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

[GHC-2]

#3647: unify handling and error messages for -X vs. {-#LANGUAGE ...#-}
pragmas/extensions
-------------------------------------------------------------+--------------
Reporter:  eflister                                          |          Owner:                  
    Type:  feature request                                   |         Status:  new              
Priority:  normal                                            |      Component:  Compiler (Parser)
 Version:  6.10.4                                            |       Severity:  trivial          
Keywords:  language pragma extensions error message warning  |       Testcase:                  
      Os:  Unknown/Multiple                                  |   Architecture:  Unknown/Multiple
-------------------------------------------------------------+--------------
 it's easy to accidentally cut and paste a -XExtentionName from a ghc error
 message into one's  {-#LANGUAGE ...#-} pragma, and then one has to track
 down the problem when that doesn't work.  it would be nice if
 -XExtentionName were accepted in the pragma list.  even though -X is ghc
 specific, i don't see that it hurts anything to be lenient in the pragma
 format accepted (a warning could be produced to indicate that the program
 will not be portable).  also, the ghc error message indicating that an
 extension should be added should print out a message that would make for
 easy cut and paste without modification into *either* one's language
 pragma or command line -X extension args.  see
 http://hackage.haskell.org/trac/ghc/ticket/3616#comment:8.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3647>
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[GHC-2]

#3647: unify handling and error messages for -X vs. {-#LANGUAGE ...#-}
pragmas/extensions
--------------------------------------------------------------+-------------
 Reporter:  eflister                                          |          Owner:                  
     Type:  feature request                                   |         Status:  new            
 Priority:  normal                                            |      Milestone:                  
Component:  Compiler (Parser)                                 |        Version:  6.10.4          
 Severity:  trivial                                           |     Resolution:                  
 Keywords:  language pragma extensions error message warning  |       Testcase:                  
       Os:  Unknown/Multiple                                  |   Architecture:  Unknown/Multiple
--------------------------------------------------------------+-------------
Comment (by duncan):

 By all means improve the error message but please do not extend the
 LANGUAGE pragma syntax. It means every other compiler and tool that has to
 know about the pragma must also be extended (and in a rather quirky way).
 Standards are a good thing! :-)

 Perhaps we can get ghc's error messages to suggest LANGUAGE pragmas rather
 than the ghc -XBlah style.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3647#comment:1>
GHC <http://www.haskell.org/ghc/>
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[GHC-2]

#3647: unify handling and error messages for -X vs. {-#LANGUAGE ...#-}
pragmas/extensions
--------------------------------------------------------------+-------------
 Reporter:  eflister                                          |          Owner:                  
     Type:  feature request                                   |         Status:  new            
 Priority:  normal                                            |      Milestone:                  
Component:  Compiler (Parser)                                 |        Version:  6.10.4          
 Severity:  trivial                                           |     Resolution:                  
 Keywords:  language pragma extensions error message warning  |       Testcase:                  
       Os:  Unknown/Multiple                                  |   Architecture:  Unknown/Multiple
--------------------------------------------------------------+-------------
Comment (by eflister):

 not to be annoying, but i don't understand why it's not ok for ghc to
 accept (with a warning) a SUPERSET of the official syntax.  that doesn't
 change the standard and it doesn't imply that any other compiler has to do
 anything different.  a warning would be the best user interaction -- "i
 know what you meant to say, and i'm doing it, you should just know that
 what you said isn't portable, and here's how to fix it.  would you like me
 to fix it for you?"

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3647#comment:2>
GHC <http://www.haskell.org/ghc/>
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[GHC-2]

#3647: unify handling and error messages for -X vs. {-#LANGUAGE ...#-}
pragmas/extensions
--------------------------------------------------------------+-------------
 Reporter:  eflister                                          |          Owner:                  
     Type:  feature request                                   |         Status:  new            
 Priority:  normal                                            |      Milestone:                  
Component:  Compiler (Parser)                                 |        Version:  6.10.4          
 Severity:  trivial                                           |     Resolution:                  
 Keywords:  language pragma extensions error message warning  |       Testcase:                  
       Os:  Unknown/Multiple                                  |   Architecture:  Unknown/Multiple
--------------------------------------------------------------+-------------
Comment (by duncan):

 Replying to [comment:2 eflister]:
 > not to be annoying, but i don't understand why it's not ok for ghc to
 accept (with a warning) a SUPERSET of the official syntax.

 At first you'd expect that accepting a superset would not cause any
 problems. However what happens is that people will start using that new
 syntax and then suddenly those packages/programs cannot be used with the
 tools that stick to the official syntax.

 > that doesn't change the standard and it doesn't imply that any other
 compiler has to do anything different.

 It doesn't change the official standard but it does change the de-facto
 standard, and other compilers and tools will have to change to keep up so
 that they can continue to process all code that people write.

 > a warning would be the best user interaction -- "i know what you meant
 to say, and i'm doing it, you should just know that what you said isn't
 portable, and here's how to fix it.  would you like me to fix it for you?"

 Certainly a nice error message is good however I would suggest that it be
 "i know what you meant to say, here's how to fix it." (and perhaps an IDE
 could also do "would you like me to fix it for you?"). Also accepting the
 program has a low benefit and a non-trivial cost.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3647#comment:3>
GHC <http://www.haskell.org/ghc/>
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