warn-redundant-constraints present as errors

[Johan Tibell]

I think using the words error and warning makes sense. For example, this is
how Clang (LLVM) does it:

format-strings.c:91:13: warning: '.*' specified field precision is missing
a matching 'int' argument
  printf("%.*d");
            ^

t.c:7:39: error: invalid operands to binary expression ('int' and 'struct
A')
  return y + func(y ? ((SomeA.X + 40) + SomeA) / 42 + SomeA.X : SomeA.X);
                       ~~~~~~~~~~~~~~ ^ ~~~~~

(Also note how lovely it is to have a caret pointing at the error.)

On Fri, Jan 9, 2015 at 10:39 AM, Simon Peyton Jones <simonpj at microsoft.com>
wrote:

>  Alan’s point is a bug – I will fix.
>
>
>
> Konstantine’s point is reasonable.  we could easily say
>
>
>
> Language/Haskell/Refact/Utils/TypeUtils.hs:3045:7: Error:
>      blah blah
>
>
>
> (the bit in red is the new bit)
>
> But I’m not sure that everyone else would want that.   If a consensus
> forms it would be easy to excecute
>
>
>
> I suppose there could be yet another flag to control it (!)
>
>
>
> Simon
>
>
>
> *From:* Konstantine Rybnikov [mailto:k-bx at k-bx.com]
> *Sent:* 09 January 2015 09:19
> *To:* Alan & Kim Zimmerman
> *Cc:* ghc-devs at haskell.org; Simon Peyton Jones
> *Subject:* Re: warn-redundant-constraints present as errors
>
>
>
> On a slightly unrelated note I should say it would be great to have errors
> contain word "Error:". This is especially nice to have because when you
> build with "-j" your error that stops compilation gets lost somewhere in
> the middle of many warnings (which my projects have, unfortunately).
>
>
>
> On Thu, Jan 8, 2015 at 11:45 PM, Alan & Kim Zimmerman <alan.zimm at gmail.com>
> wrote:
>
>     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
>
>
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