Add PullRequest.MergeableState field

[ains]

This isn't a well documented field but it's present in API responses and mentioned here
octokit/octokit.rb#626

[gmlewis]

Thank you, @ains. I have a couple questions for you.

According to the documentation here: https://developer.github.com/v3/pulls/#get-a-single-pull-request
the mergeable field ought to be sufficient, and mergeable_state is nowhere to be found (in the docs) but you say you have seen it in responses.

Have you tried using the mergeable field to see if it satisfies your needs?

If you have tried it, but it doesn't work, then I think we need to contact support@github.com and ask for clarification regarding these two fields (one documented, one not).
If this is the case, can you please provide a JSON response showing both the mergeable and mergeable_state fields and show how mergeable is not sufficient? This will help the GitHub support team figure out what is going on.

Thanks again!

[ains]

No problem @gmlewis

You can find a bit more context on the field mergeable_state in this issue octokit/octokit.rb#626,

and in this thread on the github platform forum (where they are planning to document it)
https://platform.github.community/t/documentation-about-mergeable-state/4259

Unfortunately mergeable doesn't satisfy the needs we have, if a PR can cleanly merge into a branch but fails a check (set when protecting that branch) mergeable is still true however mergeable_state will be blocked, indicating it actually shouldn't be merged.

[gmlewis]

Ah, thank you for the forum link, @ains! That is sufficient for me.
LGTM.