New comment by jchook on void-packages repository

https://github.com/void-linux/void-packages/issues/6414#issuecomment-760547883

Comment:
According to the [cabal docs](https://cabal.readthedocs.io/en/3.4/developing-packages.html#kinds-of-package-cabal-vs-ghc-vs-system)

> Library packages have to be registered with GHC for them to be available in GHCi or to be used when compiling other programs or packages.

> When you build and install a Cabal package containing a library then it gets registered with GHC automatically.

This automatic registration **does not happen** on Void, whether installed via XBPS or a `ghcup`.

Cabal silently fails to add libraries to the package database, even when I explicitly specify a package db. None of these works:

```sh
cabal install xmonad
cabal install --lib xmonad
cabal install --lib --user xmonad
cabal install --lib --global xmonad
cabal install --lib --package-db=user xmonad
cabal install --lib --package-db=$HOME/.local/share/ghcup/ghc/8.8.4/lib/ghc-8.8.4/package.conf.d xmonad
cabal install --lib --package-db=$HOME/.local/share/ghcup/ghc/8.8.4/lib/ghc-8.8.4/package.conf.d/package.cache xmonad
```

Setting `package-db` in `~/.cabal/config` has no effect. `ghc-pkg recache` did not help.

Following https://github.com/haskell/cabal/issues/6262#issuecomment-733919670, I successfully installed xmonad using `cabal v1-install xmonad`, and it properly registered in a new package known to `ghc-pkg list`. However the package installs "hidden" by default. `ghc-pkg expose xmonad` exposed it, but running `xmonad --recompile` still fails with all the same errors. *sigh*.

So far this seems like a cabal bug. It appears to silently fail to register with GHC.

- Void glibc Linux 5.9.16 x86_64
- GHC v8.8.4
- Cabal v3.2.0.0