[GHC] #10547: feature request: expanding type synonyms in error messages

[GHC]

#10547: feature request: expanding type synonyms in error messages
-------------------------------------+-------------------------------------
        Reporter:  osa1              |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  typecheck/should_fail/ExpandSynsFail1,2,3,4
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1016,
       Wiki Page:                    |  Phab:D2198
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Comment (by osa1):

 Yes, I wanted to handle that case (see also test `ExpandSynsFail3.hs`). My
 original implementation was method (1) in that web page. I just
 implemented method (3) and updated the patch. The problematic example was
 taking no time at all even with method (1), I guess it's now even faster.
 Since we have a linear behavior now maybe we can enable it by default.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10547#comment:19>
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