clippy_utils/

visitors.rs

use crate::get_enclosing_block;
use crate::msrvs::Msrv;
use crate::qualify_min_const_fn::is_stable_const_fn_at;
use crate::res::MaybeResPath as _;
use crate::ty::needs_ordered_drop;
use core::ops::ControlFlow;
use rustc_ast::visit::{VisitorResult as _, try_visit};
use rustc_hir::def::{CtorKind, DefKind, Res};
use rustc_hir::intravisit::{self, Visitor, walk_block, walk_expr, walk_qpath};
use rustc_hir::{
    self as hir, AmbigArg, AnonConst, Arm, Block, BlockCheckMode, Body, BodyId, CRATE_HIR_ID, ConstBlock, Expr,
    ExprKind, HirId, ItemId, ItemKind, LetExpr, Pat, QPath, Stmt, StructTailExpr, UnOp, UnsafeSource,
};
use rustc_lint::LateContext;
use rustc_middle::hir::nested_filter;
use rustc_middle::ty::adjustment::Adjust;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeckResults};
use rustc_span::Span;

mod internal {
    /// Trait for visitor functions to control whether or not to descend to child nodes. Implemented
    /// for only two types. `()` always descends. `Descend` allows controlled descent.
    pub trait Continue {
        fn descend(&self) -> bool;
    }
}
use internal::Continue;

impl Continue for () {
    fn descend(&self) -> bool {
        true
    }
}

/// Allows for controlled descent when using visitor functions. Use `()` instead when always
/// descending into child nodes.
#[derive(Clone, Copy)]
pub enum Descend {
    Yes,
    No,
}
impl From<bool> for Descend {
    fn from(from: bool) -> Self {
        if from { Self::Yes } else { Self::No }
    }
}
impl Continue for Descend {
    fn descend(&self) -> bool {
        matches!(self, Self::Yes)
    }
}

/// A type which can be visited.
pub trait Visitable<'tcx> {
    /// Calls the corresponding `visit_*` function on the visitor.
    fn visit<V: Visitor<'tcx>>(self, visitor: &mut V) -> V::Result;
}
impl<'tcx, T> Visitable<'tcx> for &'tcx [T]
where
    &'tcx T: Visitable<'tcx>,
{
    fn visit<V: Visitor<'tcx>>(self, visitor: &mut V) -> V::Result {
        for x in self {
            try_visit!(x.visit(visitor));
        }
        V::Result::output()
    }
}
impl<'tcx, A, B> Visitable<'tcx> for (A, B)
where
    A: Visitable<'tcx>,
    B: Visitable<'tcx>,
{
    fn visit<V: Visitor<'tcx>>(self, visitor: &mut V) -> V::Result {
        let (a, b) = self;
        try_visit!(a.visit(visitor));
        b.visit(visitor)
    }
}
impl<'tcx, T> Visitable<'tcx> for Option<T>
where
    T: Visitable<'tcx>,
{
    fn visit<V: Visitor<'tcx>>(self, visitor: &mut V) -> V::Result {
        if let Some(x) = self {
            try_visit!(x.visit(visitor));
        }
        V::Result::output()
    }
}
macro_rules! visitable_ref {
    ($t:ident, $f:ident) => {
        impl<'tcx> Visitable<'tcx> for &'tcx $t<'tcx> {
            fn visit<V: Visitor<'tcx>>(self, visitor: &mut V) -> V::Result {
                visitor.$f(self)
            }
        }
    };
}
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);

/// Calls the given function once for each expression contained. This does not enter any bodies or
/// nested items.
pub fn for_each_expr_without_closures<'tcx, B, C: Continue>(
    node: impl Visitable<'tcx>,
    f: impl FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B, C>,
) -> Option<B> {
    struct V<F> {
        f: F,
    }
    impl<'tcx, B, C: Continue, F: FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B, C>> Visitor<'tcx> for V<F> {
        type Result = ControlFlow<B>;

        fn visit_expr(&mut self, e: &'tcx Expr<'tcx>) -> Self::Result {
            match (self.f)(e) {
                ControlFlow::Continue(c) if c.descend() => walk_expr(self, e),
                ControlFlow::Break(b) => ControlFlow::Break(b),
                ControlFlow::Continue(_) => ControlFlow::Continue(()),
            }
        }

        // Avoid unnecessary `walk_*` calls.
        fn visit_ty(&mut self, _: &'tcx hir::Ty<'tcx, AmbigArg>) -> Self::Result {
            ControlFlow::Continue(())
        }
        fn visit_pat(&mut self, _: &'tcx Pat<'tcx>) -> Self::Result {
            ControlFlow::Continue(())
        }
        fn visit_qpath(&mut self, _: &'tcx QPath<'tcx>, _: HirId, _: Span) -> Self::Result {
            ControlFlow::Continue(())
        }
        // Avoid monomorphising all `visit_*` functions.
        fn visit_nested_item(&mut self, _: ItemId) -> Self::Result {
            ControlFlow::Continue(())
        }
    }
    let mut v = V { f };
    node.visit(&mut v).break_value()
}

/// Calls the given function once for each expression contained. This will enter bodies, but not
/// nested items.
pub fn for_each_expr<'tcx, B, C: Continue>(
    tcx: TyCtxt<'tcx>,
    node: impl Visitable<'tcx>,
    f: impl FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B, C>,
) -> Option<B> {
    struct V<'tcx, F> {
        tcx: TyCtxt<'tcx>,
        f: F,
    }
    impl<'tcx, B, C: Continue, F: FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B, C>> Visitor<'tcx> for V<'tcx, F> {
        type NestedFilter = nested_filter::OnlyBodies;
        type Result = ControlFlow<B>;

        fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
            self.tcx
        }

        fn visit_expr(&mut self, e: &'tcx Expr<'tcx>) -> Self::Result {
            match (self.f)(e) {
                ControlFlow::Continue(c) if c.descend() => walk_expr(self, e),
                ControlFlow::Break(b) => ControlFlow::Break(b),
                ControlFlow::Continue(_) => ControlFlow::Continue(()),
            }
        }

        // Only walk closures
        fn visit_anon_const(&mut self, _: &'tcx AnonConst) -> Self::Result {
            ControlFlow::Continue(())
        }
        // Avoid unnecessary `walk_*` calls.
        fn visit_ty(&mut self, _: &'tcx hir::Ty<'tcx, AmbigArg>) -> Self::Result {
            ControlFlow::Continue(())
        }
        fn visit_pat(&mut self, _: &'tcx Pat<'tcx>) -> Self::Result {
            ControlFlow::Continue(())
        }
        fn visit_qpath(&mut self, _: &'tcx QPath<'tcx>, _: HirId, _: Span) -> Self::Result {
            ControlFlow::Continue(())
        }
        // Avoid monomorphising all `visit_*` functions.
        fn visit_nested_item(&mut self, _: ItemId) -> Self::Result {
            ControlFlow::Continue(())
        }
    }
    let mut v = V { tcx, f };
    node.visit(&mut v).break_value()
}

/// returns `true` if expr contains match expr desugared from try
fn contains_try(expr: &Expr<'_>) -> bool {
    for_each_expr_without_closures(expr, |e| {
        if matches!(e.kind, ExprKind::Match(_, _, hir::MatchSource::TryDesugar(_))) {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_some()
}

/// calls `callback` on every expression that could be the return value of `expr`.
///
/// returns `false` if `expr` contains `?` or if `callback` ever return `false`.
pub fn find_all_ret_expressions<'hir, F>(_cx: &LateContext<'_>, expr: &'hir Expr<'hir>, callback: F) -> bool
where
    F: FnMut(&'hir Expr<'hir>) -> bool,
{
    struct RetFinder<F> {
        in_stmt: bool,
        failed: bool,
        cb: F,
    }

    struct WithStmtGuard<'a, F> {
        val: &'a mut RetFinder<F>,
        prev_in_stmt: bool,
    }

    impl<F> RetFinder<F> {
        fn inside_stmt(&mut self, in_stmt: bool) -> WithStmtGuard<'_, F> {
            let prev_in_stmt = std::mem::replace(&mut self.in_stmt, in_stmt);
            WithStmtGuard {
                val: self,
                prev_in_stmt,
            }
        }
    }

    impl<F> std::ops::Deref for WithStmtGuard<'_, F> {
        type Target = RetFinder<F>;

        fn deref(&self) -> &Self::Target {
            self.val
        }
    }

    impl<F> std::ops::DerefMut for WithStmtGuard<'_, F> {
        fn deref_mut(&mut self) -> &mut Self::Target {
            self.val
        }
    }

    impl<F> Drop for WithStmtGuard<'_, F> {
        fn drop(&mut self) {
            self.val.in_stmt = self.prev_in_stmt;
        }
    }

    impl<'hir, F: FnMut(&'hir Expr<'hir>) -> bool> Visitor<'hir> for RetFinder<F> {
        fn visit_stmt(&mut self, stmt: &'hir Stmt<'_>) {
            intravisit::walk_stmt(&mut *self.inside_stmt(true), stmt);
        }

        fn visit_expr(&mut self, expr: &'hir Expr<'_>) {
            if self.failed {
                return;
            }
            if self.in_stmt {
                match expr.kind {
                    ExprKind::Ret(Some(expr)) => self.inside_stmt(false).visit_expr(expr),
                    _ => walk_expr(self, expr),
                }
            } else {
                match expr.kind {
                    ExprKind::If(cond, then, else_opt) => {
                        self.inside_stmt(true).visit_expr(cond);
                        self.visit_expr(then);
                        if let Some(el) = else_opt {
                            self.visit_expr(el);
                        }
                    },
                    ExprKind::Match(cond, arms, _) => {
                        self.inside_stmt(true).visit_expr(cond);
                        for arm in arms {
                            self.visit_expr(arm.body);
                        }
                    },
                    ExprKind::Block(..) => walk_expr(self, expr),
                    ExprKind::Ret(Some(expr)) => self.visit_expr(expr),
                    _ => self.failed |= !(self.cb)(expr),
                }
            }
        }
    }

    !contains_try(expr) && {
        let mut ret_finder = RetFinder {
            in_stmt: false,
            failed: false,
            cb: callback,
        };
        ret_finder.visit_expr(expr);
        !ret_finder.failed
    }
}

/// Checks if the given resolved path is used in the given body.
pub fn is_res_used(cx: &LateContext<'_>, res: Res, body: BodyId) -> bool {
    for_each_expr(cx.tcx, cx.tcx.hir_body(body).value, |e| {
        if let ExprKind::Path(p) = &e.kind
            && cx.qpath_res(p, e.hir_id) == res
        {
            return ControlFlow::Break(());
        }
        ControlFlow::Continue(())
    })
    .is_some()
}

/// Checks if the given local is used.
pub fn is_local_used<'tcx>(cx: &LateContext<'tcx>, visitable: impl Visitable<'tcx>, id: HirId) -> bool {
    for_each_expr(cx.tcx, visitable, |e| {
        if e.res_local_id() == Some(id) {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_some()
}

/// Returns whether the given expression can be evaluated as a constant assuming that all its sub
/// expressions can be evaluated as constants.
fn is_const_evaluatable_helper<'tcx>(tcx: TyCtxt<'tcx>, typeck: &'tcx TypeckResults<'tcx>, e: &'tcx Expr<'_>) -> bool {
    match e.kind {
        ExprKind::Call(
            &Expr {
                kind: ExprKind::Path(ref p),
                hir_id,
                ..
            },
            _,
        ) if typeck
            .qpath_res(p, hir_id)
            .opt_def_id()
            .is_some_and(|id| is_stable_const_fn_at(tcx, CRATE_HIR_ID, id, Msrv::default())) =>
        {
            true
        },
        ExprKind::MethodCall(..)
            if typeck
                .type_dependent_def_id(e.hir_id)
                .is_some_and(|id| is_stable_const_fn_at(tcx, CRATE_HIR_ID, id, Msrv::default())) =>
        {
            true
        },
        ExprKind::Binary(_, lhs, rhs)
            if typeck.expr_ty(lhs).peel_refs().is_primitive_ty()
                && typeck.expr_ty(rhs).peel_refs().is_primitive_ty() =>
        {
            true
        },
        ExprKind::Unary(UnOp::Deref, e) if typeck.expr_ty(e).is_raw_ptr() => true,
        ExprKind::Unary(_, e) if typeck.expr_ty(e).peel_refs().is_primitive_ty() => true,
        ExprKind::Index(base, _, _)
            if matches!(typeck.expr_ty(base).peel_refs().kind(), ty::Slice(_) | ty::Array(..)) =>
        {
            true
        },
        ExprKind::Path(ref p)
            if matches!(
                typeck.qpath_res(p, e.hir_id),
                Res::Def(
                    DefKind::Const
                        | DefKind::AssocConst
                        | DefKind::AnonConst
                        | DefKind::ConstParam
                        | DefKind::Ctor(..)
                        | DefKind::Fn
                        | DefKind::AssocFn,
                    _
                ) | Res::SelfCtor(_)
            ) =>
        {
            true
        },

        ExprKind::AddrOf(..)
        | ExprKind::Array(_)
        | ExprKind::Block(..)
        | ExprKind::Cast(..)
        | ExprKind::ConstBlock(_)
        | ExprKind::DropTemps(_)
        | ExprKind::Field(..)
        | ExprKind::If(..)
        | ExprKind::Let(..)
        | ExprKind::Lit(_)
        | ExprKind::Match(..)
        | ExprKind::Repeat(..)
        | ExprKind::Struct(..)
        | ExprKind::Tup(_)
        | ExprKind::Type(..)
        | ExprKind::UnsafeBinderCast(..) => true,

        _ => false,
    }
}

/// Checks if the given expression can be evaluated as a constant at the specified node
pub fn is_const_evaluatable<'tcx>(tcx: TyCtxt<'tcx>, typeck: &'tcx TypeckResults<'tcx>, e: &'tcx Expr<'_>) -> bool {
    for_each_expr(tcx, e, move |e| {
        if !is_const_evaluatable_helper(tcx, typeck, e) {
            ControlFlow::Break(())
        } else if matches!(e.kind, ExprKind::ConstBlock(_)) {
            ControlFlow::Continue(Descend::No)
        } else {
            ControlFlow::Continue(Descend::Yes)
        }
    })
    .is_none()
}

/// Checks if the given expression can be used as a const parameter.
///
/// This is more strict than `is_const_evaluatable` as it requires that the expression does not
/// contain any type parameters or any operations on const parameters.
pub fn is_const_param_evaluatable<'tcx>(
    tcx: TyCtxt<'tcx>,
    typeck: &'tcx TypeckResults<'tcx>,
    e: &'tcx Expr<'_>,
) -> bool {
    struct V1<'tcx> {
        tcx: TyCtxt<'tcx>,
        typeck: &'tcx TypeckResults<'tcx>,
    }
    impl<'tcx> Visitor<'tcx> for V1<'tcx> {
        type NestedFilter = nested_filter::OnlyBodies;
        type Result = ControlFlow<()>;
        fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
            self.tcx
        }
        fn visit_expr(&mut self, e: &'tcx Expr<'tcx>) -> Self::Result {
            if !is_const_evaluatable_helper(self.tcx, self.typeck, e) {
                return ControlFlow::Break(());
            }
            walk_expr(self, e)
        }
        fn visit_inline_const(&mut self, c: &'tcx ConstBlock) -> Self::Result {
            V2(self.tcx).visit_inline_const(c)
        }
        fn visit_anon_const(&mut self, c: &'tcx AnonConst) -> Self::Result {
            V2(self.tcx).visit_anon_const(c)
        }
        fn visit_qpath(&mut self, qpath: &'tcx QPath<'tcx>, id: HirId, _span: Span) -> Self::Result {
            if matches!(qpath.basic_res(), Res::Def(DefKind::ConstParam | DefKind::TyParam, _)) {
                return ControlFlow::Break(());
            }
            walk_qpath(self, qpath, id)
        }
    }

    struct V2<'tcx>(TyCtxt<'tcx>);
    impl<'tcx> Visitor<'tcx> for V2<'tcx> {
        type NestedFilter = nested_filter::OnlyBodies;
        type Result = ControlFlow<()>;
        fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
            self.0
        }
        fn visit_qpath(&mut self, qpath: &'tcx QPath<'tcx>, id: HirId, _span: Span) -> Self::Result {
            if matches!(qpath.basic_res(), Res::Def(DefKind::ConstParam | DefKind::TyParam, _)) {
                return ControlFlow::Break(());
            }
            walk_qpath(self, qpath, id)
        }
    }

    // We have to work around limitations of `#![feature(generic_const_exprs)]` being unstable.
    // A const parameter (e.g. `N` in `fn foo<const N: usize>()`) can be used as is, but any
    // expression involving a const parameter (e.g. `N * 2`) will be a compiler error.
    // Any type parameter (e.g. `T` in `fn foo<T>()`) will be a compiler error.

    if let ExprKind::Path(ref qpath) = e.kind
        && matches!(qpath.basic_res(), Res::Def(DefKind::ConstParam, _))
    {
        return true;
    }

    V1 { tcx, typeck }.visit_expr(e).is_continue()
}

/// Checks if the given expression performs an unsafe operation outside of an unsafe block.
pub fn is_expr_unsafe<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> bool {
    struct V<'a, 'tcx> {
        cx: &'a LateContext<'tcx>,
    }
    impl<'tcx> Visitor<'tcx> for V<'_, 'tcx> {
        type NestedFilter = nested_filter::OnlyBodies;
        type Result = ControlFlow<()>;

        fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
            self.cx.tcx
        }
        fn visit_expr(&mut self, e: &'tcx Expr<'_>) -> Self::Result {
            match e.kind {
                ExprKind::Unary(UnOp::Deref, e) if self.cx.typeck_results().expr_ty(e).is_raw_ptr() => {
                    ControlFlow::Break(())
                },
                ExprKind::MethodCall(..)
                    if self
                        .cx
                        .typeck_results()
                        .type_dependent_def_id(e.hir_id)
                        .is_some_and(|id| self.cx.tcx.fn_sig(id).skip_binder().safety().is_unsafe()) =>
                {
                    ControlFlow::Break(())
                },
                ExprKind::Call(func, _) => match *self.cx.typeck_results().expr_ty(func).peel_refs().kind() {
                    ty::FnDef(id, _) if self.cx.tcx.fn_sig(id).skip_binder().safety().is_unsafe() => {
                        ControlFlow::Break(())
                    },
                    ty::FnPtr(_, hdr) if hdr.safety().is_unsafe() => ControlFlow::Break(()),
                    _ => walk_expr(self, e),
                },
                ExprKind::Path(ref p)
                    if self
                        .cx
                        .qpath_res(p, e.hir_id)
                        .opt_def_id()
                        .is_some_and(|id| self.cx.tcx.is_mutable_static(id)) =>
                {
                    ControlFlow::Break(())
                },
                _ => walk_expr(self, e),
            }
        }
        fn visit_block(&mut self, b: &'tcx Block<'_>) -> Self::Result {
            if matches!(b.rules, BlockCheckMode::UnsafeBlock(_)) {
                ControlFlow::Continue(())
            } else {
                walk_block(self, b)
            }
        }
        fn visit_nested_item(&mut self, id: ItemId) -> Self::Result {
            if let ItemKind::Impl(i) = &self.cx.tcx.hir_item(id).kind
                && let Some(of_trait) = i.of_trait
                && of_trait.safety.is_unsafe()
            {
                ControlFlow::Break(())
            } else {
                ControlFlow::Continue(())
            }
        }
    }
    let mut v = V { cx };
    v.visit_expr(e).is_break()
}

/// Checks if the given expression contains an unsafe block
pub fn contains_unsafe_block<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
    struct V<'cx, 'tcx> {
        cx: &'cx LateContext<'tcx>,
    }
    impl<'tcx> Visitor<'tcx> for V<'_, 'tcx> {
        type Result = ControlFlow<()>;
        type NestedFilter = nested_filter::OnlyBodies;
        fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
            self.cx.tcx
        }

        fn visit_block(&mut self, b: &'tcx Block<'_>) -> Self::Result {
            if b.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) {
                ControlFlow::Break(())
            } else {
                walk_block(self, b)
            }
        }
    }
    let mut v = V { cx };
    v.visit_expr(e).is_break()
}

/// Runs the given function for each sub-expression producing the final value consumed by the parent
/// of the give expression.
///
/// e.g. for the following expression
/// ```rust,ignore
/// if foo {
///     f(0)
/// } else {
///     1 + 1
/// }
/// ```
/// this will pass both `f(0)` and `1+1` to the given function.
pub fn for_each_value_source<'tcx, B>(
    e: &'tcx Expr<'tcx>,
    f: &mut impl FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>,
) -> ControlFlow<B> {
    match e.kind {
        ExprKind::Block(Block { expr: Some(e), .. }, _) => for_each_value_source(e, f),
        ExprKind::Match(_, arms, _) => {
            for arm in arms {
                for_each_value_source(arm.body, f)?;
            }
            ControlFlow::Continue(())
        },
        ExprKind::If(_, if_expr, Some(else_expr)) => {
            for_each_value_source(if_expr, f)?;
            for_each_value_source(else_expr, f)
        },
        ExprKind::DropTemps(e) => for_each_value_source(e, f),
        _ => f(e),
    }
}

/// Runs the given function for each path expression referencing the given local which occur after
/// the given expression.
pub fn for_each_local_use_after_expr<'tcx, B>(
    cx: &LateContext<'tcx>,
    local_id: HirId,
    expr_id: HirId,
    f: impl FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>,
) -> ControlFlow<B> {
    struct V<'cx, 'tcx, F, B> {
        cx: &'cx LateContext<'tcx>,
        local_id: HirId,
        expr_id: HirId,
        found: bool,
        res: ControlFlow<B>,
        f: F,
    }
    impl<'tcx, F: FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>, B> Visitor<'tcx> for V<'_, 'tcx, F, B> {
        type NestedFilter = nested_filter::OnlyBodies;
        fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
            self.cx.tcx
        }

        fn visit_expr(&mut self, e: &'tcx Expr<'tcx>) {
            if !self.found {
                if e.hir_id == self.expr_id {
                    self.found = true;
                } else {
                    walk_expr(self, e);
                }
                return;
            }
            if self.res.is_break() {
                return;
            }
            if e.res_local_id() == Some(self.local_id) {
                self.res = (self.f)(e);
            } else {
                walk_expr(self, e);
            }
        }
    }

    if let Some(b) = get_enclosing_block(cx, local_id) {
        let mut v = V {
            cx,
            local_id,
            expr_id,
            found: false,
            res: ControlFlow::Continue(()),
            f,
        };
        v.visit_block(b);
        v.res
    } else {
        ControlFlow::Continue(())
    }
}

// Calls the given function for every unconsumed temporary created by the expression. Note the
// function is only guaranteed to be called for types which need to be dropped, but it may be called
// for other types.
#[expect(clippy::too_many_lines)]
pub fn for_each_unconsumed_temporary<'tcx, B>(
    cx: &LateContext<'tcx>,
    e: &'tcx Expr<'tcx>,
    mut f: impl FnMut(Ty<'tcx>) -> ControlFlow<B>,
) -> ControlFlow<B> {
    // Todo: Handle partially consumed values.
    fn helper<'tcx, B>(
        typeck: &'tcx TypeckResults<'tcx>,
        consume: bool,
        e: &'tcx Expr<'tcx>,
        f: &mut impl FnMut(Ty<'tcx>) -> ControlFlow<B>,
    ) -> ControlFlow<B> {
        if !consume
            || matches!(
                typeck.expr_adjustments(e),
                [adjust, ..] if matches!(adjust.kind, Adjust::Borrow(_) | Adjust::Deref(_))
            )
        {
            match e.kind {
                ExprKind::Path(QPath::Resolved(None, p))
                    if matches!(p.res, Res::Def(DefKind::Ctor(_, CtorKind::Const), _)) =>
                {
                    f(typeck.expr_ty(e))?;
                },
                ExprKind::Path(_)
                | ExprKind::Unary(UnOp::Deref, _)
                | ExprKind::Index(..)
                | ExprKind::Field(..)
                | ExprKind::AddrOf(..) => (),
                _ => f(typeck.expr_ty(e))?,
            }
        }
        match e.kind {
            ExprKind::AddrOf(_, _, e)
            | ExprKind::Field(e, _)
            | ExprKind::Unary(UnOp::Deref, e)
            | ExprKind::Match(e, ..)
            | ExprKind::Let(&LetExpr { init: e, .. }) => {
                helper(typeck, false, e, f)?;
            },
            ExprKind::Block(&Block { expr: Some(e), .. }, _) | ExprKind::Cast(e, _) | ExprKind::Unary(_, e) => {
                helper(typeck, true, e, f)?;
            },
            ExprKind::Call(callee, args) => {
                helper(typeck, true, callee, f)?;
                for arg in args {
                    helper(typeck, true, arg, f)?;
                }
            },
            ExprKind::MethodCall(_, receiver, args, _) => {
                helper(typeck, true, receiver, f)?;
                for arg in args {
                    helper(typeck, true, arg, f)?;
                }
            },
            ExprKind::Tup(args) | ExprKind::Array(args) => {
                for arg in args {
                    helper(typeck, true, arg, f)?;
                }
            },
            ExprKind::Use(expr, _) => {
                helper(typeck, true, expr, f)?;
            },
            ExprKind::Index(borrowed, consumed, _)
            | ExprKind::Assign(borrowed, consumed, _)
            | ExprKind::AssignOp(_, borrowed, consumed) => {
                helper(typeck, false, borrowed, f)?;
                helper(typeck, true, consumed, f)?;
            },
            ExprKind::Binary(_, lhs, rhs) => {
                helper(typeck, true, lhs, f)?;
                helper(typeck, true, rhs, f)?;
            },
            ExprKind::Struct(_, fields, default) => {
                for field in fields {
                    helper(typeck, true, field.expr, f)?;
                }
                if let StructTailExpr::Base(default) = default {
                    helper(typeck, false, default, f)?;
                }
            },
            ExprKind::If(cond, then, else_expr) => {
                helper(typeck, true, cond, f)?;
                helper(typeck, true, then, f)?;
                if let Some(else_expr) = else_expr {
                    helper(typeck, true, else_expr, f)?;
                }
            },
            ExprKind::Type(e, _) | ExprKind::UnsafeBinderCast(_, e, _) => {
                helper(typeck, consume, e, f)?;
            },

            // Either drops temporaries, jumps out of the current expression, or has no sub expression.
            ExprKind::DropTemps(_)
            | ExprKind::Ret(_)
            | ExprKind::Become(_)
            | ExprKind::Break(..)
            | ExprKind::Yield(..)
            | ExprKind::Block(..)
            | ExprKind::Loop(..)
            | ExprKind::Repeat(..)
            | ExprKind::Lit(_)
            | ExprKind::ConstBlock(_)
            | ExprKind::Closure { .. }
            | ExprKind::Path(_)
            | ExprKind::Continue(_)
            | ExprKind::InlineAsm(_)
            | ExprKind::OffsetOf(..)
            | ExprKind::Err(_) => (),
        }
        ControlFlow::Continue(())
    }
    helper(cx.typeck_results(), true, e, &mut f)
}

/// Checks whether the drop order matters for any unconsumed temporary created by the given
/// [expression](Expr).
pub fn any_temporaries_need_ordered_drop<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
    for_each_unconsumed_temporary(cx, e, |ty| {
        if needs_ordered_drop(cx, ty) {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_break()
}

/// Runs the given function for each path expression referencing the given local which occur after
/// the given expression.
pub fn for_each_local_assignment<'tcx, B>(
    cx: &LateContext<'tcx>,
    local_id: HirId,
    f: impl FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>,
) -> ControlFlow<B> {
    struct V<'cx, 'tcx, F, B> {
        cx: &'cx LateContext<'tcx>,
        local_id: HirId,
        res: ControlFlow<B>,
        f: F,
    }
    impl<'tcx, F: FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>, B> Visitor<'tcx> for V<'_, 'tcx, F, B> {
        type NestedFilter = nested_filter::OnlyBodies;
        fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
            self.cx.tcx
        }

        fn visit_expr(&mut self, e: &'tcx Expr<'tcx>) {
            if let ExprKind::Assign(lhs, rhs, _) = e.kind
                && self.res.is_continue()
                && lhs.res_local_id() == Some(self.local_id)
            {
                self.res = (self.f)(rhs);
                self.visit_expr(rhs);
            } else {
                walk_expr(self, e);
            }
        }
    }

    if let Some(b) = get_enclosing_block(cx, local_id) {
        let mut v = V {
            cx,
            local_id,
            res: ControlFlow::Continue(()),
            f,
        };
        v.visit_block(b);
        v.res
    } else {
        ControlFlow::Continue(())
    }
}

/// Checks whether the given [expression](Expr) contains any `break` or `continue` expressions. This
/// does not enter any bodies or nested items, because a `break` or `continue` would not apply to the expression's
/// scope.
pub fn contains_break_or_continue(expr: &Expr<'_>) -> bool {
    for_each_expr_without_closures(expr, |e| {
        if matches!(e.kind, ExprKind::Break(..) | ExprKind::Continue(..)) {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    })
    .is_some()
}

/// If the local is only used once in `visitable` returns the path expression referencing the given
/// local
pub fn local_used_once<'tcx>(
    cx: &LateContext<'tcx>,
    visitable: impl Visitable<'tcx>,
    id: HirId,
) -> Option<&'tcx Expr<'tcx>> {
    let mut expr = None;

    let cf = for_each_expr(cx.tcx, visitable, |e| {
        if e.res_local_id() == Some(id) && expr.replace(e).is_some() {
            ControlFlow::Break(())
        } else {
            ControlFlow::Continue(())
        }
    });
    if cf.is_some() {
        return None;
    }

    expr
}