diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 0bbdcb7f09ea0..11b5131b8d788 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1260,9 +1260,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         );
 
         // `a = lhs1; b = lhs2;`.
-        let stmts = self
-            .arena
-            .alloc_from_iter(std::iter::once(destructure_let).chain(assignments.into_iter()));
+        let stmts = self.arena.alloc_from_iter(std::iter::once(destructure_let).chain(assignments));
 
         // Wrap everything in a block.
         hir::ExprKind::Block(self.block_all(whole_span, stmts, None), None)
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index 30c2d633840e7..883f82caa80d1 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -607,7 +607,7 @@ pub fn file_metadata<'ll>(cx: &CodegenCx<'ll, '_>, source_file: &SourceFile) ->
 
                     if let Ok(rel_path) = abs_path.strip_prefix(working_directory) {
                         (
-                            working_directory.to_string_lossy().into(),
+                            working_directory.to_string_lossy(),
                             rel_path.to_string_lossy().into_owned(),
                         )
                     } else {
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs
index 02a1072df6d43..eef8dbb33b49f 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs
@@ -396,7 +396,7 @@ pub fn build_coroutine_variant_struct_type_di_node<'ll, 'tcx>(
                 })
                 .collect();
 
-            state_specific_fields.into_iter().chain(common_fields.into_iter()).collect()
+            state_specific_fields.into_iter().chain(common_fields).collect()
         },
         |cx| build_generic_type_param_di_nodes(cx, coroutine_type_and_layout.ty),
     )
diff --git a/compiler/rustc_data_structures/src/sorted_map.rs b/compiler/rustc_data_structures/src/sorted_map.rs
index 60b343afbed9c..ed2e558bffa60 100644
--- a/compiler/rustc_data_structures/src/sorted_map.rs
+++ b/compiler/rustc_data_structures/src/sorted_map.rs
@@ -198,7 +198,7 @@ impl<K: Ord, V> SortedMap<K, V> {
                 if index == self.data.len() || elements.last().unwrap().0 < self.data[index].0 {
                     // We can copy the whole range without having to mix with
                     // existing elements.
-                    self.data.splice(index..index, elements.into_iter());
+                    self.data.splice(index..index, elements);
                     return;
                 }
 
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 5c252c3f9f2ce..06bdb6bf3e040 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -1560,7 +1560,7 @@ impl Expr<'_> {
             ExprKind::Call(..) => ExprPrecedence::Call,
             ExprKind::MethodCall(..) => ExprPrecedence::MethodCall,
             ExprKind::Tup(_) => ExprPrecedence::Tup,
-            ExprKind::Binary(op, ..) => ExprPrecedence::Binary(op.node.into()),
+            ExprKind::Binary(op, ..) => ExprPrecedence::Binary(op.node),
             ExprKind::Unary(..) => ExprPrecedence::Unary,
             ExprKind::Lit(_) => ExprPrecedence::Lit,
             ExprKind::Type(..) | ExprKind::Cast(..) => ExprPrecedence::Cast,
@@ -1700,11 +1700,9 @@ impl Expr<'_> {
                 // them being used only for its side-effects.
                 base.can_have_side_effects()
             }
-            ExprKind::Struct(_, fields, init) => fields
-                .iter()
-                .map(|field| field.expr)
-                .chain(init.into_iter())
-                .any(|e| e.can_have_side_effects()),
+            ExprKind::Struct(_, fields, init) => {
+                fields.iter().map(|field| field.expr).chain(init).any(|e| e.can_have_side_effects())
+            }
 
             ExprKind::Array(args)
             | ExprKind::Tup(args)
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index 5769fc5fe6408..2c574918e56c6 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -350,7 +350,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                     // Nested poly trait refs have the binders concatenated
                     let mut full_binders =
                         self.map.late_bound_vars.entry(*hir_id).or_default().clone();
-                    full_binders.extend(supertrait_bound_vars.into_iter());
+                    full_binders.extend(supertrait_bound_vars);
                     break (full_binders, BinderScopeType::Concatenating);
                 }
             }
diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs
index 74aec897f959e..ff03cf16a27f3 100644
--- a/compiler/rustc_hir_typeck/src/errors.rs
+++ b/compiler/rustc_hir_typeck/src/errors.rs
@@ -573,13 +573,13 @@ impl rustc_errors::AddToDiagnostic for CastUnknownPointerSub {
     {
         match self {
             CastUnknownPointerSub::To(span) => {
-                let msg = f(diag, crate::fluent_generated::hir_typeck_label_to.into());
+                let msg = f(diag, crate::fluent_generated::hir_typeck_label_to);
                 diag.span_label(span, msg);
-                let msg = f(diag, crate::fluent_generated::hir_typeck_note.into());
+                let msg = f(diag, crate::fluent_generated::hir_typeck_note);
                 diag.note(msg);
             }
             CastUnknownPointerSub::From(span) => {
-                let msg = f(diag, crate::fluent_generated::hir_typeck_label_from.into());
+                let msg = f(diag, crate::fluent_generated::hir_typeck_label_from);
                 diag.span_label(span, msg);
             }
         }
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 4243bce377fb4..a0178957558a2 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -1548,9 +1548,9 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     );
 
                     let candidate_obligations = impl_obligations
-                        .chain(norm_obligations.into_iter())
+                        .chain(norm_obligations)
                         .chain(ref_obligations.iter().cloned())
-                        .chain(normalization_obligations.into_iter());
+                        .chain(normalization_obligations);
 
                     // Evaluate those obligations to see if they might possibly hold.
                     for o in candidate_obligations {
diff --git a/compiler/rustc_infer/src/infer/outlives/verify.rs b/compiler/rustc_infer/src/infer/outlives/verify.rs
index ce619ae8a0d8c..bb578a482e4b5 100644
--- a/compiler/rustc_infer/src/infer/outlives/verify.rs
+++ b/compiler/rustc_infer/src/infer/outlives/verify.rs
@@ -130,12 +130,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         // see the extensive comment in projection_must_outlive
         let recursive_bound = {
             let mut components = smallvec![];
-            compute_alias_components_recursive(
-                self.tcx,
-                alias_ty_as_ty.into(),
-                &mut components,
-                visited,
-            );
+            compute_alias_components_recursive(self.tcx, alias_ty_as_ty, &mut components, visited);
             self.bound_from_components(&components, visited)
         };
 
diff --git a/compiler/rustc_infer/src/infer/relate/combine.rs b/compiler/rustc_infer/src/infer/relate/combine.rs
index 043a916679ef8..dfaca3458d66b 100644
--- a/compiler/rustc_infer/src/infer/relate/combine.rs
+++ b/compiler/rustc_infer/src/infer/relate/combine.rs
@@ -552,7 +552,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
     }
 
     pub fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>) {
-        self.obligations.extend(obligations.into_iter());
+        self.obligations.extend(obligations);
     }
 
     pub fn register_predicates(&mut self, obligations: impl IntoIterator<Item: ToPredicate<'tcx>>) {
diff --git a/compiler/rustc_mir_dataflow/src/value_analysis.rs b/compiler/rustc_mir_dataflow/src/value_analysis.rs
index 071024a0fa35d..2802f5491be03 100644
--- a/compiler/rustc_mir_dataflow/src/value_analysis.rs
+++ b/compiler/rustc_mir_dataflow/src/value_analysis.rs
@@ -956,11 +956,7 @@ impl Map {
             // The local is not tracked at all, so it does not alias anything.
             return;
         };
-        let elems = place
-            .projection
-            .iter()
-            .map(|&elem| elem.try_into())
-            .chain(tail_elem.map(Ok).into_iter());
+        let elems = place.projection.iter().map(|&elem| elem.try_into()).chain(tail_elem.map(Ok));
         for elem in elems {
             // A field aliases the parent place.
             if let Some(vi) = self.places[index].value_index {
diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
index 146cc33e8c677..ad12bce9b0232 100644
--- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
+++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
@@ -496,7 +496,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
             FlatSet::Elem(scalar) => {
                 let ty = op.ty(self.local_decls, self.tcx);
                 self.tcx.layout_of(self.param_env.and(ty)).map_or(FlatSet::Top, |layout| {
-                    FlatSet::Elem(ImmTy::from_scalar(scalar.into(), layout))
+                    FlatSet::Elem(ImmTy::from_scalar(scalar, layout))
                 })
             }
             FlatSet::Bottom => FlatSet::Bottom,
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 89919247e8228..fd7dad36c9dab 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -923,7 +923,7 @@ impl<'a> Parser<'a> {
         );
         let where_predicates_split = before_where_clause.predicates.len();
         let mut predicates = before_where_clause.predicates;
-        predicates.extend(after_where_clause.predicates.into_iter());
+        predicates.extend(after_where_clause.predicates);
         let where_clause = WhereClause {
             has_where_token: before_where_clause.has_where_token
                 || after_where_clause.has_where_token,
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index 81055431f649d..d10c8c92257db 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -215,7 +215,7 @@ fn emit_malformed_attribute(
                 } else {
                     "the following are the possible correct uses"
                 },
-                suggestions.into_iter(),
+                suggestions,
                 Applicability::HasPlaceholders,
             )
             .emit();
diff --git a/compiler/rustc_resolve/src/rustdoc.rs b/compiler/rustc_resolve/src/rustdoc.rs
index f95c0acd7509f..4ff4ccf5e9845 100644
--- a/compiler/rustc_resolve/src/rustdoc.rs
+++ b/compiler/rustc_resolve/src/rustdoc.rs
@@ -407,8 +407,7 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
         doc,
         main_body_opts(),
         Some(&mut broken_link_callback),
-    )
-    .into_iter();
+    );
     let mut links = Vec::new();
 
     while let Some(event) = event_iter.next() {
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index d46a309df5585..20d18fa4b8390 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -1579,7 +1579,7 @@ impl CheckCfg {
 pub fn build_configuration(sess: &Session, mut user_cfg: Cfg) -> Cfg {
     // Combine the configuration requested by the session (command line) with
     // some default and generated configuration items.
-    user_cfg.extend(default_configuration(sess).into_iter());
+    user_cfg.extend(default_configuration(sess));
     user_cfg
 }
 
diff --git a/compiler/rustc_smir/src/rustc_smir/context.rs b/compiler/rustc_smir/src/rustc_smir/context.rs
index 70313cc021e79..3a8289f38bdc4 100644
--- a/compiler/rustc_smir/src/rustc_smir/context.rs
+++ b/compiler/rustc_smir/src/rustc_smir/context.rs
@@ -158,7 +158,6 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
                 let crate_name = tables.tcx.crate_name(*crate_num).to_string();
                 (name == crate_name).then(|| smir_crate(tables.tcx, *crate_num))
             })
-            .into_iter()
             .flatten()
             .collect();
         crates
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index fbde7455145c2..5e154cb71da48 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -345,7 +345,7 @@ fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     // Search for a predicate like `Self : Sized` amongst the trait bounds.
     let predicates = tcx.predicates_of(def_id);
     let predicates = predicates.instantiate_identity(tcx).predicates;
-    elaborate(tcx, predicates.into_iter()).any(|pred| match pred.kind().skip_binder() {
+    elaborate(tcx, predicates).any(|pred| match pred.kind().skip_binder() {
         ty::ClauseKind::Trait(ref trait_pred) => {
             trait_pred.def_id() == sized_def_id && trait_pred.self_ty().is_param(0)
         }
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 98da3bc2fe9fa..575010ff46d85 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -220,9 +220,8 @@ pub fn impl_subject_and_oblig<'a, 'tcx>(
         selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(predicates);
     let impl_obligations = super::predicates_for_generics(cause, param_env, predicates);
 
-    let impl_obligations = impl_obligations
-        .chain(normalization_obligations1.into_iter())
-        .chain(normalization_obligations2.into_iter());
+    let impl_obligations =
+        impl_obligations.chain(normalization_obligations1).chain(normalization_obligations2);
 
     (subject, impl_obligations)
 }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 6631c42727099..b112ba65e8f47 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -743,7 +743,7 @@ pub(crate) fn clean_generics<'tcx>(
                     .into_iter()
                     .map(|(lifetime, bounds)| WherePredicate::RegionPredicate { lifetime, bounds }),
             )
-            .chain(eq_predicates.into_iter())
+            .chain(eq_predicates)
             .collect(),
     }
 }
diff --git a/src/librustdoc/html/markdown.rs b/src/librustdoc/html/markdown.rs
index dbd78ea0dc97c..89bba5ebbab49 100644
--- a/src/librustdoc/html/markdown.rs
+++ b/src/librustdoc/html/markdown.rs
@@ -1383,7 +1383,7 @@ impl LangString {
         };
 
         if custom_code_classes_in_docs {
-            call(&mut TagIterator::new(string, extra).into_iter())
+            call(&mut TagIterator::new(string, extra))
         } else {
             call(&mut tokens(string))
         }
diff --git a/src/librustdoc/lint.rs b/src/librustdoc/lint.rs
index d45040e348a24..267f1cb0b72b5 100644
--- a/src/librustdoc/lint.rs
+++ b/src/librustdoc/lint.rs
@@ -33,7 +33,7 @@ where
     let lints = || {
         lint::builtin::HardwiredLints::get_lints()
             .into_iter()
-            .chain(rustc_lint::SoftLints::get_lints().into_iter())
+            .chain(rustc_lint::SoftLints::get_lints())
     };
 
     let lint_opts = lints()
@@ -46,7 +46,7 @@ where
                 filter_call(lint)
             }
         })
-        .chain(lint_opts.into_iter())
+        .chain(lint_opts)
         .collect::<Vec<_>>();
 
     let lint_caps = lints()
diff --git a/src/librustdoc/passes/check_custom_code_classes.rs b/src/librustdoc/passes/check_custom_code_classes.rs
index 6266d3ff51d64..f246e2962fe5e 100644
--- a/src/librustdoc/passes/check_custom_code_classes.rs
+++ b/src/librustdoc/passes/check_custom_code_classes.rs
@@ -48,7 +48,7 @@ struct TestsWithCustomClasses {
 
 impl crate::doctest::Tester for TestsWithCustomClasses {
     fn add_test(&mut self, _: String, config: LangString, _: usize) {
-        self.custom_classes_found.extend(config.added_classes.into_iter());
+        self.custom_classes_found.extend(config.added_classes);
     }
 }
 
diff --git a/src/librustdoc/visit_ast.rs b/src/librustdoc/visit_ast.rs
index bbc7e5b48d1ef..42ff1210f23b2 100644
--- a/src/librustdoc/visit_ast.rs
+++ b/src/librustdoc/visit_ast.rs
@@ -168,10 +168,11 @@ impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
                     })
                     .collect::<Vec<_>>()
             })
-            .chain(
-                [Cfg::Cfg(sym::test, None), Cfg::Cfg(sym::doc, None), Cfg::Cfg(sym::doctest, None)]
-                    .into_iter(),
-            )
+            .chain([
+                Cfg::Cfg(sym::test, None),
+                Cfg::Cfg(sym::doc, None),
+                Cfg::Cfg(sym::doctest, None),
+            ])
             .collect();
 
         self.cx.cache.exact_paths = self.exact_paths;