Windows: GHC >= 9.0 boot libraries `*.conf` files: problem with the `haddock-html` paths

[mpilgrem]

This is not a bug in Cabal (the library) but a bug in GHC >= 9.0 (up to, at least, GHC 9.6.2) that Cabal may wish to accommodate with a work-around. See GHC issue: https://gitlab.haskell.org/ghc/ghc/-/issues/23476 and (because it affects Hoogle too) my Hoogle pull request that suggests that Hoogle accommodate the GHC error: ndmitchell/hoogle#405.

Stack is built on top of Cabal (the library) and I was receiving output like this below with stack build --haddock (on Windows) (extracts only) :

foo> haddock
Warning: The documentation for the following packages are not installed. No
links will be generated to these packages: base-4.16.4.0, ghc-bignum-1.2,
ghc-prim-0.8.0
Running Haddock on library for foo-0.1.0.0..
  50% (  1 /  2) in 'Lib'
  Missing documentation for:
    Module header
Warning: Lib: could not find link destinations for:

        - GHC.Types.IO

Note that the 'Warning: ...' (which is via Cabal) is complaining that no documentation is installed for GHC boot libraries, including base-4.16.4.0. It turns out that is because the base-4.16.4.0.conf file shipped with GHC 9.2.7 contains an error - the haddock-html field is not pointing to the correct location where the Haddock HTML is to be found, but to a directory that does not exist.

Proof of this is that if you manually edit the *.conf file to point to the correct location, the Cabal warning goes away (eg just for base):

foo> haddock
Warning: The documentation for the following packages are not installed. No
links will be generated to these packages: ghc-bignum-1.2, ghc-prim-0.8.0
Running Haddock on library for foo-0.1.0.0..
  50% (  1 /  2) in 'Lib'
  Missing documentation for:
    Module header

One might argue that the proper approach is for users of GHC >= 9.0 on Windows to patch the *.conf files. However, having the tools that rely on the output of ghc-pkg dump catch this may be the path of least resistence.