[GHC] #16075: Weverything ignores some OPTIONS_GHC flags

[GHC]

#16075: Weverything ignores some OPTIONS_GHC flags
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        Reporter:  crockeea          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by bgamari:

Old description:

> When I enable `-Weverything`, some `OPTIONS_GHC` pragmas are respected,
> while others are ignored. For example, with `-Weverything`, this file
>
> {{{
> main = print "hello"
>
> foo :: (Num a, Show a) => a -> IO ()
> foo = print . show
> }}}
>
> generates warnings about:
>
>   1. missing an export list
>   2. top-level binding [main] with no type sig
>   3. redundant constraint [Num a]
>
> If I add `{-# OPTIONS_GHC -fno-warn-missing-signatures -fno-warn-missing-
> export-lists -fno-warn-redundant-constraints #-}` to the top of the file
> and recompile, I expect all warnings to go away. But GHC still reports
> that `main` has no signature.
>

> Note that this problem doesn't occur with `-Wall`. With `-Wall`, the code
> snippet warns about the missing signature on `main`, but when I add the
> `OPTIONS_GHC`, the warning goes away. Thus this problem appears to be
> unique to `Weverything`.

New description:

 When I enable `-Weverything`, some `OPTIONS_GHC` pragmas are respected,
 while others are ignored. For example, with `-Weverything`, this file

 {{{
 main = print "hello"

 foo :: (Num a, Show a) => a -> IO ()
 foo = print . show
 }}}

 generates warnings about:

  1. missing an export list
  2. top-level binding [main] with no type sig
  3. redundant constraint [Num a]

 If I add `{-# OPTIONS_GHC -fno-warn-missing-signatures -fno-warn-missing-
 export-lists -fno-warn-redundant-constraints #-}` to the top of the file
 and recompile, I expect all warnings to go away. But GHC still reports
 that `main` has no signature.


 Note that this problem doesn't occur with `-Wall`. With `-Wall`, the code
 snippet warns about the missing signature on `main`, but when I add the
 `OPTIONS_GHC`, the warning goes away. Thus this problem appears to be
 unique to `Weverything`.

--

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16075#comment:3>
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