[GHC] #12820: Regression around pattern synonyms and higher-rank types

[GHC]

#12820: Regression around pattern synonyms and higher-rank types
-------------------------------------+-------------------------------------
        Reporter:  goldfire          |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 This regression was introduced somewhere between commit
 45bfd1a65978ee282d8d2cc1ddb7e3e5f4cd4717 (Refactor typechecking of pattern
 bindings) and 9417e57983dbcf7f500cca16163b11d1abb699e6 (Refactor
 occurrence-check logic).

 (I'm 90% sure it's 45bfd1a65978ee282d8d2cc1ddb7e3e5f4cd4717, but I can't
 say with certainty because that commit was in the middle of a slew of
 commits which didn't compile correctly until
 9417e57983dbcf7f500cca16163b11d1abb699e6.)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12820#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler