diff options
Diffstat (limited to 'compiler/GHC/Tc/Errors.hs')
| -rw-r--r-- | compiler/GHC/Tc/Errors.hs | 43 |
1 files changed, 25 insertions, 18 deletions
diff --git a/compiler/GHC/Tc/Errors.hs b/compiler/GHC/Tc/Errors.hs index 4f7c9dfea2..f6bb5f7d42 100644 --- a/compiler/GHC/Tc/Errors.hs +++ b/compiler/GHC/Tc/Errors.hs @@ -167,7 +167,6 @@ reportUnsolved wanted -- See Note [Deferring coercion errors to runtime] -- Used by solveEqualities for kind equalities -- (see Note [Fail fast on kind errors] in "GHC.Tc.Solver") --- and for simplifyDefault. reportAllUnsolved :: WantedConstraints -> TcM () reportAllUnsolved wanted = do { ev_binds <- newNoTcEvBinds @@ -378,15 +377,30 @@ deferringAnyBindings (CEC { cec_defer_type_errors = TypeError , cec_out_of_scope_holes = HoleError }) = False deferringAnyBindings _ = True --- | Transforms a 'ReportErrCtxt' into one that does not defer any bindings --- at all. -noDeferredBindings :: ReportErrCtxt -> ReportErrCtxt -noDeferredBindings ctxt = ctxt { cec_defer_type_errors = TypeError - , cec_expr_holes = HoleError - , cec_out_of_scope_holes = HoleError } - -{- Note [Suppressing error messages] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +maybeSwitchOffDefer :: EvBindsVar -> ReportErrCtxt -> ReportErrCtxt +-- Switch off defer-type-errors inside CoEvBindsVar +-- See Note [Failing equalities with no evidence bindings] +maybeSwitchOffDefer evb ctxt + | CoEvBindsVar{} <- evb + = ctxt { cec_defer_type_errors = TypeError + , cec_expr_holes = HoleError + , cec_out_of_scope_holes = HoleError } + | otherwise + = ctxt + +{- Note [Failing equalities with no evidence bindings] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If we go inside an implication that has no term evidence +(e.g. unifying under a forall), we can't defer type errors. You could +imagine using the /enclosing/ bindings (in cec_binds), but that may +not have enough stuff in scope for the bindings to be well typed. So +we just switch off deferred type errors altogether. See #14605. + +This is done by maybeSwitchOffDefer. It's also useful in one other +place: see Note [Wrapping failing kind equalities] in GHC.Tc.Solver. + +Note [Suppressing error messages] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The cec_suppress flag says "don't report any errors". Instead, just create evidence bindings (as usual). It's used when more important errors have occurred. @@ -445,15 +459,8 @@ reportImplic ctxt implic@(Implic { ic_skols = tvs implic' = implic { ic_skols = tvs' , ic_given = map (tidyEvVar env1) given , ic_info = info' } - ctxt1 | CoEvBindsVar{} <- evb = noDeferredBindings ctxt - | otherwise = ctxt - -- If we go inside an implication that has no term - -- evidence (e.g. unifying under a forall), we can't defer - -- type errors. You could imagine using the /enclosing/ - -- bindings (in cec_binds), but that may not have enough stuff - -- in scope for the bindings to be well typed. So we just - -- switch off deferred type errors altogether. See #14605. + ctxt1 = maybeSwitchOffDefer evb ctxt ctxt' = ctxt1 { cec_tidy = env1 , cec_encl = implic' : cec_encl ctxt |