Provide externs to rebuildModule

[thomashoneyman]

Closes #222. When implementing #209 I accidentally provided an empty array to rebuildModule for the externs; this fix properly threads the externs through. As @JordanMartinez noticed in #222 we also can remove the initNamesEnv argument as it is no longer used.

Evidence that things work once again:

[hdgarrood]

This is definitely a step in the right direction, but I’m curious about a) whether initEnv is used, and b) if we can get unused bindings to emit errors which cause CI to fail. Ideally this would have been caught before it was merged in the first place.

[JordanMartinez]

whether initEnv is used

It's used in the /search path for doing searches

[JordanMartinez]

if we can get unused bindings to emit errors which cause CI to fail

This sounds like a separate PR to me. Perhaps we should follow the hlint warnings that rhendric added to the purescript repo recently?

[hdgarrood]

No need to bring hlint in for that - GHC is already capable of generating warnings for unused bindings, and then -Werror / —pedantic will cause the build to fail if there are warnings.

[hdgarrood]

By the way, we could also keep the initNamesEnv around and use P.rebuildModule' here, as that one allows you to provide a prebuilt Env rather than having to construct it each time, as that would speed the server up a little bit. See https://github.com/purescript/purescript/blob/master/src/Language/PureScript/Make.hs, specifically how rebuildModule is the same as the primed version except that it constructs an Env out of the externs first.

[JordanMartinez]

By the way, we could also keep the initNamesEnv around and use P.rebuildModule' here

I would but rebuildModule' is not exported. Not sure if that's intentional or not. That was my initial thought when I saw how similar that was to rebuildModule.

[hdgarrood]

Ah, I see, thanks. I think that might be unintentional. It would definitely be useful in cases like this one when you’re using the compiler from Haskell.

[JordanMartinez]

I've submitted a PR to export it.