Fix clippy warnings

Fixes clippy::{cone_on_copy, filter_next, redundant_closure, single_char_pattern, len_zero,redundant_field_names, useless_format, identity_conversion, map_clone, into_iter_on_ref, needless_return, option_as_ref_deref, unused_unit, unnecessary_mut_passed}

Author: matthiaskrgr

src/librustc_attr/builtin.rs

@@ -634,7 +634,7 @@ pub fn eval_condition(
                 [NestedMetaItem::Literal(Lit { span, .. })
                 | NestedMetaItem::MetaItem(MetaItem { span, .. })] => {
                     sess.span_diagnostic
-                        .struct_span_err(*span, &*format!("expected a version literal"))
+                        .struct_span_err(*span, "expected a version literal")
                         .emit();
                     return false;
                 }

src/librustc_data_structures/tiny_list.rs

@@ -52,7 +52,7 @@ impl<T: PartialEq> TinyList<T> {
             if &e.data == data {
                 return true;
             }
-            elem = e.next.as_ref().map(|e| &**e);
+            elem = e.next.as_deref();
         }
         false
     }
@@ -62,7 +62,7 @@ impl<T: PartialEq> TinyList<T> {
         let (mut elem, mut count) = (self.head.as_ref(), 0);
         while let Some(ref e) = elem {
             count += 1;
-            elem = e.next.as_ref().map(|e| &**e);
+            elem = e.next.as_deref();
         }
         count
     }

src/librustc_infer/traits/util.rs

@@ -112,8 +112,7 @@ pub fn elaborate_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
     predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
 ) -> Elaborator<'tcx> {
-    let obligations =
-        predicates.into_iter().map(|predicate| predicate_obligation(predicate, None)).collect();
+    let obligations = predicates.map(|predicate| predicate_obligation(predicate, None)).collect();
     elaborate_obligations(tcx, obligations)
 }
 
@@ -149,7 +148,7 @@ impl Elaborator<'tcx> {
                 // Get predicates declared on the trait.
                 let predicates = tcx.super_predicates_of(data.def_id());
 
-                let obligations = predicates.predicates.into_iter().map(|(pred, span)| {
+                let obligations = predicates.predicates.iter().map(|(pred, span)| {
                     predicate_obligation(
                         pred.subst_supertrait(tcx, &data.to_poly_trait_ref()),
                         Some(*span),

src/librustc_interface/queries.rs

@@ -137,7 +137,7 @@ impl<'tcx> Queries<'tcx> {
             let result = passes::register_plugins(
                 self.session(),
                 &*self.codegen_backend().metadata_loader(),
-                self.compiler.register_lints.as_ref().map(|p| &**p).unwrap_or_else(|| empty),
+                self.compiler.register_lints.as_deref().unwrap_or_else(|| empty),
                 krate,
                 &crate_name,
             );

src/librustc_middle/dep_graph/mod.rs

@@ -72,9 +72,9 @@ impl rustc_query_system::dep_graph::DepKind for DepKind {
         })
     }
 
-    fn read_deps<OP>(op: OP) -> ()
+    fn read_deps<OP>(op: OP)
     where
-        OP: for<'a> FnOnce(Option<&'a Lock<TaskDeps>>) -> (),
+        OP: for<'a> FnOnce(Option<&'a Lock<TaskDeps>>),
     {
         ty::tls::with_context_opt(|icx| {
             let icx = if let Some(icx) = icx { icx } else { return };

src/librustc_middle/hir/mod.rs

@@ -78,7 +78,6 @@ pub fn provide(providers: &mut Providers<'_>) {
         &tcx.untracked_crate.modules[&module]
     };
     providers.hir_owner = |tcx, id| tcx.index_hir(LOCAL_CRATE).map[id].signature;
-    providers.hir_owner_nodes =
-        |tcx, id| tcx.index_hir(LOCAL_CRATE).map[id].with_bodies.as_ref().map(|nodes| &**nodes);
+    providers.hir_owner_nodes = |tcx, id| tcx.index_hir(LOCAL_CRATE).map[id].with_bodies.as_deref();
     map::provide(providers);
 }

src/librustc_middle/ty/mod.rs

@@ -280,7 +280,7 @@ impl<'tcx> AssociatedItems<'tcx> {
         &self,
         name: Symbol,
     ) -> impl '_ + Iterator<Item = &ty::AssocItem> {
-        self.items.get_by_key(&name).map(|v| *v)
+        self.items.get_by_key(&name).copied()
     }
 
     /// Returns an iterator over all associated items with the given name.

src/librustc_middle/ty/trait_def.rs

@@ -171,10 +171,7 @@ 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
-            .into_iter()
-            .chain(non_blanket_impls.into_iter().map(|(_, v)| v).flatten())
-            .cloned()
+        blanket_impls.iter().chain(non_blanket_impls.iter().map(|(_, v)| v).flatten()).cloned()
     }
 }
 

src/librustc_mir_build/hair/pattern/check_match.rs

@@ -246,7 +246,7 @@ impl<'tcx> MatchVisitor<'_, 'tcx> {
             );
         }
 
-        adt_defined_here(&mut cx, &mut err, pattern_ty, &witnesses);
+        adt_defined_here(&cx, &mut err, pattern_ty, &witnesses);
         err.note(&format!("the matched value is of type `{}`", pattern_ty));
         err.emit();
     }

src/librustc_mir_build/hair/pattern/const_to_pat.rs

@@ -121,7 +121,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                         )
                     }
                     traits::NonStructuralMatchTy::Dynamic => {
-                        format!("trait objects cannot be used in patterns")
+                        "trait objects cannot be used in patterns".to_string()
                     }
                     traits::NonStructuralMatchTy::Param => {
                         bug!("use of constant whose type is a parameter inside a pattern")