[GHC] #11220: Stack overflow instead of type check failure in Servant route

14 Dec 2015

      #11220: Stack overflow instead of type check failure in Servant route
-------------------------------------+-------------------------------------
           Reporter:  sopvop         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
  (Type checker)                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 GHC 7.10.3 eats a lot of memory and segfaults compiling this.

 {{{#!hs
 {-# LANGUAGE DataKinds      #-}
 {-# LANGUAGE EmptyDataDecls #-}
 {-# LANGUAGE TypeOperators  #-}
 module Main where

 import           Data.Proxy

 import           Servant.API -- requires servant

 data A

 apiP :: Proxy Api
 apiP = Proxy

 -- Users

 type Api = "variants" :> Get '[JSON] ()

 routeL :: URI
 routeL = safeLink apiP
   (Proxy :: Proxy ("variants" :> Get '[A] ()))
                    -- Should result in type error
                    -- '[JSON] in route but '[A] here

 main = print routeL

 }}}

 There is '[ JSON ] in Api type, but '[A] in Proxy type passed to safeLink,
 so it should result in type error.

 Correct program compiles without problems.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11220
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