Cannot find store (XDG, ghcup ghc)

[hseg]

Trying to generate a license report fails because cabal-plan looks in the
wrong location. Half of the problem is due to
haskell-CI/haskell-ci#655, but I'm working around that
as mentioned there. The other half, though, seems to be due to my
ghcup-vendored ghc writing its Cabal store under ghc-9.8.4-c895, whereas
cabal-plan expects to find it under ../store/ghc-9.8.4/.

[hseg]

I've asked help in re the second part on
IRC.
It appears we need to find the unit ID of ghc, as given by ghc-pkg field ghc id. I don't know how one does that from within Haskell code, though, but at
least I thought I'd give this start.

[phadej]

The latter part is unfortunate. cabal-plan cannot do it atm: haskell/cabal#10726

Use older GHC for now.

---

It appears we need to find the unit ID of ghc,

cabal-plan json cannot. Either the information must be in plan.json, or the path to corresponding GHC should be passed in addition to cabal-plan. I don't like doing the latter. But for former to work, cabal-install needs to be changed first.