Backpack: unknown package: hole

[ekmett]

When building this package I get this error:

mac:coda/lib/coda-set> cabal new-build
In order, the following will be built (use -v for more details):
 - coda-set-0.0.1 (lib) (first run)
Preprocessing library for coda-set-0.0.1..
Building library instantiated with Elem = <Elem>
for coda-set-0.0.1..
<command line>: unknown package: hole

If I replace the stupidly small Elem signature with a .hs stub the package compiles.

All my other backpack projects build just fine.

[phadej]

20:58  edwardk what bugs me is i don't see at all how this package is at all different than say, coda-dyck which works just fine
20:59  edwardk its literally the same cabal file with a couple of tweaks

With released 8.2.1 it works, with 8.2.1.20171030 or 8.2.2 it doesn't.

[ekmett]

I was able to reduce the issue to the (unused) {-# language CPP #-} pragma in Set.Internal.

There appears to be an issue with backpack and CPP in the release candidate.

[int-index]

The same error triggered by an unused TemplateHaskell pragma, as I reported here #4905 (comment)

[ezyang]

https://phabricator.haskell.org/D4234 is a patch which should fix this.

[ezyang]

Fix is in GHC HEAD.