CPP definitions from `.cabal` file not picked up (again)

[christiaanb]

I have some doctest that looks like this:

#if __GLASGOW_HASKELL__ >= 908 && !defined(CLASH_MULTIPLE_HIDDEN)
>>> :t readNew (blockRam (0 :> 1 :> Nil))
readNew (blockRam (0 :> 1 :> Nil))
  :: ...
     ...
     ... =>
     Signal dom addr -> Signal dom (Maybe (addr, a)) -> Signal dom a

#else
>>> :t readNew (blockRam (0 :> 1 :> Nil))
readNew (blockRam (0 :> 1 :> Nil))
  :: ...
     ...
     ...
     ...
     ... =>
     Signal dom addr -> Signal dom (Maybe (addr, a)) -> Signal dom a

#endif

which fails with:

[ERROR  ] [ThreadId 668] /home/christiaan/devel/clash-compiler/clash-prelude/src/Clash/Prelude/BlockRam.hs:842: failure in expression `:t readNew (blockRam (0 :> 1 :> Nil))'
[ERROR  ] [ThreadId 668] expected: readNew (blockRam (0 :> 1 :> Nil))
[ERROR  ] [ThreadId 668]             :: ...
[ERROR  ] [ThreadId 668]                ...
[ERROR  ] [ThreadId 668]                ... =>
[ERROR  ] [ThreadId 668]                Signal dom addr -> Signal dom (Maybe (addr, a)) -> Signal dom a
[ERROR  ] [ThreadId 668]  but got: readNew (blockRam (0 :> 1 :> Nil))
[ERROR  ] [ThreadId 668]             :: (KnownDomain dom, Eq addr,
[ERROR  ] [ThreadId 668]                 Hidden (AppendSymbol dom "_clk") (Clock dom),
[ERROR  ] [ThreadId 668]                 Hidden (AppendSymbol dom "_rst") (Reset dom),
[ERROR  ] [ThreadId 668]                        ^
[ERROR  ] [ThreadId 668]                 Hidden (AppendSymbol dom "_en") (Enable dom), Enum addr, NFDataX a,
[ERROR  ] [ThreadId 668]                 NFDataX addr, Num a) =>
[ERROR  ] [ThreadId 668]                Signal dom addr -> Signal dom (Maybe (addr, a)) -> Signal dom a

because CLASH_MULTIPLE_HIDDEN is not defined when doctests are run.

I would've reoponed #71 but I don't have permissions

[christiaanb]

Also, looking at https://github.com/martijnbastiaan/doctest-parallel/pull/73/files, which is now reverted, I wonder whether cppOptions was used correctly...

Because Cabal uses cppOptions like this:

https://github.com/haskell/cabal/blob/51da23dda752448c96a2971b43aacc2fd2e0cc59/Cabal/src/Distribution/Simple/GHC/Internal.hs#L633

ghcOptCppOptions = cppOptions bi

https://github.com/haskell/cabal/blob/51da23dda752448c96a2971b43aacc2fd2e0cc59/Cabal/src/Distribution/Simple/Program/GHC.hs#L741

 ["-optP" ++ opt | opt <- ghcOptCppOptions opts]

[martijnbastiaan]

It's a bit sad I didn't document what cases broke --- I only mentioned that stuff broke in #74. I'm tempted to reintroduce the functionality, this time using -optP.

Having said that, CPP/flag support will remain a sore point for doctest-parallel because we're manually parsing the .cabal files and extracting the relevant flags from there. This doesn't account for custom setups, cabal.project, etc.