Auto merge of #69759 - Centril:rollup-0m0yh1l, r=Centril

Rollup of 6 pull requests

Successful merges:

 - #69656 (Use .next() instead of .nth(0) on iterators.)
 - #69674 (Rename DefKind::Method and TraitItemKind::Method )
 - #69676 (Pass correct place to `discriminant_switch_effect`)
 - #69706 (Use subslice patterns in slice methods)
 - #69714 (Make PlaceRef take just one lifetime)
 - #69727 (Avoid using `unwrap()` in suggestions)

Failed merges:

 - #69589 (ast: `Mac`/`Macro` -> `MacCall`)
 - #69680 (rustc_expand: Factor out `Annotatable::into_tokens` to a separate method)

r? @ghost

Author: bors

src/libcore/slice/mod.rs

@@ -103,7 +103,7 @@ impl<T> [T] {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn first(&self) -> Option<&T> {
-        self.get(0)
+        if let [first, ..] = self { Some(first) } else { None }
     }
 
     /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
@@ -121,7 +121,7 @@ impl<T> [T] {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn first_mut(&mut self) -> Option<&mut T> {
-        self.get_mut(0)
+        if let [first, ..] = self { Some(first) } else { None }
     }
 
     /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
@@ -139,7 +139,7 @@ impl<T> [T] {
     #[stable(feature = "slice_splits", since = "1.5.0")]
     #[inline]
     pub fn split_first(&self) -> Option<(&T, &[T])> {
-        if self.is_empty() { None } else { Some((&self[0], &self[1..])) }
+        if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
     }
 
     /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
@@ -159,12 +159,7 @@ impl<T> [T] {
     #[stable(feature = "slice_splits", since = "1.5.0")]
     #[inline]
     pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
-        if self.is_empty() {
-            None
-        } else {
-            let split = self.split_at_mut(1);
-            Some((&mut split.0[0], split.1))
-        }
+        if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
     }
 
     /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
@@ -182,8 +177,7 @@ impl<T> [T] {
     #[stable(feature = "slice_splits", since = "1.5.0")]
     #[inline]
     pub fn split_last(&self) -> Option<(&T, &[T])> {
-        let len = self.len();
-        if len == 0 { None } else { Some((&self[len - 1], &self[..(len - 1)])) }
+        if let [init @ .., last] = self { Some((last, init)) } else { None }
     }
 
     /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
@@ -203,13 +197,7 @@ impl<T> [T] {
     #[stable(feature = "slice_splits", since = "1.5.0")]
     #[inline]
     pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
-        let len = self.len();
-        if len == 0 {
-            None
-        } else {
-            let split = self.split_at_mut(len - 1);
-            Some((&mut split.1[0], split.0))
-        }
+        if let [init @ .., last] = self { Some((last, init)) } else { None }
     }
 
     /// Returns the last element of the slice, or `None` if it is empty.
@@ -226,8 +214,7 @@ impl<T> [T] {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn last(&self) -> Option<&T> {
-        let last_idx = self.len().checked_sub(1)?;
-        self.get(last_idx)
+        if let [.., last] = self { Some(last) } else { None }
     }
 
     /// Returns a mutable pointer to the last item in the slice.
@@ -245,8 +232,7 @@ impl<T> [T] {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn last_mut(&mut self) -> Option<&mut T> {
-        let last_idx = self.len().checked_sub(1)?;
-        self.get_mut(last_idx)
+        if let [.., last] = self { Some(last) } else { None }
     }
 
     /// Returns a reference to an element or subslice depending on the type of

src/librustc/hir/map/blocks.rs

@@ -60,7 +60,7 @@ impl MaybeFnLike for hir::ImplItem<'_> {
 impl MaybeFnLike for hir::TraitItem<'_> {
     fn is_fn_like(&self) -> bool {
         match self.kind {
-            hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => true,
+            hir::TraitItemKind::Fn(_, hir::TraitMethod::Provided(_)) => true,
             _ => false,
         }
     }
@@ -239,7 +239,7 @@ impl<'a> FnLikeNode<'a> {
                 _ => bug!("item FnLikeNode that is not fn-like"),
             },
             Node::TraitItem(ti) => match ti.kind {
-                hir::TraitItemKind::Method(ref sig, hir::TraitMethod::Provided(body)) => {
+                hir::TraitItemKind::Fn(ref sig, hir::TraitMethod::Provided(body)) => {
                     method(ti.hir_id, ti.ident, sig, None, body, ti.span, &ti.attrs)
                 }
                 _ => bug!("trait method FnLikeNode that is not fn-like"),

src/librustc/hir/map/mod.rs

@@ -51,7 +51,7 @@ impl<'hir> Entry<'hir> {
             },
 
             Node::TraitItem(ref item) => match item.kind {
-                TraitItemKind::Method(ref sig, _) => Some(&sig.decl),
+                TraitItemKind::Fn(ref sig, _) => Some(&sig.decl),
                 _ => None,
             },
 
@@ -77,7 +77,7 @@ impl<'hir> Entry<'hir> {
             },
 
             Node::TraitItem(item) => match &item.kind {
-                TraitItemKind::Method(sig, _) => Some(sig),
+                TraitItemKind::Fn(sig, _) => Some(sig),
                 _ => None,
             },
 
@@ -101,7 +101,7 @@ impl<'hir> Entry<'hir> {
 
             Node::TraitItem(item) => match item.kind {
                 TraitItemKind::Const(_, Some(body))
-                | TraitItemKind::Method(_, TraitMethod::Provided(body)) => Some(body),
+                | TraitItemKind::Fn(_, TraitMethod::Provided(body)) => Some(body),
                 _ => None,
             },
 
@@ -326,12 +326,12 @@ impl<'hir> Map<'hir> {
             },
             Node::TraitItem(item) => match item.kind {
                 TraitItemKind::Const(..) => DefKind::AssocConst,
-                TraitItemKind::Method(..) => DefKind::Method,
+                TraitItemKind::Fn(..) => DefKind::AssocFn,
                 TraitItemKind::Type(..) => DefKind::AssocTy,
             },
             Node::ImplItem(item) => match item.kind {
                 ImplItemKind::Const(..) => DefKind::AssocConst,
-                ImplItemKind::Method(..) => DefKind::Method,
+                ImplItemKind::Method(..) => DefKind::AssocFn,
                 ImplItemKind::TyAlias(..) => DefKind::AssocTy,
                 ImplItemKind::OpaqueTy(..) => DefKind::AssocOpaqueTy,
             },
@@ -472,7 +472,7 @@ impl<'hir> Map<'hir> {
             | Node::AnonConst(_) => BodyOwnerKind::Const,
             Node::Ctor(..)
             | Node::Item(&Item { kind: ItemKind::Fn(..), .. })
-            | Node::TraitItem(&TraitItem { kind: TraitItemKind::Method(..), .. })
+            | Node::TraitItem(&TraitItem { kind: TraitItemKind::Fn(..), .. })
             | Node::ImplItem(&ImplItem { kind: ImplItemKind::Method(..), .. }) => BodyOwnerKind::Fn,
             Node::Item(&Item { kind: ItemKind::Static(_, m, _), .. }) => BodyOwnerKind::Static(m),
             Node::Expr(&Expr { kind: ExprKind::Closure(..), .. }) => BodyOwnerKind::Closure,
@@ -800,7 +800,7 @@ impl<'hir> Map<'hir> {
                     _ => false,
                 },
                 Node::TraitItem(ti) => match ti.kind {
-                    TraitItemKind::Method(..) => true,
+                    TraitItemKind::Fn(..) => true,
                     _ => false,
                 },
                 Node::ImplItem(ii) => match ii.kind {
@@ -1311,7 +1311,7 @@ fn hir_id_to_string(map: &Map<'_>, id: HirId, include_id: bool) -> String {
         Some(Node::TraitItem(ti)) => {
             let kind = match ti.kind {
                 TraitItemKind::Const(..) => "assoc constant",
-                TraitItemKind::Method(..) => "trait method",
+                TraitItemKind::Fn(..) => "trait method",
                 TraitItemKind::Type(..) => "assoc type",
             };
 

src/librustc/middle/stability.rs

@@ -250,7 +250,7 @@ pub enum EvalResult {
 fn skip_stability_check_due_to_privacy(tcx: TyCtxt<'_>, mut def_id: DefId) -> bool {
     // Check if `def_id` is a trait method.
     match tcx.def_kind(def_id) {
-        Some(DefKind::Method) | Some(DefKind::AssocTy) | Some(DefKind::AssocConst) => {
+        Some(DefKind::AssocFn) | Some(DefKind::AssocTy) | Some(DefKind::AssocConst) => {
             if let ty::TraitContainer(trait_def_id) = tcx.associated_item(def_id).container {
                 // Trait methods do not declare visibility (even
                 // for visibility info in cstore). Use containing

src/librustc/mir/mod.rs

@@ -1446,7 +1446,7 @@ impl<'tcx> Debug for TerminatorKind<'tcx> {
         match successor_count {
             0 => Ok(()),
 
-            1 => write!(fmt, " -> {:?}", self.successors().nth(0).unwrap()),
+            1 => write!(fmt, " -> {:?}", self.successors().next().unwrap()),
 
             _ => {
                 write!(fmt, " -> [")?;
@@ -1827,9 +1827,9 @@ rustc_index::newtype_index! {
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct PlaceRef<'a, 'tcx> {
+pub struct PlaceRef<'tcx> {
     pub local: Local,
-    pub projection: &'a [PlaceElem<'tcx>],
+    pub projection: &'tcx [PlaceElem<'tcx>],
 }
 
 impl<'tcx> Place<'tcx> {
@@ -1864,7 +1864,7 @@ impl<'tcx> Place<'tcx> {
         self.as_ref().as_local()
     }
 
-    pub fn as_ref(&self) -> PlaceRef<'_, 'tcx> {
+    pub fn as_ref(&self) -> PlaceRef<'tcx> {
         PlaceRef { local: self.local, projection: &self.projection }
     }
 }
@@ -1875,7 +1875,7 @@ impl From<Local> for Place<'_> {
     }
 }
 
-impl<'a, 'tcx> PlaceRef<'a, 'tcx> {
+impl<'tcx> PlaceRef<'tcx> {
     /// Finds the innermost `Local` from this `Place`, *if* it is either a local itself or
     /// a single deref of a local.
     //

src/librustc/ty/context.rs

@@ -611,7 +611,7 @@ impl<'tcx> TypeckTables<'tcx> {
         }
 
         match self.type_dependent_defs().get(expr.hir_id) {
-            Some(Ok((DefKind::Method, _))) => true,
+            Some(Ok((DefKind::AssocFn, _))) => true,
             _ => false,
         }
     }

src/librustc/ty/mod.rs

@@ -230,7 +230,7 @@ impl AssocItem {
     pub fn def_kind(&self) -> DefKind {
         match self.kind {
             AssocKind::Const => DefKind::AssocConst,
-            AssocKind::Method => DefKind::Method,
+            AssocKind::Method => DefKind::AssocFn,
             AssocKind::Type => DefKind::AssocTy,
             AssocKind::OpaqueTy => DefKind::AssocOpaqueTy,
         }
@@ -2872,7 +2872,7 @@ impl<'tcx> TyCtxt<'tcx> {
             }
         } else {
             match self.def_kind(def_id).expect("no def for `DefId`") {
-                DefKind::AssocConst | DefKind::Method | DefKind::AssocTy => true,
+                DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy => true,
                 _ => false,
             }
         };
@@ -3051,7 +3051,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// `DefId` of the impl that the method belongs to; otherwise, returns `None`.
     pub fn impl_of_method(self, def_id: DefId) -> Option<DefId> {
         let item = if def_id.krate != LOCAL_CRATE {
-            if let Some(DefKind::Method) = self.def_kind(def_id) {
+            if let Some(DefKind::AssocFn) = self.def_kind(def_id) {
                 Some(self.associated_item(def_id))
             } else {
                 None

src/librustc/ty/util.rs

@@ -357,7 +357,7 @@ impl<'tcx> TyCtxt<'tcx> {
         let mut dtor_did = None;
         let ty = self.type_of(adt_did);
         self.for_each_relevant_impl(drop_trait, ty, |impl_did| {
-            if let Some(item) = self.associated_items(impl_did).in_definition_order().nth(0) {
+            if let Some(item) = self.associated_items(impl_did).in_definition_order().next() {
                 if validate(self, impl_did).is_ok() {
                     dtor_did = Some(item.def_id);
                 }

src/librustc_ast_lowering/item.rs

@@ -761,13 +761,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let names = self.lower_fn_params_to_names(&sig.decl);
                 let (generics, sig) =
                     self.lower_method_sig(generics, sig, trait_item_def_id, false, None);
-                (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Required(names)))
+                (generics, hir::TraitItemKind::Fn(sig, hir::TraitMethod::Required(names)))
             }
             AssocItemKind::Fn(_, ref sig, ref generics, Some(ref body)) => {
                 let body_id = self.lower_fn_body_block(i.span, &sig.decl, Some(body));
                 let (generics, sig) =
                     self.lower_method_sig(generics, sig, trait_item_def_id, false, None);
-                (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Provided(body_id)))
+                (generics, hir::TraitItemKind::Fn(sig, hir::TraitMethod::Provided(body_id)))
             }
             AssocItemKind::TyAlias(_, ref generics, ref bounds, ref default) => {
                 let ty = default.as_ref().map(|x| self.lower_ty(x, ImplTraitContext::disallowed()));

src/librustc_ast_lowering/path.rs

@@ -75,7 +75,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             ParenthesizedGenericArgs::Ok
                         }
                         // `a::b::Trait(Args)::TraitItem`
-                        Res::Def(DefKind::Method, _)
+                        Res::Def(DefKind::AssocFn, _)
                         | Res::Def(DefKind::AssocConst, _)
                         | Res::Def(DefKind::AssocTy, _)
                             if i + 2 == proj_start =>