diff options
| -rw-r--r-- | compiler/GHC/Tc/Errors/Ppr.hs | 40 | ||||
| -rw-r--r-- | testsuite/tests/impredicative/T17332.stderr | 2 |
2 files changed, 24 insertions, 18 deletions
diff --git a/compiler/GHC/Tc/Errors/Ppr.hs b/compiler/GHC/Tc/Errors/Ppr.hs index 84eea92b01..406cb87b24 100644 --- a/compiler/GHC/Tc/Errors/Ppr.hs +++ b/compiler/GHC/Tc/Errors/Ppr.hs @@ -1818,30 +1818,36 @@ pprTcSolverReportMsg ctxt (CouldNotDeduce useful_givens (item :| others) mb_extr where main_msg | null useful_givens - = addArising orig no_instance_msg + = addArising orig (no_instance_msg <+> missing) | otherwise - = vcat [ addArising orig no_deduce_msg - , vcat (pp_givens useful_givens) ] + = vcat (addArising orig (no_deduce_msg <+> missing) + : pp_givens useful_givens) + supplementary = case mb_extra of Nothing -> Left [] Just (CND_Extra level ty1 ty2) -> mk_supplementary_ea_msg ctxt level ty1 ty2 orig - (wanted, wanteds) = (errorItemPred item, map errorItemPred others) orig = errorItemOrigin item - no_instance_msg - | null others - , Just (tc, _) <- splitTyConApp_maybe wanted - , isClassTyCon tc - -- Don't say "no instance" for a constraint such as "c" for a type variable c. - = text "No instance for" <+> pprParendType wanted - | otherwise - = text "Could not solve:" <+> pprTheta wanteds - no_deduce_msg - | null others - = text "Could not deduce" <+> pprParendType wanted - | otherwise - = text "Could not deduce:" <+> pprTheta wanteds + wanteds = map errorItemPred (item:others) + + no_instance_msg = + case wanteds of + [wanted] | Just (tc, _) <- splitTyConApp_maybe wanted + -- Don't say "no instance" for a constraint such as "c" for a type variable c. + , isClassTyCon tc -> text "No instance for" + _ -> text "Could not solve:" + + no_deduce_msg = + case wanteds of + [_wanted] -> text "Could not deduce" + _ -> text "Could not deduce:" + + missing = + case wanteds of + [wanted] -> pprParendType wanted + _ -> pprTheta wanteds + pprTcSolverReportMsg ctxt (AmbiguityPreventsSolvingCt item ambigs) = pprTcSolverReportInfo ctxt (Ambiguity True ambigs) <+> pprArising (errorItemOrigin item) $$ diff --git a/testsuite/tests/impredicative/T17332.stderr b/testsuite/tests/impredicative/T17332.stderr index 7d0615ad4e..f614c289ce 100644 --- a/testsuite/tests/impredicative/T17332.stderr +++ b/testsuite/tests/impredicative/T17332.stderr @@ -1,5 +1,5 @@ T17332.hs:13:7: error: - • Could not solve: () arising from a use of ‘MkDict’ + • Could not solve: a arising from a use of ‘MkDict’ • In the expression: MkDict In an equation for ‘aux’: aux = MkDict |