#12035: hs-boot knot tying insufficient for ghc --make -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: hs-boot | Operating System: Unknown/Multiple backpack | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC in one-shot mode goes through great pains to make sure that if we are typechecking A.hs with an A.hs-boot, any references to A in the interfaces we load in should point to the `TyThing`s from our LOCAL `tcg_type_env` (`_var`), not the declarations from the `hs-boot`. Indeed, it is never right to load the hi-boot file into the EPS (#10182, #10336). Because in one-shot compilation we are loading things into the EPS anew, there is not much risk of having stale `TyThing`s lying around which still refer to the old `hs-boot` ModDetails. `ghc --make` does not do a sufficient job as knot tying. Specifically, any `Id`s/`TyThing`s from the HPT which were built against the `hs-boot` ModDetails will have out-of-date information. We do manage to tie the knot if we use `tcLookupGlobal` directly, which does look in the local type environment (e.g., #12034 affects both `-c` and `--make`), but if we get our hands on a `TyThing` indirectly, we're in trouble. The case where this is most obvious is unfoldings; see #10083 for an example of GHC behaving differently between `-c` and `--make` (although, ironically, `--make`s bad behavior masks the bug). It's not entirely clear how to fix this problem. In analogy to what happens in `-c`, we should clear the stale `TyThing`s from our HPT and retypecheck them after we have setup the type environment for our `hs` file. But presently in `--make` we don't lazily load types from our home package. Maybe we should! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12035 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler