Kinder type checking

[mgsloan]

The resulting errors are ludicrously better with ( :: *) signatures:

Breaking the greet example by doing

  :<|> "greet" :> Capture "greetid" Text :> Delete '[JSON]

instead of

  :<|> "greet" :> Capture "greetid" Text :> Delete '[JSON] NoContent

Before yielded

    /home/mgsloan/oss/haskell/servant/servant-docs/example/greet.hs:94:5: error:
        • Could not deduce: Servant.API.TypeLevel.Or
                              (Servant.API.TypeLevel.IsIn
                                 ("greet" :> (Capture "greetid" Text :> Delete '[JSON] NoContent))
                                 ("hello"
                                  :> (Capture "name" Text
                                      :> (QueryParam "capital" Bool :> Get '[JSON, PlainText] Greet))))
                              (Servant.API.TypeLevel.Or
                                 (Servant.API.TypeLevel.IsIn
                                    (Capture "greetid" Text :> Delete '[JSON] NoContent)
                                    (ReqBody '[JSON] Greet
                                     :> Post '[JSON] (Headers '[Header "X-Example" Int] Greet)))
                                 (Servant.API.TypeLevel.IsIn
                                    (Capture "greetid" Text :> Delete '[JSON] NoContent)
                                    (Capture "greetid" Text :> Maybe)))
            arising from a use of ‘extraInfo’
        • In the expression:
            extraInfo
              (Proxy ::
                 Proxy ("greet"
                        :> (Capture "greetid" Text :> Delete '[JSON] NoContent)))
          In the expression:
            extraInfo
              (Proxy ::
                 Proxy ("greet"
                        :> (Capture "greetid" Text :> Delete '[JSON] NoContent)))
              $ defAction & headers <>~ ["unicorns"]
                  & notes
                      <>~
                        [DocNote "Title" ["This is some text"],
                         DocNote "Second secton" ["And some more"]]
          In an equation for ‘extra’:
              extra
                = extraInfo
                    (Proxy ::
                       Proxy ("greet"
                              :> (Capture "greetid" Text :> Delete '[JSON] NoContent)))
                    $ defAction & headers <>~ ["unicorns"]
                        & notes
                            <>~
                              [DocNote "Title" ["This is some text"],
                               DocNote "Second secton" ["And some more"]]
       |
    94 |     extraInfo (Proxy :: Proxy ("greet" :> Capture "greetid" Text :> Delete '[JSON] NoContent)) $
       |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    
    /home/mgsloan/oss/haskell/servant/servant-docs/example/greet.hs:108:13: error:
        • No instance for (HasDocs Maybe) arising from a use of ‘docsWith’
        • In the expression:
            docsWith defaultDocOptions [intro1, intro2] extra testApi
          In an equation for ‘docsGreet’:
              docsGreet
                = docsWith defaultDocOptions [intro1, intro2] extra testApi
        |
    108 | docsGreet = docsWith defaultDocOptions [intro1, intro2] extra testApi
        |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

And now yields

    /home/mgsloan/oss/haskell/servant/servant-docs/example/greet.hs:84:45: error:
        • Expecting one more argument to ‘Delete '[JSON]’
          Expected a type, but ‘Delete '[JSON]’ has kind ‘* -> *’
        • In the second argument of ‘:>’, namely ‘Delete '[JSON]’
          In the second argument of ‘:>’, namely
            ‘Capture "greetid" Text :> Delete '[JSON]’
          In the second argument of ‘:<|>’, namely
            ‘"greet" :> (Capture "greetid" Text :> Delete '[JSON])’
       |
    84 |   :<|> "greet" :> Capture "greetid" Text :> Delete '[JSON]
       |                                             ^^^^^^^^^^^^^^

[alpmestan]

Wow, the error really is a lot nicer! Great. If the CI is green, I'm definitely in favor of merging this. @phadej no objection?

[alpmestan]

@mgsloan hah. turns out there is a test that uses ReqBody with something of kind Bool, see CI error. any reasonable fix will do.

[mgsloan]

@alpmestan Funny! The type in the test was wrong, but it doesn't matter for what the test is testing.

[mgsloan]

I don't think the CI failures have anything to do with this PR anymore.

[phadej]

@mgsloan can you rebase on top of master, that should make travis green

[mgsloan]

Rebased! Let's hope CI is satisfied.

[alpmestan]

Aaaaand CI is happy. Thanks @mgsloan!

[mgsloan]

Welcome, thanks for reviewing!