- | null matching_fields
- = addErrTc (badFieldCon name field_label) `thenNF_Tc_`
- tc_fields field_tys rpats
-
- | otherwise
- = ASSERT( null extras )
- tc_fields field_tys rpats `thenTc` \ (rpats', lie_req1, tvs1, ids1, lie_avail1) ->
-
- tcLookupValue field_label `thenNF_Tc` \ sel_id ->
- tcPat tc_bndr rhs_pat rhs_ty `thenTc` \ (rhs_pat', lie_req2, tvs2, ids2, lie_avail2) ->
+ = tc_fields field_tys rpats `thenTc` \ (rpats', lie_req1, tvs1, ids1, lie_avail1) ->
+
+ (case [ty | (f,ty) <- field_tys, f == field_label] of
+
+ -- No matching field; chances are this field label comes from some
+ -- other record type (or maybe none). As well as reporting an
+ -- error we still want to typecheck the pattern, principally to
+ -- make sure that all the variables it binds are put into the
+ -- environment, else the type checker crashes later:
+ -- f (R { foo = (a,b) }) = a+b
+ -- If foo isn't one of R's fields, we don't want to crash when
+ -- typechecking the "a+b".
+ [] -> addErrTc (badFieldCon name field_label) `thenNF_Tc_`
+ newTyVarTy boxedTypeKind `thenNF_Tc_`
+ returnTc (error "Bogus selector Id", pat_ty)
+
+ -- The normal case, when the field comes from the right constructor
+ (pat_ty : extras) ->
+ ASSERT( null extras )
+ tcLookupValue field_label `thenNF_Tc` \ sel_id ->
+ returnTc (sel_id, pat_ty)
+ ) `thenTc` \ (sel_id, pat_ty) ->
+
+ tcPat tc_bndr rhs_pat pat_ty `thenTc` \ (rhs_pat', lie_req2, tvs2, ids2, lie_avail2) ->