#15203: Wrong location reported for kind error -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 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: -------------------------------------+------------------------------------- When I try to compile {{{#!hs {-# LANGUAGE PolyKinds, ConstraintKinds, TypeFamilies, FlexibleContexts #-} module Bug where import Data.Proxy type T (a :: k1) (b :: k2) = (a ~ b, Show (Proxy (a :: k1)), Show (Proxy (b :: k2))) }}} I get {{{ Bug.hs:7:80: error: • Couldn't match ‘k1’ with ‘k2’ • In the type declaration for ‘T’ | 7 | type T (a :: k1) (b :: k2) = (a ~ b, Show (Proxy (a :: k1)), Show (Proxy (b :: k2))) | ^^ }}} The problem is that the `k2` that's highlighted has nothing at all to do with the error. Indeed, some experimentation shows that GHC will highlight the first occurrence of `k2` to the right of the `=`. The error is actually from unification caused by `a ~ b`. I noticed this because I've been tightening up the way GHC does left-to- right ordering during implicit quantification (while working on something more substantial). In so doing, I made sure to prefer kind variable occurrences to the ''left'' of the = over those to the right. But then I got a testsuite failure due to a changed location of an error. This is caused by the call to `report_sig_tv_err` in `tcTyClTyVars`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15203 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler