New-style build fails during "sdist"

[peti]

I have a strange build failure at https://travis-ci.org/peti/hsyslog/jobs/234171806:

$ cabal sdist
ghc: can't find a package database at /home/travis/build/peti/hsyslog/dist-newstyle/packagedb/ghc-8.0.2

That .travis.yml file was generated with the current version (3e1b384) of make_travis_yml_2.hs and that error makes no sense to me. When I run cabal dist locally, it works just fine. Any idea what I could do to fix this issue?

[phadej]

@peti you should remove .ghc.environment.* file (e.g .in rm -rf dist line). I run into this today as well.

Could you submit a PR?

[peti]

Thank you for the suggestion! The changed removed the error. Unfortunately, now a new error just popped up (https://travis-ci.org/peti/hsyslog/jobs/235778854) which I believe to be unrelated to the travis-ci build instructions, though.

[phadej]

@peti, are you sure you use: https://github.com/phadej/cabal-doctest/blob/master/example/Setup.hs like Setup.hs, we tweaked it recently to workaround sdist issues.

[peti]

Man, this has been a long journey. :-/ Now the tests succeed with GHC 8.x, but none of the other compilers can build the project, apparently because the latest cabal-install does not provide a copy of the latest Cabal? The error during sdist looks a bit strange: https://travis-ci.org/peti/hsyslog/jobs/235822039.

[phadej]

@peti you don't need to put cabal-version: >= 1.24, the cabal-version: >= 1.10 should be enough.

The situation is a bit tricky:

• custom-setup section is supported with Cabal >= 1.24
• but you only need a cabal-install compiled against recent enough Cabal
• Cabal bundled with GHC can however be anything what setup-depends says.
• i.e. different Cabals are used in different stages.

[peti]

OK, I see. I took the >= 1.24 requirement from the doctest-cabal example at https://github.com/phadej/cabal-doctest/blob/master/example/example.cabal#L13 and assumed that would be important. Now, after removing it, the situation has improve significantly. There remains only one error with GHC 7.10.x that I cannot explain:

https://travis-ci.org/peti/hsyslog/jobs/235963325

Any idea how bytestring might end up missing? I would think that's a core package of GHC 7.10.x.

[hvr]

@peti I'm not sure yet (still looking), this seems to occur only with Cabal-1.22, but setting setup-depends: Cabal >= 1.24 makes it work.

EDIT: Now I see it; this is the infamous buildable: False bug of older Cabal versions! (see also haskell/cabal#1725 (comment) ; TLDR: you need to move the build-depends into the if-clause if you want to be compatible with Cabal < 1.24)

[peti]

Okay, thank you very much for looking at the issue. I've moved the build-depends into the conditional, as suggested. This fixes the error we've seen before, but now the build fails with

setup: The program 'hsc2hs' is required but it could not be found

instead. When I add the Cabal >= 1.24 constraint, then all builds succeed fine, but without it GHC 7.10.x appears to be in trouble.

[hvr]

Your package most likely lacks a build-tools: hsc2hs >= x.y && < z line; future cabal versions will warn about it; the reason is that cabal needs to know that it needs hsc2hs (and possibly which versions of it) at the solver-stage, so we need to inform cabal early on via the .cabal file. (this is also in line with cabal's "No untracked dependencies" design mantra)

[peti]

Phew, https://travis-ci.org/peti/hsyslog/builds/237107742 now succeeds on all platforms. Thank you very much for taking the time to walk me through this process, gentlemen.