warn-redundant-constraints present as errors

[Alan & Kim Zimmerman]

Thanks.

I've found a case where it warns of a redundant constraint, but if I remove
the constraint I get an error saying the constraint is required

--------------------------------------------
import qualified GHC           as GHC

import qualified Data.Generics as SYB

duplicateDecl :: (SYB.Data t) =>   -- **** The constraint being warned
against *******
  [GHC.LHsBind GHC.Name]  -- ^ The declaration list
  ->t                     -- ^ Any signatures are in here
  ->GHC.Name              -- ^ The identifier whose definition is to be
duplicated
  ->GHC.Name              -- ^ The new name (possibly qualified)
  ->IO [GHC.LHsBind GHC.Name]  -- ^ The result
duplicateDecl decls sigs n newFunName
 = do
     let sspan = undefined
     newSpan <- case typeSig of
        [] -> return sspan
        _  -> do
          let Just sspanSig = getSrcSpan typeSig
          toksSig <- getToksForSpan sspanSig

          let [(GHC.L sspanSig' _)] = typeSig

          return sspanSig'

     undefined
   where
     typeSig = definingSigsNames [n] sigs

-- |Find those type signatures for the specified GHC.Names.
definingSigsNames :: (SYB.Data t) =>
            [GHC.Name] -- ^ The specified identifiers.
            ->t        -- ^ A collection of declarations.
            ->[GHC.LSig GHC.Name]  -- ^ The result.
definingSigsNames pns ds = def ds
  where def = undefined

getSrcSpan = undefined
getToksForSpan = undefined

--------------------------------------------

On Fri, Jan 9, 2015 at 1:08 PM, Simon Peyton Jones <simonpj at microsoft.com>
wrote:

>  I’ve fixed this
>
>
>
> *From:* Alan & Kim Zimmerman [mailto:alan.zimm at gmail.com]
> *Sent:* 08 January 2015 21:46
> *To:* ghc-devs at haskell.org; Simon Peyton Jones
> *Subject:* warn-redundant-constraints present as errors
>
>
>
> This is a great feature, here is some feedback
>
> My syntax highlighter in emacs expects warnings to have the word "warning"
> in them.
>
> So for the two warnings reported below, the first is highlighted as an
> error, and the second as a warning
>
>
> Language/Haskell/Refact/Utils/TypeUtils.hs:3036:17:
>     Redundant constraint: SYB.Data t
>     In the type signature for:
>        duplicateDecl :: SYB.Data t =>
>                         [GHC.LHsBind GHC.Name]
>                         -> t -> GHC.Name -> GHC.Name -> RefactGhc
> [GHC.LHsBind GHC.Name]
>
> Language/Haskell/Refact/Utils/TypeUtils.hs:3045:7: Warning:
>     Defined but not used: ‘toks
>
>   This is in a ghci session, and the file loads without problems, so it
> is indeed a warning.
>
> Can we perhaps add the word "Warning" to the output for Redundant
> constraints?
>
> I also had a situation where it asked me to remove a whole lot of
> constraints from different functions, I did them in batches, so did not
> remove them all from the file at once, and at some point I had to add at
> least one of them back, albeit based on an error message.
>
>
>
> Regards
>
>   Alan
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/ghc-devs/attachments/20150109/96c5c0e9/attachment-0001.html>