rust-clippy/clippy_lints/src/dereference.rs

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use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then};
use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
use clippy_utils::sugg::has_enclosing_paren;
use clippy_utils::ty::{implements_trait, is_manually_drop, peel_mid_ty_refs};
use clippy_utils::{
expr_use_ctxt, get_parent_expr, get_parent_node, is_lint_allowed, path_to_local, DefinedTy, ExprUseNode,
};
use core::mem;
use rustc_ast::util::parser::{PREC_POSTFIX, PREC_PREFIX};
use rustc_data_structures::fx::FxIndexMap;
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use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_ty, Visitor};
use rustc_hir::{
self as hir, BindingAnnotation, Body, BodyId, BorrowKind, Expr, ExprKind, HirId, MatchSource, Mutability, Node,
Pat, PatKind, Path, QPath, TyKind, UnOp,
};
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use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt, TypeVisitableExt, TypeckResults};
use rustc_session::impl_lint_pass;
use rustc_span::symbol::sym;
use rustc_span::{Span, Symbol};
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declare_clippy_lint! {
/// ### What it does
/// Checks for explicit `deref()` or `deref_mut()` method calls.
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///
/// ### Why is this bad?
/// Dereferencing by `&*x` or `&mut *x` is clearer and more concise,
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/// when not part of a method chain.
///
/// ### Example
/// ```no_run
/// use std::ops::Deref;
/// let a: &mut String = &mut String::from("foo");
/// let b: &str = a.deref();
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/// ```
///
/// Use instead:
/// ```no_run
/// let a: &mut String = &mut String::from("foo");
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/// let b = &*a;
/// ```
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///
/// This lint excludes all of:
/// ```rust,ignore
/// let _ = d.unwrap().deref();
/// let _ = Foo::deref(&foo);
/// let _ = <Foo as Deref>::deref(&foo);
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/// ```
#[clippy::version = "1.44.0"]
pub EXPLICIT_DEREF_METHODS,
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pedantic,
"Explicit use of deref or deref_mut method while not in a method chain."
}
declare_clippy_lint! {
/// ### What it does
/// Checks for address of operations (`&`) that are going to
/// be dereferenced immediately by the compiler.
///
/// ### Why is this bad?
/// Suggests that the receiver of the expression borrows
/// the expression.
///
/// ### Known problems
/// The lint cannot tell when the implementation of a trait
/// for `&T` and `T` do different things. Removing a borrow
/// in such a case can change the semantics of the code.
///
/// ### Example
/// ```no_run
/// fn fun(_a: &i32) {}
///
/// let x: &i32 = &&&&&&5;
/// fun(&x);
/// ```
///
/// Use instead:
/// ```no_run
/// # fn fun(_a: &i32) {}
/// let x: &i32 = &5;
/// fun(x);
/// ```
#[clippy::version = "pre 1.29.0"]
pub NEEDLESS_BORROW,
style,
"taking a reference that is going to be automatically dereferenced"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for `ref` bindings which create a reference to a reference.
///
/// ### Why is this bad?
/// The address-of operator at the use site is clearer about the need for a reference.
///
/// ### Example
/// ```no_run
/// let x = Some("");
/// if let Some(ref x) = x {
/// // use `x` here
/// }
/// ```
///
/// Use instead:
/// ```no_run
/// let x = Some("");
/// if let Some(x) = x {
/// // use `&x` here
/// }
/// ```
#[clippy::version = "1.54.0"]
pub REF_BINDING_TO_REFERENCE,
pedantic,
"`ref` binding to a reference"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for dereferencing expressions which would be covered by auto-deref.
///
/// ### Why is this bad?
/// This unnecessarily complicates the code.
///
/// ### Example
/// ```no_run
/// let x = String::new();
/// let y: &str = &*x;
/// ```
/// Use instead:
/// ```no_run
/// let x = String::new();
/// let y: &str = &x;
/// ```
#[clippy::version = "1.64.0"]
pub EXPLICIT_AUTO_DEREF,
complexity,
"dereferencing when the compiler would automatically dereference"
}
impl_lint_pass!(Dereferencing<'_> => [
EXPLICIT_DEREF_METHODS,
NEEDLESS_BORROW,
REF_BINDING_TO_REFERENCE,
EXPLICIT_AUTO_DEREF,
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]);
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#[derive(Default)]
pub struct Dereferencing<'tcx> {
state: Option<(State, StateData<'tcx>)>,
// While parsing a `deref` method call in ufcs form, the path to the function is itself an
// expression. This is to store the id of that expression so it can be skipped when
// `check_expr` is called for it.
skip_expr: Option<HirId>,
/// The body the first local was found in. Used to emit lints when the traversal of the body has
/// been finished. Note we can't lint at the end of every body as they can be nested within each
/// other.
current_body: Option<BodyId>,
/// The list of locals currently being checked by the lint.
/// If the value is `None`, then the binding has been seen as a ref pattern, but is not linted.
/// This is needed for or patterns where one of the branches can be linted, but another can not
/// be.
///
/// e.g. `m!(x) | Foo::Bar(ref x)`
ref_locals: FxIndexMap<HirId, Option<RefPat>>,
}
#[derive(Debug)]
struct StateData<'tcx> {
first_expr: &'tcx Expr<'tcx>,
adjusted_ty: Ty<'tcx>,
}
struct DerefedBorrow {
count: usize,
msg: &'static str,
stability: TyCoercionStability,
for_field_access: Option<Symbol>,
}
enum State {
// Any number of deref method calls.
DerefMethod {
// The number of calls in a sequence which changed the referenced type
ty_changed_count: usize,
is_ufcs: bool,
/// The required mutability
mutbl: Mutability,
},
DerefedBorrow(DerefedBorrow),
ExplicitDeref {
mutability: Option<Mutability>,
},
ExplicitDerefField {
name: Symbol,
derefs_manually_drop: bool,
},
Reborrow {
mutability: Mutability,
},
Borrow {
mutability: Mutability,
},
}
// A reference operation considered by this lint pass
enum RefOp {
Method { mutbl: Mutability, is_ufcs: bool },
Deref,
AddrOf(Mutability),
}
struct RefPat {
/// Whether every usage of the binding is dereferenced.
always_deref: bool,
/// The spans of all the ref bindings for this local.
spans: Vec<Span>,
/// The applicability of this suggestion.
app: Applicability,
/// All the replacements which need to be made.
replacements: Vec<(Span, String)>,
/// The [`HirId`] that the lint should be emitted at.
hir_id: HirId,
}
impl<'tcx> LateLintPass<'tcx> for Dereferencing<'tcx> {
#[expect(clippy::too_many_lines)]
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
// Skip path expressions from deref calls. e.g. `Deref::deref(e)`
if Some(expr.hir_id) == self.skip_expr.take() {
return;
}
if let Some(local) = path_to_local(expr) {
self.check_local_usage(cx, expr, local);
}
// Stop processing sub expressions when a macro call is seen
if expr.span.from_expansion() {
if let Some((state, data)) = self.state.take() {
report(cx, expr, state, data, cx.typeck_results());
}
return;
}
let typeck = cx.typeck_results();
let Some((kind, sub_expr)) = try_parse_ref_op(cx.tcx, typeck, expr) else {
// The whole chain of reference operations has been seen
if let Some((state, data)) = self.state.take() {
report(cx, expr, state, data, typeck);
}
return;
};
match (self.state.take(), kind) {
(None, kind) => {
let expr_ty = typeck.expr_ty(expr);
let use_cx = expr_use_ctxt(cx, expr);
let adjusted_ty = match &use_cx {
Some(use_cx) => match use_cx.adjustments {
[.., a] => a.target,
_ => expr_ty,
},
_ => typeck.expr_ty_adjusted(expr),
};
match (use_cx, kind) {
(Some(use_cx), RefOp::Deref) => {
let sub_ty = typeck.expr_ty(sub_expr);
if let ExprUseNode::FieldAccess(name) = use_cx.node
&& !use_cx.moved_before_use
&& !ty_contains_field(sub_ty, name.name)
{
self.state = Some((
State::ExplicitDerefField {
name: name.name,
derefs_manually_drop: is_manually_drop(sub_ty),
},
StateData {
first_expr: expr,
adjusted_ty,
},
));
} else if sub_ty.is_ref()
// Linting method receivers would require verifying that name lookup
// would resolve the same way. This is complicated by trait methods.
&& !use_cx.node.is_recv()
&& let Some(ty) = use_cx.node.defined_ty(cx)
&& TyCoercionStability::for_defined_ty(cx, ty, use_cx.node.is_return()).is_deref_stable()
{
self.state = Some((
State::ExplicitDeref { mutability: None },
StateData {
first_expr: expr,
adjusted_ty,
},
));
}
},
(_, RefOp::Method { mutbl, is_ufcs })
if !is_lint_allowed(cx, EXPLICIT_DEREF_METHODS, expr.hir_id)
// Allow explicit deref in method chains. e.g. `foo.deref().bar()`
&& (is_ufcs || !in_postfix_position(cx, expr)) =>
{
let ty_changed_count = usize::from(!deref_method_same_type(expr_ty, typeck.expr_ty(sub_expr)));
self.state = Some((
State::DerefMethod {
ty_changed_count,
is_ufcs,
mutbl,
},
StateData {
first_expr: expr,
adjusted_ty,
},
));
},
(Some(use_cx), RefOp::AddrOf(mutability)) => {
// Find the number of times the borrow is auto-derefed.
let mut iter = use_cx.adjustments.iter();
let mut deref_count = 0usize;
let next_adjust = loop {
match iter.next() {
Some(adjust) => {
if !matches!(adjust.kind, Adjust::Deref(_)) {
break Some(adjust);
} else if !adjust.target.is_ref() {
deref_count += 1;
break iter.next();
}
deref_count += 1;
},
None => break None,
};
};
let stability = use_cx.node.defined_ty(cx).map_or(TyCoercionStability::None, |ty| {
TyCoercionStability::for_defined_ty(cx, ty, use_cx.node.is_return())
});
let can_auto_borrow = match use_cx.node {
ExprUseNode::FieldAccess(_)
if !use_cx.moved_before_use && matches!(sub_expr.kind, ExprKind::Field(..)) =>
{
// `DerefMut` will not be automatically applied to `ManuallyDrop<_>`
// field expressions when the base type is a union and the parent
// expression is also a field access.
//
// e.g. `&mut x.y.z` where `x` is a union, and accessing `z` requires a
// deref through `ManuallyDrop<_>` will not compile.
!adjust_derefs_manually_drop(use_cx.adjustments, expr_ty)
},
ExprUseNode::Callee | ExprUseNode::FieldAccess(_) => true,
ExprUseNode::MethodArg(hir_id, _, 0) if !use_cx.moved_before_use => {
// Check for calls to trait methods where the trait is implemented
// on a reference.
// Two cases need to be handled:
// * `self` methods on `&T` will never have auto-borrow
// * `&self` methods on `&T` can have auto-borrow, but `&self` methods on `T` will take
// priority.
if let Some(fn_id) = typeck.type_dependent_def_id(hir_id)
&& let Some(trait_id) = cx.tcx.trait_of_item(fn_id)
&& let arg_ty = cx
.tcx
.erase_regions(use_cx.adjustments.last().map_or(expr_ty, |a| a.target))
&& let ty::Ref(_, sub_ty, _) = *arg_ty.kind()
&& let args =
typeck.node_args_opt(hir_id).map(|args| &args[1..]).unwrap_or_default()
&& let impl_ty =
if cx.tcx.fn_sig(fn_id).instantiate_identity().skip_binder().inputs()[0]
.is_ref()
{
// Trait methods taking `&self`
sub_ty
} else {
// Trait methods taking `self`
arg_ty
}
&& impl_ty.is_ref()
&& implements_trait(
cx,
impl_ty,
trait_id,
&args[..cx.tcx.generics_of(trait_id).params.len() - 1],
)
{
false
} else {
true
}
},
_ => false,
};
let deref_msg =
"this expression creates a reference which is immediately dereferenced by the compiler";
let borrow_msg = "this expression borrows a value the compiler would automatically borrow";
// Determine the required number of references before any can be removed. In all cases the
// reference made by the current expression will be removed. After that there are four cases to
// handle.
//
// 1. Auto-borrow will trigger in the current position, so no further references are required.
// 2. Auto-deref ends at a reference, or the underlying type, so one extra needs to be left to
// handle the automatically inserted re-borrow.
// 3. Auto-deref hits a user-defined `Deref` impl, so at least one reference needs to exist to
// start auto-deref.
// 4. If the chain of non-user-defined derefs ends with a mutable re-borrow, and re-borrow
// adjustments will not be inserted automatically, then leave one further reference to avoid
// moving a mutable borrow. e.g.
//
// ```rust
// fn foo<T>(x: &mut Option<&mut T>, y: &mut T) {
// let x = match x {
// // Removing the borrow will cause `x` to be moved
// Some(x) => &mut *x,
// None => y
// };
// }
// ```
let (required_refs, msg) = if can_auto_borrow {
(1, if deref_count == 1 { borrow_msg } else { deref_msg })
} else if let Some(&Adjustment {
kind: Adjust::Borrow(AutoBorrow::Ref(_, mutability)),
..
}) = next_adjust
&& matches!(mutability, AutoBorrowMutability::Mut { .. })
&& !stability.is_reborrow_stable()
{
(3, deref_msg)
} else {
(2, deref_msg)
};
if deref_count >= required_refs {
self.state = Some((
State::DerefedBorrow(DerefedBorrow {
// One of the required refs is for the current borrow expression, the remaining ones
// can't be removed without breaking the code. See earlier comment.
count: deref_count - required_refs,
msg,
stability,
for_field_access: if let ExprUseNode::FieldAccess(name) = use_cx.node
&& !use_cx.moved_before_use
{
Some(name.name)
} else {
None
},
}),
StateData {
first_expr: expr,
adjusted_ty: use_cx.adjustments.last().map_or(expr_ty, |a| a.target),
},
));
} else if stability.is_deref_stable()
// Auto-deref doesn't combine with other adjustments
&& next_adjust.map_or(true, |a| matches!(a.kind, Adjust::Deref(_) | Adjust::Borrow(_)))
&& iter.all(|a| matches!(a.kind, Adjust::Deref(_) | Adjust::Borrow(_)))
{
self.state = Some((
State::Borrow { mutability },
StateData {
first_expr: expr,
adjusted_ty: use_cx.adjustments.last().map_or(expr_ty, |a| a.target),
},
));
}
},
(None, _) | (_, RefOp::Method { .. }) => (),
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}
},
(
Some((
State::DerefMethod {
mutbl,
ty_changed_count,
..
},
data,
)),
RefOp::Method { is_ufcs, .. },
) => {
self.state = Some((
State::DerefMethod {
ty_changed_count: if deref_method_same_type(typeck.expr_ty(expr), typeck.expr_ty(sub_expr)) {
ty_changed_count
} else {
ty_changed_count + 1
},
is_ufcs,
mutbl,
},
data,
));
},
(Some((State::DerefedBorrow(state), data)), RefOp::AddrOf(_)) if state.count != 0 => {
self.state = Some((
State::DerefedBorrow(DerefedBorrow {
count: state.count - 1,
..state
}),
data,
));
},
(Some((State::DerefedBorrow(state), data)), RefOp::AddrOf(mutability)) => {
let adjusted_ty = data.adjusted_ty;
let stability = state.stability;
report(cx, expr, State::DerefedBorrow(state), data, typeck);
if stability.is_deref_stable() {
self.state = Some((
State::Borrow { mutability },
StateData {
first_expr: expr,
adjusted_ty,
},
));
}
},
(Some((State::DerefedBorrow(state), data)), RefOp::Deref) => {
let adjusted_ty = data.adjusted_ty;
let stability = state.stability;
let for_field_access = state.for_field_access;
report(cx, expr, State::DerefedBorrow(state), data, typeck);
if let Some(name) = for_field_access
&& let sub_expr_ty = typeck.expr_ty(sub_expr)
&& !ty_contains_field(sub_expr_ty, name)
{
self.state = Some((
State::ExplicitDerefField {
name,
derefs_manually_drop: is_manually_drop(sub_expr_ty),
},
StateData {
first_expr: expr,
adjusted_ty,
},
));
} else if stability.is_deref_stable()
&& let Some(parent) = get_parent_expr(cx, expr)
{
self.state = Some((
State::ExplicitDeref { mutability: None },
StateData {
first_expr: parent,
adjusted_ty,
},
));
}
},
(Some((State::Borrow { mutability }, data)), RefOp::Deref) => {
if typeck.expr_ty(sub_expr).is_ref() {
self.state = Some((State::Reborrow { mutability }, data));
} else {
self.state = Some((
State::ExplicitDeref {
mutability: Some(mutability),
},
data,
));
}
},
(Some((State::Reborrow { mutability }, data)), RefOp::Deref) => {
self.state = Some((
State::ExplicitDeref {
mutability: Some(mutability),
},
data,
));
},
(state @ Some((State::ExplicitDeref { .. }, _)), RefOp::Deref) => {
self.state = state;
},
(
Some((
State::ExplicitDerefField {
name,
derefs_manually_drop,
},
data,
)),
RefOp::Deref,
) if let sub_expr_ty = typeck.expr_ty(sub_expr)
&& !ty_contains_field(sub_expr_ty, name) =>
{
self.state = Some((
State::ExplicitDerefField {
name,
derefs_manually_drop: derefs_manually_drop || is_manually_drop(sub_expr_ty),
},
data,
));
},
(Some((state, data)), _) => report(cx, expr, state, data, typeck),
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}
}
fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
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if let PatKind::Binding(BindingAnnotation::REF, id, name, _) = pat.kind {
if let Some(opt_prev_pat) = self.ref_locals.get_mut(&id) {
// This binding id has been seen before. Add this pattern to the list of changes.
if let Some(prev_pat) = opt_prev_pat {
if pat.span.from_expansion() {
// Doesn't match the context of the previous pattern. Can't lint here.
*opt_prev_pat = None;
} else {
prev_pat.spans.push(pat.span);
prev_pat.replacements.push((
pat.span,
snippet_with_context(cx, name.span, pat.span.ctxt(), "..", &mut prev_pat.app)
.0
.into(),
));
}
}
return;
}
if !pat.span.from_expansion()
&& let ty::Ref(_, tam, _) = *cx.typeck_results().pat_ty(pat).kind()
// only lint immutable refs, because borrowed `&mut T` cannot be moved out
&& let ty::Ref(_, _, Mutability::Not) = *tam.kind()
{
let mut app = Applicability::MachineApplicable;
let snip = snippet_with_context(cx, name.span, pat.span.ctxt(), "..", &mut app).0;
self.current_body = self.current_body.or(cx.enclosing_body);
self.ref_locals.insert(
id,
Some(RefPat {
always_deref: true,
spans: vec![pat.span],
app,
replacements: vec![(pat.span, snip.into())],
hir_id: pat.hir_id,
}),
);
}
}
}
fn check_body_post(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
if Some(body.id()) == self.current_body {
for pat in self.ref_locals.drain(..).filter_map(|(_, x)| x) {
let replacements = pat.replacements;
let app = pat.app;
let lint = if pat.always_deref {
NEEDLESS_BORROW
} else {
REF_BINDING_TO_REFERENCE
};
span_lint_hir_and_then(
cx,
lint,
pat.hir_id,
pat.spans,
"this pattern creates a reference to a reference",
|diag| {
diag.multipart_suggestion("try", replacements, app);
},
);
}
self.current_body = None;
}
}
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}
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fn try_parse_ref_op<'tcx>(
tcx: TyCtxt<'tcx>,
typeck: &'tcx TypeckResults<'_>,
expr: &'tcx Expr<'_>,
) -> Option<(RefOp, &'tcx Expr<'tcx>)> {
let (is_ufcs, def_id, arg) = match expr.kind {
ExprKind::MethodCall(_, arg, [], _) => (false, typeck.type_dependent_def_id(expr.hir_id)?, arg),
ExprKind::Call(
Expr {
kind: ExprKind::Path(path),
hir_id,
..
},
[arg],
) => (true, typeck.qpath_res(path, *hir_id).opt_def_id()?, arg),
ExprKind::Unary(UnOp::Deref, sub_expr) if !typeck.expr_ty(sub_expr).is_unsafe_ptr() => {
return Some((RefOp::Deref, sub_expr));
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},
ExprKind::AddrOf(BorrowKind::Ref, mutability, sub_expr) => return Some((RefOp::AddrOf(mutability), sub_expr)),
_ => return None,
};
if tcx.is_diagnostic_item(sym::deref_method, def_id) {
Some((
RefOp::Method {
mutbl: Mutability::Not,
is_ufcs,
},
arg,
))
} else if tcx.trait_of_item(def_id)? == tcx.lang_items().deref_mut_trait()? {
Some((
RefOp::Method {
mutbl: Mutability::Mut,
is_ufcs,
},
arg,
))
} else {
None
}
}
// Checks if the adjustments contains a deref of `ManuallyDrop<_>`
fn adjust_derefs_manually_drop<'tcx>(adjustments: &'tcx [Adjustment<'tcx>], mut ty: Ty<'tcx>) -> bool {
adjustments.iter().any(|a| {
let ty = mem::replace(&mut ty, a.target);
matches!(a.kind, Adjust::Deref(Some(ref op)) if op.mutbl == Mutability::Mut) && is_manually_drop(ty)
})
}
// Checks whether the type for a deref call actually changed the type, not just the mutability of
// the reference.
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fn deref_method_same_type<'tcx>(result_ty: Ty<'tcx>, arg_ty: Ty<'tcx>) -> bool {
match (result_ty.kind(), arg_ty.kind()) {
(ty::Ref(_, result_ty, _), ty::Ref(_, arg_ty, _)) => result_ty == arg_ty,
// The result type for a deref method is always a reference
// Not matching the previous pattern means the argument type is not a reference
// This means that the type did change
_ => false,
}
}
fn in_postfix_position<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
if let Some(parent) = get_parent_expr(cx, e)
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&& parent.span.eq_ctxt(e.span)
{
match parent.kind {
ExprKind::Call(child, _) | ExprKind::MethodCall(_, child, _, _) | ExprKind::Index(child, _, _)
if child.hir_id == e.hir_id =>
{
true
},
ExprKind::Match(.., MatchSource::TryDesugar(_) | MatchSource::AwaitDesugar) | ExprKind::Field(_, _) => true,
_ => false,
}
} else {
false
}
}
#[derive(Clone, Copy)]
enum TyCoercionStability {
Deref,
Reborrow,
None,
}
impl TyCoercionStability {
fn is_deref_stable(self) -> bool {
matches!(self, Self::Deref)
}
fn is_reborrow_stable(self) -> bool {
matches!(self, Self::Deref | Self::Reborrow)
}
fn for_defined_ty<'tcx>(cx: &LateContext<'tcx>, ty: DefinedTy<'tcx>, for_return: bool) -> Self {
match ty {
DefinedTy::Hir(ty) => Self::for_hir_ty(ty),
DefinedTy::Mir(ty) => Self::for_mir_ty(
cx.tcx,
ty.param_env,
cx.tcx.instantiate_bound_regions_with_erased(ty.value),
for_return,
),
}
}
// Checks the stability of type coercions when assigned to a binding with the given explicit type.
//
// e.g.
// let x = Box::new(Box::new(0u32));
// let y1: &Box<_> = x.deref();
// let y2: &Box<_> = &x;
//
// Here `y1` and `y2` would resolve to different types, so the type `&Box<_>` is not stable when
// switching to auto-dereferencing.
fn for_hir_ty<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> Self {
let TyKind::Ref(_, ty) = &ty.kind else {
return Self::None;
};
let mut ty = ty;
loop {
break match ty.ty.kind {
TyKind::Ref(_, ref ref_ty) => {
ty = ref_ty;
continue;
},
TyKind::Path(
QPath::TypeRelative(_, path)
| QPath::Resolved(
_,
Path {
segments: [.., path], ..
},
),
) => {
if let Some(args) = path.args
&& args.args.iter().any(|arg| match arg {
hir::GenericArg::Infer(_) => true,
hir::GenericArg::Type(ty) => ty_contains_infer(ty),
_ => false,
})
{
Self::Reborrow
} else {
Self::Deref
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}
},
TyKind::Slice(_)
| TyKind::Array(..)
| TyKind::Ptr(_)
| TyKind::BareFn(_)
| TyKind::Never
| TyKind::Tup(_)
| TyKind::Path(_) => Self::Deref,
TyKind::OpaqueDef(..)
| TyKind::Infer
| TyKind::Typeof(..)
| TyKind::TraitObject(..)
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| TyKind::InferDelegation(..)
| TyKind::AnonAdt(..)
| TyKind::Err(_) => Self::Reborrow,
};
}
}
fn for_mir_ty<'tcx>(tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>, for_return: bool) -> Self {
let ty::Ref(_, mut ty, _) = *ty.kind() else {
return Self::None;
};
ty = tcx.try_normalize_erasing_regions(param_env, ty).unwrap_or(ty);
loop {
break match *ty.kind() {
ty::Ref(_, ref_ty, _) => {
ty = ref_ty;
continue;
},
ty::Param(_) if for_return => Self::Deref,
ty::Alias(ty::Weak | ty::Inherent, _) => unreachable!("should have been normalized away above"),
ty::Alias(ty::Projection, _) if !for_return && ty.has_non_region_param() => Self::Reborrow,
ty::Infer(_)
| ty::Error(_)
| ty::Bound(..)
| ty::Alias(ty::Opaque, ..)
| ty::Placeholder(_)
| ty::Dynamic(..)
| ty::Param(_) => Self::Reborrow,
ty::Adt(_, args)
if ty.has_placeholders()
|| ty.has_opaque_types()
|| (!for_return && args.has_non_region_param()) =>
{
Self::Reborrow
},
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Array(..)
| ty::Float(_)
| ty::RawPtr(..)
| ty::FnPtr(_)
| ty::Str
| ty::Slice(..)
| ty::Adt(..)
| ty::Foreign(_)
| ty::FnDef(..)
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| ty::Coroutine(..)
| ty::CoroutineWitness(..)
| ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Never
| ty::Tuple(_)
| ty::Alias(ty::Projection, _) => Self::Deref,
};
}
}
}
// Checks whether a type is inferred at some point.
// e.g. `_`, `Box<_>`, `[_]`
fn ty_contains_infer(ty: &hir::Ty<'_>) -> bool {
struct V(bool);
impl Visitor<'_> for V {
fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
if self.0
|| matches!(
ty.kind,
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TyKind::OpaqueDef(..) | TyKind::Infer | TyKind::Typeof(_) | TyKind::Err(_)
)
{
self.0 = true;
} else {
walk_ty(self, ty);
}
}
fn visit_generic_arg(&mut self, arg: &hir::GenericArg<'_>) {
if self.0 || matches!(arg, hir::GenericArg::Infer(_)) {
self.0 = true;
} else if let hir::GenericArg::Type(ty) = arg {
self.visit_ty(ty);
}
}
}
let mut v = V(false);
v.visit_ty(ty);
v.0
}
fn ty_contains_field(ty: Ty<'_>, name: Symbol) -> bool {
if let ty::Adt(adt, _) = *ty.kind() {
adt.is_struct() && adt.all_fields().any(|f| f.name == name)
} else {
false
}
}
#[expect(clippy::needless_pass_by_value, clippy::too_many_lines)]
fn report<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'_>,
state: State,
data: StateData<'tcx>,
typeck: &'tcx TypeckResults<'tcx>,
) {
match state {
State::DerefMethod {
ty_changed_count,
is_ufcs,
mutbl,
} => {
let mut app = Applicability::MachineApplicable;
let (expr_str, _expr_is_macro_call) =
snippet_with_context(cx, expr.span, data.first_expr.span.ctxt(), "..", &mut app);
let ty = typeck.expr_ty(expr);
let (_, ref_count) = peel_mid_ty_refs(ty);
let deref_str = if ty_changed_count >= ref_count && ref_count != 0 {
// a deref call changing &T -> &U requires two deref operators the first time
// this occurs. One to remove the reference, a second to call the deref impl.
"*".repeat(ty_changed_count + 1)
} else {
"*".repeat(ty_changed_count)
};
let addr_of_str = if ty_changed_count < ref_count {
// Check if a reborrow from &mut T -> &T is required.
if mutbl == Mutability::Not && matches!(ty.kind(), ty::Ref(_, _, Mutability::Mut)) {
"&*"
} else {
""
}
} else if mutbl == Mutability::Mut {
"&mut "
} else {
"&"
};
// expr_str (the suggestion) is never shown if is_final_ufcs is true, since it's
// `expr.kind == ExprKind::Call`. Therefore, this is, afaik, always unnecessary.
/*
expr_str = if !expr_is_macro_call && is_final_ufcs && expr.precedence().order() < PREC_PREFIX {
Cow::Owned(format!("({expr_str})"))
} else {
expr_str
};
*/
// Fix #10850, do not lint if it's `Foo::deref` instead of `foo.deref()`.
if is_ufcs {
return;
}
span_lint_and_sugg(
cx,
EXPLICIT_DEREF_METHODS,
data.first_expr.span,
match mutbl {
Mutability::Not => "explicit `deref` method call",
Mutability::Mut => "explicit `deref_mut` method call",
},
"try",
format!("{addr_of_str}{deref_str}{expr_str}"),
app,
);
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},
State::DerefedBorrow(state) => {
let mut app = Applicability::MachineApplicable;
let (snip, snip_is_macro) =
snippet_with_context(cx, expr.span, data.first_expr.span.ctxt(), "..", &mut app);
span_lint_hir_and_then(
cx,
NEEDLESS_BORROW,
data.first_expr.hir_id,
data.first_expr.span,
state.msg,
|diag| {
let (precedence, calls_field) = match get_parent_node(cx.tcx, data.first_expr.hir_id) {
Some(Node::Expr(e)) => match e.kind {
ExprKind::Call(callee, _) if callee.hir_id != data.first_expr.hir_id => (0, false),
ExprKind::Call(..) => (PREC_POSTFIX, matches!(expr.kind, ExprKind::Field(..))),
_ => (e.precedence().order(), false),
},
_ => (0, false),
};
let sugg = if !snip_is_macro
&& (calls_field || expr.precedence().order() < precedence)
&& !has_enclosing_paren(&snip)
{
format!("({snip})")
} else {
snip.into()
};
diag.span_suggestion(data.first_expr.span, "change this to", sugg, app);
},
);
},
State::ExplicitDeref { mutability } => {
if matches!(
expr.kind,
ExprKind::Block(..)
| ExprKind::ConstBlock(_)
| ExprKind::If(..)
| ExprKind::Loop(..)
| ExprKind::Match(..)
) && let ty::Ref(_, ty, _) = data.adjusted_ty.kind()
&& ty.is_sized(cx.tcx, cx.param_env)
{
// Rustc bug: auto deref doesn't work on block expression when targeting sized types.
return;
}
let (prefix, precedence) = if let Some(mutability) = mutability
&& !typeck.expr_ty(expr).is_ref()
{
let prefix = match mutability {
Mutability::Not => "&",
Mutability::Mut => "&mut ",
};
(prefix, PREC_PREFIX)
} else {
("", 0)
};
span_lint_hir_and_then(
cx,
EXPLICIT_AUTO_DEREF,
data.first_expr.hir_id,
data.first_expr.span,
"deref which would be done by auto-deref",
|diag| {
let mut app = Applicability::MachineApplicable;
let (snip, snip_is_macro) =
snippet_with_context(cx, expr.span, data.first_expr.span.ctxt(), "..", &mut app);
let sugg =
if !snip_is_macro && expr.precedence().order() < precedence && !has_enclosing_paren(&snip) {
format!("{prefix}({snip})")
} else {
format!("{prefix}{snip}")
};
diag.span_suggestion(data.first_expr.span, "try", sugg, app);
},
);
},
State::ExplicitDerefField {
derefs_manually_drop, ..
} => {
let (snip_span, needs_parens) = if matches!(expr.kind, ExprKind::Field(..))
&& (derefs_manually_drop
|| adjust_derefs_manually_drop(
typeck.expr_adjustments(data.first_expr),
typeck.expr_ty(data.first_expr),
)) {
// `DerefMut` will not be automatically applied to `ManuallyDrop<_>`
// field expressions when the base type is a union and the parent
// expression is also a field access.
//
// e.g. `&mut x.y.z` where `x` is a union, and accessing `z` requires a
// deref through `ManuallyDrop<_>` will not compile.
let parent_id = cx.tcx.parent_hir_id(expr.hir_id);
if parent_id == data.first_expr.hir_id {
return;
}
(cx.tcx.hir_node(parent_id).expect_expr().span, true)
} else {
(expr.span, false)
};
span_lint_hir_and_then(
cx,
EXPLICIT_AUTO_DEREF,
data.first_expr.hir_id,
data.first_expr.span,
"deref which would be done by auto-deref",
|diag| {
let mut app = Applicability::MachineApplicable;
let snip = snippet_with_context(cx, snip_span, data.first_expr.span.ctxt(), "..", &mut app).0;
let sugg = if needs_parens {
format!("({snip})")
} else {
snip.into_owned()
};
diag.span_suggestion(data.first_expr.span, "try", sugg, app);
},
);
},
State::Borrow { .. } | State::Reborrow { .. } => (),
}
}
impl<'tcx> Dereferencing<'tcx> {
fn check_local_usage(&mut self, cx: &LateContext<'tcx>, e: &Expr<'tcx>, local: HirId) {
if let Some(outer_pat) = self.ref_locals.get_mut(&local) {
if let Some(pat) = outer_pat {
// Check for auto-deref
if !matches!(
cx.typeck_results().expr_adjustments(e),
[
Adjustment {
kind: Adjust::Deref(_),
..
},
Adjustment {
kind: Adjust::Deref(_),
..
},
..
]
) {
match get_parent_expr(cx, e) {
// Field accesses are the same no matter the number of references.
Some(Expr {
kind: ExprKind::Field(..),
..
}) => (),
Some(&Expr {
span,
kind: ExprKind::Unary(UnOp::Deref, _),
..
}) if !span.from_expansion() => {
// Remove explicit deref.
let snip = snippet_with_context(cx, e.span, span.ctxt(), "..", &mut pat.app).0;
pat.replacements.push((span, snip.into()));
},
Some(parent) if !parent.span.from_expansion() => {
// Double reference might be needed at this point.
if parent.precedence().order() == PREC_POSTFIX {
// Parentheses would be needed here, don't lint.
*outer_pat = None;
} else {
pat.always_deref = false;
let snip = snippet_with_context(cx, e.span, parent.span.ctxt(), "..", &mut pat.app).0;
pat.replacements.push((e.span, format!("&{snip}")));
}
},
_ if !e.span.from_expansion() => {
// Double reference might be needed at this point.
pat.always_deref = false;
let snip = snippet_with_applicability(cx, e.span, "..", &mut pat.app);
pat.replacements.push((e.span, format!("&{snip}")));
},
// Edge case for macros. The span of the identifier will usually match the context of the
// binding, but not if the identifier was created in a macro. e.g. `concat_idents` and proc
// macros
_ => *outer_pat = None,
}
}
}
}
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}
}