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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2021-02-15 22:36:16 +0000 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2021-03-01 17:30:21 -0500 |
| commit | 7730713b747e66c93b4fe45478981a6e2ebfc7e2 (patch) | |
| tree | 64301948eb33d227cfc01aa57be2fdda60a2c13c /compiler/GHC/Tc/Errors.hs | |
| parent | 8c425bd83b3d622cd055ad015daca3539a6670de (diff) | |
| download | haskell-7730713b747e66c93b4fe45478981a6e2ebfc7e2.tar.gz | |
Unify result type earlier to improve error messages
Ticket #19364 helpfully points out that we do not currently take
advantage of pushing the result type of an application into the
arguments. This makes error messages notably less good.
The fix is rather easy: move the result-type unification step earlier.
It's even a bit more efficient; in the the checking case we now
do one less zonk.
See Note [Unify with expected type before typechecking arguments]
in GHC.Tc.Gen.App
This change generally improves error messages, but it made one worse:
typecheck/should_fail/T16204c. That led me to the realisation that
a good error can be replaced by a less-good one, which provoked
me to change GHC.Tc.Solver.Interact.inertsCanDischarge. It's
explained in the new Note [Combining equalities]
One other refactoring: I discovered that KindEqOrigin didn't need a
Maybe in its type -- a nice simplification.
Diffstat (limited to 'compiler/GHC/Tc/Errors.hs')
| -rw-r--r-- | compiler/GHC/Tc/Errors.hs | 17 |
1 files changed, 7 insertions, 10 deletions
diff --git a/compiler/GHC/Tc/Errors.hs b/compiler/GHC/Tc/Errors.hs index 0e687040e0..82dbd65848 100644 --- a/compiler/GHC/Tc/Errors.hs +++ b/compiler/GHC/Tc/Errors.hs @@ -1901,7 +1901,7 @@ tk_eq_msg ctxt ct ty1 ty2 orig@(TypeEqOrigin { uo_actual = act count_args ty = count isVisibleBinder $ fst $ splitPiTys ty tk_eq_msg ctxt ct ty1 ty2 - (KindEqOrigin cty1 mb_cty2 sub_o mb_sub_t_or_k) + (KindEqOrigin cty1 cty2 sub_o mb_sub_t_or_k) = vcat [ headline_eq_msg False ct ty1 ty2 , supplementary_msg ] where @@ -1911,17 +1911,15 @@ tk_eq_msg ctxt ct ty1 ty2 supplementary_msg = sdocOption sdocPrintExplicitCoercions $ \printExplicitCoercions -> - case mb_cty2 of - Just cty2 - | printExplicitCoercions - || not (cty1 `pickyEqType` cty2) - -> vcat [ hang (text "When matching" <+> sub_whats) - 2 (vcat [ ppr cty1 <+> dcolon <+> + if printExplicitCoercions + || not (cty1 `pickyEqType` cty2) + then vcat [ hang (text "When matching" <+> sub_whats) + 2 (vcat [ ppr cty1 <+> dcolon <+> ppr (tcTypeKind cty1) , ppr cty2 <+> dcolon <+> ppr (tcTypeKind cty2) ]) , mk_supplementary_ea_msg ctxt sub_t_or_k cty1 cty2 sub_o ] - _ -> text "When matching the kind of" <+> quotes (ppr cty1) + else text "When matching the kind of" <+> quotes (ppr cty1) tk_eq_msg _ _ _ _ _ = panic "typeeq_mismatch_msg" @@ -2873,8 +2871,7 @@ relevantBindings want_filtering ctxt ct -- For *kind* errors, report the relevant bindings of the -- enclosing *type* equality, because that's more useful for the programmer ; let extra_tvs = case tidy_orig of - KindEqOrigin t1 m_t2 _ _ -> tyCoVarsOfTypes $ - t1 : maybeToList m_t2 + KindEqOrigin t1 t2 _ _ -> tyCoVarsOfTypes [t1,t2] _ -> emptyVarSet ct_fvs = tyCoVarsOfCt ct `unionVarSet` extra_tvs |