diff options
Diffstat (limited to 'compiler/GHC/Rename/Utils.hs')
| -rw-r--r-- | compiler/GHC/Rename/Utils.hs | 53 |
1 files changed, 48 insertions, 5 deletions
diff --git a/compiler/GHC/Rename/Utils.hs b/compiler/GHC/Rename/Utils.hs index 6bced4930d..2edd8a2663 100644 --- a/compiler/GHC/Rename/Utils.hs +++ b/compiler/GHC/Rename/Utils.hs @@ -492,17 +492,48 @@ wildcardDoc herald = $$ nest 2 (text "Possible fix" <> colon <+> text "omit the" <+> quotes (text "..")) -addNameClashErrRn :: RdrName -> [GlobalRdrElt] -> RnM () +{- +Note [Skipping ambiguity errors at use sites of local declarations] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In general, we do not report ambiguous occurrences at use sites where all the +clashing names are defined locally, because the error will have been reported at +the definition site, and we want to avoid an error cascade. + +However, when DuplicateRecordFields is enabled, it is possible to define the +same field name multiple times, so we *do* need to report an error at the use +site when there is ambiguity between multiple fields. Moreover, when +NoFieldSelectors is enabled, it is possible to define a field with the same name +as a non-field, so again we need to report ambiguity at the use site. + +We can skip reporting an ambiguity error whenever defining the GREs must have +yielded a duplicate declarations error. More precisely, we can skip if: + + * there are at least two non-fields amongst the GREs; or + + * there are at least two fields amongst the GREs, and DuplicateRecordFields is + *disabled*; or + + * there is at least one non-field, at least one field, and NoFieldSelectors is + *disabled*. + +These conditions ensure that a duplicate local declaration will have been +reported. See also Note [Reporting duplicate local declarations] in +GHC.Rename.Names). + +-} + +addNameClashErrRn :: RdrName -> NE.NonEmpty GlobalRdrElt -> RnM () addNameClashErrRn rdr_name gres - | all isLocalGRE gres && not (all isRecFldGRE gres) - -- If there are two or more *local* defns, we'll have reported - = return () -- that already, and we don't want an error cascade + | all isLocalGRE gres && can_skip + -- If there are two or more *local* defns, we'll usually have reported that + -- already, and we don't want an error cascade. + = return () | otherwise = addErr (vcat [ text "Ambiguous occurrence" <+> quotes (ppr rdr_name) , text "It could refer to" , nest 3 (vcat (msg1 : msgs)) ]) where - (np1:nps) = gres + np1 NE.:| nps = gres msg1 = text "either" <+> ppr_gre np1 msgs = [text " or" <+> ppr_gre np | np <- nps] ppr_gre gre = sep [ pp_greMangledName gre <> comma @@ -533,6 +564,18 @@ addNameClashErrRn rdr_name gres = pprPanic "addNameClassErrRn" (ppr gre $$ ppr iss) -- Invariant: either 'lcl' is True or 'iss' is non-empty + -- If all the GREs are defined locally, can we skip reporting an ambiguity + -- error at use sites, because it will have been reported already? See + -- Note [Skipping ambiguity errors at use sites of local declarations] + can_skip = num_non_flds >= 2 + || (num_flds >= 2 && not (isDuplicateRecFldGRE (head flds))) + || (num_non_flds >= 1 && num_flds >= 1 + && not (isNoFieldSelectorGRE (head flds))) + (flds, non_flds) = NE.partition isRecFldGRE gres + num_flds = length flds + num_non_flds = length non_flds + + shadowedNameWarn :: OccName -> [SDoc] -> SDoc shadowedNameWarn occ shadowed_locs = sep [text "This binding for" <+> quotes (ppr occ) |