use values() or keys() respectively when iterating only over keys or values of maps.

src/librustc/traits/structural_impls.rs

@@ -234,7 +234,7 @@ impl BoundNamesCollector {
             start = false;
             write!(fmt, "{}", r)?;
         }
-        for (_, t) in &self.types {
+        for t in self.types.values() {
             if !start {
                 write!(fmt, ", ")?;
             }

src/librustc_builtin_macros/format.rs

@@ -188,7 +188,7 @@ fn parse_args<'a>(
                 let mut err = ecx
                     .struct_span_err(e.span, "positional arguments cannot follow named arguments");
                 err.span_label(e.span, "positional arguments must be before named arguments");
-                for (_, pos) in &names {
+                for pos in names.values() {
                     err.span_label(args[*pos].span, "named argument");
                 }
                 err.emit();

src/librustc_hir/hir.rs

@@ -679,15 +679,15 @@ impl Crate<'_> {
     where
         V: itemlikevisit::ItemLikeVisitor<'hir>,
     {
-        for (_, item) in &self.items {
+        for item in self.items.values() {
             visitor.visit_item(item);
         }
 
-        for (_, trait_item) in &self.trait_items {
+        for trait_item in self.trait_items.values() {
             visitor.visit_trait_item(trait_item);
         }
 
-        for (_, impl_item) in &self.impl_items {
+        for impl_item in self.impl_items.values() {
             visitor.visit_impl_item(impl_item);
         }
     }

src/librustc_infer/infer/lexical_region_resolve/mod.rs

@@ -751,7 +751,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         let dummy_source = graph.add_node(());
         let dummy_sink = graph.add_node(());
 
-        for (constraint, _) in &self.data.constraints {
+        for constraint in self.data.constraints.keys() {
             match *constraint {
                 Constraint::VarSubVar(a_id, b_id) => {
                     graph.add_edge(

src/librustc_infer/infer/region_constraints/leak_check.rs

@@ -34,7 +34,7 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
         assert!(self.in_snapshot());
 
         // Go through each placeholder that we created.
-        for (_, &placeholder_region) in placeholder_map {
+        for &placeholder_region in placeholder_map.values() {
             // Find the universe this placeholder inhabits.
             let placeholder = match placeholder_region {
                 ty::RePlaceholder(p) => p,

src/librustc_resolve/late/lifetimes.rs

@@ -347,7 +347,7 @@ fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap {
             lifetime_uses: &mut Default::default(),
             missing_named_lifetime_spots: vec![],
         };
-        for (_, item) in &krate.items {
+        for item in krate.items.values() {
             visitor.visit_item(item);
         }
     }

src/librustc_typeck/astconv.rs

@@ -1652,7 +1652,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
 
         for (projection_bound, _) in &bounds.projection_bounds {
-            for (_, def_ids) in &mut associated_types {
+            for def_ids in associated_types.values_mut() {
                 def_ids.remove(&projection_bound.projection_def_id());
             }
         }