Internal error, using pattern synonym as instance head

{-# LANGUAGE PatternSynonyms, DataKinds #-}

pattern A = True

class    F a
instance F A

when loaded in ghci it results in an internal error

% g internal.hs
GHCi, version 7.11.20151216: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( internal.hs, interpreted )

internal.hs:5:12: error:
    • GHC internal error: ‘A’ is not in scope during type checking, but it passed the renamer
      tcl_env of environment: []
    • In the first argument of ‘F’, namely ‘A’
      In the instance declaration for ‘F A’
Failed, modules loaded: none.
Prelude> 

changed weight to 5

added Tbug Trac import labels

changed the description

assigned to @rae

This smells like my fault, but it also looks quite easy to fix.

assigned to @simonpj and unassigned @rae

Actually it's not your fault. I'm on it.

closed

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

Fixed by

commit c069be815aa0bce2eb2c9621a36f114badda2318
Author: Simon Peyton Jones <simonpj@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(-)

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	- → patsyn/should_fail/T11265

changed milestone to %8.0.1

added Pnormal label