[GHC] #14218: GHC.Stack.HasCallStack not compatible with constraint synonyms

[GHC]

#14218: GHC.Stack.HasCallStack not compatible with constraint synonyms
-------------------------------------+-------------------------------------
        Reporter:  ntc2              |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by gridaphobe):

 Oh dear..

 Ben's explanation sounds plausible to me, though I didn't realize
 constraint synonyms worked this way. I would have expected them to be
 transparent to GHC like regular type synonyms, i.e. the `C` constraint
 would be expanded and we'd get two separate dictionaries rather than a
 compound dictionary.

 If this is actually how constraint synonyms work, a simple fix could be to
 expand them and treat the member constraints individually. But maybe
 there's a good reason for the current behavior?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14218#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler