#13990: Core Lint error on empty case -------------------------------------+------------------------------------- Reporter: mbieleck | Owner: (none) Type: bug | Status: patch Priority: highest | Milestone: 8.2.3 Component: Compiler | Version: 8.2.1-rc3 Resolution: | Keywords: core-lint | case Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4160 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
But should we leave the scrut_diverges warning in place?
You are referring to this code in the `Case` equation for `lintCoreExpr`: {{{ -- See Note [No alternatives lint check] ; when (null alts) $ do { checkL (not (exprIsHNF scrut)) (text "No alternatives for a case scrutinee in head-normal form:" <+> ppr scrut) ; checkWarnL scrut_diverges (text "No alternatives for a case scrutinee not known to diverge for sure:" <+> ppr scrut) } }}} Well, suppose `x :: T Bool`, where `T` is in comment:8. Then if I say something like {{{ case x of {} }}} then `x` is not sure to diverge but the case branches are legitimately empty. Maybe you can add an example like this in a `Note` explaining why there is no null-alts check here? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13990#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler