[GHC] #3647: unify handling and error messages for -X vs. {-#LANGUAGE ...#-} pragmas/extensions

[GHC]

#3647: unify handling and error messages for -X vs. {-#LANGUAGE ...#-}
pragmas/extensions
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        Reporter:  eflister          |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  6.10.4
  (Parser)                           |         Keywords:  language pragma
      Resolution:                    |  extensions error message warning
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by nomeata):

 I’m joining the “we need something copyable” section (as expressed in
 #8269), and I’d also throw in the argument that it is better practice to
 use {-# LANGUAGE ... #-} than flags.

 (To be honest I never understood why there are flags at all: If a source
 file uses a multi-way if, then it better declares that. Ok, so for GHCi
 you need command flags, but for anything else?..)

 Since error messages compactness is an issue I’m in favour of
 {{{
   `Foo' has no constructors (EmptyDataDecls permits this)
 }}}
 since by now most GHC users will readily recognize CamelCaseWords as
 language extensions. This should hopefully make everyone happy.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3647#comment:19>
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