cc-options do not get passed to GHC

[bitonic]

cc-options currently do not get seem to get passed to GHC. It would be useful if they were, since GHC is capable of compiling C/C++ files and now it might more than before given the addition of addForeignFile in GHC 8.2, which lets users compile and link C/C++ files from TH.

[bitonic]

Note that in practice one needs to put the cc options both in cc-options and in ghc-options via -optc, since inline-c is often used with hsc2hs which does get the flags from cc-options.

[bitonic]

Note that the same happens for linking: extra-libraries are not passed to GHC, which makes loadDLL fail when it dlopens shared libraries referring to any of the specified extra-libraries.

[bitonic]

Note that cabal even emits warnings like

Warning: Instead of 'ghc-options: -lceres ...' use 'extra-libraries:
ceres ...'

even if they do not have the same effect.

[ezyang]

Related issue #3700

Not passing extra-libraries to GHC as -l is probably a separate bug. If this doesn't cause any regressions, we probably should do this, at the very least when other-extensions: TemplateHaskell is specified, and maybe unconditionally.

[ezyang]

@bitonic If you're interested in solving this ticket I'd be happy to advise.

[basvandijk]

I just run into this today when building haskell-opencv with cabal-install. I got the following error:

<no location info>: error:
    ghc: panic! (the 'impossible' happened)
  (GHC version 8.4.4 for x86_64-unknown-linux):
	Loading temp shared object failed: 
          /run/user/1001/ghc14715_0/libghc_95.so: 
            undefined symbol: _Znwm

Note that _Znwm demangles to: operator new(unsigned long).

After adding ghc-options: -lstdc++ to opencv.cabal the build succeeded.

Note that I did get the warning:
Warning: Instead of 'ghc-options: -lstdc++' use 'extra-libraries: stdc++'

[phadej]

For the record, haskell-opencv does specify:

    extra-libraries:   stdc++

---

I agree with Edward, "Unconditional passing of extra-libraries as -l flags to GHC" patch is probably easy to write (and if CI is green, to merge).

[domenkozar]

It's the same issue with cxx-options: -std=c++14, it still needs ghc-options: -optc-std=c++14 when using inline-c-pp as previously mentioned.

It's going to be a bit easier in GHC 8.8: https://gitlab.haskell.org/ghc/ghc/issues/16477

[phadej]

Is this similar problem as with ld-options as with @nh2 recently fixed?

[ulysses4ever]

This issue was marked high-priority a while ago. Since then, there were a number of updates around passing options between cabal and GHC. To determine whether these updates had any impact in the issue, a minimal reproducer would be helpful.

Do we have a minimal reproducer?

[phadej]

#9801