`doctest`s need `--write-ghc-environment-files=always`

[andreasabel]

See:

• https://github.com/isovector/type-errors/issues/9

Can we default to write-ghc-environment-files: always or would that break other packages? In the latter case, could we allow users to activate write-ghc-environment-files: always in the test settings?

See also:

• #991
• #981

[peterbecich]

Just noting for myself, ~this allows the DocTests to work~ unreliably:

cabal build --write-ghc-environment-files=always
cabal test DocTests --write-ghc-environment=always

[peterbecich]

@andreasabel , I can't make this work reliably. Can you give me the command to make the DocTests succeed? Thanks

[andreasabel]

Do you mean for hackage-server? (Because this issue is about user packages uploaded to hackage that have doctests.)

[peterbecich]

Oh, I misunderstood. Yes, I meant for hackage-server.

Are you able to run the hackage-server DocTests reliably?

[andreasabel]

Well, yes, CI runs them every time. I just tried them locally.

• cabal.project says: write-ghc-environment-files: always, so we are good there.
• cabal build (necessary!)
• cabal test DocTests

Works.

[peterbecich]

For me, locally, with GHC 9.6, either of these causes the error:

cabal build --write-ghc-environment-files=always all; cabal test DocTests --write-ghc-environment=always

cabal build all; cabal test DocTests

However, with GHC 9.8, either succeeds.

The Nix Flake has GHC 9.6.

Thanks @andreasabel , that resolves it for now