Added ExactSizeIterator bound to return types

in librustc in several places

Author: Bartłomiej Kuras

src/bootstrap/lib.rs

@@ -1274,7 +1274,7 @@ impl Build {
         t!(fs::remove_dir_all(dir))
     }
 
-    fn read_dir(&self, dir: &Path) -> impl Iterator<Item=fs::DirEntry> {
+    fn read_dir(&self, dir: &Path) -> impl Iterator<Item=fs::DirEntry> + ExactSizeIterator {
         let iter = match fs::read_dir(dir) {
             Ok(v) => v,
             Err(_) if self.config.dry_run => return vec![].into_iter(),

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>> + 'a + Captures<'tcx> {
+    ) -> impl Iterator<Item = PredicateObligation<'tcx>> + ExactSizeIterator + '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>> {
+    pub fn elements(&self) -> impl Iterator<Item=&Region<'tcx>> + ExactSizeIterator {
         self.relation.elements()
     }
 

src/librustc/mir/mod.rs

@@ -282,15 +282,15 @@ impl<'tcx> Body<'tcx> {
 
     /// Returns an iterator over all function arguments.
     #[inline]
-    pub fn args_iter(&self) -> impl Iterator<Item = Local> {
+    pub fn args_iter(&self) -> impl Iterator<Item = Local> + ExactSizeIterator {
         let arg_count = self.arg_count;
-        (1..=arg_count).map(Local::new)
+        (1..arg_count+1).map(Local::new)
     }
 
     /// Returns an iterator over all user-defined variables and compiler-generated temporaries (all
     /// locals that are neither arguments nor the return place).
     #[inline]
-    pub fn vars_and_temps_iter(&self) -> impl Iterator<Item = Local> {
+    pub fn vars_and_temps_iter(&self) -> impl Iterator<Item = Local> + ExactSizeIterator {
         let arg_count = self.arg_count;
         let local_count = self.local_decls.len();
         (arg_count + 1..local_count).map(Local::new)
@@ -2384,11 +2384,15 @@ impl<'tcx> UserTypeProjections {
         UserTypeProjections { contents: projs.collect() }
     }
 
-    pub fn projections_and_spans(&self) -> impl Iterator<Item = &(UserTypeProjection, Span)> {
+    pub fn projections_and_spans(&self)
+        -> impl Iterator<Item = &(UserTypeProjection, Span)> + ExactSizeIterator
+    {
         self.contents.iter()
     }
 
-    pub fn projections(&self) -> impl Iterator<Item = &UserTypeProjection> {
+    pub fn projections(&self)
+        -> impl Iterator<Item = &UserTypeProjection> + ExactSizeIterator
+    {
         self.contents.iter().map(|&(ref user_type, _span)| user_type)
     }
 

src/librustc/traits/specialize/specialization_graph.rs

@@ -414,7 +414,9 @@ impl<'tcx> Node {
     }
 
     /// Iterate over the items defined directly by the given (impl or trait) node.
-    pub fn items(&self, tcx: TyCtxt<'tcx>) -> ty::AssocItemsIterator<'tcx> {
+    pub fn items(&self, tcx: TyCtxt<'tcx>)
+        -> impl Iterator<Item = ty::AssocItem> + ExactSizeIterator + Clone + '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>)> + Captures<'tcx> {
+    ) -> impl Iterator<Item = (VariantIdx, Discr<'tcx>)> + ExactSizeIterator + Captures<'tcx> {
         let repr_type = self.repr.discr_type();
         let initial = repr_type.initial_discriminant(tcx);
         let mut prev_discr = None::<Discr<'tcx>>;
@@ -2740,7 +2740,9 @@ 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> + Captures<'tcx> + 'tcx {
+    pub fn body_owners(self)
+        -> impl Iterator<Item = DefId> + ExactSizeIterator + Captures<'tcx> + 'tcx
+    {
         self.hir().krate()
                   .body_ids
                   .iter()
@@ -3116,6 +3118,12 @@ 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>> + 'tcx {
+    ) -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + '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>> + 'tcx {
+    ) -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + '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>> + Captures<'tcx>> {
+    ) -> impl Iterator<Item = impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + Captures<'tcx>> {
         let layout = tcx.generator_layout(def_id);
         layout.variant_fields.iter().map(move |variant| {
             variant.iter().map(move |field| {
@@ -563,7 +563,9 @@ 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>> {
+    pub fn prefix_tys(self, def_id: DefId, tcx: TyCtxt<'tcx>)
+        -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator
+    {
         self.upvar_tys(def_id, tcx)
     }
 }
@@ -580,7 +582,7 @@ impl<'tcx> UpvarSubsts<'tcx> {
         self,
         def_id: DefId,
         tcx: TyCtxt<'tcx>,
-    ) -> impl Iterator<Item = Ty<'tcx>> + 'tcx {
+    ) -> impl Iterator<Item = Ty<'tcx>> + ExactSizeIterator + '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,

src/librustc_data_structures/graph/implementation/mod.rs

@@ -186,14 +186,18 @@ impl<N: Debug, E: Debug> Graph<N, E> {
 
     // # Iterating over nodes, edges
 
-    pub fn enumerated_nodes(&self) -> impl Iterator<Item = (NodeIndex, &Node<N>)> {
+    pub fn enumerated_nodes(&self)
+        -> impl Iterator<Item = (NodeIndex, &Node<N>)> + ExactSizeIterator
+    {
         self.nodes
             .iter()
             .enumerate()
             .map(|(idx, n)| (NodeIndex(idx), n))
     }
 
-    pub fn enumerated_edges(&self) -> impl Iterator<Item = (EdgeIndex, &Edge<E>)> {
+    pub fn enumerated_edges(&self)
+        -> impl Iterator<Item = (EdgeIndex, &Edge<E>)> + ExactSizeIterator
+    {
         self.edges
             .iter()
             .enumerate()

src/librustc_data_structures/transitive_relation.rs

@@ -60,7 +60,7 @@ impl<T: Clone + Debug + Eq + Hash> TransitiveRelation<T> {
         self.edges.is_empty()
     }
 
-    pub fn elements(&self) -> impl Iterator<Item=&T> {
+    pub fn elements(&self) -> impl Iterator<Item=&T> + ExactSizeIterator {
         self.elements.iter()
     }
 

src/librustc_incremental/persist/dirty_clean.rs

@@ -449,7 +449,7 @@ impl DirtyCleanVisitor<'tcx> {
         &self,
         labels: &'l Labels,
         def_id: DefId
-    ) -> impl Iterator<Item = DepNode> + 'l {
+    ) -> impl Iterator<Item = DepNode> + ExactSizeIterator + 'l {
         let def_path_hash = self.tcx.def_path_hash(def_id);
         labels
             .iter()