#16002: Type family equation with wrong name is silently accepted (GHC 8.6+ only) -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.6.2 Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: GHC accepts | Unknown/Multiple invalid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Ah, it's due to this change: {{{#!diff kcLTyClDecl :: LTyClDecl GhcRn -> TcM () -- See Note [Kind checking for type and class decls] kcLTyClDecl (L loc decl) + | hsDeclHasCusk decl + = traceTc "kcTyClDecl skipped due to cusk" (ppr tc_name) + | otherwise = setSrcSpan loc $ tcAddDeclCtxt decl $ - do { traceTc "kcTyClDecl {" (ppr (tyClDeclLName decl)) + do { traceTc "kcTyClDecl {" (ppr tc_name) ; kcTyClDecl decl - ; traceTc "kcTyClDecl done }" (ppr (tyClDeclLName decl)) } + ; traceTc "kcTyClDecl done }" (ppr tc_name) } + where + tc_name = tyClDeclLName decl }}} Note that `kcTyClDecl` (which performs the validity check needed to reject `A x = x` above) is only invoked when a type family declaration lacks a CUSK! NB: This code no longer exists in GHC HEAD, as it has since been refactored into [http://git.haskell.org/ghc.git/blob/5f1d949ab9e09b8d95319633854b7959df06eb58... kcTyClGroup]: {{{#!hs kcTyClGroup decls = do { ... ; let (cusk_decls, no_cusk_decls) = partition (hsDeclHasCusk . unLoc) decls ; ... ; mapM_ kcLTyClDecl no_cusk_decls ; ... } }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16002#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler