#12610: Emit tab warning promptly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: high | Milestone: 8.0.2 Component: Compiler | Version: 8.0.1 (Parser) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs p = let x = 4 [tab]y = 5 in 12 }}} produces `error: parse error on input ‘y’` and nothing else. The problem is caused by a tab appearing to the user to line up `x` with `y` but actually placing `y` in the wrong column. The user typically will scratch their head and then post a question on StackOverflow. There they'll be told to use `-fwarn-tabs`, but ''that option won't help'' (and it's probably already on) because GHC will exit with a parse error before it gets around to giving the warning. I suspect the solution is probably to emit the tab warning in the lexer, but one of the parsing gurus will probably know better. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12610 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler