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Opened by Domen Kožar@domenkozarReporter

A more aggressive version of -fprint-expanded-synonyms that prints all type synonyms

Using GHC 8.2.2 and stack build --ghc-options=-fprint-expanded-synonyms I have the following type synonym for servant:

type Get302 (cts :: [*]) (hs :: [*]) = Verb 'GET 302 cts
  (Headers (Header "Location" String ': hs) NoContent)

and get the following error message when String is mismatched for Text:

        • Couldn't match type ‘Text’ with ‘[Char]’
          Expected type: AsServerT App
                         :- ("login"
                             :> ("callback"
                                 :> (QueryParam "code" Text
                                     :> (QueryParam "state" Text
                                         :> MyApp.Types.Servant.Get302
                                              '[PlainText]
                                              '[Header "Set-Cookie" SetCookie,
                                                Header "Set-Cookie" SetCookie]))))
            Actual type: Maybe Code
                         -> Maybe Text
                         -> App
                              (Headers
                                 '[Header "Location" Text, Header "Set-Cookie" SetCookie,
                                   Header "Set-Cookie" SetCookie]
                                 NoContent)

The error is confusing as type synonym is not expanded and offending Header is missing from the output in the expected type.

Edited by Ryan Scott