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| author | simonpj@microsoft.com <unknown> | 2010-10-08 09:43:48 +0000 |
|---|---|---|
| committer | simonpj@microsoft.com <unknown> | 2010-10-08 09:43:48 +0000 |
| commit | 5e86045ae5f90d9138e395fde5792e50ac8f8afd (patch) | |
| tree | 933ce346909db9e6202b69481cd3071461bb7922 /compiler | |
| parent | 2b0c363dcaa51295571bc72a2fa0b72bf0ff353a (diff) | |
| download | haskell-5e86045ae5f90d9138e395fde5792e50ac8f8afd.tar.gz | |
Suppress knock-on typechecker errors
The error cascade caused puzzling errors in T4093b, and
suppressing some seems like a good plan. Very few test
outputs change.
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/typecheck/TcErrors.lhs | 23 |
1 files changed, 17 insertions, 6 deletions
diff --git a/compiler/typecheck/TcErrors.lhs b/compiler/typecheck/TcErrors.lhs index 293b3a7958..0ade93c29f 100644 --- a/compiler/typecheck/TcErrors.lhs +++ b/compiler/typecheck/TcErrors.lhs @@ -33,7 +33,7 @@ import Outputable import DynFlags import StaticFlags( opt_PprStyle_Debug ) import Data.List( partition ) -import Control.Monad( unless ) +import Control.Monad( when, unless ) \end{code} %************************************************************************ @@ -117,17 +117,28 @@ reportTidyImplic ctxt implic reportTidyWanteds :: ReportErrCtxt -> WantedConstraints -> TcM () reportTidyWanteds ctxt unsolved - = do { let (flats, implics) = splitWanteds unsolved - (ambigs, others) = partition is_ambiguous (bagToList flats) - ; groupErrs (reportFlat ctxt) others - ; mapBagM_ (reportTidyImplic ctxt) implics - ; ifErrsM (return ()) $ + = do { let (flats, implics) = splitWanteds unsolved + (ambigs, non_ambigs) = partition is_ambiguous (bagToList flats) + (tv_eqs, others) = partition is_tv_eq non_ambigs + + ; groupErrs (reportEqErrs ctxt) tv_eqs + ; when (null tv_eqs) $ groupErrs (reportFlat ctxt) others + ; when (null tv_eqs) $ mapBagM_ (reportTidyImplic ctxt) implics + -- Only report ambiguity if no other errors happened -- See Note [Avoiding spurious errors] + ; when (isEmptyBag implics && null non_ambigs) $ reportAmbigErrs ctxt skols ambigs } where skols = foldr (unionVarSet . ic_skols) emptyVarSet (cec_encl ctxt) + -- Report equalities of form (a~ty) first. They are usually + -- skolem-equalities, and they cause confusing knock-on + -- effects in other errors; see test T4093b. + is_tv_eq c | EqPred ty1 ty2 <- wantedEvVarPred c + = tcIsTyVarTy ty1 || tcIsTyVarTy ty2 + | otherwise = False + -- Treat it as "ambiguous" if -- (a) it is a class constraint -- (b) it constrains only type variables |