible to anyone who doesn't care.

It's ... convoluted and maybe not the best idea, but also I think I've seen the pattern a hundred times so at least it's got convention going for it.

[l3nz]

Implemented ver 0.3.11