#15918: GHC panic from QuantifiedConstraints(?) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.2 Resolution: | Keywords: | QuantifiedConstraints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
See the comments around that use of isReflexiveCo.
Which comments? I think you may be referring to `Note [Respecting definitional equality]` in `TyCoRep`. Anything else? Let me also note that * In GHC today we use `mkNakedCastTy` which absolutely does not remove the casts that the above `Note` says it should. * The typechecker is careful to push casts out of the way when solving equalities, which helps. But it still has lots of `tcSplitX` calls.
I think that's problematic.
What do you suggest we do? As comment:3 shows, if we have `mkTcCastTy` we'll need `mkTcAppTy`. And `tcSubstTy` and `tcSubstTheta`. And `tcInstDFunType`. It's pretty hard to be sure that we've nailed all the places. Duplicating all this stuff doesn't smell right to me. Hmm. Currently `mkCastTy` will remove a cast between `Type` and `Coercion`, because the two are equal in Core. But such a cast would yield a typechecker error (which is what both #15799 and this ticket involve), so we'd never get as far as Core. How bad would it be if `mkCastTy` did not remove a cast between `Type` and `Coercion`? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15918#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler