diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index 6a0ace04d4b..b94b8c87216 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -230,7 +230,7 @@ impl AttrItem {
     }
 
     pub fn meta_kind(&self) -> Option<MetaItemKind> {
-        Some(MetaItemKind::from_mac_args(&self.args)?)
+        MetaItemKind::from_mac_args(&self.args)
     }
 }
 
diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index 0a96e60d4d3..6c44fb0df23 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -823,7 +823,7 @@ fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
             );
             let mut all_stable = true;
             for ident in
-                attr.meta_item_list().into_iter().flatten().map(|nested| nested.ident()).flatten()
+                attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident())
             {
                 let name = ident.name;
                 let stable_since = lang_features
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index ec68f6eb0f8..90ddf791450 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -292,7 +292,7 @@ pub unsafe fn create_module<'ll>(
             "sign-return-address-all\0".as_ptr().cast(),
             pac_opts.leaf.into(),
         );
-        let is_bkey = if pac_opts.key == PAuthKey::A { false } else { true };
+        let is_bkey: bool = pac_opts.key != PAuthKey::A;
         llvm::LLVMRustAddModuleFlag(
             llmod,
             llvm::LLVMModFlagBehavior::Error,
diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs
index c21d19a6227..6976999c0e4 100644
--- a/compiler/rustc_codegen_ssa/src/mir/place.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/place.rs
@@ -476,7 +476,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 mir::ProjectionElem::Subslice { from, to, from_end } => {
                     let mut subslice = cg_base.project_index(bx, bx.cx().const_usize(from as u64));
                     let projected_ty =
-                        PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, elem.clone()).ty;
+                        PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, *elem).ty;
                     subslice.layout = bx.cx().layout_of(self.monomorphize(projected_ty));
 
                     if subslice.layout.is_unsized() {
diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index 8065911afb9..f71fb58cf6b 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -1039,7 +1039,7 @@ fn check_matcher_core(
                                 ));
                                 err.span_suggestion(
                                     span,
-                                    &format!("try a `pat_param` fragment specifier instead"),
+                                    "try a `pat_param` fragment specifier instead",
                                     suggestion,
                                     Applicability::MaybeIncorrect,
                                 );
diff --git a/compiler/rustc_middle/src/middle/stability.rs b/compiler/rustc_middle/src/middle/stability.rs
index 03cca51dc0b..fedf456ccc8 100644
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@@ -198,7 +198,7 @@ fn deprecation_message(
     } else {
         let since = since.as_ref().map(Symbol::as_str);
 
-        if since.as_deref() == Some("TBD") {
+        if since == Some("TBD") {
             format!("use of {} `{}` that will be deprecated in a future Rust version", kind, path)
         } else {
             format!(
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index b59fb6afe6f..7c57d42631a 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -855,7 +855,7 @@ impl<'tcx> Relate<'tcx> for ty::ProjectionPredicate<'tcx> {
     ) -> RelateResult<'tcx, ty::ProjectionPredicate<'tcx>> {
         Ok(ty::ProjectionPredicate {
             projection_ty: relation.relate(a.projection_ty, b.projection_ty)?,
-            term: relation.relate(a.term, b.term)?.into(),
+            term: relation.relate(a.term, b.term)?,
         })
     }
 }
diff --git a/compiler/rustc_middle/src/ty/trait_def.rs b/compiler/rustc_middle/src/ty/trait_def.rs
index 597f7dd95a2..8f4cc182e7f 100644
--- a/compiler/rustc_middle/src/ty/trait_def.rs
+++ b/compiler/rustc_middle/src/ty/trait_def.rs
@@ -210,7 +210,7 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn all_impls(self, def_id: DefId) -> impl Iterator<Item = DefId> + 'tcx {
         let TraitImpls { blanket_impls, non_blanket_impls } = self.trait_impls_of(def_id);
 
-        blanket_impls.iter().chain(non_blanket_impls.iter().map(|(_, v)| v).flatten()).cloned()
+        blanket_impls.iter().chain(non_blanket_impls.iter().flat_map(|(_, v)| v)).cloned()
     }
 }
 
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index 46de6d939a1..da921904523 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -140,7 +140,7 @@ fn covered_code_regions<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Vec<&'tcx Cod
     let body = mir_body(tcx, def_id);
     body.basic_blocks()
         .iter()
-        .map(|data| {
+        .flat_map(|data| {
             data.statements.iter().filter_map(|statement| match statement.kind {
                 StatementKind::Coverage(box ref coverage) => {
                     if is_inlined(body, statement) {
@@ -152,7 +152,6 @@ fn covered_code_regions<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Vec<&'tcx Cod
                 _ => None,
             })
         })
-        .flatten()
         .collect()
 }
 
diff --git a/compiler/rustc_monomorphize/src/partitioning/mod.rs b/compiler/rustc_monomorphize/src/partitioning/mod.rs
index 67597a0d7b4..b8684a09fd7 100644
--- a/compiler/rustc_monomorphize/src/partitioning/mod.rs
+++ b/compiler/rustc_monomorphize/src/partitioning/mod.rs
@@ -220,18 +220,16 @@ pub fn partition<'tcx>(
         let mut cgus: Vec<_> = post_inlining.codegen_units.iter_mut().collect();
         cgus.sort_by_key(|cgu| cgu.size_estimate());
 
-        let dead_code_cgu = if let Some(cgu) = cgus
-            .into_iter()
-            .rev()
-            .filter(|cgu| cgu.items().iter().any(|(_, (linkage, _))| *linkage == Linkage::External))
-            .next()
-        {
-            cgu
-        } else {
-            // If there are no CGUs that have externally linked items,
-            // then we just pick the first CGU as a fallback.
-            &mut post_inlining.codegen_units[0]
-        };
+        let dead_code_cgu =
+            if let Some(cgu) = cgus.into_iter().rev().find(|cgu| {
+                cgu.items().iter().any(|(_, (linkage, _))| *linkage == Linkage::External)
+            }) {
+                cgu
+            } else {
+                // If there are no CGUs that have externally linked items,
+                // then we just pick the first CGU as a fallback.
+                &mut post_inlining.codegen_units[0]
+            };
         dead_code_cgu.make_code_coverage_dead_code_cgu();
     }
 
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 7b74b137d21..def23005fbe 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -2156,7 +2156,7 @@ impl<'a> Parser<'a> {
                             | PatKind::TupleStruct(qself @ None, path, _)
                             | PatKind::Path(qself @ None, path) => match &first_pat.kind {
                                 PatKind::Ident(_, ident, _) => {
-                                    path.segments.insert(0, PathSegment::from_ident(ident.clone()));
+                                    path.segments.insert(0, PathSegment::from_ident(*ident));
                                     path.span = new_span;
                                     show_sugg = true;
                                     first_pat = pat;
@@ -2183,8 +2183,8 @@ impl<'a> Parser<'a> {
                                             Path {
                                                 span: new_span,
                                                 segments: vec![
-                                                    PathSegment::from_ident(old_ident.clone()),
-                                                    PathSegment::from_ident(ident.clone()),
+                                                    PathSegment::from_ident(*old_ident),
+                                                    PathSegment::from_ident(*ident),
                                                 ],
                                                 tokens: None,
                                             },
@@ -2194,7 +2194,7 @@ impl<'a> Parser<'a> {
                                     }
                                     PatKind::Path(old_qself, old_path) => {
                                         let mut segments = old_path.segments.clone();
-                                        segments.push(PathSegment::from_ident(ident.clone()));
+                                        segments.push(PathSegment::from_ident(*ident));
                                         let path = PatKind::Path(
                                             old_qself.clone(),
                                             Path { span: new_span, segments, tokens: None },
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index 62ed104aef3..4b57aa1f24a 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -260,7 +260,7 @@ impl<'a> Parser<'a> {
             let ate_comma = self.eat(&token::Comma);
 
             if self.eat_keyword_noexpect(kw::Where) {
-                let msg = &format!("cannot define duplicate `where` clauses on an item");
+                let msg = "cannot define duplicate `where` clauses on an item";
                 let mut err = self.struct_span_err(self.token.span, msg);
                 err.span_label(lo, "previous `where` clause starts here");
                 err.span_suggestion_verbose(
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 4b85531557c..9a2fb3b86e2 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -1362,8 +1362,7 @@ impl<'a> Resolver<'a> {
                     .filter(|(_, module)| {
                         current_module.is_ancestor_of(module) && !ptr::eq(current_module, *module)
                     })
-                    .map(|(_, module)| module.kind.name())
-                    .flatten(),
+                    .flat_map(|(_, module)| module.kind.name()),
             )
             .filter(|c| !c.to_string().is_empty())
             .collect::<Vec<_>>();
@@ -1859,7 +1858,7 @@ crate fn show_candidates(
         let instead = if instead { " instead" } else { "" };
         let mut msg = format!("consider importing {} {}{}", determiner, kind, instead);
 
-        for note in accessible_path_strings.iter().map(|cand| cand.3.as_ref()).flatten() {
+        for note in accessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
             err.note(note);
         }
 
@@ -1942,7 +1941,7 @@ crate fn show_candidates(
                 multi_span.push_span_label(span, format!("`{}`: not accessible", name));
             }
 
-            for note in inaccessible_path_strings.iter().map(|cand| cand.3.as_ref()).flatten() {
+            for note in inaccessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
                 err.note(note);
             }
 
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index f9926a71c30..129db038f4a 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -1163,7 +1163,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                         err.span_suggestion(
                             span,
                             &"use this syntax instead",
-                            format!("{path_str}"),
+                            path_str.to_string(),
                             Applicability::MaybeIncorrect,
                         );
                     }
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index f22b4e8d072..c3df17c83bb 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -1437,8 +1437,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                                     self.tcx
                                         .associated_items(did)
                                         .in_definition_order()
-                                        .filter(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
-                                        .next()
+                                        .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
                                 },
                             )
                         })
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 5f338664c9a..f5d531e631e 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -959,7 +959,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
                 infcx.inner.borrow_mut().projection_cache().insert_term(cache_key, result.clone());
             }
             obligations.extend(result.obligations);
-            Ok(Some(result.value.into()))
+            Ok(Some(result.value))
         }
         Ok(Projected::NoProgress(projected_ty)) => {
             let result = Normalized { value: projected_ty, obligations: vec![] };
diff --git a/compiler/rustc_typeck/src/astconv/errors.rs b/compiler/rustc_typeck/src/astconv/errors.rs
index a49d6e24f26..7e9abe3a250 100644
--- a/compiler/rustc_typeck/src/astconv/errors.rs
+++ b/compiler/rustc_typeck/src/astconv/errors.rs
@@ -211,8 +211,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         );
 
         let all_candidate_names: Vec<_> = all_candidates()
-            .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
-            .flatten()
+            .flat_map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
             .filter_map(
                 |item| if item.kind == ty::AssocKind::Type { Some(item.name) } else { None },
             )
diff --git a/compiler/rustc_typeck/src/check/check.rs b/compiler/rustc_typeck/src/check/check.rs
index fba8292b467..1650a62f79f 100644
--- a/compiler/rustc_typeck/src/check/check.rs
+++ b/compiler/rustc_typeck/src/check/check.rs
@@ -392,7 +392,7 @@ fn check_union_fields(tcx: TyCtxt<'_>, span: Span, item_def_id: LocalDefId) -> b
                     "when the type does not implement `Copy`, \
                     wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped",
                     vec![
-                        (ty_span.shrink_to_lo(), format!("std::mem::ManuallyDrop<")),
+                        (ty_span.shrink_to_lo(), "std::mem::ManuallyDrop<".into()),
                         (ty_span.shrink_to_hi(), ">".into()),
                     ],
                     Applicability::MaybeIncorrect,
diff --git a/compiler/rustc_typeck/src/check/demand.rs b/compiler/rustc_typeck/src/check/demand.rs
index d0e96e7538c..e7eadb760c7 100644
--- a/compiler/rustc_typeck/src/check/demand.rs
+++ b/compiler/rustc_typeck/src/check/demand.rs
@@ -340,7 +340,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
                 Some(ident) => format!("{}: ", ident),
-                None => format!(""),
+                None => String::new(),
             };
 
             match &compatible_variants[..] {
@@ -683,7 +683,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                         let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
                             Some(ident) => format!("{}: ", ident),
-                            None => format!(""),
+                            None => String::new(),
                         };
 
                         if let Some(hir::Node::Expr(hir::Expr {
@@ -875,7 +875,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             };
                             let prefix = match self.maybe_get_struct_pattern_shorthand_field(expr) {
                                 Some(ident) => format!("{}: ", ident),
-                                None => format!(""),
+                                None => String::new(),
                             };
                             let (span, suggestion) = if self.is_else_if_block(expr) {
                                 // Don't suggest nonsense like `else *if`
diff --git a/compiler/rustc_typeck/src/check/generator_interior/drop_ranges.rs b/compiler/rustc_typeck/src/check/generator_interior/drop_ranges.rs
index c4e7d6a199e..972dd622d6e 100644
--- a/compiler/rustc_typeck/src/check/generator_interior/drop_ranges.rs
+++ b/compiler/rustc_typeck/src/check/generator_interior/drop_ranges.rs
@@ -246,7 +246,7 @@ impl DropRangesBuilder {
 
     fn add_control_edge(&mut self, from: PostOrderId, to: PostOrderId) {
         trace!("adding control edge from {:?} to {:?}", from, to);
-        self.node_mut(from.into()).successors.push(to.into());
+        self.node_mut(from).successors.push(to);
     }
 }
 
diff --git a/compiler/rustc_typeck/src/check/generator_interior/drop_ranges/cfg_build.rs b/compiler/rustc_typeck/src/check/generator_interior/drop_ranges/cfg_build.rs
index e2a4d9c1b3a..cfed784ea72 100644
--- a/compiler/rustc_typeck/src/check/generator_interior/drop_ranges/cfg_build.rs
+++ b/compiler/rustc_typeck/src/check/generator_interior/drop_ranges/cfg_build.rs
@@ -527,7 +527,7 @@ impl DropRangesBuilder {
 
     fn drop_at(&mut self, value: TrackedValue, location: PostOrderId) {
         let value = self.tracked_value_index(value);
-        self.node_mut(location.into()).drops.push(value);
+        self.node_mut(location).drops.push(value);
     }
 
     fn reinit_at(&mut self, value: TrackedValue, location: PostOrderId) {
@@ -537,7 +537,7 @@ impl DropRangesBuilder {
             // ignore this.
             None => return,
         };
-        self.node_mut(location.into()).reinits.push(value);
+        self.node_mut(location).reinits.push(value);
     }
 
     /// Looks up PostOrderId for any control edges added by HirId and adds a proper edge for them.
diff --git a/compiler/rustc_typeck/src/collect/type_of.rs b/compiler/rustc_typeck/src/collect/type_of.rs
index 90555b213c1..cd7343a3211 100644
--- a/compiler/rustc_typeck/src/collect/type_of.rs
+++ b/compiler/rustc_typeck/src/collect/type_of.rs
@@ -527,7 +527,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                       // FIXME(associated_const_equality): add a useful error message here.
                       tcx.ty_error_with_message(
                         DUMMY_SP,
-                        &format!("Could not find associated const on trait"),
+                        "Could not find associated const on trait",
                     )
                   }
                 }