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| author | Ziyang Liu <unsafeFixIO@gmail.com> | 2021-10-19 12:39:58 -0700 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2021-10-29 05:01:50 -0400 |
| commit | 522eab3f056905db47110c73dac1833f4a2880f2 (patch) | |
| tree | 2d9989fa00bf090d3b034ee6d272a5057aadc109 /compiler/GHC/Tc/Errors.hs | |
| parent | 638f65482ca5265c268aa97abfcc14cdc27e46ba (diff) | |
| download | haskell-522eab3f056905db47110c73dac1833f4a2880f2.tar.gz | |
Show family TyCons in mk_dict_error in the case of a single match
Diffstat (limited to 'compiler/GHC/Tc/Errors.hs')
| -rw-r--r-- | compiler/GHC/Tc/Errors.hs | 28 |
1 files changed, 26 insertions, 2 deletions
diff --git a/compiler/GHC/Tc/Errors.hs b/compiler/GHC/Tc/Errors.hs index ff6525f24d..7177f7347f 100644 --- a/compiler/GHC/Tc/Errors.hs +++ b/compiler/GHC/Tc/Errors.hs @@ -46,6 +46,7 @@ import GHC.Types.Name.Set import GHC.Types.SrcLoc import GHC.Types.Basic import GHC.Types.Error +import GHC.Types.Unique.Set ( nonDetEltsUniqSet ) import GHC.Rename.Unbound ( unknownNameSuggestions, WhatLooking(..) ) import GHC.Unit.Module @@ -2491,6 +2492,17 @@ mkDictErr ctxt cts -- but we really only want to report the latter elim_superclasses cts = mkMinimalBySCs ctPred cts +-- [Note: mk_dict_err] +-- ~~~~~~~~~~~~~~~~~~~ +-- Different dictionary error messages are reported depending on the number of +-- matches and unifiers: +-- +-- - No matches, regardless of unifiers: report "No instance for ...". +-- - Two or more matches, regardless of unifiers: report "Overlapping instances for ...", +-- and show the matching and unifying instances. +-- - One match, one or more unifiers: report "Overlapping instances for", show the +-- matching and unifying instances, and say "The choice depends on the instantion of ..., +-- and the result of evaluating ...". mk_dict_err :: HasCallStack => ReportErrCtxt -> (Ct, ClsInstLookupResult) -> TcM SDoc -- Report an overlap error if this class constraint results @@ -2680,12 +2692,24 @@ mk_dict_err ctxt@(CEC {cec_encl = implics}) (ct, (matches, unifiers, unsafe_over , nest 2 (vcat (pp_givens useful_givens))] , ppWhen (isSingleton matches) $ - parens (vcat [ text "The choice depends on the instantiation of" <+> - quotes (pprWithCommas ppr (tyCoVarsOfTypesList tys)) + parens (vcat [ ppUnless (null tyCoVars) $ + text "The choice depends on the instantiation of" <+> + quotes (pprWithCommas ppr tyCoVars) + , ppUnless (null famTyCons) $ + if (null tyCoVars) + then + text "The choice depends on the result of evaluating" <+> + quotes (pprWithCommas ppr famTyCons) + else + text "and the result of evaluating" <+> + quotes (pprWithCommas ppr famTyCons) , ppWhen (null (matching_givens)) $ vcat [ text "To pick the first instance above, use IncoherentInstances" , text "when compiling the other instance declarations"] ])] + where + tyCoVars = tyCoVarsOfTypesList tys + famTyCons = filter isFamilyTyCon $ concatMap (nonDetEltsUniqSet . tyConsOfType) tys matching_givens = mapMaybe matchable useful_givens |