Introduce Config::transactAsync

[as-cii]

Refs: #9508

This method is supposed to wrap asynchronous code within a Config transaction. It accepts a callback which must return a Promise: when this resolves or gets rejected (or the callback throws an error) we complete the transaction.

I am not super happy with the name I've chosen for this API, as it would have probably been better to follow Node's conventions (i.e. rename ::transact to ::transactSync and name the new one ::transact): unfortunately that method name was already taken and it's part of the public API.

Another thought was to include this feature right inside the existing ::transact method: although possible, the resulting method would need to conform to two different contracts based on the return type of callback, which feels somewhat misleading for clients. In the end having a separate method felt somewhat cleaner.

Feedback super welcome! 🙇

/cc: @nathansobo @joshaber @atom/feedback

[nathansobo]

Yeah, someday I think we can fix these warts in our API, but for now I think 2 methods is a good idea.

[nathansobo]

Are the multiple arguments needed here? Seems like you only call resolve or reject.

[as-cii]

Yeah, I guess so: this is a function that returns a function (i.e. curried), so when called with endTransaction(resolve), for instance, will return a function that:

• Ends the transaction.
• Calls resolve with all the passed arguments.

When used like result.then(endTransaction(resolve)), resolve will be invoked with all the arguments available in then's callback. This means that a potential client could use this API like the following:

atom.config.transactAsync(-> Promise.resolve(1)).then((n) -> console.log("Output: #{n}"))
#=> Output: 1

Although we're not using it in our production code, it seemed reasonable to follow the Promise API semantics when I implemented this. What do you think?

[nathansobo]

Ah, I missed the currying. So long as you test it I'm cool having the functionality.

[as-cii]

✅ I tested this behavior in c6cb37a 👍

I am going to as soon as the build gets 💚

[thomasjo]

Nice!