Simon Peyton Jones pushed to branch wip/T26255 at Glasgow Haskell Compiler / GHC Commits: 6dcf6444 by Simon Peyton Jones at 2025-08-04T17:49:41+01:00 Better position for custom errors - - - - - 1 changed file: - compiler/GHC/Tc/Errors.hs Changes: ===================================== compiler/GHC/Tc/Errors.hs ===================================== @@ -600,11 +600,32 @@ reportWanteds ctxt tc_lvl wc@(WC { wc_simple = simples, wc_impl = implics -- (see GHC.Tc.Utils.insolublWantedCt) is caught here, otherwise -- we might suppress its error message, and proceed on past -- type checking to get a Lint error later - report1 = [ given_eq_spec + report1 = [ -- We put implicit lifting errors first, because are solid errors + -- See "Implicit lifting" in GHC.Tc.Gen.Splice + -- Note [Lifecycle of an untyped splice, and PendingRnSplice] + ("implicit lifting", is_implicit_lifting, True, mkImplicitLiftingReporter) + + -- Next, solid equality errors + , given_eq_spec , ("insoluble2", utterly_wrong, True, mkGroupReporter mkEqErr) , ("skolem eq1", very_wrong, True, mkSkolReporter) , ("FixedRuntimeRep", is_FRR, True, mkGroupReporter mkFRRErr) , ("skolem eq2", skolem_eq, True, mkSkolReporter) + + -- Put custom type errors after solid equality errors. In #26255 we + -- had a custom error (T <= F alpha) which was suppressing a far more + -- informative (K Int ~ [K alpha]). That mismatch between K and [] is + -- definitely wrong; and if it was fixed we'd know alpha:=Int, and hence + -- perhaps be able to solve T <= F alpha, by reducing F Int. + -- + -- Custom errors should precede "non-tv eq", becuase if we have + -- () ~ TypeError blah + -- we want to report it as a custom error, /not/ as a mis-match + -- between TypeError and ()! + , ("custom_error", is_user_type_error, True, mkUserTypeErrorReporter) + -- (Handles TypeError and Unsatisfiable) + + -- "non-tv-eq": equalities (ty1 ~ ty2) where ty1 is not a tyvar , ("non-tv eq", non_tv_eq, True, mkSkolReporter) -- The only remaining equalities are alpha ~ ty, @@ -615,14 +636,6 @@ reportWanteds ctxt tc_lvl wc@(WC { wc_simple = simples, wc_impl = implics , ("Homo eqs", is_homo_equality, True, mkGroupReporter mkEqErr) , ("Other eqs", is_equality, True, mkGroupReporter mkEqErr) - -- Put custom type errors after solid equality errors. In #26255 we - -- had a custom error (T <= F alpha) which was suppressing a far more - -- informative (K Int ~ [K alpha]). That mismatch between K and [] is - -- definitely wrong; and if it was fixed we'd know alpha:=Int, and hence - -- perhaps be able to solve T <= F alpha, by reducing F Int. - , ("custom_error", is_user_type_error, True, mkUserTypeErrorReporter) - -- (Handles TypeError and Unsatisfiable) - , ("implicit lifting", is_implicit_lifting, True, mkImplicitLiftingReporter) ] -- report2: we suppress these if there are insolubles elsewhere in the tree View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/6dcf6444d49189a5081b78bb81d7714f... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/6dcf6444d49189a5081b78bb81d7714f... You're receiving this email because of your account on gitlab.haskell.org.