[GHC] #10106: GHC doesn't warn on typos in language pragmas

[GHC]

#10106: GHC doesn't warn on typos in language pragmas
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        Reporter:  sdemos            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Linux             |            Architecture:  x86_64
 Type of failure:  Incorrect         |  (amd64)
  warning at compile-time            |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #10076            |  Differential Revisions:
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Comment (by simonpj):

 The underlying issue here is:

  * A "warning" differs from an "error", in that only the latter halt
 compilation (unless you use `-Werror`.

  * We do not display warnings if there are any errors, to draw attention
 to the errors.

 Maybe we need some kind of in-between thing, say a "prominent warning".
 It is like a warning in that it does not halt compilation.  But it is not
 suppressed by errors.  Then a mis-spelled pragma could be a "prominent
 warning".

 Bizarrely, we currently have no fewer than '''seven''' levels of severity
 for output messages:
 {{{
 data Severity
   = SevOutput
   | SevDump
   | SevInteractive
   | SevInfo
   | SevWarning
   | SevError
   | SevFatal
 }}}
 (in `Error.hs`).  The intended semantics of these levels is entirely
 undocumented, and I have no clue what they mean.  I would love this to
 documented; probably we can nuke several levels.  But adding
 `SevProminentWarning` (properly documented) would arguably do little harm.

 But someone would have to want to do it.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10106#comment:5>
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