Allow creating multiple backports from one pull request

[m-kuhn]

Fix #17

Disclaimer: I have never written TypeScript before and have used the github online editor. Needs careful review!

[m-kuhn]

Apparently when backporting to multiple branches, there is only one comment about a backport failure, even if multiple backports fail. This makes it hard to quickly see which backports need to be done manually.

@tibdex do you have an idea why this is? Some throttling on github side maybe?

[tibdex]

It's because I use p-series:

backport/src/backport.ts

Lines 137 to 141 in 35fd5c5

	return pSeries(
	backportLabels.map(label => () =>
	backportForLabel({ label, octokit, owner, pullRequestNumber, repo }),
	),
	);

And its doc says:

Returns a Promise that is fulfilled when all promises returned from calling the functions in tasks are fulfilled, or rejects if any of the promises reject. The fulfilled value is an Array of the fulfilled values.

It would indeed be better to try them all, even if one rebase failed.

[m-kuhn]

That sounds reasonable.
Are you aware of a better alternative? If you are able to give me an initial hint, I can try to make a pull request.

[tibdex]

Tracking this with #27, the fix should be fairly easy.

[m-kuhn]

In fact I fail to understand the documentation you cited. From what I can see it mentions the aggregated end result of the promise but doesn't talk about continuation after a rejected function. p-all and friends docs look very similar to me. It's likely related to the fact that the whole concept and terminology with "promises" is new to me.

[tibdex]

You can see the fix in c252bc6, tell me if you don't understand something ;)