Kill varEnvElts in zonkEnvIds

This localizes the nondeterminism that varEnvElts could
have introduced, so that it's obvious that it's benign.

Test Plan: ./validate

Reviewers: simonpj, austin, bgamari

Subscribers: thomie, simonmar

Differential Revision: https://phabricator.haskell.org/D2390

GHC Trac Issues: #4012

3 files changed, 14 insertions, 6 deletions

diff --git a/compiler/main/HscTypes.hs b/compiler/main/HscTypes.hs
index 99c51cd328..d297a83898 100644
--- a/compiler/main/HscTypes.hs
+++ b/compiler/main/HscTypes.hs
@@ -87,7 +87,7 @@ module HscTypes (
         TypeEnv, lookupType, lookupTypeHscEnv, mkTypeEnv, emptyTypeEnv,
         typeEnvFromEntities, mkTypeEnvWithImplicits,
         extendTypeEnv, extendTypeEnvList,
-        extendTypeEnvWithIds,
+        extendTypeEnvWithIds, plusTypeEnv,
         lookupTypeEnv,
         typeEnvElts, typeEnvTyCons, typeEnvIds, typeEnvPatSyns,
         typeEnvDataCons, typeEnvCoAxioms, typeEnvClasses,
@@ -1941,6 +1941,9 @@ extendTypeEnvWithIds :: TypeEnv -> [Id] -> TypeEnv
 extendTypeEnvWithIds env ids
   = extendNameEnvList env [(getName id, AnId id) | id <- ids]
 
+plusTypeEnv :: TypeEnv -> TypeEnv -> TypeEnv
+plusTypeEnv env1 env2 = plusNameEnv env1 env2
+
 -- | Find the 'TyThing' for the given 'Name' by using all the resources
 -- at our disposal: the compiled modules in the 'HomePackageTable' and the
 -- compiled modules in other packages that live in 'PackageTypeEnv'. Note
diff --git a/compiler/typecheck/TcHsSyn.hs b/compiler/typecheck/TcHsSyn.hs
index a50cb4d306..ad75033932 100644
--- a/compiler/typecheck/TcHsSyn.hs
+++ b/compiler/typecheck/TcHsSyn.hs
@@ -53,7 +53,9 @@ import TyCon
 import Coercion
 import ConLike
 import DataCon
+import HscTypes
 import Name
+import NameEnv
 import Var
 import VarSet
 import VarEnv
@@ -256,8 +258,11 @@ setZonkType :: ZonkEnv -> UnboundTyVarZonker -> ZonkEnv
 setZonkType (ZonkEnv _ ty_env id_env) zonk_ty
   = ZonkEnv zonk_ty ty_env id_env
 
-zonkEnvIds :: ZonkEnv -> [Id]
-zonkEnvIds (ZonkEnv _ _ id_env) = varEnvElts id_env
+zonkEnvIds :: ZonkEnv -> TypeEnv
+zonkEnvIds (ZonkEnv _ _ id_env) =
+  mkNameEnv [(getName id, AnId id) | id <- nonDetEltsUFM id_env]
+  -- It's OK to use nonDetEltsUFM here because we forget the ordering
+  -- immediately by creating a TypeEnv
 
 zonkIdOcc :: ZonkEnv -> TcId -> Id
 -- Ids defined in this module should be in the envt;
@@ -357,7 +362,7 @@ zonkTopLExpr e = zonkLExpr emptyZonkEnv e
 zonkTopDecls :: Bag EvBind
              -> LHsBinds TcId
              -> [LRuleDecl TcId] -> [LVectDecl TcId] -> [LTcSpecPrag] -> [LForeignDecl TcId]
-             -> TcM ([Id],
+             -> TcM (TypeEnv,
                      Bag EvBind,
                      LHsBinds Id,
                      [LForeignDecl Id],
diff --git a/compiler/typecheck/TcRnDriver.hs b/compiler/typecheck/TcRnDriver.hs
index 48b055b85a..c551356ad3 100644
--- a/compiler/typecheck/TcRnDriver.hs
+++ b/compiler/typecheck/TcRnDriver.hs
@@ -521,13 +521,13 @@ tcRnSrcDecls explicit_mod_hdr decls
                          tcg_fords     = fords } = tcg_env
             ; all_ev_binds = cur_ev_binds `unionBags` new_ev_binds } ;
 
-      ; (bind_ids, ev_binds', binds', fords', imp_specs', rules', vects')
+      ; (bind_env, ev_binds', binds', fords', imp_specs', rules', vects')
             <- {-# SCC "zonkTopDecls" #-}
                zonkTopDecls all_ev_binds binds rules vects
                             imp_specs fords ;
       ; traceTc "Tc11" empty
 
-      ; let { final_type_env = extendTypeEnvWithIds type_env bind_ids
+      ; let { final_type_env = plusTypeEnv type_env bind_env
             ; tcg_env' = tcg_env { tcg_binds    = binds',
                                    tcg_ev_binds = ev_binds',
                                    tcg_imp_specs = imp_specs',