[GHC] #15379: Don't reject user-written instances of KnownNat and friends in hsig files

[GHC]

#15379: Don't reject user-written instances of KnownNat and friends in hsig files
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        Reporter:  ezyang            |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:  backpack
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4988
       Wiki Page:                    |
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Comment (by ppk):

 Replying to [comment:14 ppk]:
 > Some of the test cases in `backpack/should_fail/` are failing. Of which
 I think the bkpfail46.bkp is actually //not giving// a compilation failure
 (and hence the test is failing).
 > Can you have a look at this test case ? Was this a previous limitation
 of backpack that was
 > now fixed or is it the case that some thing that should not have been
 acceptable is now being
 > accepted (thereby seriously questioning the type safety).

 The test cases were failing not due to changes here but due to problems in
 the dependent patch for #15138  (see comment:5:ticket:15138 and
 comm:6:ticket:15138). This comment is therefore irrelevant
 for deciding on this patch.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15379#comment:17>
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