fix a couple of clippy warnings:

filter_next
manual_strip
redundant_static_lifetimes
single_char_pattern
unnecessary_cast
unused_unit
op_ref
redundant_closure
useless_conversion

compiler/rustc_ast/src/attr/mod.rs

@@ -360,7 +360,7 @@ pub fn list_contains_name(items: &[NestedMetaItem], name: Symbol) -> bool {
 impl MetaItem {
     fn token_trees_and_spacings(&self) -> Vec<TreeAndSpacing> {
         let mut idents = vec![];
-        let mut last_pos = BytePos(0 as u32);
+        let mut last_pos = BytePos(0_u32);
         for (i, segment) in self.path.segments.iter().enumerate() {
             let is_first = i == 0;
             if !is_first {

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -739,7 +739,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 "cannot infer {} {} {} `{}`{}",
                 kind_str, preposition, descr, type_name, parent_desc
             )
-            .into()
         }
     }
 }

compiler/rustc_interface/src/util.rs

@@ -246,10 +246,10 @@ pub fn get_codegen_backend(sopts: &config::Options) -> Box<dyn CodegenBackend> {
 
     INIT.call_once(|| {
         #[cfg(feature = "llvm")]
-        const DEFAULT_CODEGEN_BACKEND: &'static str = "llvm";
+        const DEFAULT_CODEGEN_BACKEND: &str = "llvm";
 
         #[cfg(not(feature = "llvm"))]
-        const DEFAULT_CODEGEN_BACKEND: &'static str = "cranelift";
+        const DEFAULT_CODEGEN_BACKEND: &str = "cranelift";
 
         let codegen_name = sopts
             .debugging_opts
@@ -414,11 +414,10 @@ pub fn get_codegen_sysroot(backend_name: &str) -> fn() -> Box<dyn CodegenBackend
             let libdir = filesearch::relative_target_lib_path(&sysroot, &target);
             sysroot.join(libdir).with_file_name("codegen-backends")
         })
-        .filter(|f| {
+        .find(|f| {
             info!("codegen backend candidate: {}", f.display());
             f.exists()
-        })
-        .next();
+        });
     let sysroot = sysroot.unwrap_or_else(|| {
         let candidates = sysroot_candidates
             .iter()

compiler/rustc_middle/src/middle/stability.rs

@@ -399,7 +399,7 @@ impl<'tcx> TyCtxt<'tcx> {
         def_id: DefId,
         id: Option<HirId>,
         span: Span,
-        unmarked: impl FnOnce(Span, DefId) -> (),
+        unmarked: impl FnOnce(Span, DefId),
     ) {
         let soft_handler = |lint, span, msg: &_| {
             self.struct_span_lint_hir(lint, id.unwrap_or(hir::CRATE_HIR_ID), span, |lint| {

compiler/rustc_middle/src/mir/terminator.rs

@@ -46,7 +46,7 @@ impl SwitchTargets {
     pub fn new(targets: impl Iterator<Item = (u128, BasicBlock)>, otherwise: BasicBlock) -> Self {
         let (values, mut targets): (SmallVec<_>, SmallVec<_>) = targets.unzip();
         targets.push(otherwise);
-        Self { values: values.into(), targets }
+        Self { values, targets }
     }
 
     /// Builds a switch targets definition that jumps to `then` if the tested value equals `value`,

compiler/rustc_mir/src/borrow_check/diagnostics/conflict_errors.rs

@@ -120,7 +120,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 let move_out = self.move_data.moves[(*move_site).moi];
                 let moved_place = &self.move_data.move_paths[move_out.path].place;
                 // `*(_1)` where `_1` is a `Box` is actually a move out.
-                let is_box_move = moved_place.as_ref().projection == &[ProjectionElem::Deref]
+                let is_box_move = moved_place.as_ref().projection == [ProjectionElem::Deref]
                     && self.body.local_decls[moved_place.local].ty.is_box();
 
                 !is_box_move

compiler/rustc_mir/src/transform/match_branches.rs

@@ -63,7 +63,7 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
             };
 
             // Check that destinations are identical, and if not, then don't optimize this block
-            if &bbs[first].terminator().kind != &bbs[second].terminator().kind {
+            if bbs[first].terminator().kind != bbs[second].terminator().kind {
                 continue;
             }
 

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1886,9 +1886,8 @@ impl<'tcx> LifetimeContext<'_, 'tcx> {
                         if snippet.starts_with('&') && !snippet.starts_with("&'") {
                             introduce_suggestion
                                 .push((param.span, format!("&'a {}", &snippet[1..])));
-                        } else if snippet.starts_with("&'_ ") {
-                            introduce_suggestion
-                                .push((param.span, format!("&'a {}", &snippet[4..])));
+                        } else if let Some(stripped) = snippet.strip_prefix("&'_ ") {
+                            introduce_suggestion.push((param.span, format!("&'a {}", &stripped)));
                         }
                     }
                 }

compiler/rustc_span/src/lib.rs

@@ -1574,7 +1574,7 @@ fn normalize_src(src: &mut String, start_pos: BytePos) -> Vec<NormalizedPos> {
 
 /// Removes UTF-8 BOM, if any.
 fn remove_bom(src: &mut String, normalized_pos: &mut Vec<NormalizedPos>) {
-    if src.starts_with("\u{feff}") {
+    if src.starts_with('\u{feff}') {
         src.drain(..3);
         normalized_pos.push(NormalizedPos { pos: BytePos(0), diff: 3 });
     }

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1388,11 +1388,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
         trait_ref: &ty::PolyTraitRef<'tcx>,
     ) {
         let get_trait_impl = |trait_def_id| {
-            self.tcx.find_map_relevant_impl(
-                trait_def_id,
-                trait_ref.skip_binder().self_ty(),
-                |impl_def_id| Some(impl_def_id),
-            )
+            self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
         };
         let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
         let all_traits = self.tcx.all_traits(LOCAL_CRATE);

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -499,7 +499,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                         Err(ErrorHandled::TooGeneric) => {
                             pending_obligation.stalled_on = substs
                                 .iter()
-                                .filter_map(|ty| TyOrConstInferVar::maybe_from_generic_arg(ty))
+                                .filter_map(TyOrConstInferVar::maybe_from_generic_arg)
                                 .collect();
                             ProcessResult::Unchanged
                         }