cabal-doctest
=============
[](https://hackage.haskell.org/package/cabal-doctest) [](https://travis-ci.org/phadej/cabal-doctest)
A `Setup.hs` helper for running `doctests`.
Simple example
--------------
For most use cases—a `.cabal` file with a single library containing
doctests—adapting the simple example located
[here](https://github.com/phadej/cabal-doctest/tree/master/simple-example)
will be sufficient. (Note that this 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](https://github.com/haskell/cabal/issues/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:
```haskell
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:
```haskell
module Main where
import Build_doctests (flags, pkgs, module_sources)
import Data.Foldable (traverse_)
import System.Environment.Compat (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
```
(The `System.Environment.Compat` module is from the `base-compat`
package. That's already in the transitive closure of `doctest`'s
dependencies. `System.Environment.unsetEnv` was added with GHC 7.8 so,
if you don't need to support versions of GHC older than 7.8, you can
use `System.Environment` from `base` instead.)
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.
Simplest approach is to use `x-doctest-components` field, for example
```
x-doctest-components: lib lib:internal exe:example
```
In that case, the testdrive is general:
```haskell
module Main where
import Build_doctests (Component (..), components)
import Data.Foldable (for_)
import System.Environment.Compat (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's also a more explicit approach: if you have an executable named `foo`,
then separate values named `flags_exe_foo`, `pkgs_exe_foo`, and `module_sources_exe_foo` will
be generated in `Build_doctests`. If the name has hyphens in it
(e.g., `my-exe`), then `cabal-doctest` will convert those hyphens to
underscores (e.g., you'd get `flags_my_exe`, `pkgs_my_exe`, and
`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.Compat (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
[this example](https://github.com/phadej/cabal-doctest/tree/master/multiple-components-example)
for more details.
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](https://github.com/phadej/cabal-doctest/issues/19).
A hacky workaround for this problem is to depend on the library itself in a
`doctests` test suite. See
[the simple example's .cabal file](https://github.com/phadej/cabal-doctest/blob/master/simple-example/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/GH-2094](https://github.com/commercialhaskell/stack/issues/2094))
* There is [an issue in the Cabal issue tracker](https://github.com/haskell/cabal/issues/2327)
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 (ambiguous 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
```
* From version 2, Stack sets the `GHC_ENVRIONMENT` 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`.
Copyright
---------
Copyright 2017 Oleg Grenrus.
Available under the BSD 3-clause license.