Typed holes treated as exceptions

[acowley]

If you try to get info (or doc) on an expression within a module that includes typed holes, ghc-mod is tripped up by an exception regarding the typed hole.

Expected result: typed holes shouldn't stop info or doc from working. I'm taking a quick look at this now; any guidance is appreciated.

[DanielG]

Probably just needs the same fix as this: #438 (comment)

[acowley]

Okay, I think I have this going now, but it obviously overlaps a lot with your link. Do you want to wait for that fix to come in, or should I open a PR for this bit?

Edit: Not sure how I forgot this: thank you! Tracking that down was turning into a very deep rabbit hole without any apparent satisfying conclusion.

[acowley]

Some additional commentary for the record, this is a tragic bit of the GHC API. Opt_DeferTypeErrors should imply Opt_DeferTypedHoles. This might even be important to the type checker, I don't know. Within GHC, there is an API for enforcing these implications (setGeneralFlag'). However it is not exported, so we use gopt_set, and deal with issues like this.

[DanielG]

I suppose we can always ask them to expose that? Then at least the workarounds can be removed in like 6 years? (3 major versions from now xD).

[DanielG]

What do you mean by overlap? Just rebase your stuff on top of serras' I was going to merge that anyways.

[acowley]

The simple patch is to replace the definition of deferErrors with @serras 's definition for deferErrorsAndHoles as this is what deferErrors should be doing anyway (if we had access to the right API, our deferErrors would be exactly deferErrorsAndHoles). We also don't need setWarnTypedHoles. I can rebase those simplifications on @serras's patch if you want, or you can do it after merging, or perhaps @serras can add it to his branch.

I talked to Austin a little about fixing this in GHC. He's still on vacation, but when he gets back he can help get these through since it really is a silly mistake in the GHC API.

[DanielG]

Just rebase on top of his branch he doesn't have time to work on this stuff ATM.

[DanielG]

Actually you can also just cherry-pick the commit if you like.

[acowley]

Done #539