cabal-doctest

A Setup.hs helper for running doctests.

Example Usage

See [https://github.com/phadej/cabal-doctest/tree/master/example] for an example package. (Note that the example requires Cabal-1.24 or later, but you can relax this bound safely, although running doctests won’t be supported on versions of Cabal older than 1.24.)

To use this library in your Setup.hs, you should specify a custom-setup section in your .cabal file. For example:

custom-setup
 setup-depends:
   base >= 4 && <5,
   Cabal,
   cabal-doctest >= 1 && <1.1

/Note:/ Cabal dependency is needed because of Cabal/GH-4288 bug.

You’ll also need to specify build-type: Custom at the top of the .cabal file. Now put this into your Setup.hs file:

module Main where

import Distribution.Extra.Doctest (defaultMainWithDoctests)

main :: IO ()
main = defaultMainWithDoctests "doctests"

When you build your project, this Setup will generate a Build_doctests module. To use it in a testsuite, simply do this:

module Main where

import Build_doctests (flags, pkgs, module_sources)
import Data.Foldable (traverse_)
import Test.DocTest (doctest)

main :: IO ()
main = do
    traverse_ putStrLn args -- optionally print arguments
    doctest args
  where
    args = flags ++ pkgs ++ module_sources

Additional configuration

The cabal-doctest based Setup.hs supports few extensions fields in pkg.cabal files to customise the doctest runner behaviour, without customising the default doctest.hs.

test-suite doctests:
  if impl(ghc >= 8.0)
    x-doctest-options: -fdiagnostics-color=never
  x-doctest-source-dirs: test
  x-doctest-modules: Servant.Utils.LinksSpec

  ...

• x-doctest-options Additional arguments passed into doctest command.
• x-doctest-modules Additional modules to doctest. May be useful if you have doctest in test or executables (i.e not default library complonent).
• x-doctest-src-dirs Additional source directories to look for the modules.

Notes

• Recent versions of Cabal (for instance, 2.0) can choose to build a package’s doctest test suite before the library. However, in order for cabal-doctest to work correctly, the library must be built first, as doctest relies on the presence of generated files that are only created when the library is built. See #19.

  A hacky workaround for this problem is to depend on the library itself in a doctests test suite. See the example’s .cabal file for a demonstration. (This assumes that the test suite has the ability to read build artifacts from the library, a separate build component. In practice, this assumption holds, which is why this library works at all.)

• custom-setup section is supported starting from cabal-install-1.24. For older cabal-install's you have to install custom setup dependencies manually.

• stack respects custom-setup starting from version 1.3.3. Before that you have to use explicit-setup-deps setting in your stack.yaml. (stack/GH-2094)

• There is an issue in the Cabal issue tracker about adding cabal doctest command. After that command is implemented, this library will be deprecated.

• You can use x-doctest-options field in test-suite doctests to pass additional flags to the doctest.

• For build-type: Configure packages, you can use defaultMainAutoconfWithDoctests function to make custom Setup.hs script.

• If you use the default . in hs-source-dirs, then running doctests might fail with weird errors (ambigious module errors). Workaround is to move sources under src/ or some non-top-level directory.

• extensions: field isn’t supported. Upgrade your .cabal file to use at least cabal-version: >= 1.10 and use default-extensions or other-extensions.

• If you use QuickCheck properties (prop>) in your doctests, the test-suite doctest should depend on QuickCheck and template-haskell. This is a little HACK: These dependencies aren’t needed to build the doctests test-suite executable. However, as we let Cabal resolve dependencies, we can pass the resolved (and installed!) package identifiers to to the doctest command. This way, QuickCheck and template-haskell are available to doctest, otherwise you’ll get errors like:

    Variable not in scope:
      mkName
        :: [Char]
           -> template-haskell-2.11.1.0:Language.Haskell.TH.Syntax.Name

or

    Variable not in scope:
      polyQuickCheck
        :: Language.Haskell.TH.Syntax.Name -> Language.Haskell.TH.Lib.ExpQ

Copyright

Copyright 2017 Oleg Grenrus.

Available under the BSD 3-clause license.