Re: [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
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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:                    |
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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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