#13332: Report unrecognized pragmas earlier -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => newcomer -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13332#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13332: Report unrecognized pragmas earlier -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ThreeFx): Replying to [comment:2 richardfung]:

Hi! I'd like to try my hand at this but was hoping someone could give me some guidance.

From my looking so far, it would appear that the current error message is from somewhere in the typechecker (smallerMsg) while the warning we want to show up is in the Lexer.

I would have expected the warning in the lexer to show up first though since presumably the lexer runs before the typechecker. Could anyone give me a pointer to where I should look to understand what the issue is?

You're correct that the lexer runs before the type checker - after all, you need to know what to typecheck. I suspect that `{-# LANUGAGE UndecidableInstances #-}` is not parsed as pragma but as nested comment. In order to verify this I would look at the lexer and see if this is actually the case. If it isn't, definitely check what this actually gets lexed as - too bad there is no `-ddump-lexed` option. If it is, I'd probably consider adding a lexing warning for unrecognized pragma keywords (`LANGUAGE`, `OPTIONS_GHC`, ...). Maybe this could also be extended to all pragmas, not only file headers. Anyway this may be completely wrong - it's just my opinion on where to start. Happy hacking! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13332#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13332: Report unrecognized pragmas earlier -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton): According to the ticket description, GHC does generate a warning about the unknown pragma `LANUGAGE`; but only when there isn't an error in the module. I think there is some logic somewhere for not displaying warnings when there are also errors to report, on the grounds that the errors are more important (and may be the cause of the warnings). However, here clearly the warning about `LANUGAGE` is the cause of the consequent errors. We should probably have some notion of "important warnings" that get displayed even when there are errors to report as well. I think this may have been discussed on another ticket as well, which had a similar sort of issue; but I can't find it at the moment. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13332#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13332: Report unrecognized pragmas earlier -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by mpickering): * keywords: newcomer => Comment: I investigated this today. The relevant code path starts in `ghc/Main.hs` under the comment "do the business" which catches and displays errors. Warnings on the other hand are dealt with by `runHsc` and are already baked into the `HscMonad`. The main logic of how the parser and type checker link together is in `hscTypecheck`. The typechecker is invoked by the `tcRnModule` function but wrapped with `ioMsgMaybe` which throws an error if the typechecker fails. It seems like the best solution would be to also stop using `throwIO` to report errors and also bake them into the `Hsc` type so that `runHsc` deals with throwing both warnings and exceptions so we can isolate the logic and which are displayed into one place. I fear that this would be quite a difficult change as a lot of the compiler is designed using these unchecked exceptions. Thanks for looking at this Richard but I agree that it's not very easy to fix properly. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13332#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler