cabal-doctest
=============
[](https://hackage.haskell.org/package/cabal-doctest) [](https://github.com/ulidtko/cabal-doctest/actions/workflows/haskell-ci.yml)
A `Setup.hs` helper for running [doctests][].
[doctests]: https://github.com/sol/doctest#readme
Simple example
--------------
[simple example]: https://github.com/ulidtko/cabal-doctest/tree/master/simple-example
[simple-example.cabal]: https://github.com/ulidtko/cabal-doctest/tree/master/simple-example/simple-example.cabal
Follow [simple example][] for the common case of a single-library `.cabal` package with doctests.
To recap the example's code:
1. specify `build-type: Custom` in your `.cabal` file;
2. declare dependencies of `Setup.hs`:
```
custom-setup
setup-depends:
base >= 4 && <5,
cabal-doctest >= 1 && <1.1
```
See [Notes](#notes) below for a caveat with cabal-install < 2.4.
3. Populate `Setup.hs` like so:
```haskell
module Main where
import Distribution.Extra.Doctest (defaultMainWithDoctests)
main :: IO ()
main = defaultMainWithDoctests "doctests"
```
Assuming your test-suite is called `doctests`, this `Setup` will generate a `Build_doctests`
module during package build. If your test-suite goes by name `foo`,
`defaultMainWithDoctests "foo"` creates a `Build_foo` module.
4. Use the generated module in a testsuite, simply like so:
```haskell
module Main where
import Build_doctests (flags, pkgs, module_sources)
import Data.Foldable (traverse_)
import System.Environment (unsetEnv)
import Test.DocTest (doctest)
main :: IO ()
main = do
traverse_ putStrLn args -- optionally print arguments
unsetEnv "GHC_ENVIRONMENT" -- see 'Notes'; you may not need this
doctest args
where
args = flags ++ pkgs ++ module_sources
```
Ultimately, `cabal test` or `stack test` should run the doctests of your package.
Example with multiple cabal components
--------------------------------------
`cabal-doctest` also supports more exotic use cases where a `.cabal` file
contains more components with doctests than just the main library, including:
* doctests in executables,
* doctests in internal libraries (if using `Cabal-2.0` or later).
Unlike the simple example shown above, these examples involve _named_
components. You don't need to change the `Setup.hs` script to support
this use case. However, in this scenario `Build_doctests` will generate extra
copies of the `flags`, `pkgs`, and `module_sources` values for each additional
named component.
The simplest approach is to use `x-doctest-components` field in `.cabal`:
```
x-doctest-components: lib lib:internal exe:example
```
In that case, the test driver is generally:
```haskell
module Main where
import Build_doctests (Component (..), components)
import Data.Foldable (for_)
import System.Environment (unsetEnv)
import Test.DocTest (doctest)
main :: IO ()
main = for_ components $ \(Component name flags pkgs sources) -> do
print name
putStrLn "----------------------------------------"
let args = flags ++ pkgs ++ sources
for_ args putStrLn
unsetEnv "GHC_ENVIRONMENT"
doctest args
```
There is also a more explicit approach: if you have an executable named `foo`, then
`Build_doctest` will contain `flags_exe_foo`, `pkgs_exe_foo`, and `module_sources_exe_foo`.
If the name has hyphens in it (e.g., `my-exe`), `cabal-doctest` will convert them to
underscores (e.g., you'd get `flags_my_exe`, `pkgs_my_exe`, `module_sources_my_exe`).
Internal library `bar` values will have a `_lib_bar` suffix.
An example testsuite driver for this use case might look like this:
```haskell
module Main where
import Build_doctests
(flags, pkgs, module_sources,
flags_exe_my_exe, pkgs_exe_my_exe, module_sources_exe_my_exe)
import Data.Foldable (traverse_)
import System.Environment (unsetEnv)
import Test.DocTest
main :: IO ()
main = do
unsetEnv "GHC_ENVRIONMENT"
-- doctests for library
traverse_ putStrLn libArgs
doctest libArgs
-- doctests for executable
traverse_ putStrLn exeArgs
doctest exeArgs
where
libArgs = flags ++ pkgs ++ module_sources
exeArgs = flags_exe_my_exe ++ pkgs_exe_my_exe ++ module_sources_exe_my_exe
```
See the [multiple-components-example][].
[multiple-components-example]: https://github.com/ulidtko/cabal-doctest/tree/master/multiple-components-example
Additional configuration
------------------------
The `cabal-doctest` based `Setup.hs` supports a 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 component).
* `x-doctest-src-dirs` Additional source directories to look for the modules.
Notes
-----
* If support for cabal-install < 2.4 is required, you'll have to
add `Cabal` to `setup-depends`; see issue [haskell/cabal#4288][].
* Some 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 [simple-example.cabal][]
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#2094][].
* With base < 4.7 (GHC < 7.8, pre-2014), `System.Environment.unsetEnv` function
will need to be imported from `base-compat` library. It is already in transitive
dependencies of `doctest`. Simply declare the dependency upon `base-compat`, and
then `import System.Environment.Compat (unsetEnv)` if you need that old GHC.
* 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 (ambiguous module errors). Workaround is
to move sources under `src/` or some non-top-level directory.
* The `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
```
* From version 2, Stack sets the `GHC_ENVIRONMENT` variable, and GHC
(as invoked by `doctest`) will pick that up. This is undesirable:
`cabal-doctest` passes all the necessary information on the command
line already, and can lead to ambiguous module errors as GHC will
load the environment in addition to what `cabal-doctest` instructs
it to.
Hence, `cabal-doctest` tells GHC to ignore package environments
altogether on the command line. However, this is only possible since
GHC 8.2. If you are using `cabal-doctest` with Stack 2 and GHC 8.0
or earlier and seeing ambiguous module errors or other mysterious
failures, try manually unsetting `GHC_ENVIRONMENT` before invoking
`doctest`.
* If you are on Nix. `doctest` will not pick up your version of GHC if you
don't point it towards it, and therefore will result in "cannot satisfy -package-id" errors.
You will need to set `NIX_GHC` and `NIX_GHC_LIBDIR` within your environment in order
for doctest to pick up your GHC. Put the following in `shell.nix` and run `nix-shell`.
```nix
# shell.nix
{ pkgs ? import <nixpkgs> {} }:
let
myHaskell = (pkgs.haskellPackages.ghcWithHoogle (p: with p; [
# Put your dependencies here
containers
hslogger
]));
in
pkgs.mkShell {
name = "myPackage";
# These environment variables are important. Without these,
# doctest doesn't pick up nix's version of ghc, and will fail
# claiming it can't find your dependencies
shellHook = ''
export NIX_GHC=${myHaskell}/bin/ghc
export NIX_GHC_LIBDIR=${myHaskell}/lib/ghc-8.10.7
'';
buildInputs = with pkgs; [
myHaskell
];
}
```
[#19]: https://github.com/ulidtko/cabal-doctest/issues/19
[haskell/cabal#4288]: https://github.com/haskell/cabal/issues/4288
[stack#2094]: https://github.com/commercialhaskell/stack/issues/2094
Copyright
---------
Copyright 2017 Oleg Grenrus.
With contributions from:
* Ryan Scott
* Andreas Abel
* Max Ulidtko
Available under the BSD 3-clause license.