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rust-clippy/clippy_lints/src/dereference.rs
Santiago Pastorino 3f059a49a4 Introduce PredicateKind::Clause
2022-11-25 00:04:54 -03:00

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use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then};
use clippy_utils::mir::{enclosing_mir, expr_local, local_assignments, used_exactly_once, PossibleBorrowerMap};
use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
use clippy_utils::sugg::has_enclosing_paren;
use clippy_utils::ty::{expr_sig, is_copy, peel_mid_ty_refs, ty_sig, variant_of_res};
use clippy_utils::{
fn_def_id, get_parent_expr, get_parent_expr_for_hir, is_lint_allowed, meets_msrv, msrvs, path_to_local,
walk_to_expr_usage,
};
use rustc_ast::util::parser::{PREC_POSTFIX, PREC_PREFIX};
use rustc_data_structures::fx::FxIndexMap;
use rustc_data_structures::graph::iterate::{CycleDetector, TriColorDepthFirstSearch};
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_ty, Visitor};
use rustc_hir::{
self as hir,
def_id::{DefId, LocalDefId},
BindingAnnotation, Body, BodyId, BorrowKind, Closure, Expr, ExprKind, FnRetTy, GenericArg, HirId, ImplItem,
ImplItemKind, Item, ItemKind, Local, MatchSource, Mutability, Node, Pat, PatKind, Path, QPath, TraitItem,
TraitItemKind, TyKind, UnOp,
};
use rustc_index::bit_set::BitSet;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::mir::{Rvalue, StatementKind};
use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
use rustc_middle::ty::{
self, Binder, BoundVariableKind, Clause, EarlyBinder, FnSig, GenericArgKind, List, ParamTy, PredicateKind,
ProjectionPredicate, Ty, TyCtxt, TypeVisitable, TypeckResults,
};
use rustc_semver::RustcVersion;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{symbol::sym, Span, Symbol};
use rustc_trait_selection::infer::InferCtxtExt as _;
use rustc_trait_selection::traits::{query::evaluate_obligation::InferCtxtExt as _, Obligation, ObligationCause};
use std::collections::VecDeque;
declare_clippy_lint! {
/// ### What it does
/// Checks for explicit `deref()` or `deref_mut()` method calls.
///
/// ### Why is this bad?
/// Dereferencing by `&*x` or `&mut *x` is clearer and more concise,
/// when not part of a method chain.
///
/// ### Example
/// ```rust
/// use std::ops::Deref;
/// let a: &mut String = &mut String::from("foo");
/// let b: &str = a.deref();
/// ```
///
/// Use instead:
/// ```rust
/// let a: &mut String = &mut String::from("foo");
/// let b = &*a;
/// ```
///
/// This lint excludes:
/// ```rust,ignore
/// let _ = d.unwrap().deref();
/// ```
#[clippy::version = "1.44.0"]
pub EXPLICIT_DEREF_METHODS,
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.
///
/// ### Example
/// ```rust
/// fn fun(_a: &i32) {}
///
/// let x: &i32 = &&&&&&5;
/// fun(&x);
/// ```
///
/// Use instead:
/// ```rust
/// # 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
/// ```rust
/// let x = Some("");
/// if let Some(ref x) = x {
/// // use `x` here
/// }
/// ```
///
/// Use instead:
/// ```rust
/// 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
/// ```rust
/// let x = String::new();
/// let y: &str = &*x;
/// ```
/// Use instead:
/// ```rust
/// 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,
]);
#[derive(Default)]
pub struct Dereferencing<'tcx> {
state: Option<(State, StateData)>,
// 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>>,
/// Stack of (body owner, `PossibleBorrowerMap`) pairs. Used by
/// `needless_borrow_impl_arg_position` to determine when a borrowed expression can instead
/// be moved.
possible_borrowers: Vec<(LocalDefId, PossibleBorrowerMap<'tcx, 'tcx>)>,
// `IntoIterator` for arrays requires Rust 1.53.
msrv: Option<RustcVersion>,
}
impl<'tcx> Dereferencing<'tcx> {
#[must_use]
pub fn new(msrv: Option<RustcVersion>) -> Self {
Self {
msrv,
..Dereferencing::default()
}
}
}
#[derive(Debug)]
struct StateData {
/// Span of the top level expression
span: Span,
hir_id: HirId,
position: Position,
}
#[derive(Debug)]
struct DerefedBorrow {
count: usize,
msg: &'static str,
snip_expr: Option<HirId>,
}
#[derive(Debug)]
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_final_ufcs: bool,
/// The required mutability
target_mut: Mutability,
},
DerefedBorrow(DerefedBorrow),
ExplicitDeref {
mutability: Option<Mutability>,
},
ExplicitDerefField {
name: Symbol,
},
Reborrow {
mutability: Mutability,
},
Borrow {
mutability: Mutability,
},
}
// A reference operation considered by this lint pass
enum RefOp {
Method(Mutability),
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);
}
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);
}
return;
};
match (self.state.take(), kind) {
(None, kind) => {
let expr_ty = typeck.expr_ty(expr);
let (position, adjustments) = walk_parents(cx, &mut self.possible_borrowers, expr, self.msrv);
match kind {
RefOp::Deref => {
if let Position::FieldAccess {
name,
of_union: false,
} = position
&& !ty_contains_field(typeck.expr_ty(sub_expr), name)
{
self.state = Some((
State::ExplicitDerefField { name },
StateData { span: expr.span, hir_id: expr.hir_id, position },
));
} else if position.is_deref_stable() {
self.state = Some((
State::ExplicitDeref { mutability: None },
StateData { span: expr.span, hir_id: expr.hir_id, position },
));
}
}
RefOp::Method(target_mut)
if !is_lint_allowed(cx, EXPLICIT_DEREF_METHODS, expr.hir_id)
&& position.lint_explicit_deref() =>
{
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_final_ufcs: matches!(expr.kind, ExprKind::Call(..)),
target_mut,
},
StateData {
span: expr.span,
hir_id: expr.hir_id,
position
},
));
},
RefOp::AddrOf(mutability) => {
// Find the number of times the borrow is auto-derefed.
let mut iter = 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,
};
};
// 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.
// 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 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";
let impl_msg = "the borrowed expression implements the required traits";
let (required_refs, msg, snip_expr) = if position.can_auto_borrow() {
(1, if deref_count == 1 { borrow_msg } else { deref_msg }, None)
} else if let Position::ImplArg(hir_id) = position {
(0, impl_msg, Some(hir_id))
} else if let Some(&Adjust::Borrow(AutoBorrow::Ref(_, mutability))) =
next_adjust.map(|a| &a.kind)
{
if matches!(mutability, AutoBorrowMutability::Mut { .. }) && !position.is_reborrow_stable()
{
(3, deref_msg, None)
} else {
(2, deref_msg, None)
}
} else {
(2, deref_msg, None)
};
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,
snip_expr,
}),
StateData { span: expr.span, hir_id: expr.hir_id, position },
));
} else if position.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 {
span: expr.span,
hir_id: expr.hir_id,
position
},
));
}
},
RefOp::Method(..) => (),
}
},
(
Some((
State::DerefMethod {
target_mut,
ty_changed_count,
..
},
data,
)),
RefOp::Method(_),
) => {
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_final_ufcs: matches!(expr.kind, ExprKind::Call(..)),
target_mut,
},
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 position = data.position;
report(cx, expr, State::DerefedBorrow(state), data);
if position.is_deref_stable() {
self.state = Some((
State::Borrow { mutability },
StateData {
span: expr.span,
hir_id: expr.hir_id,
position,
},
));
}
},
(Some((State::DerefedBorrow(state), data)), RefOp::Deref) => {
let position = data.position;
report(cx, expr, State::DerefedBorrow(state), data);
if let Position::FieldAccess{name, ..} = position
&& !ty_contains_field(typeck.expr_ty(sub_expr), name)
{
self.state = Some((
State::ExplicitDerefField { name },
StateData { span: expr.span, hir_id: expr.hir_id, position },
));
} else if position.is_deref_stable() {
self.state = Some((
State::ExplicitDeref { mutability: None },
StateData { span: expr.span, hir_id: expr.hir_id, position },
));
}
},
(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 }, data)), RefOp::Deref)
if !ty_contains_field(typeck.expr_ty(sub_expr), name) =>
{
self.state = Some((State::ExplicitDerefField { name }, data));
},
(Some((state, data)), _) => report(cx, expr, state, data),
}
}
fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
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_chain! {
if !pat.span.from_expansion();
if let ty::Ref(_, tam, _) = *cx.typeck_results().pat_ty(pat).kind();
// only lint immutable refs, because borrowed `&mut T` cannot be moved out
if let ty::Ref(_, _, Mutability::Not) = *tam.kind();
then {
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 self.possible_borrowers.last().map_or(false, |&(local_def_id, _)| {
local_def_id == cx.tcx.hir().body_owner_def_id(body.id())
}) {
self.possible_borrowers.pop();
}
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 this", replacements, app);
},
);
}
self.current_body = None;
}
}
extract_msrv_attr!(LateContext);
}
fn try_parse_ref_op<'tcx>(
tcx: TyCtxt<'tcx>,
typeck: &'tcx TypeckResults<'_>,
expr: &'tcx Expr<'_>,
) -> Option<(RefOp, &'tcx Expr<'tcx>)> {
let (def_id, arg) = match expr.kind {
ExprKind::MethodCall(_, arg, [], _) => (typeck.type_dependent_def_id(expr.hir_id)?, arg),
ExprKind::Call(
Expr {
kind: ExprKind::Path(path),
hir_id,
..
},
[arg],
) => (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));
},
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(Mutability::Not), arg))
} else if tcx.trait_of_item(def_id)? == tcx.lang_items().deref_mut_trait()? {
Some((RefOp::Method(Mutability::Mut), arg))
} else {
None
}
}
// Checks whether the type for a deref call actually changed the type, not just the mutability of
// the reference.
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,
}
}
/// The position of an expression relative to it's parent.
#[derive(Clone, Copy, Debug)]
enum Position {
MethodReceiver,
/// The method is defined on a reference type. e.g. `impl Foo for &T`
MethodReceiverRefImpl,
Callee,
ImplArg(HirId),
FieldAccess {
name: Symbol,
of_union: bool,
}, // union fields cannot be auto borrowed
Postfix,
Deref,
/// Any other location which will trigger auto-deref to a specific time.
/// Contains the precedence of the parent expression and whether the target type is sized.
DerefStable(i8, bool),
/// Any other location which will trigger auto-reborrowing.
/// Contains the precedence of the parent expression.
ReborrowStable(i8),
/// Contains the precedence of the parent expression.
Other(i8),
}
impl Position {
fn is_deref_stable(self) -> bool {
matches!(self, Self::DerefStable(..))
}
fn is_reborrow_stable(self) -> bool {
matches!(self, Self::DerefStable(..) | Self::ReborrowStable(_))
}
fn can_auto_borrow(self) -> bool {
matches!(
self,
Self::MethodReceiver | Self::FieldAccess { of_union: false, .. } | Self::Callee
)
}
fn lint_explicit_deref(self) -> bool {
matches!(self, Self::Other(_) | Self::DerefStable(..) | Self::ReborrowStable(_))
}
fn precedence(self) -> i8 {
match self {
Self::MethodReceiver
| Self::MethodReceiverRefImpl
| Self::Callee
| Self::FieldAccess { .. }
| Self::Postfix => PREC_POSTFIX,
Self::ImplArg(_) | Self::Deref => PREC_PREFIX,
Self::DerefStable(p, _) | Self::ReborrowStable(p) | Self::Other(p) => p,
}
}
}
/// Walks up the parent expressions attempting to determine both how stable the auto-deref result
/// is, and which adjustments will be applied to it. Note this will not consider auto-borrow
/// locations as those follow different rules.
#[expect(clippy::too_many_lines)]
fn walk_parents<'tcx>(
cx: &LateContext<'tcx>,
possible_borrowers: &mut Vec<(LocalDefId, PossibleBorrowerMap<'tcx, 'tcx>)>,
e: &'tcx Expr<'_>,
msrv: Option<RustcVersion>,
) -> (Position, &'tcx [Adjustment<'tcx>]) {
let mut adjustments = [].as_slice();
let mut precedence = 0i8;
let ctxt = e.span.ctxt();
let position = walk_to_expr_usage(cx, e, &mut |parent, child_id| {
// LocalTableInContext returns the wrong lifetime, so go use `expr_adjustments` instead.
if adjustments.is_empty() && let Node::Expr(e) = cx.tcx.hir().get(child_id) {
adjustments = cx.typeck_results().expr_adjustments(e);
}
match parent {
Node::Local(Local { ty: Some(ty), span, .. }) if span.ctxt() == ctxt => {
Some(binding_ty_auto_deref_stability(cx, ty, precedence, List::empty()))
},
Node::Item(&Item {
kind: ItemKind::Static(..) | ItemKind::Const(..),
owner_id,
span,
..
})
| Node::TraitItem(&TraitItem {
kind: TraitItemKind::Const(..),
owner_id,
span,
..
})
| Node::ImplItem(&ImplItem {
kind: ImplItemKind::Const(..),
owner_id,
span,
..
}) if span.ctxt() == ctxt => {
let ty = cx.tcx.type_of(owner_id.def_id);
Some(ty_auto_deref_stability(cx, ty, precedence).position_for_result(cx))
},
Node::Item(&Item {
kind: ItemKind::Fn(..),
owner_id,
span,
..
})
| Node::TraitItem(&TraitItem {
kind: TraitItemKind::Fn(..),
owner_id,
span,
..
})
| Node::ImplItem(&ImplItem {
kind: ImplItemKind::Fn(..),
owner_id,
span,
..
}) if span.ctxt() == ctxt => {
let output = cx
.tcx
.erase_late_bound_regions(cx.tcx.fn_sig(owner_id.to_def_id()).output());
Some(ty_auto_deref_stability(cx, output, precedence).position_for_result(cx))
},
Node::ExprField(field) if field.span.ctxt() == ctxt => match get_parent_expr_for_hir(cx, field.hir_id) {
Some(Expr {
hir_id,
kind: ExprKind::Struct(path, ..),
..
}) => variant_of_res(cx, cx.qpath_res(path, *hir_id))
.and_then(|variant| variant.fields.iter().find(|f| f.name == field.ident.name))
.map(|field_def| {
ty_auto_deref_stability(cx, cx.tcx.type_of(field_def.did), precedence).position_for_arg()
}),
_ => None,
},
Node::Expr(parent) if parent.span.ctxt() == ctxt => match parent.kind {
ExprKind::Ret(_) => {
let owner_id = cx.tcx.hir().body_owner(cx.enclosing_body.unwrap());
Some(
if let Node::Expr(
closure_expr @ Expr {
kind: ExprKind::Closure(closure),
..
},
) = cx.tcx.hir().get(owner_id)
{
closure_result_position(cx, closure, cx.typeck_results().expr_ty(closure_expr), precedence)
} else {
let output = cx
.tcx
.erase_late_bound_regions(cx.tcx.fn_sig(cx.tcx.hir().local_def_id(owner_id)).output());
ty_auto_deref_stability(cx, output, precedence).position_for_result(cx)
},
)
},
ExprKind::Closure(closure) => Some(closure_result_position(
cx,
closure,
cx.typeck_results().expr_ty(parent),
precedence,
)),
ExprKind::Call(func, _) if func.hir_id == child_id => {
(child_id == e.hir_id).then_some(Position::Callee)
},
ExprKind::Call(func, args) => args
.iter()
.position(|arg| arg.hir_id == child_id)
.zip(expr_sig(cx, func))
.and_then(|(i, sig)| {
sig.input_with_hir(i).map(|(hir_ty, ty)| {
match hir_ty {
// Type inference for closures can depend on how they're called. Only go by the explicit
// types here.
Some(hir_ty) => {
binding_ty_auto_deref_stability(cx, hir_ty, precedence, ty.bound_vars())
},
None => {
// `e.hir_id == child_id` for https://github.com/rust-lang/rust-clippy/issues/9739
// `!call_is_qualified(func)` for https://github.com/rust-lang/rust-clippy/issues/9782
if e.hir_id == child_id
&& !call_is_qualified(func)
&& let ty::Param(param_ty) = ty.skip_binder().kind()
{
needless_borrow_impl_arg_position(
cx,
possible_borrowers,
parent,
i,
*param_ty,
e,
precedence,
msrv,
)
} else {
ty_auto_deref_stability(cx, cx.tcx.erase_late_bound_regions(ty), precedence)
.position_for_arg()
}
},
}
})
}),
ExprKind::MethodCall(method, receiver, args, _) => {
let id = cx.typeck_results().type_dependent_def_id(parent.hir_id).unwrap();
if receiver.hir_id == child_id {
// 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 e.hir_id != child_id {
return Some(Position::ReborrowStable(precedence))
} else if let Some(trait_id) = cx.tcx.trait_of_item(id)
&& let arg_ty = cx.tcx.erase_regions(cx.typeck_results().expr_ty_adjusted(e))
&& let ty::Ref(_, sub_ty, _) = *arg_ty.kind()
&& let subs = cx
.typeck_results()
.node_substs_opt(parent.hir_id).map(|subs| &subs[1..]).unwrap_or_default()
&& let impl_ty = if cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref() {
// Trait methods taking `&self`
sub_ty
} else {
// Trait methods taking `self`
arg_ty
} && impl_ty.is_ref()
&& let infcx = cx.tcx.infer_ctxt().build()
&& infcx
.type_implements_trait(trait_id, [impl_ty.into()].into_iter().chain(subs.iter().copied()), cx.param_env)
.must_apply_modulo_regions()
{
return Some(Position::MethodReceiverRefImpl)
}
return Some(Position::MethodReceiver);
}
args.iter().position(|arg| arg.hir_id == child_id).map(|i| {
let ty = cx.tcx.fn_sig(id).skip_binder().inputs()[i + 1];
// `e.hir_id == child_id` for https://github.com/rust-lang/rust-clippy/issues/9739
// `method.args.is_none()` for https://github.com/rust-lang/rust-clippy/issues/9782
if e.hir_id == child_id && method.args.is_none() && let ty::Param(param_ty) = ty.kind() {
needless_borrow_impl_arg_position(
cx,
possible_borrowers,
parent,
i + 1,
*param_ty,
e,
precedence,
msrv,
)
} else {
ty_auto_deref_stability(
cx,
cx.tcx.erase_late_bound_regions(cx.tcx.fn_sig(id).input(i + 1)),
precedence,
)
.position_for_arg()
}
})
},
ExprKind::Field(child, name) if child.hir_id == e.hir_id => Some(Position::FieldAccess {
name: name.name,
of_union: is_union(cx.typeck_results(), child),
}),
ExprKind::Unary(UnOp::Deref, child) if child.hir_id == e.hir_id => Some(Position::Deref),
ExprKind::Match(child, _, MatchSource::TryDesugar | MatchSource::AwaitDesugar)
| ExprKind::Index(child, _)
if child.hir_id == e.hir_id =>
{
Some(Position::Postfix)
},
_ if child_id == e.hir_id => {
precedence = parent.precedence().order();
None
},
_ => None,
},
_ => None,
}
})
.unwrap_or(Position::Other(precedence));
(position, adjustments)
}
fn is_union<'tcx>(typeck: &'tcx TypeckResults<'_>, path_expr: &'tcx Expr<'_>) -> bool {
typeck
.expr_ty_adjusted(path_expr)
.ty_adt_def()
.map_or(false, rustc_middle::ty::AdtDef::is_union)
}
fn closure_result_position<'tcx>(
cx: &LateContext<'tcx>,
closure: &'tcx Closure<'_>,
ty: Ty<'tcx>,
precedence: i8,
) -> Position {
match closure.fn_decl.output {
FnRetTy::Return(hir_ty) => {
if let Some(sig) = ty_sig(cx, ty)
&& let Some(output) = sig.output()
{
binding_ty_auto_deref_stability(cx, hir_ty, precedence, output.bound_vars())
} else {
Position::Other(precedence)
}
},
FnRetTy::DefaultReturn(_) => Position::Other(precedence),
}
}
// Checks the stability of auto-deref 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 binding_ty_auto_deref_stability<'tcx>(
cx: &LateContext<'tcx>,
ty: &'tcx hir::Ty<'_>,
precedence: i8,
binder_args: &'tcx List<BoundVariableKind>,
) -> Position {
let TyKind::Rptr(_, ty) = &ty.kind else {
return Position::Other(precedence);
};
let mut ty = ty;
loop {
break match ty.ty.kind {
TyKind::Rptr(_, 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 {
GenericArg::Infer(_) => true,
GenericArg::Type(ty) => ty_contains_infer(ty),
_ => false,
})
{
Position::ReborrowStable(precedence)
} else {
Position::DerefStable(
precedence,
cx.tcx
.erase_late_bound_regions(Binder::bind_with_vars(
cx.typeck_results().node_type(ty.ty.hir_id),
binder_args,
))
.is_sized(cx.tcx, cx.param_env.without_caller_bounds()),
)
}
},
TyKind::Slice(_) => Position::DerefStable(precedence, false),
TyKind::Array(..) | TyKind::Ptr(_) | TyKind::BareFn(_) => Position::DerefStable(precedence, true),
TyKind::Never
| TyKind::Tup(_)
| TyKind::Path(_) => Position::DerefStable(
precedence,
cx.tcx
.erase_late_bound_regions(Binder::bind_with_vars(
cx.typeck_results().node_type(ty.ty.hir_id),
binder_args,
))
.is_sized(cx.tcx, cx.param_env.without_caller_bounds()),
),
TyKind::OpaqueDef(..) | TyKind::Infer | TyKind::Typeof(..) | TyKind::TraitObject(..) | TyKind::Err => {
Position::ReborrowStable(precedence)
},
};
}
}
// 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,
TyKind::OpaqueDef(..) | TyKind::Infer | TyKind::Typeof(_) | TyKind::Err
)
{
self.0 = true;
} else {
walk_ty(self, ty);
}
}
fn visit_generic_arg(&mut self, arg: &GenericArg<'_>) {
if self.0 || matches!(arg, GenericArg::Infer(_)) {
self.0 = true;
} else if let GenericArg::Type(ty) = arg {
self.visit_ty(ty);
}
}
}
let mut v = V(false);
v.visit_ty(ty);
v.0
}
fn call_is_qualified(expr: &Expr<'_>) -> bool {
if let ExprKind::Path(path) = &expr.kind {
match path {
QPath::Resolved(_, path) => path.segments.last().map_or(false, |segment| segment.args.is_some()),
QPath::TypeRelative(_, segment) => segment.args.is_some(),
QPath::LangItem(..) => false,
}
} else {
false
}
}
// Checks whether:
// * child is an expression of the form `&e` in an argument position requiring an `impl Trait`
// * `e`'s type implements `Trait` and is copyable
// If the conditions are met, returns `Some(Position::ImplArg(..))`; otherwise, returns `None`.
// The "is copyable" condition is to avoid the case where removing the `&` means `e` would have to
// be moved, but it cannot be.
#[expect(clippy::too_many_arguments, clippy::too_many_lines)]
fn needless_borrow_impl_arg_position<'tcx>(
cx: &LateContext<'tcx>,
possible_borrowers: &mut Vec<(LocalDefId, PossibleBorrowerMap<'tcx, 'tcx>)>,
parent: &Expr<'tcx>,
arg_index: usize,
param_ty: ParamTy,
mut expr: &Expr<'tcx>,
precedence: i8,
msrv: Option<RustcVersion>,
) -> Position {
let destruct_trait_def_id = cx.tcx.lang_items().destruct_trait();
let sized_trait_def_id = cx.tcx.lang_items().sized_trait();
let Some(callee_def_id) = fn_def_id(cx, parent) else { return Position::Other(precedence) };
let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
let substs_with_expr_ty = cx
.typeck_results()
.node_substs(if let ExprKind::Call(callee, _) = parent.kind {
callee.hir_id
} else {
parent.hir_id
});
let predicates = cx.tcx.param_env(callee_def_id).caller_bounds();
let projection_predicates = predicates
.iter()
.filter_map(|predicate| {
if let PredicateKind::Clause(Clause::Projection(projection_predicate)) = predicate.kind().skip_binder() {
Some(projection_predicate)
} else {
None
}
})
.collect::<Vec<_>>();
let mut trait_with_ref_mut_self_method = false;
// If no traits were found, or only the `Destruct`, `Sized`, or `Any` traits were found, return.
if predicates
.iter()
.filter_map(|predicate| {
if let PredicateKind::Clause(Clause::Trait(trait_predicate)) = predicate.kind().skip_binder()
&& trait_predicate.trait_ref.self_ty() == param_ty.to_ty(cx.tcx)
{
Some(trait_predicate.trait_ref.def_id)
} else {
None
}
})
.inspect(|trait_def_id| {
trait_with_ref_mut_self_method |= has_ref_mut_self_method(cx, *trait_def_id);
})
.all(|trait_def_id| {
Some(trait_def_id) == destruct_trait_def_id
|| Some(trait_def_id) == sized_trait_def_id
|| cx.tcx.is_diagnostic_item(sym::Any, trait_def_id)
})
{
return Position::Other(precedence);
}
// See:
// - https://github.com/rust-lang/rust-clippy/pull/9674#issuecomment-1289294201
// - https://github.com/rust-lang/rust-clippy/pull/9674#issuecomment-1292225232
if projection_predicates
.iter()
.any(|projection_predicate| is_mixed_projection_predicate(cx, callee_def_id, projection_predicate))
{
return Position::Other(precedence);
}
// `substs_with_referent_ty` can be constructed outside of `check_referent` because the same
// elements are modified each time `check_referent` is called.
let mut substs_with_referent_ty = substs_with_expr_ty.to_vec();
let mut check_reference_and_referent = |reference, referent| {
let referent_ty = cx.typeck_results().expr_ty(referent);
if !is_copy(cx, referent_ty)
&& (referent_ty.has_significant_drop(cx.tcx, cx.param_env)
|| !referent_used_exactly_once(cx, possible_borrowers, reference))
{
return false;
}
// https://github.com/rust-lang/rust-clippy/pull/9136#pullrequestreview-1037379321
if trait_with_ref_mut_self_method && !matches!(referent_ty.kind(), ty::Ref(_, _, Mutability::Mut)) {
return false;
}
if !replace_types(
cx,
param_ty,
referent_ty,
fn_sig,
arg_index,
&projection_predicates,
&mut substs_with_referent_ty,
) {
return false;
}
predicates.iter().all(|predicate| {
if let PredicateKind::Clause(Clause::Trait(trait_predicate)) = predicate.kind().skip_binder()
&& cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_predicate.trait_ref.def_id)
&& let ty::Param(param_ty) = trait_predicate.self_ty().kind()
&& let GenericArgKind::Type(ty) = substs_with_referent_ty[param_ty.index as usize].unpack()
&& ty.is_array()
&& !meets_msrv(msrv, msrvs::ARRAY_INTO_ITERATOR)
{
return false;
}
let predicate = EarlyBinder(predicate).subst(cx.tcx, &substs_with_referent_ty);
let obligation = Obligation::new(cx.tcx, ObligationCause::dummy(), cx.param_env, predicate);
let infcx = cx.tcx.infer_ctxt().build();
infcx.predicate_must_hold_modulo_regions(&obligation)
})
};
let mut needless_borrow = false;
while let ExprKind::AddrOf(_, _, referent) = expr.kind {
if !check_reference_and_referent(expr, referent) {
break;
}
expr = referent;
needless_borrow = true;
}
if needless_borrow {
Position::ImplArg(expr.hir_id)
} else {
Position::Other(precedence)
}
}
fn has_ref_mut_self_method(cx: &LateContext<'_>, trait_def_id: DefId) -> bool {
cx.tcx
.associated_items(trait_def_id)
.in_definition_order()
.any(|assoc_item| {
if assoc_item.fn_has_self_parameter {
let self_ty = cx.tcx.fn_sig(assoc_item.def_id).skip_binder().inputs()[0];
matches!(self_ty.kind(), ty::Ref(_, _, Mutability::Mut))
} else {
false
}
})
}
fn is_mixed_projection_predicate<'tcx>(
cx: &LateContext<'tcx>,
callee_def_id: DefId,
projection_predicate: &ProjectionPredicate<'tcx>,
) -> bool {
let generics = cx.tcx.generics_of(callee_def_id);
// The predicate requires the projected type to equal a type parameter from the parent context.
if let Some(term_ty) = projection_predicate.term.ty()
&& let ty::Param(term_param_ty) = term_ty.kind()
&& (term_param_ty.index as usize) < generics.parent_count
{
// The inner-most self type is a type parameter from the current function.
let mut projection_ty = projection_predicate.projection_ty;
loop {
match projection_ty.self_ty().kind() {
ty::Projection(inner_projection_ty) => {
projection_ty = *inner_projection_ty;
}
ty::Param(param_ty) => {
return (param_ty.index as usize) >= generics.parent_count;
}
_ => {
return false;
}
}
}
} else {
false
}
}
fn referent_used_exactly_once<'tcx>(
cx: &LateContext<'tcx>,
possible_borrowers: &mut Vec<(LocalDefId, PossibleBorrowerMap<'tcx, 'tcx>)>,
reference: &Expr<'tcx>,
) -> bool {
let mir = enclosing_mir(cx.tcx, reference.hir_id);
if let Some(local) = expr_local(cx.tcx, reference)
&& let [location] = *local_assignments(mir, local).as_slice()
&& let Some(statement) = mir.basic_blocks[location.block].statements.get(location.statement_index)
&& let StatementKind::Assign(box (_, Rvalue::Ref(_, _, place))) = statement.kind
&& !place.has_deref()
// Ensure not in a loop (https://github.com/rust-lang/rust-clippy/issues/9710)
&& TriColorDepthFirstSearch::new(&mir.basic_blocks).run_from(location.block, &mut CycleDetector).is_none()
{
let body_owner_local_def_id = cx.tcx.hir().enclosing_body_owner(reference.hir_id);
if possible_borrowers
.last()
.map_or(true, |&(local_def_id, _)| local_def_id != body_owner_local_def_id)
{
possible_borrowers.push((body_owner_local_def_id, PossibleBorrowerMap::new(cx, mir)));
}
let possible_borrower = &mut possible_borrowers.last_mut().unwrap().1;
// If `only_borrowers` were used here, the `copyable_iterator::warn` test would fail. The reason is
// that `PossibleBorrowerVisitor::visit_terminator` considers `place.local` a possible borrower of
// itself. See the comment in that method for an explanation as to why.
possible_borrower.bounded_borrowers(&[local], &[local, place.local], place.local, location)
&& used_exactly_once(mir, place.local).unwrap_or(false)
} else {
false
}
}
// Iteratively replaces `param_ty` with `new_ty` in `substs`, and similarly for each resulting
// projected type that is a type parameter. Returns `false` if replacing the types would have an
// effect on the function signature beyond substituting `new_ty` for `param_ty`.
// See: https://github.com/rust-lang/rust-clippy/pull/9136#discussion_r927212757
fn replace_types<'tcx>(
cx: &LateContext<'tcx>,
param_ty: ParamTy,
new_ty: Ty<'tcx>,
fn_sig: FnSig<'tcx>,
arg_index: usize,
projection_predicates: &[ProjectionPredicate<'tcx>],
substs: &mut [ty::GenericArg<'tcx>],
) -> bool {
let mut replaced = BitSet::new_empty(substs.len());
let mut deque = VecDeque::with_capacity(substs.len());
deque.push_back((param_ty, new_ty));
while let Some((param_ty, new_ty)) = deque.pop_front() {
// If `replaced.is_empty()`, then `param_ty` and `new_ty` are those initially passed in.
if !fn_sig
.inputs_and_output
.iter()
.enumerate()
.all(|(i, ty)| (replaced.is_empty() && i == arg_index) || !ty.contains(param_ty.to_ty(cx.tcx)))
{
return false;
}
substs[param_ty.index as usize] = ty::GenericArg::from(new_ty);
// The `replaced.insert(...)` check provides some protection against infinite loops.
if replaced.insert(param_ty.index) {
for projection_predicate in projection_predicates {
if projection_predicate.projection_ty.self_ty() == param_ty.to_ty(cx.tcx)
&& let Some(term_ty) = projection_predicate.term.ty()
&& let ty::Param(term_param_ty) = term_ty.kind()
{
let item_def_id = projection_predicate.projection_ty.item_def_id;
let assoc_item = cx.tcx.associated_item(item_def_id);
let projection = cx.tcx
.mk_projection(assoc_item.def_id, cx.tcx.mk_substs_trait(new_ty, []));
if let Ok(projected_ty) = cx.tcx.try_normalize_erasing_regions(cx.param_env, projection)
&& substs[term_param_ty.index as usize] != ty::GenericArg::from(projected_ty)
{
deque.push_back((*term_param_ty, projected_ty));
}
}
}
}
}
true
}
struct TyPosition<'tcx> {
position: Position,
ty: Option<Ty<'tcx>>,
}
impl From<Position> for TyPosition<'_> {
fn from(position: Position) -> Self {
Self { position, ty: None }
}
}
impl<'tcx> TyPosition<'tcx> {
fn new_deref_stable_for_result(precedence: i8, ty: Ty<'tcx>) -> Self {
Self {
position: Position::ReborrowStable(precedence),
ty: Some(ty),
}
}
fn position_for_result(self, cx: &LateContext<'tcx>) -> Position {
match (self.position, self.ty) {
(Position::ReborrowStable(precedence), Some(ty)) => {
Position::DerefStable(precedence, ty.is_sized(cx.tcx, cx.param_env))
},
(position, _) => position,
}
}
fn position_for_arg(self) -> Position {
self.position
}
}
// Checks whether a type is stable when switching to auto dereferencing,
fn ty_auto_deref_stability<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, precedence: i8) -> TyPosition<'tcx> {
let ty::Ref(_, mut ty, _) = *ty.kind() else {
return Position::Other(precedence).into();
};
loop {
break match *ty.kind() {
ty::Ref(_, ref_ty, _) => {
ty = ref_ty;
continue;
},
ty::Param(_) => TyPosition::new_deref_stable_for_result(precedence, ty),
ty::Projection(_) if ty.has_non_region_param() => TyPosition::new_deref_stable_for_result(precedence, ty),
ty::Infer(_) | ty::Error(_) | ty::Bound(..) | ty::Opaque(..) | ty::Placeholder(_) | ty::Dynamic(..) => {
Position::ReborrowStable(precedence).into()
},
ty::Adt(..) if ty.has_placeholders() || ty.has_opaque_types() => {
Position::ReborrowStable(precedence).into()
},
ty::Adt(_, substs) if substs.has_non_region_param() => {
TyPosition::new_deref_stable_for_result(precedence, ty)
},
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Array(..)
| ty::Float(_)
| ty::RawPtr(..)
| ty::FnPtr(_) => Position::DerefStable(precedence, true).into(),
ty::Str | ty::Slice(..) => Position::DerefStable(precedence, false).into(),
ty::Adt(..)
| ty::Foreign(_)
| ty::FnDef(..)
| ty::Generator(..)
| ty::GeneratorWitness(..)
| ty::Closure(..)
| ty::Never
| ty::Tuple(_)
| ty::Projection(_) => {
Position::DerefStable(precedence, ty.is_sized(cx.tcx, cx.param_env.without_caller_bounds())).into()
},
};
}
}
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) {
match state {
State::DerefMethod {
ty_changed_count,
is_final_ufcs,
target_mut,
} => {
let mut app = Applicability::MachineApplicable;
let (expr_str, expr_is_macro_call) = snippet_with_context(cx, expr.span, data.span.ctxt(), "..", &mut app);
let ty = cx.typeck_results().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 target_mut == Mutability::Not && matches!(ty.kind(), ty::Ref(_, _, Mutability::Mut)) {
"&*"
} else {
""
}
} else if target_mut == Mutability::Mut {
"&mut "
} else {
"&"
};
let expr_str = if !expr_is_macro_call && is_final_ufcs && expr.precedence().order() < PREC_PREFIX {
format!("({expr_str})")
} else {
expr_str.into_owned()
};
span_lint_and_sugg(
cx,
EXPLICIT_DEREF_METHODS,
data.span,
match target_mut {
Mutability::Not => "explicit `deref` method call",
Mutability::Mut => "explicit `deref_mut` method call",
},
"try this",
format!("{addr_of_str}{deref_str}{expr_str}"),
app,
);
},
State::DerefedBorrow(state) => {
let mut app = Applicability::MachineApplicable;
let snip_expr = state.snip_expr.map_or(expr, |hir_id| cx.tcx.hir().expect_expr(hir_id));
let (snip, snip_is_macro) = snippet_with_context(cx, snip_expr.span, data.span.ctxt(), "..", &mut app);
span_lint_hir_and_then(cx, NEEDLESS_BORROW, data.hir_id, data.span, state.msg, |diag| {
let calls_field = matches!(expr.kind, ExprKind::Field(..)) && matches!(data.position, Position::Callee);
let sugg = if !snip_is_macro
&& !has_enclosing_paren(&snip)
&& (expr.precedence().order() < data.position.precedence() || calls_field)
{
format!("({snip})")
} else {
snip.into()
};
diag.span_suggestion(data.span, "change this to", sugg, app);
});
},
State::ExplicitDeref { mutability } => {
if matches!(
expr.kind,
ExprKind::Block(..)
| ExprKind::ConstBlock(_)
| ExprKind::If(..)
| ExprKind::Loop(..)
| ExprKind::Match(..)
) && matches!(data.position, Position::DerefStable(_, true))
{
// Rustc bug: auto deref doesn't work on block expression when targeting sized types.
return;
}
let (prefix, precedence) = if let Some(mutability) = mutability
&& !cx.typeck_results().expr_ty(expr).is_ref()
{
let prefix = match mutability {
Mutability::Not => "&",
Mutability::Mut => "&mut ",
};
(prefix, 0)
} else {
("", data.position.precedence())
};
span_lint_hir_and_then(
cx,
EXPLICIT_AUTO_DEREF,
data.hir_id,
data.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.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.span, "try this", sugg, app);
},
);
},
State::ExplicitDerefField { .. } => {
if matches!(
expr.kind,
ExprKind::Block(..)
| ExprKind::ConstBlock(_)
| ExprKind::If(..)
| ExprKind::Loop(..)
| ExprKind::Match(..)
) && matches!(data.position, Position::DerefStable(_, true))
{
// Rustc bug: auto deref doesn't work on block expression when targeting sized types.
return;
}
span_lint_hir_and_then(
cx,
EXPLICIT_AUTO_DEREF,
data.hir_id,
data.span,
"deref which would be done by auto-deref",
|diag| {
let mut app = Applicability::MachineApplicable;
let snip = snippet_with_context(cx, expr.span, data.span.ctxt(), "..", &mut app).0;
diag.span_suggestion(data.span, "try this", snip.into_owned(), 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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