Re: Status of the rich errors proposal

Ben Gamari is, I believe, leading the effort with that proposal. It continues to get attention but has not yet blossomed to something we're ready to debate widely. This is a hard nut to crack, and we'd like to get it right. So I guess all there is to say right now is that the effort is ongoing, but we don't have anything concrete to report at the moment. Richard

On Oct 23, 2019, at 7:52 AM, Javier Neira Sanchez wrote:

Hi, lately i am being collaborated in the haskell-ide-engine (hie) repo and one of the issues i get to fix was related with the parsing of ghc errors. It turns out that delimiters of terms in errors are different in windows (`term') and *nix (‘term’) systems and that drive to parse errors. Quite code actions and diagnostics are based in parsing them and they were broken in windows. I am afraid that the code is very brittle and close to human readable error messages. the actual code look like this:

-- | Extract a term from a compiler message. -- It looks for terms delimited between '‘' and '’' falling back to '`' and '\'' -- (the used ones in Windows systems). extractTerm :: T.Text -> T.Text extractTerm txt = case extract '‘' '’' txt of "" -> extract '`' '\'' txt -- Needed for windows term -> term where extract b e = T.dropWhile (== b) . T.dropWhileEnd (== e) . T.dropAround (\c -> c /= b && c /= e)

or

extractImportableTerm :: T.Text -> Maybe (T.Text, SymbolImport SymbolType) extractImportableTerm dirtyMsg = do (n, s) <- extractedTerm let n' = T.strip n return (n', s) where importMsg = S.headMay -- Get rid of the rename suggestion parts $ T.splitOn "Perhaps you meant " $ T.replace "\n" " " -- Get rid of trailing/leading whitespace on each individual line $ T.unlines $ map T.strip $ T.lines $ T.replace "* " "" -- Needed for Windows $ T.replace "• " "" dirtyMsg extractTerm prefix symTy = importMsg >>= T.stripPrefix prefix >>= \name -> Just (name, Import symTy) extractType b = extractTerm ("Not in scope: type constructor or class " <> b) Type extractedTerm = asum [ extractTerm "Variable not in scope: " Symbol , extractType "‘" , extractType "`" -- Needed for windows , extractTerm "Data constructor not in scope: " Constructor]

It is clearly unsatisfactory but hard to improve without changing the messages to make it more structured. Moreover any legitimate change on errors to make it better will likely break it.

After exposing my worries in the hie irc channel, @mpickering pointed out that it is already a proposal to improve error messages:

https://github.com/bgamari/ghc-proposals/blob/rich-errors-proposal/proposals... https://github.com/bgamari/ghc-proposals/blob/rich-errors-proposal/proposals...

that nicely will improve the state of things.

Otoh there are already a way to output ghc errors as json (see https://gitlab.haskell.org/ghc/ghc/issues/13190 https://gitlab.haskell.org/ghc/ghc/issues/13190). It contains valuable info about the error in specific fields but the message itself is in plain text. So merging both features will let tools to handle compiler errors without use the ghc api directly if needed.

what is the status of the proposal? hie an other tooling developers will welcome it very heartly.

Thanks in advance! _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs