diff options
Diffstat (limited to 'compiler/GHC/Tc/Errors.hs')
| -rw-r--r-- | compiler/GHC/Tc/Errors.hs | 72 |
1 files changed, 44 insertions, 28 deletions
diff --git a/compiler/GHC/Tc/Errors.hs b/compiler/GHC/Tc/Errors.hs index d597c95b72..93c047ca32 100644 --- a/compiler/GHC/Tc/Errors.hs +++ b/compiler/GHC/Tc/Errors.hs @@ -69,7 +69,7 @@ import GHC.Utils.FV ( fvVarList, unionFV ) import Control.Monad ( when ) import Data.Foldable ( toList ) -import Data.List ( partition, mapAccumL, nub, sortBy, unfoldr ) +import Data.List ( partition, mapAccumL, sortBy, unfoldr ) import {-# SOURCE #-} GHC.Tc.Errors.Hole ( findValidHoleFits ) @@ -215,7 +215,13 @@ report_unsolved type_errors expr_holes -- If we are deferring we are going to need /all/ evidence around, -- including the evidence produced by unflattening (zonkWC) ; let tidy_env = tidyFreeTyCoVars emptyTidyEnv free_tvs - free_tvs = tyCoVarsOfWCList wanted + free_tvs = filterOut isCoVar $ + tyCoVarsOfWCList wanted + -- tyCoVarsOfWC returns free coercion *holes*, even though + -- they are "bound" by other wanted constraints. They in + -- turn may mention variables bound further in, which makes + -- no sense. Really we should not return those holes at all; + -- for now we just filter them out. ; traceTc "reportUnsolved (after zonking):" $ vcat [ text "Free tyvars:" <+> pprTyVars free_tvs @@ -832,7 +838,11 @@ eq_lhs_type ct1 ct2 _ -> pprPanic "mkSkolReporter" (ppr ct1 $$ ppr ct2) cmp_loc :: Ct -> Ct -> Ordering -cmp_loc ct1 ct2 = ctLocSpan (ctLoc ct1) `compare` ctLocSpan (ctLoc ct2) +cmp_loc ct1 ct2 = get ct1 `compare` get ct2 + where + get ct = realSrcSpanStart (ctLocSpan (ctLoc ct)) + -- Reduce duplication by reporting only one error from each + -- /starting/ location even if the end location differs reportGroup :: (ReportErrCtxt -> [Ct] -> TcM ErrMsg) -> Reporter reportGroup mk_err ctxt cts = @@ -1451,14 +1461,15 @@ mkTyVarEqErr dflags ctxt report ct tv1 ty2 ; mkTyVarEqErr' dflags ctxt report ct tv1 ty2 } mkTyVarEqErr' dflags ctxt report ct tv1 ty2 - | isUserSkolem ctxt tv1 -- ty2 won't be a meta-tyvar; we would have - -- swapped in Solver.Canonical.canEqTyVarHomo + | isSkolemTyVar tv1 -- ty2 won't be a meta-tyvar; we would have + -- swapped in Solver.Canonical.canEqTyVarHomo || isTyVarTyVar tv1 && not (isTyVarTy ty2) || ctEqRel ct == ReprEq -- The cases below don't really apply to ReprEq (except occurs check) = mkErrorMsgFromCt ctxt ct $ mconcat [ headline_msg , extraTyVarEqInfo ctxt tv1 ty2 + , suggestAddSig ctxt ty1 ty2 , report ] @@ -1594,17 +1605,6 @@ mkEqInfoMsg ct ty1 ty2 <+> text "is a non-injective type family" | otherwise = empty -isUserSkolem :: ReportErrCtxt -> TcTyVar -> Bool --- See Note [Reporting occurs-check errors] -isUserSkolem ctxt tv - = isSkolemTyVar tv && any is_user_skol_tv (cec_encl ctxt) - where - is_user_skol_tv (Implic { ic_skols = sks, ic_info = skol_info }) - = tv `elem` sks && is_user_skol_info skol_info - - is_user_skol_info (InferSkol {}) = False - is_user_skol_info _ = True - misMatchOrCND :: Bool -> ReportErrCtxt -> Ct -> TcType -> TcType -> Report -- If oriented then ty1 is actual, ty2 is expected @@ -1724,21 +1724,29 @@ extraTyVarInfo ctxt tv suggestAddSig :: ReportErrCtxt -> TcType -> TcType -> Report -- See Note [Suggest adding a type signature] -suggestAddSig ctxt ty1 ty2 - | null inferred_bndrs +suggestAddSig ctxt ty1 _ty2 + | null inferred_bndrs -- No let-bound inferred binders in context = mempty | [bndr] <- inferred_bndrs = important $ text "Possible fix: add a type signature for" <+> quotes (ppr bndr) | otherwise = important $ text "Possible fix: add type signatures for some or all of" <+> (ppr inferred_bndrs) where - inferred_bndrs = nub (get_inf ty1 ++ get_inf ty2) - get_inf ty | Just tv <- tcGetTyVar_maybe ty - , isSkolemTyVar tv - , ((InferSkol prs, _) : _) <- getSkolemInfo (cec_encl ctxt) [tv] - = map fst prs - | otherwise - = [] + inferred_bndrs = case tcGetTyVar_maybe ty1 of + Just tv | isSkolemTyVar tv -> find (cec_encl ctxt) False tv + _ -> [] + + -- 'find' returns the binders of an InferSkol for 'tv', + -- provided there is an intervening implication with + -- ic_no_eqs = False (i.e. a GADT match) + find [] _ _ = [] + find (implic:implics) seen_eqs tv + | tv `elem` ic_skols implic + , InferSkol prs <- ic_info implic + , seen_eqs + = map fst prs + | otherwise + = find implics (seen_eqs || not (ic_no_eqs implic)) tv -------------------- misMatchMsg :: ReportErrCtxt -> Ct -> TcType -> TcType -> Report @@ -2183,9 +2191,8 @@ sameOccExtra ty1 ty2 mod = nameModule nm loc = nameSrcSpan nm -{- -Note [Suggest adding a type signature] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +{- Note [Suggest adding a type signature] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The OutsideIn algorithm rejects GADT programs that don't have a principal type, and indeed some that do. Example: data T a where @@ -2199,6 +2206,15 @@ untouchable type variable. So suggestAddSig sees if the offending type variable is bound by an *inferred* signature, and suggests adding a declared signature instead. +More specifically, we suggest adding a type sig if we have p ~ ty, and +p is a skolem bound by an InferSkol. Those skolems were created from +unification variables in simplifyInfer. Why didn't we unify? It must +have been because of an intervening GADT or existential, making it +untouchable. Either way, a type signature would help. For GADTs, it +might make it typeable; for existentials the attempt to write a +signature will fail -- or at least will produce a better error message +next time + This initially came up in #8968, concerning pattern synonyms. Note [Disambiguating (X ~ X) errors] |