[GHC] #13494: ASSERT failed in compiler/typecheck/TcErrors.hs

[GHC]

#13494: ASSERT failed in compiler/typecheck/TcErrors.hs
-------------------------------------+-------------------------------------
           Reporter:  nomeata        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 One of the commits in the range
 https://github.com/ghc/ghc/compare/a6675a93efe7...de4723fd6d97
 which were commited by SPJ, broke running the test suite with a `-DDEBUG`
 compiler:

 {{{
 +++ /tmp/ghctest-sw9832/test   spaces/./indexed-
 types/should_fail/T2627b.run/T2627b.comp.stderr.normalised      2017-03-27
 16:28:10.448037112 +0000
 @@ -1,13 +1,17 @@
 +ghc: panic! (the 'impossible' happened)
 +  (GHC version 8.3.20170327 for x86_64-unknown-linux):
 +       ASSERT failed!
 +  b0_a1gy[tau:4]
 +  Call stack:
 +      CallStack (from HasCallStack):
 +        prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable
 +        callStackDoc, called at
 compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable
 +        assertPprPanic, called at
 compiler/typecheck/TcErrors.hs:<line>:<column> in <package-id>:TcErrors
 +  Call stack:
 +      CallStack (from HasCallStack):
 +        prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable
 +        callStackDoc, called at
 compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable
 +        pprPanic, called at compiler/utils/Outputable.hs:<line>:<column>
 in <package-id>:Outputable
 +        assertPprPanic, called at
 compiler/typecheck/TcErrors.hs:<line>:<column> in <package-id>:TcErrors

 -T2627b.hs:20:24:
 -     Couldn't match type ‘b0’ with ‘Dual (Dual b0)’
 -        arising from a use of ‘conn’
 -        ‘b0’ is untouchable
 -          inside the constraints: b ~ W e f
 -          bound by a pattern with constructor:
 -                     Wr :: forall e f. e -> Comm f -> Comm (W e f),
 -                   in an equation for ‘conn’
 -          at T2627b.hs:20:14-19
 -     In the expression: conn undefined undefined
 -      In an equation for ‘conn’:
 -          conn (Rd k) (Wr a r) = conn undefined undefined
 +Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 See https://s3.amazonaws.com/archive.travis-ci.org/jobs/215578687/log.txt
 for a full log.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13494>
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