Changing GHC Error Message Wrapping

Wed Jan 8 17:11:23 UTC 2014

Well, the Show instance for a type (any type) cannot possibly respect pprCols.  It can't:  show :: a -> String!  No command-line inputs.

I suggest something more like

doc sdoc = do { dflags <- getDynFlags; unqual <- getPrintUnqual; return (showSDocForUser dflags unqual doc }

Simon

From: Andrew Gibiansky [mailto:andrew.gibiansky at gmail.com]
Sent: 08 January 2014 00:09
To: Simon Peyton Jones
Cc: Erik de Castro Lopo; ghc-devs at haskell.org
Subject: Re: Changing GHC Error Message Wrapping

Hello all,

I figured out that this isn't quite a bug and figured out how to do what I wanted. It turns out that the `Show` instance for SourceError does not respect `pprCols` - I don't know if that's a reasonable expectation (although it's what I expected). I ended up using the following code to print these messages:

  flip gcatch handler $ do
    runStmt "let f (x, y, z, w, e, r, d , ax, b ,c,ex ,g ,h) = (x :: Int) + y + z" RunToCompletion
    runStmt "f (1, 2, 3)" RunToCompletion
    return ()
  where
    handler :: SourceError -> Ghc ()
    handler srcerr = do
      let msgs = bagToList $ srcErrorMessages srcerr
      forM_ msgs $ \msg -> do
        s <- doc $ errMsgShortDoc msg
        liftIO $ putStrLn s

doc :: GhcMonad m => SDoc -> m String
doc sdoc = do
  flags <- getSessionDynFlags
  let cols = pprCols flags
      d = runSDoc sdoc (initSDocContext flags defaultUserStyle)
  return $ Pretty.fullRender Pretty.PageMode cols 1.5 string_txt "" d
  where
    string_txt :: Pretty.TextDetails -> String -> String
    string_txt (Pretty.Chr c)   s  = c:s
    string_txt (Pretty.Str s1)  s2 = s1 ++ s2
    string_txt (Pretty.PStr s1) s2 = unpackFS s1 ++ s2
    string_txt (Pretty.LStr s1 _) s2 = unpackLitString s1 ++ s2

As far as I can tell, there is no simpler way, every function in `Pretty` except for `fullRender` just assumes a default of 100-char lines.

-- Andrew

On Tue, Jan 7, 2014 at 11:29 AM, Andrew Gibiansky <andrew.gibiansky at gmail.com<mailto:andrew.gibiansky at gmail.com>> wrote:
Simon,

That's exactly what I'm looking for! But it seems that doing it dynamically in the GHC API doesn't work (as in my first email where I tried to adjust pprCols via setSessionDynFlags).

I'm going to look into the source as what ppr-cols=N actually sets and probably file a bug - because this seems like buggy behaviour...

Andrew

On Tue, Jan 7, 2014 at 4:14 AM, Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>> wrote:
-dppr-cols=N changes the width of the output page; you could try a large number there.  There isn't a setting meaning "infinity", sadly.

Simon

From: Andrew Gibiansky [mailto:andrew.gibiansky at gmail.com<mailto:andrew.gibiansky at gmail.com>]
Sent: 07 January 2014 03:04
To: Simon Peyton Jones
Cc: Erik de Castro Lopo; ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>

Subject: Re: Changing GHC Error Message Wrapping

Thanks Simon.

In general I think multiline tuples should have many elements per line, but honestly the tuple case was a very specific example. If possible, I'd like to change the *overall* wrapping for *all* error messages - how does `sep` know when to break lines? there's clearly a numeric value for the number of columns somewhere, but where is it, and is it user-adjustable?

For now I am just hacking around this by special-casing some error messages and "un-doing" the line wrapping by parsing the messages and joining lines back together.

Thanks,
Andrew

On Mon, Jan 6, 2014 at 7:44 AM, Simon Peyton-Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>> wrote:
I think it's line 705 in types/TypeRep.lhs

pprTcApp p pp tc tys
  | isTupleTyCon tc && tyConArity tc == length tys
  = pprPromotionQuote tc <>
    tupleParens (tupleTyConSort tc) (sep (punctuate comma (map (pp TopPrec) tys)))

If you change 'sep' to 'fsep', you'll get behaviour more akin to paragraph-filling (hence the "f").   Give it a try.  You'll get validation failure from the testsuite, but you can see whether you think the result is better or worse.  In general, should multi-line tuples be printed with many elements per line, or just one?

Simon

From: ghc-devs [mailto:ghc-devs-bounces at haskell.org<mailto:ghc-devs-bounces at haskell.org>] On Behalf Of Andrew Gibiansky
Sent: 04 January 2014 17:30
To: Erik de Castro Lopo
Cc: ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>
Subject: Re: Changing GHC Error Message Wrapping

Apologize for the broken image formatting.

With the code I posted above, I get the following output:

Couldn't match expected type `(GHC.Types.Int<http://GHC.Types.Int>,
                               GHC.Types.Int<http://GHC.Types.Int>,
                               GHC.Types.Int<http://GHC.Types.Int>,
                               t0,
                               t10,
                               t20,
                               t30,
                               t40,
                               t50,
                               t60,
                               t70,
                               t80,
                               t90)'
            with actual type `(t1, t2, t3)'

I would like the types to be on the same line, or at least wrapped to a larger number of columns.

Does  anyone know how to do this, or where in the GHC source this wrapping is done?

Thanks!
Andrew

On Sat, Jan 4, 2014 at 2:55 AM, Erik de Castro Lopo <mle+hs at mega-nerd.com<mailto:mle+hs at mega-nerd.com>> wrote:
Carter Schonwald wrote:

> hey andrew, your image link isn't working (i'm using gmail)
I think the list software filters out image attachments.

Erik
--
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/
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