avoid full-slicing slices

If we already have a slice, there is no need to get another full-range slice from that, just use the original.
clippy::redundant_slicing

compiler/rustc_ast_lowering/src/item.rs

@@ -135,7 +135,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let parent_generics = match self.items.get(&parent_hir_id).unwrap().kind {
             hir::ItemKind::Impl(hir::Impl { ref generics, .. })
-            | hir::ItemKind::Trait(_, _, ref generics, ..) => &generics.params[..],
+            | hir::ItemKind::Trait(_, _, ref generics, ..) => generics.params,
             _ => &[],
         };
         let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1681,7 +1681,7 @@ impl<'a> State<'a> {
         self.ibox(INDENT_UNIT);
         self.s.word("[");
         self.print_inner_attributes_inline(attrs);
-        self.commasep_exprs(Inconsistent, &exprs[..]);
+        self.commasep_exprs(Inconsistent, exprs);
         self.s.word("]");
         self.end();
     }
@@ -1722,7 +1722,7 @@ impl<'a> State<'a> {
         self.print_inner_attributes_inline(attrs);
         self.commasep_cmnt(
             Consistent,
-            &fields[..],
+            fields,
             |s, field| {
                 s.print_outer_attributes(&field.attrs);
                 s.ibox(INDENT_UNIT);
@@ -1757,7 +1757,7 @@ impl<'a> State<'a> {
     fn print_expr_tup(&mut self, exprs: &[P<ast::Expr>], attrs: &[ast::Attribute]) {
         self.popen();
         self.print_inner_attributes_inline(attrs);
-        self.commasep_exprs(Inconsistent, &exprs[..]);
+        self.commasep_exprs(Inconsistent, exprs);
         if exprs.len() == 1 {
             self.s.word(",");
         }

compiler/rustc_builtin_macros/src/format.rs

@@ -270,7 +270,7 @@ impl<'a, 'b> Context<'a, 'b> {
                     parse::ArgumentNamed(s) => Named(s),
                 };
 
-                let ty = Placeholder(match &arg.format.ty[..] {
+                let ty = Placeholder(match arg.format.ty {
                     "" => "Display",
                     "?" => "Debug",
                     "e" => "LowerExp",

compiler/rustc_builtin_macros/src/format_foreign.rs

@@ -312,7 +312,7 @@ pub mod printf {
                 return Some((Substitution::Escape, &s[start + 2..]));
             }
 
-            Cur::new_at(&s[..], start)
+            Cur::new_at(s, start)
         };
 
         // This is meant to be a translation of the following regex:
@@ -673,7 +673,7 @@ pub mod shell {
                 _ => { /* fall-through */ }
             }
 
-            Cur::new_at(&s[..], start)
+            Cur::new_at(s, start)
         };
 
         let at = at.at_next_cp()?;

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -709,7 +709,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             let (tup, args) = args.split_last().unwrap();
             (args, Some(tup))
         } else {
-            (&args[..], None)
+            (args, None)
         };
 
         'make_args: for (i, arg) in first_args.iter().enumerate() {

compiler/rustc_hir_pretty/src/lib.rs

@@ -392,7 +392,7 @@ impl<'a> State<'a> {
                     &f.decl,
                     None,
                     &f.generic_params,
-                    &f.param_names[..],
+                    f.param_names,
                 );
             }
             hir::TyKind::OpaqueDef(..) => self.s.word("/*impl Trait*/"),
@@ -1200,7 +1200,7 @@ impl<'a> State<'a> {
         self.s.word("{");
         self.commasep_cmnt(
             Consistent,
-            &fields[..],
+            fields,
             |s, field| {
                 s.ibox(INDENT_UNIT);
                 if !field.is_shorthand {

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

@@ -671,7 +671,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 if !impl_candidates.is_empty() && e.span.contains(span) {
                     if let Some(expr) = exprs.first() {
                         if let ExprKind::Path(hir::QPath::Resolved(_, path)) = expr.kind {
-                            if let [path_segment] = &path.segments[..] {
+                            if let [path_segment] = path.segments {
                                 let candidate_len = impl_candidates.len();
                                 let suggestions = impl_candidates.iter().map(|candidate| {
                                     format!(

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -866,7 +866,7 @@ impl EncodeContext<'a, 'tcx> {
 
     fn encode_variances_of(&mut self, def_id: DefId) {
         debug!("EncodeContext::encode_variances_of({:?})", def_id);
-        record!(self.tables.variances[def_id] <- &self.tcx.variances_of(def_id)[..]);
+        record!(self.tables.variances[def_id] <- self.tcx.variances_of(def_id));
     }
 
     fn encode_item_type(&mut self, def_id: DefId) {

compiler/rustc_middle/src/hir/map/mod.rs

@@ -854,22 +854,22 @@ impl<'hir> Map<'hir> {
     /// corresponding to the node-ID.
     pub fn attrs(&self, id: HirId) -> &'hir [ast::Attribute] {
         self.find_entry(id).map_or(&[], |entry| match entry.node {
-            Node::Param(a) => &a.attrs[..],
+            Node::Param(a) => a.attrs,
             Node::Local(l) => &l.attrs[..],
-            Node::Item(i) => &i.attrs[..],
+            Node::Item(i) => i.attrs,
-            Node::ForeignItem(fi) => &fi.attrs[..],
+            Node::ForeignItem(fi) => fi.attrs,
-            Node::TraitItem(ref ti) => &ti.attrs[..],
+            Node::TraitItem(ref ti) => ti.attrs,
-            Node::ImplItem(ref ii) => &ii.attrs[..],
+            Node::ImplItem(ref ii) => ii.attrs,
-            Node::Variant(ref v) => &v.attrs[..],
+            Node::Variant(ref v) => v.attrs,
-            Node::Field(ref f) => &f.attrs[..],
+            Node::Field(ref f) => f.attrs,
             Node::Expr(ref e) => &*e.attrs,
             Node::Stmt(ref s) => s.kind.attrs(|id| self.item(id.id)),
             Node::Arm(ref a) => &*a.attrs,
-            Node::GenericParam(param) => &param.attrs[..],
+            Node::GenericParam(param) => param.attrs,
             // Unit/tuple structs/variants take the attributes straight from
             // the struct/variant definition.
             Node::Ctor(..) => self.attrs(self.get_parent_item(id)),
-            Node::Crate(item) => &item.attrs[..],
+            Node::Crate(item) => item.attrs,
             Node::MacroDef(def) => def.attrs,
             Node::AnonConst(..)
             | Node::PathSegment(..)

compiler/rustc_middle/src/ty/query/on_disk_cache.rs

@@ -427,7 +427,7 @@ impl<'sess> OnDiskCache<'sess> {
 
             fn sorted_cnums_including_local_crate(tcx: TyCtxt<'_>) -> Vec<CrateNum> {
                 let mut cnums = vec![LOCAL_CRATE];
-                cnums.extend_from_slice(&tcx.crates()[..]);
+                cnums.extend_from_slice(tcx.crates());
                 cnums.sort_unstable();
                 // Just to be sure...
                 cnums.dedup();

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1105,7 +1105,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         }
 
         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
-            for assoc_item in &items[..] {
+            for assoc_item in items {
                 if assoc_item.ident == ident {
                     return Some(match &assoc_item.kind {
                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,

compiler/rustc_target/src/spec/mod.rs

@@ -1492,7 +1492,7 @@ impl Target {
             } );
             ($key_name:ident = $json_name:expr, optional) => ( {
                 let name = $json_name;
-                if let Some(o) = obj.find(&name[..]) {
+                if let Some(o) = obj.find(name) {
                     base.$key_name = o
                         .as_string()
                         .map(|s| s.to_string() );

compiler/rustc_typeck/src/astconv/errors.rs

@@ -237,7 +237,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
         }
         if let ([], [bound]) = (&potential_assoc_types[..], &trait_bounds) {
-            match &bound.trait_ref.path.segments[..] {
+            match bound.trait_ref.path.segments {
                 // FIXME: `trait_ref.path.span` can point to a full path with multiple
                 // segments, even though `trait_ref.path.segments` is of length `1`. Work
                 // around that bug here, even though it should be fixed elsewhere.

compiler/rustc_typeck/src/astconv/mod.rs

@@ -2374,7 +2374,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             crate::collect::placeholder_type_error(
                 tcx,
                 ident_span.map(|sp| sp.shrink_to_hi()),
-                &generics.params[..],
+                generics.params,
                 visitor.0,
                 true,
                 hir_ty,

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -897,7 +897,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 return (
                     path.res,
                     opt_qself.as_ref().map(|qself| self.to_ty(qself)),
-                    &path.segments[..],
+                    path.segments,
                 );
             }
             QPath::TypeRelative(ref qself, ref segment) => (self.to_ty(qself), qself, segment),

compiler/rustc_typeck/src/check/method/suggest.rs

@@ -600,7 +600,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                     });
                                     if let Some(hir::Node::Item(hir::Item { kind, .. })) = node {
                                         if let Some(g) = kind.generics() {
-                                            let key = match &g.where_clause.predicates[..] {
+                                            let key = match g.where_clause.predicates {
                                                 [.., pred] => (pred.span().shrink_to_hi(), false),
                                                 [] => (
                                                     g.where_clause

compiler/rustc_typeck/src/collect.rs

@@ -229,14 +229,7 @@ fn reject_placeholder_type_signatures_in_item(tcx: TyCtxt<'tcx>, item: &'tcx hir
     let mut visitor = PlaceholderHirTyCollector::default();
     visitor.visit_item(item);
 
-    placeholder_type_error(
+    placeholder_type_error(tcx, Some(generics.span), generics.params, visitor.0, suggest, None);
-        tcx,
-        Some(generics.span),
-        &generics.params[..],
-        visitor.0,
-        suggest,
-        None,
-    );
 }
 
 impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
@@ -417,7 +410,7 @@ impl AstConv<'tcx> for ItemCtxt<'tcx> {
                         | hir::ItemKind::Struct(_, generics)
                         | hir::ItemKind::Union(_, generics) => {
                             let lt_name = get_new_lifetime_name(self.tcx, poly_trait_ref, generics);
-                            let (lt_sp, sugg) = match &generics.params[..] {
+                            let (lt_sp, sugg) = match generics.params {
                                 [] => (generics.span, format!("<{}>", lt_name)),
                                 [bound, ..] => {
                                     (bound.span.shrink_to_lo(), format!("{}, ", lt_name))

src/bootstrap/flags.rs

@@ -347,7 +347,7 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`",
         };
 
         // Done specifying what options are possible, so do the getopts parsing
-        let matches = opts.parse(&args[..]).unwrap_or_else(|e| {
+        let matches = opts.parse(args).unwrap_or_else(|e| {
             // Invalid argument/option format
             println!("\n{}\n", e);
             usage(1, &opts, false, &subcommand_help);

src/librustdoc/clean/mod.rs

@@ -975,7 +975,7 @@ where
 {
     fn clean(&self, cx: &DocContext<'_>) -> FnDecl {
         FnDecl {
-            inputs: (&self.0.inputs[..], self.1).clean(cx),
+            inputs: (self.0.inputs, self.1).clean(cx),
             output: self.0.output.clean(cx),
             c_variadic: self.0.c_variadic,
             attrs: Attributes::default(),
@@ -1939,7 +1939,7 @@ impl Clean<String> for Symbol {
 impl Clean<BareFunctionDecl> for hir::BareFnTy<'_> {
     fn clean(&self, cx: &DocContext<'_>) -> BareFunctionDecl {
         let (generic_params, decl) = enter_impl_trait(cx, || {
-            (self.generic_params.clean(cx), (&*self.decl, &self.param_names[..]).clean(cx))
+            (self.generic_params.clean(cx), (&*self.decl, self.param_names).clean(cx))
         });
         BareFunctionDecl { unsafety: self.unsafety, abi: self.abi, decl, generic_params }
     }