[GHC] #12489: undefined in view pattern inside pattern synonym causes GHC to panic

[GHC]

#12489: undefined in view pattern inside pattern synonym causes GHC to panic
-------------------------------------+-------------------------------------
        Reporter:  pkmx              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
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:                    |
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"f352e5cd7bb629fe0ca3b913bfbe7bee43d62f3a/ghc" f352e5c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f352e5cd7bb629fe0ca3b913bfbe7bee43d62f3a"
 Keep the bindings local during defaultCallStacks

 defaultCallStacks generates evidence bindings for call stacks,
 but wasn't setting the binding site correctly.  As a result
 they were simply discarded in the case of pattern synonyms,
 giving rise to Trac #12489.

 The fix is easy; and I added an ASSERT to catch the error earlier.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12489#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler