[GHC] #12688: derived Show instances aren't protected from RebindableSyntax+OverloadedStrings

[GHC]

#12688: derived Show instances aren't protected from
RebindableSyntax+OverloadedStrings
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        Reporter:  daviddarais       |                Owner:  RyanGlScott
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  rebindablesyntax overloadedstrings
                                     |  deriving show string
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Well, we've certainly changed the way deriving works in the past to
 accommodate the presence of `RebindableSyntax` (see #11396 and #12080 for
 examples). But those were quite small, non-invasive changes. On the other
 hand, derived `Show` instances make heavy use of string literals, so I
 don't think changing the derived `Show` methods is really an option here.

 Simon, are you suggesting just disabling `RebindableSyntax` entirely for
 derived code? I'd be fine with that.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12688#comment:2>
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