#15814: Orphan Instance Overlap Error Message -------------------------------------+------------------------------------- Reporter: parsonsmatt | Owner: (none) Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.4.3 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D5377 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Thanks for working on this. Indeed, a careful `Note` to explain how it works, and some more type signatures on local definitions, would be helpful. I could not understand the code. I think your idea is something like this, supposing we are compiling module M, and are reporting an instance whose dictionary function is `$df`. * Given a `$df` we know the module D in which it is defined, via `nameModule`. * If that module D is * M itself, or * one of the module that M directly imports * an orphan module we can report how `$df` came to be in scope. * Those three cases are easy because we have that info to hand in the `TcGblEnv`. You code looks a bit complicated if I'm right, but maybe I'm missing something. I also wonder about doing the full job, when `$df` is in scope indirectly. After all, that's the situation in which the user is going to be most puzzled! What we want is to ask * For each `import B`, does `B` transitively import `D`? And that info is also conveniently available, in the `mi_deps` field of each `ModIface`. So it should be easy to do to full job, no exceptions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15814#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler