stack-building Agda with cpphs on Windows fails with ghcup-installed ghcs 9.2 and 9.4

[andreasabel]

I experience build failures of Agda in this combination

• Windows (local Windows 10, gha windows-2022)
• stack (latest)
• cpphs
• recently ghcup installed ghc (tested 9.4.5 9.4.4 9.4.3 9.2.7)

https://github.com/agda/agda/actions/runs/4827829386/jobs/8600964097#step:12:25

Agda       > C:\Users\RUNNER~1\AppData\Local\Temp\ghc1952_0\ghc_25.hscpp:1:7: error:
Agda       >     lexical error in pragma at character '1'
Agda       >   |
Agda       > 1 | #line 1 ".stack-work 

This issue goes away when one of:

• letting stack install ghc
• not using cpphs but default C preproc.
• using a non-recent ghc (I tried 8.8.4, ghcup-installed now, and 8.10.7, ghcup-installed 2022-08-14)

Original report here:

• Agda build failure with cpphs and GHC 9.4.5 on Windows commercialhaskell/stack#6111

[andreasabel]

I confirmed this problem with cpphs independent of Agda here:

• WIP: cpphs dogfood hackage-trustees/malcolm-wallace-universe#20

The experiments there seem to suggest that ghcup-installed GHC 9.x does not work with cpphs under Windows, but GHC 8.10.7 does.
When building with stack, GHC 9.x installed with stack or choco works with cpphs, but then not GHC 8.10.7. (This is a situation where ghcup outperforms the other installation methods.)

[hasufell]

I think we will have to involve GHC devs or cpphs devs here. I'm afraid I don't know too much about how cpphs interacts with GHC.

@bgamari @angerman @mpickering

[angerman]

I'm lost. What are the relevant cpphs versions? Does stack install a different cpphs?

I'm not terribly surprised that this would go away, if you use the stock that ghc assumes, and no one really saw the cpphs issue; I don't know how widespread that use is.

[andreasabel]

I'm lost. What are the relevant cpphs versions?

Latest, I suppose, which would be 1.20.9.1.

Does stack install a different cpphs?

Maybe, but it should at least use the current cpphs in the testsuite for cpphs, which is in:

• WIP: cpphs dogfood hackage-trustees/malcolm-wallace-universe#20

Is cpphs still a thing or should the Haskell community drop it? I do so, after seeing the mess it causes on Windows:

• Remove cabal flag cpphs agda/agda#6600

[hasufell]

Latest, I suppose, which would be 1.20.9.1.

You suppose? Did you actually verify?

[andreasabel]

Latest, I suppose, which would be 1.20.9.1.

Here is the hard evidence:

• cabal: https://github.com/hackage-trustees/malcolm-wallace-universe/actions/runs/4858876155/jobs/8660803517#step:6:5
• stack: https://github.com/hackage-trustees/malcolm-wallace-universe/actions/runs/4858876154/jobs/8660803702#step:7:5

[andreasabel]

Update: I consider cpphs dead, so I don't care about this issue any longer.

• Remove cabal flag cpphs agda/agda#6600