[GHC] #12386: Infinite loop when showing type family error

[GHC]

#12386: Infinite loop when showing type family error
-------------------------------------+-------------------------------------
        Reporter:  elliottt          |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.2
       Component:  Compiler (Type    |              Version:  8.0.1
  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):

 * priority:  normal => high
 * failure:  None/Unknown => Compile-time crash
 * component:  Compiler => Compiler (Type checker)
 * milestone:   => 8.0.2


@@ -4,1 +4,1 @@
- {{{
+ {{{#!hs

New description:

 When attempting to load this code in ghci with ghc-8.0.1, I get an
 infinite loop while it attempts to display the error:

 {{{#!hs
 {-# LANGUAGE TypeFamilies #-}

 class C a where
   type family F a t :: *

   type family T a :: *
   type T a = F a
 }}}

 {{{
 catbug :: ~/Scratch/ast-experiment » ghci test.hs
 GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /Users/trevor/.ghci
 [1 of 1] Compiling Main             ( test.hs, interpreted )

 test.hs:7:14: error:
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12386#comment:3>
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