Cabal-4569 happens when running `cabal repl --enable-multi-repl all`

[Kleidukos]

How to reproduce:

$ git clone https://github.com/haskell-servant/servant
$ cabal repl --enable-multi-repl all

[…]


Running Haddock on library for servant-multipart-api-0.12.1...
Error: [Cabal-4569]
internal error when calculating transitive package dependencies.
Debug info: []

[…]

Running Haddock on library for servant-js-0.9.4.2...
Error: [Cabal-4569]
internal error when calculating transitive package dependencies.
Debug info: []

etc, etc.

No debug info is provided, so uh, no idea what's going on.

[ulysses4ever]

/cc @mpickering

[mpickering]

There is something quite broken with cabal_macros.h and multiple home units, I can see how to fix it and I think we should do that before 3.14.

[Kleidukos]

@mpickering What do you have in mind? I have some trouble understanding the root cause here.

[mpickering]

Fix in #10248