Support for mixins

[dcastro]

I'm trying to get doctest+cabal-doctest to work on a project, but I can't get it to play ball with mixins.

Namely, I'm using a custom prelude and using mixins: base hiding (Prelude) to hide the default one. But it seems doctest doesn't seem to recognize this mixin and says there are two preludes in scope.

I've created a test project here, so we can reproduce this issue: https://github.com/dcastro/doctest-mixins
stack build works fine, but stack test fails.

$ stack build doctest-mixins:lib doctest-mixins:test:doctests --no-run-tests
doctest-mixins> configure (lib + test)
Configuring doctest-mixins-0.1.0.0...
doctest-mixins> build (lib + test)
Preprocessing library for doctest-mixins-0.1.0.0..
Building library for doctest-mixins-0.1.0.0..
Preprocessing test suite 'doctests' for doctest-mixins-0.1.0.0..
Building test suite 'doctests' for doctest-mixins-0.1.0.0..
[1 of 2] Compiling Build_doctests
Linking .stack-work/dist/x86_64-linux-tinfo6/Cabal-3.0.1.0/build/doctests/doctests ...
            
Warning: The following modules should be added to exposed-modules or other-modules in /home/dc/dev/other/doctest-mixins/doctest-mixins.cabal:
             - In test:doctests:
                 Build_doctests
             - In test:doctests:
                 Build_doctests
         
         Missing modules in the cabal file are likely to cause undefined reference errors from the linker, along with other problems.
doctest-mixins> copy/register
Installing library in /home/dc/dev/other/doctest-mixins/.stack-work/install/x86_64-linux-tinfo6/f379cbdb645e2f7b975c4e9af6625e7b004143a74d5f8f815a31249737060a3e/8.8.3/lib/x86_64-linux-ghc-8.8.3/doctest-mixins-0.1.0.0-J9NorAghXcQDDEeMJ3tfFn
Registering library for doctest-mixins-0.1.0.0..
doctest-mixins> Test running disabled by --no-run-tests flag.
Completed 2 action(s).

$ stack test doctest-mixins:test:doctests

doctest-mixins> test (suite: doctests)
            
Progress 1/2: doctest-mixins-i
-i/home/dc/dev/other/doctest-mixins/.stack-work/dist/x86_64-linux-tinfo6/Cabal-3.0.1.0/build/autogen
-i/home/dc/dev/other/doctest-mixins/.stack-work/dist/x86_64-linux-tinfo6/Cabal-3.0.1.0/build
-i/home/dc/dev/other/doctest-mixins/src
-package-env=-
-hide-all-packages
-no-user-package-db
-package-db=/home/dc/.stack/snapshots/x86_64-linux-tinfo6/f379cbdb645e2f7b975c4e9af6625e7b004143a74d5f8f815a31249737060a3e/8.8.3/pkgdb
-package-db=/home/dc/dev/other/doctest-mixins/.stack-work/install/x86_64-linux-tinfo6/f379cbdb645e2f7b975c4e9af6625e7b004143a74d5f8f815a31249737060a3e/8.8.3/pkgdb
-package-db=.stack-work/dist/x86_64-linux-tinfo6/Cabal-3.0.1.0/package.conf.inplace
-optP-include
-optP.stack-work/dist/x86_64-linux-tinfo6/Cabal-3.0.1.0/build/autogen/cabal_macros.h
-package-id=base-4.13.0.0
-package-id=morley-prelude-0.3.0-emFluUQAgu2cOHiMlTd8V
-package-id=doctest-0.16.3-AoCHnIRCAFH3tdcWc14oMy
-package=doctest-mixins-0.1.0.0
Main
Paths_doctest_mixins

/home/dc/dev/other/doctest-mixins/src/Main.hs:1:8: error:
    Ambiguous module name ‘Prelude’:
      it was found in multiple packages:
      base-4.13.0.0 morley-prelude-0.3.0
  |
1 | module Main where
  |        ^^^^
                            
doctest-mixins> Test suite doctests failed
Completed 2 action(s).      
Test suite failure for package doctest-mixins-0.1.0.0
    doctests:  exited with: ExitFailure 1
Logs printed to console

I've first reported this issue in sol/doctest#289. It was suggested that maybe cabal-doctest would be the ideal place to solve this issue.

If it helps, I've also uploaded the output of cabal build lib:doctest-mixins -v3 in a gist.

[phadej]

build-type: Custom and mixins (or backpack in general) just don't work together.

[dcastro]

@phadej Ah, that's sad to hear :/ Is that an intrinsic limitation, or is there a chance (even if slim) mixins and Custom may work in the future?

[phadej]

In theory they could. In practice it requires a lot of engineering (which I think is wasted work).

I have made cabal-docspec which allows to run doctests on anything you can build with cabal-install: https://github.com/phadej/cabal-extras/tree/master/cabal-docspec; If you have a choice use it. I'm tempted to deprecate cabal-doctest in the near future, as I have no use for it myself and there is a replacement (though not strictly better, there are different - IMHO better - trade-offs).

[dcastro]

Interesting! How would I go about using it? For example, in this test repo, how would I enable cabal-docspec?

[phadej]

Please read the manual first.

[dcastro]

Oh, I completely missed the manual.md, I was looking for a readme.md 😅 Thanks, I'll have a look!