No context in error messages

[Corentin Dupont]

Anyway, I think I figured it out:
Hint is using the Show instance of ErrMsg.
But it is defined only in term of errMsgShortString:

https://www.haskell.org/ghc/docs/7.6.3/html/libraries/ghc-7.6.3/src/ErrUtils.html#ErrMsg

So we are missing the context infos.



On Tue, Sep 9, 2014 at 12:01 AM, Corentin Dupont <corentin.dupont at gmail.com>
wrote:

> Hi everybody,
> I am working with Hint, after some discussion with Daniel Gorin, I decided
> to post here, I hope it's the right place.
> My problem with Hint is that I cannot get context in error messages while
> interpreting a string. If you run the attached file example.hs, you get:
>
> GhcError {errMsg = "No instance for (GHC.Num.Num GHC.Base.String)\n
> arising from a use of `GHC.Num.+'\nPossible fix:\n  add an instance
> declaration for (GHC.Num.Num GHC.Base.String)"}
>
> There is no context (line number, code snippets...), plus the error
> message uses fully qualified names, which is not very readable.
> It's very hard to figure out where the problem is when interpreting a long
> string.
> But the same error in a file that is loaded with Hint gives the correct
> message (uncomment the putStrLn in SomeModule.hs to get it):
>
> GhcError {errMsg = "<no location info>:\n    [1 of 1] Compiling
> SomeModule       ( SomeModule.hs, interpreted )"},GhcError {errMsg =
> "SomeModule.hs:5:22:\n    No instance for (Num String) arising from a use
> of `+'\n    Possible fix: add an instance declaration for (Num String)\n
> In the second argument of `($)', namely `\"bar\" + 1'\n    In a stmt of a
> 'do' block: putStrLn $ \"bar\" + 1\n    In the expression:\n      do {
> putStrLn \"bar\";\n           putStrLn $ \"bar\" + 1 }"}
>
> This error is much better: it gives line number plus some code snippets
> ("In the second argument of...").
>
> There might be a flag that is not correctly set in GHC? After a quick look
> I'm thinking of GHC.DynFlags (I'm no expert). Now it is configured with:
> configureDynFlags :: GHC.DynFlags -> GHC.DynFlags
> configureDynFlags dflags = dflags{GHC.ghcMode    = GHC.CompManager,
>                                   GHC.hscTarget  = GHC.HscInterpreted,
>                                   GHC.ghcLink    = GHC.LinkInMemory,
>                                   GHC.verbosity  = 0}
>
> Thanks,
> Corentin
>
>
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