Added ExactSizeIterator bound to return types

This reverts commit d97379a96e.

src/librustc/infer/canonical/query_response.rs

@@ -574,7 +574,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         unsubstituted_region_constraints: &'a [QueryOutlivesConstraint<'tcx>],
         result_subst: &'a CanonicalVarValues<'tcx>,
-    ) -> impl Iterator<Item = PredicateObligation<'tcx>> + ExactSizeIterator + 'a + Captures<'tcx> {
+    ) -> impl Iterator<Item = PredicateObligation<'tcx>> + 'a + Captures<'tcx> {
         unsubstituted_region_constraints
             .iter()
             .map(move |constraint| {

src/librustc/infer/outlives/free_region_map.rs

@@ -11,7 +11,7 @@ pub struct FreeRegionMap<'tcx> {
 }
 
 impl<'tcx> FreeRegionMap<'tcx> {
-    pub fn elements(&self) -> impl Iterator<Item=&Region<'tcx>> + ExactSizeIterator {
+    pub fn elements(&self) -> impl Iterator<Item=&Region<'tcx>> {
         self.relation.elements()
     }
 

src/librustc/mir/mod.rs

@@ -284,7 +284,7 @@ impl<'tcx> Body<'tcx> {
     #[inline]
     pub fn args_iter(&self) -> impl Iterator<Item = Local> + ExactSizeIterator {
         let arg_count = self.arg_count;
-        (1..arg_count+1).map(Local::new)
+        (1..arg_count + 1).map(Local::new)
     }
 
     /// Returns an iterator over all user-defined variables and compiler-generated temporaries (all

src/librustc/traits/specialize/specialization_graph.rs

@@ -414,9 +414,7 @@ impl<'tcx> Node {
     }
 
     /// Iterate over the items defined directly by the given (impl or trait) node.
-    pub fn items(&self, tcx: TyCtxt<'tcx>)
-        -> impl Iterator<Item = ty::AssocItem> + ExactSizeIterator + Clone + 'tcx
-    {
+    pub fn items(&self, tcx: TyCtxt<'tcx>) -> ty::AssocItemsIterator<'tcx> {
         tcx.associated_items(self.def_id())
     }
 

src/librustc/ty/mod.rs

@@ -2376,7 +2376,7 @@ impl<'tcx> AdtDef {
     pub fn discriminants(
         &'tcx self,
         tcx: TyCtxt<'tcx>,
-    ) -> impl Iterator<Item = (VariantIdx, Discr<'tcx>)> + ExactSizeIterator + Captures<'tcx> {
+    ) -> impl Iterator<Item = (VariantIdx, Discr<'tcx>)> + Captures<'tcx> {
         let repr_type = self.repr.discr_type();
         let initial = repr_type.initial_discriminant(tcx);
         let mut prev_discr = None::<Discr<'tcx>>;
@@ -2740,9 +2740,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Returns an iterator of the `DefId`s for all body-owners in this
     /// crate. If you would prefer to iterate over the bodies
     /// themselves, you can do `self.hir().krate().body_ids.iter()`.
-    pub fn body_owners(self)
-        -> impl Iterator<Item = DefId> + ExactSizeIterator + Captures<'tcx> + 'tcx
-    {
+    pub fn body_owners(self) -> impl Iterator<Item = DefId> + Captures<'tcx> + 'tcx {
         self.hir().krate()
                   .body_ids
                   .iter()
@@ -3118,12 +3116,6 @@ impl Iterator for AssocItemsIterator<'_> {
     }
 }
 
-impl ExactSizeIterator for AssocItemsIterator<'_> {
-    fn len(&self) -> usize {
-        self.def_ids.len() - self.next_index
-    }
-}
-
 fn associated_item(tcx: TyCtxt<'_>, def_id: DefId) -> AssocItem {
     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
     let parent_id = tcx.hir().get_parent_item(id);

src/librustc/ty/sty.rs

@@ -345,7 +345,7 @@ impl<'tcx> ClosureSubsts<'tcx> {
         self,
         def_id: DefId,
         tcx: TyCtxt<'_>,
-    ) -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + 'tcx {
+    ) -> impl Iterator<Item = Ty<'tcx>> + 'tcx {
         let SplitClosureSubsts { upvar_kinds, .. } = self.split(def_id, tcx);
         upvar_kinds.iter().map(|t| {
             if let GenericArgKind::Type(ty) = t.unpack() {
@@ -433,7 +433,7 @@ impl<'tcx> GeneratorSubsts<'tcx> {
         self,
         def_id: DefId,
         tcx: TyCtxt<'_>,
-    ) -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + 'tcx {
+    ) -> impl Iterator<Item = Ty<'tcx>> + 'tcx {
         let SplitGeneratorSubsts { upvar_kinds, .. } = self.split(def_id, tcx);
         upvar_kinds.iter().map(|t| {
             if let GenericArgKind::Type(ty) = t.unpack() {
@@ -551,7 +551,7 @@ impl<'tcx> GeneratorSubsts<'tcx> {
         self,
         def_id: DefId,
         tcx: TyCtxt<'tcx>,
-    ) -> impl Iterator<Item = impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + Captures<'tcx>> {
+    ) -> impl Iterator<Item = impl Iterator<Item = Ty<'tcx>> + Captures<'tcx>> {
         let layout = tcx.generator_layout(def_id);
         layout.variant_fields.iter().map(move |variant| {
             variant.iter().map(move |field| {
@@ -563,9 +563,7 @@ impl<'tcx> GeneratorSubsts<'tcx> {
     /// This is the types of the fields of a generator which are not stored in a
     /// variant.
     #[inline]
-    pub fn prefix_tys(self, def_id: DefId, tcx: TyCtxt<'tcx>)
-        -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator
-    {
+    pub fn prefix_tys(self, def_id: DefId, tcx: TyCtxt<'tcx>) -> impl Iterator<Item = Ty<'tcx>> {
         self.upvar_tys(def_id, tcx)
     }
 }
@@ -582,7 +580,7 @@ impl<'tcx> UpvarSubsts<'tcx> {
         self,
         def_id: DefId,
         tcx: TyCtxt<'tcx>,
-    ) -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + 'tcx {
+    ) -> impl Iterator<Item = Ty<'tcx>> + 'tcx {
         let upvar_kinds = match self {
             UpvarSubsts::Closure(substs) => substs.as_closure().split(def_id, tcx).upvar_kinds,
             UpvarSubsts::Generator(substs) => substs.as_generator().split(def_id, tcx).upvar_kinds,