Hello,

I also see this error for building packages that need cabal-doctest, as the configure step needs the package database. There's actually some packages in guix that already modify the configure step to do this, like ghc-cairo: https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/haskell-xyz.scm#n1465

As noted there, the package database should be passed to runhaskell itself, not just what it runs. This would allow other packages that need a module for configuring to work. Attached is a patch to modify haskell-build-system to do this, though not only for the configure command (seemed easiest to just do that for now). I'm submitting the patch with comments there about possible modifications.

I can confirm with this that pcg-random builds, as well as packages I've been trying that need cabal-doctest (note, I tested using guix's package of cabal-doctest, no need to add that as well).

Comments welcome here, especially as I'm pretty new to Haskell still and guix completely, or on patch submission (sending shortly).

John