Make warnings come out in deterministic order

Fixes Trac #1053

diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index fe7b1d8..da18ef1 100644 (file)
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -274,11 +274,11 @@ tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
     checkValidAndMissingATs clas inst_tys ats
       = do { -- Issue a warning for each class AT that is not defined in this
             -- instance.
-          ; let classDefATs = listToNameSet . map tyConName . classATs $ clas
-                 definedATs  = listToNameSet . map (tcdName.unLoc.fst)  $ ats
-                omitted     = classDefATs `minusNameSet` definedATs
+          ; let class_ats   = map tyConName (classATs clas)
+                 defined_ats = listToNameSet . map (tcdName.unLoc.fst)  $ ats
+                omitted     = filterOut (`elemNameSet` defined_ats) class_ats
           ; warn <- doptM Opt_WarnMissingMethods
-          ; mapM_ (warnTc warn . omittedATWarn) (nameSetToList omitted)
+          ; mapM_ (warnTc warn . omittedATWarn) omitted
           
             -- Ensure that all AT indexes that correspond to class parameters
             -- coincide with the types in the instance head.  All remaining