use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
+use clippy_utils::sugg::has_enclosing_paren;
use clippy_utils::ty::peel_mid_ty_refs;
use clippy_utils::{get_parent_expr, get_parent_node, is_lint_allowed, path_to_local};
use rustc_ast::util::parser::{PREC_POSTFIX, PREC_PREFIX};
Pat, PatKind, UnOp,
};
use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
-use rustc_middle::ty::{self, Ty, TyCtxt, TyS, TypeckResults};
+use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeckResults};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{symbol::sym, Span};
-use std::iter;
declare_clippy_lint! {
/// ### What it does
struct StateData {
/// Span of the top level expression
span: Span,
- /// The required mutability
- target_mut: Mutability,
}
enum State {
// 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 {
- count: u32,
+ count: usize,
+ required_precedence: i8,
+ msg: &'static str,
},
}
}
impl<'tcx> LateLintPass<'tcx> for Dereferencing {
- #[allow(clippy::too_many_lines)]
+ #[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() {
1
},
is_final_ufcs: matches!(expr.kind, ExprKind::Call(..)),
- },
- StateData {
- span: expr.span,
target_mut,
},
+ StateData { span: expr.span },
));
},
RefOp::AddrOf => {
// Find the number of times the borrow is auto-derefed.
let mut iter = find_adjustments(cx.tcx, typeck, expr).iter();
- if let Some((i, adjust)) = iter.by_ref().enumerate().find_map(|(i, adjust)| {
- if !matches!(adjust.kind, Adjust::Deref(_)) {
- Some((i, adjust))
- } else if !adjust.target.is_ref() {
- // Add one to the number of references found.
- Some((i + 1, adjust))
+ 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 (required_refs, required_precedence, msg) = if is_auto_borrow_position(parent, expr.hir_id)
+ {
+ (1, PREC_POSTFIX, if deref_count == 1 { borrow_msg } else { deref_msg })
+ } else if let Some(&Adjust::Borrow(AutoBorrow::Ref(_, mutability))) =
+ next_adjust.map(|a| &a.kind)
+ {
+ if matches!(mutability, AutoBorrowMutability::Mut { .. })
+ && !is_auto_reborrow_position(parent)
+ {
+ (3, 0, deref_msg)
} else {
- None
- }
- }) {
- // Found two consecutive derefs. At least one can be removed.
- if i > 1 {
- let target_mut = iter::once(adjust)
- .chain(iter)
- .find_map(|adjust| match adjust.kind {
- Adjust::Borrow(AutoBorrow::Ref(_, m)) => Some(m.into()),
- _ => None,
- })
- // This default should never happen. Auto-deref always reborrows.
- .unwrap_or(Mutability::Not);
- self.state = Some((
- // Subtract one for the current borrow expression, and one to cover the last
- // reference which can't be removed (it's either reborrowed, or needed for
- // auto-deref to happen).
- State::DerefedBorrow {
- count:
- // Truncation here would require more than a `u32::MAX` level reference. The compiler
- // does not support this.
- #[allow(clippy::cast_possible_truncation)]
- { i as u32 - 2 }
- },
- StateData {
- span: expr.span,
- target_mut,
- },
- ));
+ (2, 0, deref_msg)
}
+ } else {
+ (2, 0, deref_msg)
+ };
+
+ if deref_count >= required_refs {
+ self.state = Some((
+ State::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,
+ required_precedence,
+ msg,
+ },
+ StateData { span: expr.span },
+ ));
}
},
_ => (),
}
},
- (Some((State::DerefMethod { ty_changed_count, .. }, data)), 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 + 1
},
is_final_ufcs: matches!(expr.kind, ExprKind::Call(..)),
+ target_mut,
},
data,
));
},
- (Some((State::DerefedBorrow { count }, data)), RefOp::AddrOf) if count != 0 => {
- self.state = Some((State::DerefedBorrow { count: count - 1 }, data));
+ (
+ Some((
+ State::DerefedBorrow {
+ count,
+ required_precedence,
+ msg,
+ },
+ data,
+ )),
+ RefOp::AddrOf,
+ ) if count != 0 => {
+ self.state = Some((
+ State::DerefedBorrow {
+ count: count - 1,
+ required_precedence,
+ msg,
+ },
+ data,
+ ));
},
(Some((state, data)), _) => report(cx, expr, state, data),
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::MethodCall(_, [arg], _) => (typeck.type_dependent_def_id(expr.hir_id)?, arg),
ExprKind::Call(
Expr {
kind: ExprKind::Path(path),
// the reference.
fn deref_method_same_type(result_ty: Ty<'_>, arg_ty: Ty<'_>) -> bool {
match (result_ty.kind(), arg_ty.kind()) {
- (ty::Ref(_, result_ty, _), ty::Ref(_, arg_ty, _)) => TyS::same_type(result_ty, arg_ty),
+ (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
match parent.kind {
// Leave deref calls in the middle of a method chain.
// e.g. x.deref().foo()
- ExprKind::MethodCall(_, _, [self_arg, ..], _) if self_arg.hir_id == child_id => false,
+ ExprKind::MethodCall(_, [self_arg, ..], _) if self_arg.hir_id == child_id => false,
// Leave deref calls resulting in a called function
// e.g. (x.deref())()
| ExprKind::Continue(..)
| ExprKind::Ret(..)
| ExprKind::InlineAsm(..)
- | ExprKind::LlvmInlineAsm(..)
| ExprKind::Struct(..)
| ExprKind::Repeat(..)
| ExprKind::Yield(..) => true,
}
}
+/// Checks if the given expression is in a position which can be auto-reborrowed.
+/// Note: This is only correct assuming auto-deref is already occurring.
+fn is_auto_reborrow_position(parent: Option<Node<'_>>) -> bool {
+ match parent {
+ Some(Node::Expr(parent)) => matches!(parent.kind, ExprKind::MethodCall(..) | ExprKind::Call(..)),
+ Some(Node::Local(_)) => true,
+ _ => false,
+ }
+}
+
+/// Checks if the given expression is a position which can auto-borrow.
+fn is_auto_borrow_position(parent: Option<Node<'_>>, child_id: HirId) -> bool {
+ if let Some(Node::Expr(parent)) = parent {
+ match parent.kind {
+ // ExprKind::MethodCall(_, [self_arg, ..], _) => self_arg.hir_id == child_id,
+ ExprKind::Field(..) => true,
+ ExprKind::Call(f, _) => f.hir_id == child_id,
+ _ => false,
+ }
+ } else {
+ false
+ }
+}
+
/// Adjustments are sometimes made in the parent block rather than the expression itself.
fn find_adjustments<'tcx>(
tcx: TyCtxt<'tcx>,
}
}
-#[allow(clippy::needless_pass_by_value)]
+#[expect(clippy::needless_pass_by_value)]
fn report(cx: &LateContext<'_>, expr: &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 addr_of_str = if ty_changed_count < ref_count {
// Check if a reborrow from &mut T -> &T is required.
- if data.target_mut == Mutability::Not && matches!(ty.kind(), ty::Ref(_, _, Mutability::Mut)) {
+ if target_mut == Mutability::Not && matches!(ty.kind(), ty::Ref(_, _, Mutability::Mut)) {
"&*"
} else {
""
}
- } else if data.target_mut == Mutability::Mut {
+ } else if target_mut == Mutability::Mut {
"&mut "
} else {
"&"
cx,
EXPLICIT_DEREF_METHODS,
data.span,
- match data.target_mut {
+ match target_mut {
Mutability::Not => "explicit `deref` method call",
Mutability::Mut => "explicit `deref_mut` method call",
},
app,
);
},
- State::DerefedBorrow { .. } => {
+ State::DerefedBorrow {
+ required_precedence,
+ msg,
+ ..
+ } => {
let mut app = Applicability::MachineApplicable;
let snip = snippet_with_context(cx, expr.span, data.span.ctxt(), "..", &mut app).0;
span_lint_and_sugg(
cx,
NEEDLESS_BORROW,
data.span,
- &format!(
- "this expression borrows a reference (`{}`) that is immediately dereferenced by the compiler",
- cx.typeck_results().expr_ty(expr),
- ),
+ msg,
"change this to",
- snip.into(),
+ if required_precedence > expr.precedence().order() && !has_enclosing_paren(&snip) {
+ format!("({})", snip)
+ } else {
+ snip.into()
+ },
app,
);
},
projects / rust.git / blobdiff