Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: ac9fb269 by Simon Peyton Jones at 2025-05-20T09:19:04-04:00 Track rewriter sets more accurately in constraint solving This MR addresses #26003, by refactoring the arcane intricacies of Note [Equalities with incompatible kinds]. NB: now retitled to Note [Equalities with heterogeneous kinds]. and the main Note for this MR. In particular: * Abandon invariant (COERCION-HOLE) in Note [Unification preconditions] in GHC.Tc.Utils.Unify. * Abandon invariant (TyEq:CH)) in Note [Canonical equalities] in GHC.Tc.Types.Constraint. * Instead: add invariant (REWRITERS) to Note [Unification preconditions]: unify only if the constraint has an empty rewriter set. Implementation: * In canEqCanLHSFinish_try_unification, skip trying unification if there is a non-empty rewriter set. * To do this, make sure the rewriter set is zonked; do so in selectNextWorkItem, which also deals with prioritisation. * When a coercion hole is filled, kick out inert equalities that have that hole as a rewriter. It might now be unlocked and available to unify. * Remove the ad-hoc `ch_hetero_kind` field of `CoercionHole`. * In `selectNextWorkItem`, priorities equalities withan empty rewriter set. * Defaulting: see (DE6) in Note [Defaulting equalities] and Note [Limited defaulting in the ambiguity check] * Concreteness checks: there is some extra faff to try to get decent error messages when the FRR (representation-polymorphism) checks fail. In partiular, add a "When unifying..." explanation when the representation-polymorphism check arose from another constraint. - - - - - 65 changed files: - compiler/GHC/Core/Coercion.hs - compiler/GHC/Core/Predicate.hs - compiler/GHC/Core/TyCo/Rep.hs - compiler/GHC/Core/TyCo/Tidy.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Errors/Types.hs - compiler/GHC/Tc/Gen/HsType.hs - compiler/GHC/Tc/Plugin.hs - compiler/GHC/Tc/Solver.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/InertSet.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Utils/Unify.hs - compiler/GHC/Tc/Zonk/TcType.hs - compiler/GHC/Types/Error/Codes.hs - testsuite/tests/dependent/should_fail/T11471.stderr - testsuite/tests/diagnostic-codes/codes.stdout - testsuite/tests/indexed-types/should_fail/T8227.stderr - testsuite/tests/indexed-types/should_fail/T9662.stderr - testsuite/tests/partial-sigs/should_fail/T14040a.stderr - testsuite/tests/partial-sigs/should_fail/T14584.stderr - testsuite/tests/polykinds/T14172.stderr - testsuite/tests/polykinds/T14846.stderr - testsuite/tests/rep-poly/RepPolyArgument.stderr - testsuite/tests/rep-poly/RepPolyBackpack1.stderr - testsuite/tests/rep-poly/RepPolyBinder.stderr - testsuite/tests/rep-poly/RepPolyDoBind.stderr - testsuite/tests/rep-poly/RepPolyDoBody1.stderr - testsuite/tests/rep-poly/RepPolyDoBody2.stderr - testsuite/tests/rep-poly/RepPolyLeftSection2.stderr - testsuite/tests/rep-poly/RepPolyMagic.stderr - testsuite/tests/rep-poly/RepPolyMcBind.stderr - testsuite/tests/rep-poly/RepPolyMcBody.stderr - testsuite/tests/rep-poly/RepPolyMcGuard.stderr - testsuite/tests/rep-poly/RepPolyNPlusK.stderr - testsuite/tests/rep-poly/RepPolyPatBind.stderr - testsuite/tests/rep-poly/RepPolyRecordUpdate.stderr - testsuite/tests/rep-poly/RepPolyRightSection.stderr - testsuite/tests/rep-poly/RepPolyRule1.stderr - testsuite/tests/rep-poly/RepPolyTuple.stderr - testsuite/tests/rep-poly/RepPolyTuple4.stderr - testsuite/tests/rep-poly/RepPolyTupleSection.stderr - testsuite/tests/rep-poly/RepPolyWrappedVar.stderr - testsuite/tests/rep-poly/T11473.stderr - testsuite/tests/rep-poly/T12709.stderr - testsuite/tests/rep-poly/T12973.stderr - testsuite/tests/rep-poly/T13233.stderr - testsuite/tests/rep-poly/T13929.stderr - testsuite/tests/rep-poly/T14561.stderr - testsuite/tests/rep-poly/T14561b.stderr - testsuite/tests/rep-poly/T17817.stderr - testsuite/tests/rep-poly/T19615.stderr - testsuite/tests/rep-poly/T19709b.stderr - testsuite/tests/rep-poly/T21906.stderr - testsuite/tests/rep-poly/T23903.stderr - testsuite/tests/rep-poly/UnliftedNewtypesCoerceFail.stderr - testsuite/tests/typecheck/no_skolem_info/T14040.stderr - testsuite/tests/typecheck/should_compile/T25266a.stderr - testsuite/tests/typecheck/should_fail/T16204c.stderr - testsuite/tests/typecheck/should_fail/T7696.stderr - testsuite/tests/typecheck/should_fail/T8603.stderr The diff was not included because it is too large. View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/ac9fb269786a10221729731a4776c28b... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/ac9fb269786a10221729731a4776c28b... You're receiving this email because of your account on gitlab.haskell.org.