Auto merge of #88615 - flip1995:clippyup, r=Manishearth

Update Clippy

r? `@Manishearth`

12 files changed, 519 insertions, 164 deletions

diff --git a/src/tools/clippy/clippy_utils/Cargo.toml b/src/tools/clippy/clippy_utils/Cargo.toml
index c65b2958ec5..4c038a99795 100644
--- a/src/tools/clippy/clippy_utils/Cargo.toml
+++ b/src/tools/clippy/clippy_utils/Cargo.toml
@@ -1,15 +1,11 @@
 [package]
 name = "clippy_utils"
-version = "0.1.56"
+version = "0.1.57"
 edition = "2018"
 publish = false
 
 [dependencies]
 if_chain = "1.0.0"
-itertools = "0.9"
-regex-syntax = "0.6"
-serde = { version = "1.0", features = ["derive"] }
-unicode-normalization = "0.1"
 rustc-semver="1.1.0"
 
 [features]
diff --git a/src/tools/clippy/clippy_utils/src/diagnostics.rs b/src/tools/clippy/clippy_utils/src/diagnostics.rs
index 71cfa196fc3..9302e5c21fa 100644
--- a/src/tools/clippy/clippy_utils/src/diagnostics.rs
+++ b/src/tools/clippy/clippy_utils/src/diagnostics.rs
@@ -21,7 +21,7 @@ fn docs_link(diag: &mut DiagnosticBuilder<'_>, lint: &'static Lint) {
                 "for further information visit https://rust-lang.github.io/rust-clippy/{}/index.html#{}",
                 &option_env!("RUST_RELEASE_NUM").map_or("master".to_string(), |n| {
                     // extract just major + minor version and ignore patch versions
-                    format!("rust-{}", n.rsplitn(2, '.').nth(1).unwrap())
+                    format!("rust-{}", n.rsplit_once('.').unwrap().1)
                 }),
                 lint
             ));
diff --git a/src/tools/clippy/clippy_utils/src/higher.rs b/src/tools/clippy/clippy_utils/src/higher.rs
index c06b894a738..05a4a014319 100644
--- a/src/tools/clippy/clippy_utils/src/higher.rs
+++ b/src/tools/clippy/clippy_utils/src/higher.rs
@@ -6,33 +6,38 @@ use crate::{is_expn_of, match_def_path, paths};
 use if_chain::if_chain;
 use rustc_ast::ast::{self, LitKind};
 use rustc_hir as hir;
-use rustc_hir::{Block, BorrowKind, Expr, ExprKind, LoopSource, Node, Pat, StmtKind, UnOp};
+use rustc_hir::{Arm, Block, BorrowKind, Expr, ExprKind, LoopSource, MatchSource, Node, Pat, StmtKind, UnOp};
 use rustc_lint::LateContext;
 use rustc_span::{sym, ExpnKind, Span, Symbol};
 
 /// The essential nodes of a desugared for loop as well as the entire span:
 /// `for pat in arg { body }` becomes `(pat, arg, body)`. Return `(pat, arg, body, span)`.
 pub struct ForLoop<'tcx> {
+    /// `for` loop item
     pub pat: &'tcx hir::Pat<'tcx>,
+    /// `IntoIterator` argument
     pub arg: &'tcx hir::Expr<'tcx>,
+    /// `for` loop body
     pub body: &'tcx hir::Expr<'tcx>,
+    /// entire `for` loop span
     pub span: Span,
 }
 
 impl<'tcx> ForLoop<'tcx> {
     #[inline]
+    /// Parses a desugared `for` loop
     pub fn hir(expr: &Expr<'tcx>) -> Option<Self> {
         if_chain! {
-            if let hir::ExprKind::Match(ref iterexpr, ref arms, hir::MatchSource::ForLoopDesugar) = expr.kind;
+            if let hir::ExprKind::Match(iterexpr, arms, hir::MatchSource::ForLoopDesugar) = expr.kind;
             if let Some(first_arm) = arms.get(0);
-            if let hir::ExprKind::Call(_, ref iterargs) = iterexpr.kind;
+            if let hir::ExprKind::Call(_, iterargs) = iterexpr.kind;
             if let Some(first_arg) = iterargs.get(0);
             if iterargs.len() == 1 && arms.len() == 1 && first_arm.guard.is_none();
-            if let hir::ExprKind::Loop(ref block, ..) = first_arm.body.kind;
+            if let hir::ExprKind::Loop(block, ..) = first_arm.body.kind;
             if block.expr.is_none();
             if let [ _, _, ref let_stmt, ref body ] = *block.stmts;
-            if let hir::StmtKind::Local(ref local) = let_stmt.kind;
-            if let hir::StmtKind::Expr(ref body_expr) = body.kind;
+            if let hir::StmtKind::Local(local) = let_stmt.kind;
+            if let hir::StmtKind::Expr(body_expr) = body.kind;
             then {
                 return Some(Self {
                     pat: &*local.pat,
@@ -46,14 +51,19 @@ impl<'tcx> ForLoop<'tcx> {
     }
 }
 
+/// An `if` expression without `DropTemps`
 pub struct If<'hir> {
+    /// `if` condition
     pub cond: &'hir Expr<'hir>,
-    pub r#else: Option<&'hir Expr<'hir>>,
+    /// `if` then expression
     pub then: &'hir Expr<'hir>,
+    /// `else` expression
+    pub r#else: Option<&'hir Expr<'hir>>,
 }
 
 impl<'hir> If<'hir> {
     #[inline]
+    /// Parses an `if` expression
     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
         if let ExprKind::If(
             Expr {
@@ -64,21 +74,27 @@ impl<'hir> If<'hir> {
             r#else,
         ) = expr.kind
         {
-            Some(Self { cond, r#else, then })
+            Some(Self { cond, then, r#else })
         } else {
             None
         }
     }
 }
 
+/// An `if let` expression
 pub struct IfLet<'hir> {
+    /// `if let` pattern
     pub let_pat: &'hir Pat<'hir>,
+    /// `if let` scrutinee
     pub let_expr: &'hir Expr<'hir>,
+    /// `if let` then expression
     pub if_then: &'hir Expr<'hir>,
+    /// `if let` else expression
     pub if_else: Option<&'hir Expr<'hir>>,
 }
 
 impl<'hir> IfLet<'hir> {
+    /// Parses an `if let` expression
     pub fn hir(cx: &LateContext<'_>, expr: &Expr<'hir>) -> Option<Self> {
         if let ExprKind::If(
             Expr {
@@ -92,7 +108,14 @@ impl<'hir> IfLet<'hir> {
             let hir = cx.tcx.hir();
             let mut iter = hir.parent_iter(expr.hir_id);
             if let Some((_, Node::Block(Block { stmts: [], .. }))) = iter.next() {
-                if let Some((_, Node::Expr(Expr { kind: ExprKind::Loop(_, _, LoopSource::While, _), .. }))) = iter.next() {
+                if let Some((
+                    _,
+                    Node::Expr(Expr {
+                        kind: ExprKind::Loop(_, _, LoopSource::While, _),
+                        ..
+                    }),
+                )) = iter.next()
+                {
                     // while loop desugar
                     return None;
                 }
@@ -108,14 +131,49 @@ impl<'hir> IfLet<'hir> {
     }
 }
 
+/// An `if let` or `match` expression. Useful for lints that trigger on one or the other.
+pub enum IfLetOrMatch<'hir> {
+    /// Any `match` expression
+    Match(&'hir Expr<'hir>, &'hir [Arm<'hir>], MatchSource),
+    /// scrutinee, pattern, then block, else block
+    IfLet(
+        &'hir Expr<'hir>,
+        &'hir Pat<'hir>,
+        &'hir Expr<'hir>,
+        Option<&'hir Expr<'hir>>,
+    ),
+}
+
+impl<'hir> IfLetOrMatch<'hir> {
+    /// Parses an `if let` or `match` expression
+    pub fn parse(cx: &LateContext<'_>, expr: &Expr<'hir>) -> Option<Self> {
+        match expr.kind {
+            ExprKind::Match(expr, arms, source) => Some(Self::Match(expr, arms, source)),
+            _ => IfLet::hir(cx, expr).map(
+                |IfLet {
+                     let_expr,
+                     let_pat,
+                     if_then,
+                     if_else,
+                 }| { Self::IfLet(let_expr, let_pat, if_then, if_else) },
+            ),
+        }
+    }
+}
+
+/// An `if` or `if let` expression
 pub struct IfOrIfLet<'hir> {
+    /// `if` condition that is maybe a `let` expression
     pub cond: &'hir Expr<'hir>,
-    pub r#else: Option<&'hir Expr<'hir>>,
+    /// `if` then expression
     pub then: &'hir Expr<'hir>,
+    /// `else` expression
+    pub r#else: Option<&'hir Expr<'hir>>,
 }
 
 impl<'hir> IfOrIfLet<'hir> {
     #[inline]
+    /// Parses an `if` or `if let` expression
     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
         if let ExprKind::If(cond, then, r#else) = expr.kind {
             if let ExprKind::DropTemps(new_cond) = cond.kind {
@@ -126,7 +184,7 @@ impl<'hir> IfOrIfLet<'hir> {
                 });
             }
             if let ExprKind::Let(..) = cond.kind {
-                return Some(Self { cond, r#else, then });
+                return Some(Self { cond, then, r#else });
             }
         }
         None
@@ -155,7 +213,7 @@ impl<'a> Range<'a> {
         }
 
         match expr.kind {
-            hir::ExprKind::Call(ref path, ref args)
+            hir::ExprKind::Call(path, args)
                 if matches!(
                     path.kind,
                     hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, _))
@@ -167,7 +225,7 @@ impl<'a> Range<'a> {
                     limits: ast::RangeLimits::Closed,
                 })
             },
-            hir::ExprKind::Struct(ref path, ref fields, None) => match path {
+            hir::ExprKind::Struct(path, fields, None) => match &path {
                 hir::QPath::LangItem(hir::LangItem::RangeFull, _) => Some(Range {
                     start: None,
                     end: None,
@@ -213,7 +271,7 @@ impl<'a> VecArgs<'a> {
     /// from `vec!`.
     pub fn hir(cx: &LateContext<'_>, expr: &'a hir::Expr<'_>) -> Option<VecArgs<'a>> {
         if_chain! {
-            if let hir::ExprKind::Call(ref fun, ref args) = expr.kind;
+            if let hir::ExprKind::Call(fun, args) = expr.kind;
             if let hir::ExprKind::Path(ref qpath) = fun.kind;
             if is_expn_of(fun.span, "vec").is_some();
             if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
@@ -225,10 +283,10 @@ impl<'a> VecArgs<'a> {
                 else if match_def_path(cx, fun_def_id, &paths::SLICE_INTO_VEC) && args.len() == 1 {
                     // `vec![a, b, c]` case
                     if_chain! {
-                        if let hir::ExprKind::Box(ref boxed) = args[0].kind;
-                        if let hir::ExprKind::Array(ref args) = boxed.kind;
+                        if let hir::ExprKind::Box(boxed) = args[0].kind;
+                        if let hir::ExprKind::Array(args) = boxed.kind;
                         then {
-                            return Some(VecArgs::Vec(&*args));
+                            return Some(VecArgs::Vec(args));
                         }
                     }
 
@@ -247,14 +305,17 @@ impl<'a> VecArgs<'a> {
     }
 }
 
+/// A desugared `while` loop
 pub struct While<'hir> {
-    pub if_cond: &'hir Expr<'hir>,
-    pub if_then: &'hir Expr<'hir>,
-    pub if_else: Option<&'hir Expr<'hir>>,
+    /// `while` loop condition
+    pub condition: &'hir Expr<'hir>,
+    /// `while` loop body
+    pub body: &'hir Expr<'hir>,
 }
 
 impl<'hir> While<'hir> {
     #[inline]
+    /// Parses a desugared `while` loop
     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
         if let ExprKind::Loop(
             Block {
@@ -263,11 +324,11 @@ impl<'hir> While<'hir> {
                         kind:
                             ExprKind::If(
                                 Expr {
-                                    kind: ExprKind::DropTemps(if_cond),
+                                    kind: ExprKind::DropTemps(condition),
                                     ..
                                 },
-                                if_then,
-                                if_else_ref,
+                                body,
+                                _,
                             ),
                         ..
                     }),
@@ -278,59 +339,53 @@ impl<'hir> While<'hir> {
             _,
         ) = expr.kind
         {
-            let if_else = *if_else_ref;
-            return Some(Self {
-                if_cond,
-                if_then,
-                if_else,
-            });
+            return Some(Self { condition, body });
         }
         None
     }
 }
 
+/// A desugared `while let` loop
 pub struct WhileLet<'hir> {
-    pub if_expr: &'hir Expr<'hir>,
+    /// `while let` loop item pattern
     pub let_pat: &'hir Pat<'hir>,
+    /// `while let` loop scrutinee
     pub let_expr: &'hir Expr<'hir>,
+    /// `while let` loop body
     pub if_then: &'hir Expr<'hir>,
-    pub if_else: Option<&'hir Expr<'hir>>,
 }
 
 impl<'hir> WhileLet<'hir> {
     #[inline]
+    /// Parses a desugared `while let` loop
     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
         if let ExprKind::Loop(
             Block {
-                expr: Some(if_expr), ..
+                expr:
+                    Some(Expr {
+                        kind:
+                            ExprKind::If(
+                                Expr {
+                                    kind: ExprKind::Let(let_pat, let_expr, _),
+                                    ..
+                                },
+                                if_then,
+                                _,
+                            ),
+                        ..
+                    }),
+                ..
             },
             _,
             LoopSource::While,
             _,
         ) = expr.kind
         {
-            if let Expr {
-                kind:
-                    ExprKind::If(
-                        Expr {
-                            kind: ExprKind::Let(let_pat, let_expr, _),
-                            ..
-                        },
-                        if_then,
-                        if_else_ref,
-                    ),
-                ..
-            } = if_expr
-            {
-                let if_else = *if_else_ref;
-                return Some(Self {
-                    if_expr,
-                    let_pat,
-                    let_expr,
-                    if_then,
-                    if_else,
-                });
-            }
+            return Some(Self {
+                let_pat,
+                let_expr,
+                if_then,
+            });
         }
         None
     }
@@ -532,7 +587,7 @@ pub fn is_from_for_desugar(local: &hir::Local<'_>) -> bool {
     // }
     // ```
     if_chain! {
-        if let Some(ref expr) = local.init;
+        if let Some(expr) = local.init;
         if let hir::ExprKind::Match(_, _, hir::MatchSource::ForLoopDesugar) = expr.kind;
         then {
             return true;
diff --git a/src/tools/clippy/clippy_utils/src/hir_utils.rs b/src/tools/clippy/clippy_utils/src/hir_utils.rs
index a44f2df2fd6..6e9a1de21ee 100644
--- a/src/tools/clippy/clippy_utils/src/hir_utils.rs
+++ b/src/tools/clippy/clippy_utils/src/hir_utils.rs
@@ -232,9 +232,7 @@ impl HirEqInterExpr<'_, '_, '_> {
             (&ExprKind::If(lc, lt, ref le), &ExprKind::If(rc, rt, ref re)) => {
                 self.eq_expr(lc, rc) && self.eq_expr(&**lt, &**rt) && both(le, re, |l, r| self.eq_expr(l, r))
             },
-            (&ExprKind::Let(ref lp, ref le, _), &ExprKind::Let(ref rp, ref re, _)) => {
-                self.eq_pat(lp, rp) && self.eq_expr(le, re)
-            },
+            (&ExprKind::Let(lp, le, _), &ExprKind::Let(rp, re, _)) => self.eq_pat(lp, rp) && self.eq_expr(le, re),
             (&ExprKind::Lit(ref l), &ExprKind::Lit(ref r)) => l.node == r.node,
             (&ExprKind::Loop(lb, ref ll, ref lls, _), &ExprKind::Loop(rb, ref rl, ref rls, _)) => {
                 lls == rls && self.eq_block(lb, rb) && both(ll, rl, |l, r| l.ident.name == r.ident.name)
@@ -668,7 +666,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                     }
                 }
             },
-            ExprKind::Let(ref pat, ref expr, _) => {
+            ExprKind::Let(pat, expr, _) => {
                 self.hash_expr(expr);
                 self.hash_pat(pat);
             },
diff --git a/src/tools/clippy/clippy_utils/src/lib.rs b/src/tools/clippy/clippy_utils/src/lib.rs
index 0906f958cfb..da259511fe0 100644
--- a/src/tools/clippy/clippy_utils/src/lib.rs
+++ b/src/tools/clippy/clippy_utils/src/lib.rs
@@ -2,6 +2,7 @@
 #![feature(in_band_lifetimes)]
 #![feature(iter_zip)]
 #![feature(rustc_private)]
+#![feature(control_flow_enum)]
 #![recursion_limit = "512"]
 #![cfg_attr(feature = "deny-warnings", deny(warnings))]
 #![allow(clippy::missing_errors_doc, clippy::missing_panics_doc, clippy::must_use_candidate)]
@@ -62,23 +63,27 @@ use std::collections::hash_map::Entry;
 use std::hash::BuildHasherDefault;
 
 use if_chain::if_chain;
-use rustc_ast::ast::{self, Attribute, BorrowKind, LitKind};
+use rustc_ast::ast::{self, Attribute, LitKind};
 use rustc_data_structures::unhash::UnhashMap;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
+use rustc_hir::hir_id::{HirIdMap, HirIdSet};
 use rustc_hir::intravisit::{self, walk_expr, ErasedMap, FnKind, NestedVisitorMap, Visitor};
-use rustc_hir::LangItem::{ResultErr, ResultOk};
+use rustc_hir::LangItem::{OptionNone, ResultErr, ResultOk};
 use rustc_hir::{
     def, Arm, BindingAnnotation, Block, Body, Constness, Destination, Expr, ExprKind, FnDecl, GenericArgs, HirId, Impl,
-    ImplItem, ImplItemKind, IsAsync, Item, ItemKind, LangItem, Local, MatchSource, Node, Param, Pat, PatKind, Path,
-    PathSegment, PrimTy, QPath, Stmt, StmtKind, TraitItem, TraitItemKind, TraitRef, TyKind, UnOp,
+    ImplItem, ImplItemKind, IsAsync, Item, ItemKind, LangItem, Local, MatchSource, Mutability, Node, Param, Pat,
+    PatKind, Path, PathSegment, PrimTy, QPath, Stmt, StmtKind, TraitItem, TraitItemKind, TraitRef, TyKind, UnOp,
 };
 use rustc_lint::{LateContext, Level, Lint, LintContext};
 use rustc_middle::hir::exports::Export;
 use rustc_middle::hir::map::Map;
+use rustc_middle::hir::place::PlaceBase;
 use rustc_middle::ty as rustc_ty;
-use rustc_middle::ty::{layout::IntegerExt, DefIdTree, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
+use rustc_middle::ty::binding::BindingMode;
+use rustc_middle::ty::{layout::IntegerExt, BorrowKind, DefIdTree, Ty, TyCtxt, TypeAndMut, TypeFoldable, UpvarCapture};
 use rustc_semver::RustcVersion;
 use rustc_session::Session;
 use rustc_span::hygiene::{ExpnKind, MacroKind};
@@ -89,7 +94,7 @@ use rustc_span::{Span, DUMMY_SP};
 use rustc_target::abi::Integer;
 
 use crate::consts::{constant, Constant};
-use crate::ty::{can_partially_move_ty, is_recursively_primitive_type};
+use crate::ty::{can_partially_move_ty, is_copy, is_recursively_primitive_type};
 
 pub fn parse_msrv(msrv: &str, sess: Option<&Session>, span: Option<Span>) -> Option<RustcVersion> {
     if let Ok(version) = RustcVersion::parse(msrv) {
@@ -255,7 +260,17 @@ pub fn in_macro(span: Span) -> bool {
 }
 
 pub fn is_unit_expr(expr: &Expr<'_>) -> bool {
-    matches!(expr.kind, ExprKind::Block(Block { stmts: [], expr: None, .. }, _) | ExprKind::Tup([]))
+    matches!(
+        expr.kind,
+        ExprKind::Block(
+            Block {
+                stmts: [],
+                expr: None,
+                ..
+            },
+            _
+        ) | ExprKind::Tup([])
+    )
 }
 
 /// Checks if given pattern is a wildcard (`_`)
@@ -629,12 +644,106 @@ pub fn can_mut_borrow_both(cx: &LateContext<'_>, e1: &Expr<'_>, e2: &Expr<'_>) -
     false
 }
 
+/// Returns true if the `def_id` associated with the `path` is recognized as a "default-equivalent"
+/// constructor from the std library
+fn is_default_equivalent_ctor(cx: &LateContext<'_>, def_id: DefId, path: &QPath<'_>) -> bool {
+    let std_types_symbols = &[
+        sym::string_type,
+        sym::vec_type,
+        sym::vecdeque_type,
+        sym::LinkedList,
+        sym::hashmap_type,
+        sym::BTreeMap,
+        sym::hashset_type,
+        sym::BTreeSet,
+        sym::BinaryHeap,
+    ];
+
+    if let QPath::TypeRelative(_, method) = path {
+        if method.ident.name == sym::new {
+            if let Some(impl_did) = cx.tcx.impl_of_method(def_id) {
+                if let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def() {
+                    return std_types_symbols
+                        .iter()
+                        .any(|&symbol| cx.tcx.is_diagnostic_item(symbol, adt.did));
+                }
+            }
+        }
+    }
+    false
+}
+
+/// Returns true if the expr is equal to `Default::default()` of it's type when evaluated.
+/// It doesn't cover all cases, for example indirect function calls (some of std
+/// functions are supported) but it is the best we have.
+pub fn is_default_equivalent(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
+    match &e.kind {
+        ExprKind::Lit(lit) => match lit.node {
+            LitKind::Bool(false) | LitKind::Int(0, _) => true,
+            LitKind::Str(s, _) => s.is_empty(),
+            _ => false,
+        },
+        ExprKind::Tup(items) | ExprKind::Array(items) => items.iter().all(|x| is_default_equivalent(cx, x)),
+        ExprKind::Repeat(x, _) => is_default_equivalent(cx, x),
+        ExprKind::Call(repl_func, _) => if_chain! {
+            if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
+            if let Some(repl_def_id) = cx.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
+            if is_diag_trait_item(cx, repl_def_id, sym::Default)
+                || is_default_equivalent_ctor(cx, repl_def_id, repl_func_qpath);
+            then {
+                true
+            }
+            else {
+                false
+            }
+        },
+        ExprKind::Path(qpath) => is_lang_ctor(cx, qpath, OptionNone),
+        ExprKind::AddrOf(rustc_hir::BorrowKind::Ref, _, expr) => matches!(expr.kind, ExprKind::Array([])),
+        _ => false,
+    }
+}
+
 /// Checks if the top level expression can be moved into a closure as is.
-pub fn can_move_expr_to_closure_no_visit(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, jump_targets: &[HirId]) -> bool {
+/// Currently checks for:
+/// * Break/Continue outside the given loop HIR ids.
+/// * Yield/Return statments.
+/// * Inline assembly.
+/// * Usages of a field of a local where the type of the local can be partially moved.
+///
+/// For example, given the following function:
+///
+/// ```
+/// fn f<'a>(iter: &mut impl Iterator<Item = (usize, &'a mut String)>) {
+///     for item in iter {
+///         let s = item.1;
+///         if item.0 > 10 {
+///             continue;
+///         } else {
+///             s.clear();
+///         }
+///     }
+/// }
+/// ```
+///
+/// When called on the expression `item.0` this will return false unless the local `item` is in the
+/// `ignore_locals` set. The type `(usize, &mut String)` can have the second element moved, so it
+/// isn't always safe to move into a closure when only a single field is needed.
+///
+/// When called on the `continue` expression this will return false unless the outer loop expression
+/// is in the `loop_ids` set.
+///
+/// Note that this check is not recursive, so passing the `if` expression will always return true
+/// even though sub-expressions might return false.
+pub fn can_move_expr_to_closure_no_visit(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    loop_ids: &[HirId],
+    ignore_locals: &HirIdSet,
+) -> bool {
     match expr.kind {
         ExprKind::Break(Destination { target_id: Ok(id), .. }, _)
         | ExprKind::Continue(Destination { target_id: Ok(id), .. })
-            if jump_targets.contains(&id) =>
+            if loop_ids.contains(&id) =>
         {
             true
         },
@@ -646,25 +755,170 @@ pub fn can_move_expr_to_closure_no_visit(cx: &LateContext<'tcx>, expr: &'tcx Exp
         | ExprKind::LlvmInlineAsm(_) => false,
         // Accessing a field of a local value can only be done if the type isn't
         // partially moved.
-        ExprKind::Field(base_expr, _)
-            if matches!(
-                base_expr.kind,
-                ExprKind::Path(QPath::Resolved(_, Path { res: Res::Local(_), .. }))
-            ) && can_partially_move_ty(cx, cx.typeck_results().expr_ty(base_expr)) =>
-        {
+        ExprKind::Field(
+            &Expr {
+                hir_id,
+                kind:
+                    ExprKind::Path(QPath::Resolved(
+                        _,
+                        Path {
+                            res: Res::Local(local_id),
+                            ..
+                        },
+                    )),
+                ..
+            },
+            _,
+        ) if !ignore_locals.contains(local_id) && can_partially_move_ty(cx, cx.typeck_results().node_type(hir_id)) => {
             // TODO: check if the local has been partially moved. Assume it has for now.
             false
-        }
+        },
         _ => true,
     }
 }
 
-/// Checks if the expression can be moved into a closure as is.
-pub fn can_move_expr_to_closure(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
+/// How a local is captured by a closure
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CaptureKind {
+    Value,
+    Ref(Mutability),
+}
+impl CaptureKind {
+    pub fn is_imm_ref(self) -> bool {
+        self == Self::Ref(Mutability::Not)
+    }
+}
+impl std::ops::BitOr for CaptureKind {
+    type Output = Self;
+    fn bitor(self, rhs: Self) -> Self::Output {
+        match (self, rhs) {
+            (CaptureKind::Value, _) | (_, CaptureKind::Value) => CaptureKind::Value,
+            (CaptureKind::Ref(Mutability::Mut), CaptureKind::Ref(_))
+            | (CaptureKind::Ref(_), CaptureKind::Ref(Mutability::Mut)) => CaptureKind::Ref(Mutability::Mut),
+            (CaptureKind::Ref(Mutability::Not), CaptureKind::Ref(Mutability::Not)) => CaptureKind::Ref(Mutability::Not),
+        }
+    }
+}
+impl std::ops::BitOrAssign for CaptureKind {
+    fn bitor_assign(&mut self, rhs: Self) {
+        *self = *self | rhs;
+    }
+}
+
+/// Given an expression referencing a local, determines how it would be captured in a closure.
+/// Note as this will walk up to parent expressions until the capture can be determined it should
+/// only be used while making a closure somewhere a value is consumed. e.g. a block, match arm, or
+/// function argument (other than a receiver).
+pub fn capture_local_usage(cx: &LateContext<'tcx>, e: &Expr<'_>) -> CaptureKind {
+    fn pat_capture_kind(cx: &LateContext<'_>, pat: &Pat<'_>) -> CaptureKind {
+        let mut capture = CaptureKind::Ref(Mutability::Not);
+        pat.each_binding_or_first(&mut |_, id, span, _| match cx
+            .typeck_results()
+            .extract_binding_mode(cx.sess(), id, span)
+            .unwrap()
+        {
+            BindingMode::BindByValue(_) if !is_copy(cx, cx.typeck_results().node_type(id)) => {
+                capture = CaptureKind::Value;
+            },
+            BindingMode::BindByReference(Mutability::Mut) if capture != CaptureKind::Value => {
+                capture = CaptureKind::Ref(Mutability::Mut);
+            },
+            _ => (),
+        });
+        capture
+    }
+
+    debug_assert!(matches!(
+        e.kind,
+        ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(_), .. }))
+    ));
+
+    let map = cx.tcx.hir();
+    let mut child_id = e.hir_id;
+    let mut capture = CaptureKind::Value;
+    let mut capture_expr_ty = e;
+
+    for (parent_id, parent) in map.parent_iter(e.hir_id) {
+        if let [Adjustment {
+            kind: Adjust::Deref(_) | Adjust::Borrow(AutoBorrow::Ref(..)),
+            target,
+        }, ref adjust @ ..] = *cx
+            .typeck_results()
+            .adjustments()
+            .get(child_id)
+            .map_or(&[][..], |x| &**x)
+        {
+            if let rustc_ty::RawPtr(TypeAndMut { mutbl: mutability, .. }) | rustc_ty::Ref(_, _, mutability) =
+                *adjust.last().map_or(target, |a| a.target).kind()
+            {
+                return CaptureKind::Ref(mutability);
+            }
+        }
+
+        match parent {
+            Node::Expr(e) => match e.kind {
+                ExprKind::AddrOf(_, mutability, _) => return CaptureKind::Ref(mutability),
+                ExprKind::Index(..) | ExprKind::Unary(UnOp::Deref, _) => capture = CaptureKind::Ref(Mutability::Not),
+                ExprKind::Assign(lhs, ..) | ExprKind::Assign(_, lhs, _) if lhs.hir_id == child_id => {
+                    return CaptureKind::Ref(Mutability::Mut);
+                },
+                ExprKind::Field(..) => {
+                    if capture == CaptureKind::Value {
+                        capture_expr_ty = e;
+                    }
+                },
+                ExprKind::Let(pat, ..) => {
+                    let mutability = match pat_capture_kind(cx, pat) {
+                        CaptureKind::Value => Mutability::Not,
+                        CaptureKind::Ref(m) => m,
+                    };
+                    return CaptureKind::Ref(mutability);
+                },
+                ExprKind::Match(_, arms, _) => {
+                    let mut mutability = Mutability::Not;
+                    for capture in arms.iter().map(|arm| pat_capture_kind(cx, arm.pat)) {
+                        match capture {
+                            CaptureKind::Value => break,
+                            CaptureKind::Ref(Mutability::Mut) => mutability = Mutability::Mut,
+                            CaptureKind::Ref(Mutability::Not) => (),
+                        }
+                    }
+                    return CaptureKind::Ref(mutability);
+                },
+                _ => break,
+            },
+            Node::Local(l) => match pat_capture_kind(cx, l.pat) {
+                CaptureKind::Value => break,
+                capture @ CaptureKind::Ref(_) => return capture,
+            },
+            _ => break,
+        }
+
+        child_id = parent_id;
+    }
+
+    if capture == CaptureKind::Value && is_copy(cx, cx.typeck_results().expr_ty(capture_expr_ty)) {
+        // Copy types are never automatically captured by value.
+        CaptureKind::Ref(Mutability::Not)
+    } else {
+        capture
+    }
+}
+
+/// Checks if the expression can be moved into a closure as is. This will return a list of captures
+/// if so, otherwise, `None`.
+pub fn can_move_expr_to_closure(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<HirIdMap<CaptureKind>> {
     struct V<'cx, 'tcx> {
         cx: &'cx LateContext<'tcx>,
+        // Stack of potential break targets contained in the expression.
         loops: Vec<HirId>,
+        /// Local variables created in the expression. These don't need to be captured.
+        locals: HirIdSet,
+        /// Whether this expression can be turned into a closure.
         allow_closure: bool,
+        /// Locals which need to be captured, and whether they need to be by value, reference, or
+        /// mutable reference.
+        captures: HirIdMap<CaptureKind>,
     }
     impl Visitor<'tcx> for V<'_, 'tcx> {
         type Map = ErasedMap<'tcx>;
@@ -676,24 +930,67 @@ pub fn can_move_expr_to_closure(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) ->
             if !self.allow_closure {
                 return;
             }
-            if let ExprKind::Loop(b, ..) = e.kind {
-                self.loops.push(e.hir_id);
-                self.visit_block(b);
-                self.loops.pop();
-            } else {
-                self.allow_closure &= can_move_expr_to_closure_no_visit(self.cx, e, &self.loops);
-                walk_expr(self, e);
+
+            match e.kind {
+                ExprKind::Path(QPath::Resolved(None, &Path { res: Res::Local(l), .. })) => {
+                    if !self.locals.contains(&l) {
+                        let cap = capture_local_usage(self.cx, e);
+                        self.captures.entry(l).and_modify(|e| *e |= cap).or_insert(cap);
+                    }
+                },
+                ExprKind::Closure(..) => {
+                    let closure_id = self.cx.tcx.hir().local_def_id(e.hir_id).to_def_id();
+                    for capture in self.cx.typeck_results().closure_min_captures_flattened(closure_id) {
+                        let local_id = match capture.place.base {
+                            PlaceBase::Local(id) => id,
+                            PlaceBase::Upvar(var) => var.var_path.hir_id,
+                            _ => continue,
+                        };
+                        if !self.locals.contains(&local_id) {
+                            let capture = match capture.info.capture_kind {
+                                UpvarCapture::ByValue(_) => CaptureKind::Value,
+                                UpvarCapture::ByRef(borrow) => match borrow.kind {
+                                    BorrowKind::ImmBorrow => CaptureKind::Ref(Mutability::Not),
+                                    BorrowKind::UniqueImmBorrow | BorrowKind::MutBorrow => {
+                                        CaptureKind::Ref(Mutability::Mut)
+                                    },
+                                },
+                            };
+                            self.captures
+                                .entry(local_id)
+                                .and_modify(|e| *e |= capture)
+                                .or_insert(capture);
+                        }
+                    }
+                },
+                ExprKind::Loop(b, ..) => {
+                    self.loops.push(e.hir_id);
+                    self.visit_block(b);
+                    self.loops.pop();
+                },
+                _ => {
+                    self.allow_closure &= can_move_expr_to_closure_no_visit(self.cx, e, &self.loops, &self.locals);
+                    walk_expr(self, e);
+                },
             }
         }
+
+        fn visit_pat(&mut self, p: &'tcx Pat<'tcx>) {
+            p.each_binding_or_first(&mut |_, id, _, _| {
+                self.locals.insert(id);
+            });
+        }
     }
 
     let mut v = V {
         cx,
         allow_closure: true,
         loops: Vec::new(),
+        locals: HirIdSet::default(),
+        captures: HirIdMap::default(),
     };
     v.visit_expr(expr);
-    v.allow_closure
+    v.allow_closure.then(|| v.captures)
 }
 
 /// Returns the method names and argument list of nested method call expressions that make up
@@ -1365,13 +1662,13 @@ pub fn if_sequence<'tcx>(mut expr: &'tcx Expr<'tcx>) -> (Vec<&'tcx Expr<'tcx>>,
 
     while let Some(higher::IfOrIfLet { cond, then, r#else }) = higher::IfOrIfLet::hir(expr) {
         conds.push(&*cond);
-        if let ExprKind::Block(ref block, _) = then.kind {
+        if let ExprKind::Block(block, _) = then.kind {
             blocks.push(block);
         } else {
             panic!("ExprKind::If node is not an ExprKind::Block");
         }
 
-        if let Some(ref else_expr) = r#else {
+        if let Some(else_expr) = r#else {
             expr = else_expr;
         } else {
             break;
@@ -1708,7 +2005,7 @@ pub fn peel_hir_expr_while<'tcx>(
 pub fn peel_n_hir_expr_refs(expr: &'a Expr<'a>, count: usize) -> (&'a Expr<'a>, usize) {
     let mut remaining = count;
     let e = peel_hir_expr_while(expr, |e| match e.kind {
-        ExprKind::AddrOf(BorrowKind::Ref, _, e) if remaining != 0 => {
+        ExprKind::AddrOf(ast::BorrowKind::Ref, _, e) if remaining != 0 => {
             remaining -= 1;
             Some(e)
         },
@@ -1722,7 +2019,7 @@ pub fn peel_n_hir_expr_refs(expr: &'a Expr<'a>, count: usize) -> (&'a Expr<'a>,
 pub fn peel_hir_expr_refs(expr: &'a Expr<'a>) -> (&'a Expr<'a>, usize) {
     let mut count = 0;
     let e = peel_hir_expr_while(expr, |e| match e.kind {
-        ExprKind::AddrOf(BorrowKind::Ref, _, e) => {
+        ExprKind::AddrOf(ast::BorrowKind::Ref, _, e) => {
             count += 1;
             Some(e)
         },
diff --git a/src/tools/clippy/clippy_utils/src/msrvs.rs b/src/tools/clippy/clippy_utils/src/msrvs.rs
index 4a9c4fd0276..fa57dfbb57e 100644
--- a/src/tools/clippy/clippy_utils/src/msrvs.rs
+++ b/src/tools/clippy/clippy_utils/src/msrvs.rs
@@ -13,9 +13,12 @@ macro_rules! msrv_aliases {
 // names may refer to stabilized feature flags or library items
 msrv_aliases! {
     1,53,0 { OR_PATTERNS }
+    1,52,0 { STR_SPLIT_ONCE }
     1,50,0 { BOOL_THEN }
+    1,47,0 { TAU }
     1,46,0 { CONST_IF_MATCH }
     1,45,0 { STR_STRIP_PREFIX }
+    1,43,0 { LOG2_10, LOG10_2 }
     1,42,0 { MATCHES_MACRO }
     1,41,0 { RE_REBALANCING_COHERENCE, RESULT_MAP_OR_ELSE }
     1,40,0 { MEM_TAKE, NON_EXHAUSTIVE, OPTION_AS_DEREF }
diff --git a/src/tools/clippy/clippy_utils/src/paths.rs b/src/tools/clippy/clippy_utils/src/paths.rs
index b0c3fe1e5a7..d7e46c2d3eb 100644
--- a/src/tools/clippy/clippy_utils/src/paths.rs
+++ b/src/tools/clippy/clippy_utils/src/paths.rs
@@ -68,6 +68,7 @@ pub const IO_WRITE: [&str; 3] = ["std", "io", "Write"];
 pub const IPADDR_V4: [&str; 5] = ["std", "net", "ip", "IpAddr", "V4"];
 pub const IPADDR_V6: [&str; 5] = ["std", "net", "ip", "IpAddr", "V6"];
 pub const ITER_REPEAT: [&str; 5] = ["core", "iter", "sources", "repeat", "repeat"];
+pub const ITERTOOLS_NEXT_TUPLE: [&str; 3] = ["itertools", "Itertools", "next_tuple"];
 #[cfg(feature = "internal-lints")]
 pub const KW_MODULE: [&str; 3] = ["rustc_span", "symbol", "kw"];
 #[cfg(feature = "internal-lints")]
diff --git a/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs b/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs
index 4fb9e6b07e7..8f14b590d27 100644
--- a/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs
+++ b/src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs
@@ -36,9 +36,7 @@ pub fn is_min_const_fn(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, msrv: Option<&Ru
                 ty::PredicateKind::ObjectSafe(_) => panic!("object safe predicate on function: {:#?}", predicate),
                 ty::PredicateKind::ClosureKind(..) => panic!("closure kind predicate on function: {:#?}", predicate),
                 ty::PredicateKind::Subtype(_) => panic!("subtype predicate on function: {:#?}", predicate),
-                ty::PredicateKind::Coerce(_) => {
-                    panic!("coerce predicate on function: {:#?}", predicate)
-                },
+                ty::PredicateKind::Coerce(_) => panic!("coerce predicate on function: {:#?}", predicate),
                 ty::PredicateKind::Trait(pred) => {
                     if Some(pred.def_id()) == tcx.lang_items().sized_trait() {
                         continue;
diff --git a/src/tools/clippy/clippy_utils/src/sugg.rs b/src/tools/clippy/clippy_utils/src/sugg.rs
index 65d93e8f86e..ab05a0b4238 100644
--- a/src/tools/clippy/clippy_utils/src/sugg.rs
+++ b/src/tools/clippy/clippy_utils/src/sugg.rs
@@ -329,7 +329,7 @@ fn has_enclosing_paren(sugg: impl AsRef<str>) -> bool {
     }
 }
 
-// Copied from the rust standart library, and then edited
+/// Copied from the rust standard library, and then edited
 macro_rules! forward_binop_impls_to_ref {
     (impl $imp:ident, $method:ident for $t:ty, type Output = $o:ty) => {
         impl $imp<$t> for &$t {
diff --git a/src/tools/clippy/clippy_utils/src/ty.rs b/src/tools/clippy/clippy_utils/src/ty.rs
index 3cd8ed5aa2c..d6f9ebe89bc 100644
--- a/src/tools/clippy/clippy_utils/src/ty.rs
+++ b/src/tools/clippy/clippy_utils/src/ty.rs
@@ -10,7 +10,7 @@ use rustc_hir::{TyKind, Unsafety};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::LateContext;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
-use rustc_middle::ty::{self, TyCtxt, AdtDef, IntTy, Ty, TypeFoldable, UintTy};
+use rustc_middle::ty::{self, AdtDef, IntTy, Ty, TyCtxt, TypeFoldable, UintTy};
 use rustc_span::sym;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::DUMMY_SP;
@@ -224,6 +224,13 @@ fn is_normalizable_helper<'tcx>(
     result
 }
 
+/// Returns true iff the given type is a non aggregate primitive (a bool or char, any integer or
+/// floating-point number type). For checking aggregation of primitive types (e.g. tuples and slices
+/// of primitive type) see `is_recursively_primitive_type`
+pub fn is_non_aggregate_primitive_type(ty: Ty<'_>) -> bool {
+    matches!(ty.kind(), ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_))
+}
+
 /// Returns true iff the given type is a primitive (a bool or char, any integer or floating-point
 /// number type, a str, or an array, slice, or tuple of those types).
 pub fn is_recursively_primitive_type(ty: Ty<'_>) -> bool {
diff --git a/src/tools/clippy/clippy_utils/src/usage.rs b/src/tools/clippy/clippy_utils/src/usage.rs
index ac885e99944..098ec175fe2 100644
--- a/src/tools/clippy/clippy_utils/src/usage.rs
+++ b/src/tools/clippy/clippy_utils/src/usage.rs
@@ -1,10 +1,9 @@
 use crate as utils;
 use rustc_hir as hir;
-use rustc_hir::def::Res;
 use rustc_hir::intravisit;
 use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
 use rustc_hir::HirIdSet;
-use rustc_hir::{Expr, ExprKind, HirId, Path};
+use rustc_hir::{Expr, ExprKind, HirId};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::LateContext;
 use rustc_middle::hir::map::Map;
@@ -35,12 +34,8 @@ pub fn mutated_variables<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) ->
     Some(delegate.used_mutably)
 }
 
-pub fn is_potentially_mutated<'tcx>(variable: &'tcx Path<'_>, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
-    if let Res::Local(id) = variable.res {
-        mutated_variables(expr, cx).map_or(true, |mutated| mutated.contains(&id))
-    } else {
-        true
-    }
+pub fn is_potentially_mutated<'tcx>(variable: HirId, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
+    mutated_variables(expr, cx).map_or(true, |mutated| mutated.contains(&variable))
 }
 
 struct MutVarsDelegate {
diff --git a/src/tools/clippy/clippy_utils/src/visitors.rs b/src/tools/clippy/clippy_utils/src/visitors.rs
index ce00106dd4d..503effbdad5 100644
--- a/src/tools/clippy/clippy_utils/src/visitors.rs
+++ b/src/tools/clippy/clippy_utils/src/visitors.rs
@@ -4,6 +4,7 @@ use rustc_hir::intravisit::{self, walk_expr, ErasedMap, NestedVisitorMap, Visito
 use rustc_hir::{def::Res, Arm, Block, Body, BodyId, Destination, Expr, ExprKind, HirId, Stmt};
 use rustc_lint::LateContext;
 use rustc_middle::hir::map::Map;
+use std::ops::ControlFlow;
 
 /// returns `true` if expr contains match expr desugared from try
 fn contains_try(expr: &hir::Expr<'_>) -> bool {
@@ -133,62 +134,6 @@ where
     }
 }
 
-pub struct LocalUsedVisitor<'hir> {
-    hir: Map<'hir>,
-    pub local_hir_id: HirId,
-    pub used: bool,
-}
-
-impl<'hir> LocalUsedVisitor<'hir> {
-    pub fn new(cx: &LateContext<'hir>, local_hir_id: HirId) -> Self {
-        Self {
-            hir: cx.tcx.hir(),
-            local_hir_id,
-            used: false,
-        }
-    }
-
-    fn check<T>(&mut self, t: T, visit: fn(&mut Self, T)) -> bool {
-        visit(self, t);
-        std::mem::replace(&mut self.used, false)
-    }
-
-    pub fn check_arm(&mut self, arm: &'hir Arm<'_>) -> bool {
-        self.check(arm, Self::visit_arm)
-    }
-
-    pub fn check_body(&mut self, body: &'hir Body<'_>) -> bool {
-        self.check(body, Self::visit_body)
-    }
-
-    pub fn check_expr(&mut self, expr: &'hir Expr<'_>) -> bool {
-        self.check(expr, Self::visit_expr)
-    }
-
-    pub fn check_stmt(&mut self, stmt: &'hir Stmt<'_>) -> bool {
-        self.check(stmt, Self::visit_stmt)
-    }
-}
-
-impl<'v> Visitor<'v> for LocalUsedVisitor<'v> {
-    type Map = Map<'v>;
-
-    fn visit_expr(&mut self, expr: &'v Expr<'v>) {
-        if self.used {
-            return;
-        }
-        if path_to_local_id(expr, self.local_hir_id) {
-            self.used = true;
-        } else {
-            walk_expr(self, expr);
-        }
-    }
-
-    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
-        NestedVisitorMap::OnlyBodies(self.hir)
-    }
-}
-
 /// A type which can be visited.
 pub trait Visitable<'tcx> {
     /// Calls the corresponding `visit_*` function on the visitor.
@@ -203,7 +148,22 @@ macro_rules! visitable_ref {
         }
     };
 }
+visitable_ref!(Arm, visit_arm);
 visitable_ref!(Block, visit_block);
+visitable_ref!(Body, visit_body);
+visitable_ref!(Expr, visit_expr);
+visitable_ref!(Stmt, visit_stmt);
+
+// impl<'tcx, I: IntoIterator> Visitable<'tcx> for I
+// where
+//     I::Item: Visitable<'tcx>,
+// {
+//     fn visit<V: Visitor<'tcx>>(self, visitor: &mut V) {
+//         for x in self {
+//             x.visit(visitor);
+//         }
+//     }
+// }
 
 /// Calls the given function for each break expression.
 pub fn visit_break_exprs<'tcx>(
@@ -260,3 +220,48 @@ pub fn is_res_used(cx: &LateContext<'_>, res: Res, body: BodyId) -> bool {
     v.visit_expr(&cx.tcx.hir().body(body).value);
     v.found
 }
+
+/// Calls the given function for each usage of the given local.
+pub fn for_each_local_usage<'tcx, B>(
+    cx: &LateContext<'tcx>,
+    visitable: impl Visitable<'tcx>,
+    id: HirId,
+    f: impl FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>,
+) -> ControlFlow<B> {
+    struct V<'tcx, B, F> {
+        map: Map<'tcx>,
+        id: HirId,
+        f: F,
+        res: ControlFlow<B>,
+    }
+    impl<'tcx, B, F: FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>> Visitor<'tcx> for V<'tcx, B, F> {
+        type Map = Map<'tcx>;
+        fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+            NestedVisitorMap::OnlyBodies(self.map)
+        }
+
+        fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
+            if self.res.is_continue() {
+                if path_to_local_id(e, self.id) {
+                    self.res = (self.f)(e);
+                } else {
+                    walk_expr(self, e);
+                }
+            }
+        }
+    }
+
+    let mut v = V {
+        map: cx.tcx.hir(),
+        id,
+        f,
+        res: ControlFlow::CONTINUE,
+    };
+    visitable.visit(&mut v);
+    v.res
+}
+
+/// Checks if the given local is used.
+pub fn is_local_used(cx: &LateContext<'tcx>, visitable: impl Visitable<'tcx>, id: HirId) -> bool {
+    for_each_local_usage(cx, visitable, id, |_| ControlFlow::BREAK).is_break()
+}