github resolver shorthand hardcodes default branch

[pbrisbin]

We're experimenting with remote, custom snapshots and wanted to use the github:user:repo:path shorthand, but we can't because we use main as our default branch and it expands to master.

I'm not sure how you would go about addressing this limitation, but I just wanted to raise it and see what you thought. I'm happy to implement the fix, if we can come up with one.

[pbrisbin]

And, I immediately had an idea. What about,

resolver: github:user:repo:path@ref

Where @master is the default, preserving the behavior of all existing code. One could specify tags or branches there, which sounds useful in general.

[qrilka]

@pbrisbin what about the solution we use for Stack templates - https://github.com/commercialhaskell/stack/blob/255cd830627870cdef34b5e54d670ef07882523e/src/Stack/New.hs#L206-L208 ?

[pbrisbin]

What version of the object does the contents/ API return? I assume it's "latest on default branch". If so, then yeah that totally unblocks me to use main. However, my follow-up @ref idea gives you more, since users could pull tags or other branches by that mechanism.

[qrilka]

Sure, the point is to have @ref optional and use the default branch correctly

[pbrisbin]

I don't think we can do both, can we?

1. Respect @ref, default to @master when missing, continue with raw.github.com/...
2. Fetch api.github.com/.../contents

(1) will open up @ref syntax generally, but when not used continues to hard-code master.

(2) will respect default branch, but cannot be used to select not default branch.

What am I missing?

[qrilka]

I guess we should have information whether @ref was specified or not and use either raw.github.com or api.github.com. That would slightly complicate the code but will be slightly more user-friendly.

[qrilka]

BTW api.github.com also supports branches, see https://api.github.com/repos/commercialhaskell/stack/contents/README.md?ref=master

[pbrisbin]

Neat. Seems like API + ?ref would be ideal. Could be tricky implementation-wise, since the code in question here is pure:

githubSnapshotLocation :: Text -> Text -> Text -> RawSnapshotLocation

And expected to give a URL directly to the content (not to an API with a .content field).

I like the way Pantry's machinery (unlike templates) is just a series of syntactic expansions from (e.g.) lts-X.Y to github:commercialhaskell:stackage-snapshots:/lts/X/Y.yaml to https://raw.github.com/.... Introducing, the API call and .content access kind of breaks that. But it would be valuable for omiting @ref to result in respecting default branch, instead of a static default.

So maybe worth it, but it would expand the diff significantly to implement.