os conditionals not supported in custom-setup

[joeyh]

My Setup.hs needs WIn32 to build on windows. So, I tried adding to its custom-setup stanza:

  custom-setup
    Setup-Depends: base (>= 4.5)
  if os(Windows)
    Setup-Depends: Win32

cabal fails to parse that:

'parseField' called on a non-field. This is possibly a bug in Cabal.
Please report it to the developers: https://github.com/haskell/cabal/issues/new
CallStack (from HasCallStack):
error, called at ./Distribution/PackageDescription/Utils.hs:21:16 in Cabal-2.0.0.2-B4YxsRmpeLCDyDZ1N9nEz7:Distribution.PackageDescription.Utils- exit 1

cabal-install version 2.0.0.0
compiled using version 2.0.0.2 of the Cabal library

[phadej]

The current solution is to abstract custom-setup code into own package. i.e.

name: mypkg

custom-setup:
  setup-depends: mypkg-custom-setup

[phadej]

... alternatively you could use something like unix-compat, it might be good enough for you.

[joeyh]

Unfortunately, I'm working around a bug in unix-compat with Win32..

…

-- see shy jo

[23Skidoo]

@dcoutts, do you think this should be supported? IIRC, the decision to keep the format of custom-setup simple was deliberate.

[grayjay]

I think this is a duplicate of #4286.