[GHC] #13446: Deferred type error sneaks in with -fno-defer-type-errors enabled

[GHC]

#13446: Deferred type error sneaks in with -fno-defer-type-errors enabled
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.0.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC accepts       |            Test Case:
  invalid program                    |  typecheck/should_fail/T13446
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * status:  new => merge
 * testcase:   => typecheck/should_fail/T13446
 * milestone:   => 8.2.1


Comment:

 Done by
 {{{
 commit e0ad55f894a8d85dcc099c33c63cfe3d4515d464
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Mon Mar 27 10:32:08 2017 +0100

     Fix error-message suppress on given equalities

     I'd got the logic slightly wrong when reporting type errors
     for insoluble 'given' equalities.  We suppress insoluble givens
     under some circumstances (see Note [Given errors]), but we then
     suppressed subsequent 'wanted' errors because the (suppressed)
     'given' error "won".  Result: no errors at all :-(.

     This patch fixes it and
      - Renames TcType.isTyVarUnderDatatype to the more
        perspicuous TcType.isInsolubleOccursCheck

     In doing this I realise that I don't understand why we need
     to keep the insolubles partitioned out separately at all...
     but that is for another day.
 }}}
 Worth merging.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13446#comment:5>
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