gnu: ghc-9.2: Make Cabal respect GHC_PACKAGE_PATH

**tl;dr** Applying this patch makes Cabal work in Guix environments
and ensures that Cabal picks up Haskell packages installed via Guix.

Guix makes heavy use of GHC_PACKAGE_PATH to make GHC pickup Haskell
packages installed via the Guix package manager. The environment
variable is set using native-search-paths from the GHC packages.

Unfortunately, upstream Cabal does presently not respect
GHC_PACKAGE_PATH. If this environment variable is set, `cabal build`
and other commands will terminate. For building packages, Guix does
not make much use of cabal-install hence this is not as big of an
issue. However, cabal-install does therefore presently not work
out-of-the-box in environments created by Guix. For example,
in `guix shell` environments. This makes it essentially impossible
to use Guix for setting up development environments for Haskell software.

Cabal upstream is aware of this issue and a patch exists to workaround
this problem. The patch is currently not merged upstream due to issues
related to reconfiguration (changing GHC_PACKAGE_PATH between `cabal
configure` and `cabal build`). However, I would argue that this edge
case is not that relevant for Guix and therefore propose including
this patch with the Cabal Guix package. As outlined above, cabal-install
is not usable by default presently, and I would therefore argue that
this is a major improvement over the current situation. I am willing to
work with Cabal upstream to have this issue fixed upstream eventually.

Note that this requires patching the GHC package instead of the
cabal-install package as Guix uses the version of the Cabal package
<https://hackage.haskell.org/package/Cabal> distributed with GHC.

See: https://github.com/haskell/cabal/issues/3728

* gnu/packages/haskell-apps.scm (cabal-install): Include patch
to support the GHC_PACKAGE_PATH environment variable.

Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>
Signed-off-by: Lars-Dominik Braun <lars@6xq.net>
Change-Id: Ib77ffa937b878690d0e2d8964b534842b99da039

0 files changed, 0 insertions, 0 deletions