[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
--------------------------------+-------------------------------------------
  Reporter:  eflister           |          Owner:                                                  
      Type:  feature request    |         Status:  infoneeded                                      
  Priority:  normal             |      Milestone:  7.0.1                                           
 Component:  Compiler (Parser)  |        Version:  6.10.4                                          
Resolution:                     |       Keywords:  language pragma extensions error message warning
  Testcase:                     |      Blockedby:                                                  
Difficulty:                     |             Os:  Unknown/Multiple                                
  Blocking:                     |   Architecture:  Unknown/Multiple                                
   Failure:  None/Unknown       |  
--------------------------------+-------------------------------------------
Changes (by michalt):

 * cc: michal.terepeta@… (added)
  * status:  new => infoneeded


Comment:

 To be honest -X<extension> error messages are a bit annoying at times. But
 what
 output exactly do we want? For instance now GHC reports something
 like this:
 {{{
   `Foo' has no constructors (-XEmptyDataDecls permits this)
 }}}
 maybe removing -X would be better?
 {{{
   `Foo' has no constructors (EmptyDataDecls permits this)
 }}}
 or
 {{{
   `Foo' has no constructors (-XEmptyDataDecls/EmptyDataDecls permits this)
 }}}
 or even
 {{{
   `Foo' has no constructors (-XEmptyDataDecls/LANGUAGE EmptyDataDecls
 permits this)
 }}}
 Personally I think simply removing -X would be both readable and easy to
 paste
 (I usually specify the extensions in LANGUAGE pragmas and not as a command
 line
 arguments). On the other hand the last one is easiest for pasting but
 quite a
 bit longer and somewhat less readable. Any opinions?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3647#comment:8>
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