[GHC] #11265: Internal error, using pattern synonym as instance head

[GHC]

#11265: Internal error, using pattern synonym as instance head
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  simonpj
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  patsyn/should_fail/T11265
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * testcase:   => patsyn/should_fail/T11265
 * status:  new => closed
 * resolution:   => fixed


Comment:

 Thanks for reporting this, with a nice small repro case.

 Fixed by
 {{{
 commit c069be815aa0bce2eb2c9621a36f114badda2318
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Mon Dec 21 14:18:32 2015 +0000

     Add a pattern-syn form of PromotionErr

     The main change is to add PatSynPE to PromotionErr, so that
     when we get an ill-staged use of a pattern synonym we get a
     civilised error message.

     We were already doing this in half-baked form in tcValBinds, but
     this patch tidies up the impl (which previously used a hack rather
     than APromotionErr), and does it in tcTyClsInstDecls too.


 >---------------------------------------------------------------

 c069be815aa0bce2eb2c9621a36f114badda2318
  compiler/hsSyn/HsBinds.hs                         |  15 ----
  compiler/typecheck/TcBinds.hs                     |  53 +++--------
  compiler/typecheck/TcEnv.hs                       | 103
 +++++++++++++++++++++-
  compiler/typecheck/TcHsType.hs                    |   1 +
  compiler/typecheck/TcRnDriver.hs                  |  80 ++++++-----------
  compiler/typecheck/TcRnTypes.hs                   |   5 ++
  testsuite/tests/patsyn/should_fail/T11265.hs      |   6 ++
  testsuite/tests/patsyn/should_fail/T11265.stderr  |   6 ++
  testsuite/tests/patsyn/should_fail/T9161-1.stderr |   7 +-
  testsuite/tests/patsyn/should_fail/T9161-2.stderr |   3 +-
  testsuite/tests/patsyn/should_fail/all.T          |   1 +
  11 files changed, 163 insertions(+), 117 deletions(-)
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11265#comment:4>
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