Make the child process closer to a real Promise

[callumlocke]

Execa doesn't implement .finally() on the child process. This is making it difficult to come up with a correct Flow type definition for it – see discussion on this PR.

Would you object to adding a .finally() method to execa's spawned child process, to make it fully implement Promise?

The .finally() method is at Stage 4 and is in the latest draft spec.

[sindresorhus]

Sure, PR welcome :)

You can use https://github.com/es-shims/Promise.prototype.finally to test it. See: sindresorhus/p-cancelable@870529d

[bradfordlemley]

Would it be possible (or desirable) to define execa as returning an enhanced Promise, rather than an enhanced child process? I.e., extend Promise type like bluebird's flowdef?

There are several defs in flow-typed that extend Promise and that seems like the ideal pattern for Promise compatibility, if possible.

[sindresorhus]

Yes, that’s what I would type it as.