#13102: orphan family instances can leak through the EPS in --make mode -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In --make mode there is a single EPS whose `eps_fam_inst_env` holds all type family instances that have been read from interface files from external packages for any reason. The type checker uses this field pervasively via `tcGetFamInstEnvs`. When compiling multiple files it's fairly easy to set up a situation in which 1. the first module to be compiled `A` loads an interface file `O.hi` from another package containing an orphan family instance (say, because it imports the module directly); 2. a later module `B` uses this instance to reduce a type, even though `B` has no dependency at all on the module `O` defining the instance. (The only tricky bit in arranging this is that since `B` cannot depend on `A`, a little good fortune is needed for GHC to decide to compile `B` after `A`.) Now another module could import `B` and obtain a function whose definition relies on a type family instance that is not visible from `B` at all, compromising type safety. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13102 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler