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

[GHC]

#11220: Stack overflow instead of type check failure in Servant route
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        Reporter:  sopvop            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.3
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * cc: goldfire (added)


Old description:

> 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.

New description:

 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#comment:3>
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