[GHC] #15954: LiberalTypeSynonyms unsaturation check doesn't kick in

[GHC]

#15954: LiberalTypeSynonyms unsaturation check doesn't kick in
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.3
       Component:  Compiler (Type    |              Version:  8.6.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D5402
       Wiki Page:                    |
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Comment (by simonpj):

 PS.  Here's an idea.  In `check_syn_tc_app`, you could wrap the recursive
 call to `check_type` in `addErrCtxt "In the expansion of type synonym
 <blah>`.  That would give us the best of both worlds, including for the
 trickier case I described in comment:5

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15954#comment:7>
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