quotes pretty-printer not working as comments specify

I am currently working on a parser for GHC error messages, and would actually prefer that this remain unfixed, as this would make GHC error messages slightly harder to parse.

From compiler/utils/Outputable.lhs

-- quotes encloses something in single quotes...
-- but it omits them if the thing ends in a single quote
-- so that we don't get `foo''.  Instead we just have foo'.
quotes d = SDoc $ \sty -> 
           let pp_d = runSDoc d sty in
           case show pp_d of
             ('\'' : _) -> pp_d
             _other     -> Pretty.quotes pp_d

This implementation does not match the comment - the code is checking for a leading single-quote, not for a trailing one. Therefore the following code does result in the foo'' ` that the comment specifically mentions:

foo' :: (Show a) => a -> IO ()
foo' = print
main = foo' print

Test.hs:3:8:
    No instance for (Show (a0 -> IO ()))
      arising from a use of `foo''
    Possible fix: add an instance declaration for (Show (a0 -> IO ()))
    In the expression: foo' print
    In an equation for `main': main = foo' print

Trac metadata

Trac field	Value
Version	7.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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