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needless_borrow: do not contradict dangerous_implicit_autorefs (#14810)
Rust 1.88 introduces the `dangerous_implicit_autorefs` lint which warns about using implicit autorefs on a place obtained from a raw pointer, as this may create aliasing issues. Prevent `clippy::needless_borrow` from triggering in this case, by disabling the lint when taking a reference on a raw pointer dereference. There might be a better way for doing this in the long run with a finer way of distinguish the problematic cases, but this will prevent Clippy from contradicting the compiler in the meantime. Fixes #14743 changelog: [`needless_borrow`]: do not contradict the compiler's `dangerous_implicit_autorefs` lint even though the refererences are not mandatory @rustbot label +beta-nominated <!-- TRIAGEBOT_START --> <!-- TRIAGEBOT_SUMMARY_START --> ### Summary Notes - [Beta nomination for 1.88](#14810 (comment)) by [samueltardieu](https://github.com/samueltardieu) Generated by triagebot, see [help](https://forge.rust-lang.org/triagebot/note.html) for how to add more <!-- TRIAGEBOT_SUMMARY_DATA_START$${"entries_by_url":{"https://github.com/rust-lang/rust-clippy/pull/14810#issuecomment-2883753957":{"title":"Beta nomination for 1.88","comment_url":"https://github.com/rust-lang/rust-clippy/pull/14810#issuecomment-2883753957","author":"samueltardieu"}}}$$TRIAGEBOT_SUMMARY_DATA_END --> <!-- TRIAGEBOT_SUMMARY_END --> <!-- TRIAGEBOT_END -->
2 parents 5dccb10 + 0a059d9 commit 7ab910f

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‎clippy_lints/src/dereference.rs

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Original file line numberDiff line numberDiff line change
@@ -986,6 +986,15 @@ fn report<'tcx>(
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);
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},
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State::DerefedBorrow(state) => {
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// Do not suggest removing a non-mandatory `&` in `&*rawptr` in an `unsafe` context,
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// as this may make rustc trigger its `dangerous_implicit_autorefs` lint.
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if let ExprKind::AddrOf(BorrowKind::Ref, _, subexpr) = data.first_expr.kind
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&& let ExprKind::Unary(UnOp::Deref, subsubexpr) = subexpr.kind
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&& cx.typeck_results().expr_ty_adjusted(subsubexpr).is_raw_ptr()
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{
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return;
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}
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let mut app = Applicability::MachineApplicable;
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let (snip, snip_is_macro) =
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snippet_with_context(cx, expr.span, data.first_expr.span.ctxt(), "..", &mut app);

‎tests/ui/needless_borrow.fixed

Lines changed: 12 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -107,9 +107,6 @@ fn main() {
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let x = (1, 2);
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let _ = x.0;
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//~^ needless_borrow
110-
let x = &x as *const (i32, i32);
111-
let _ = unsafe { (*x).0 };
112-
//~^ needless_borrow
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114111
// Issue #8367
115112
trait Foo {
@@ -289,3 +286,15 @@ fn issue_12268() {
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290287
// compiler
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}
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fn issue_14743<T>(slice: &[T]) {
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let _ = slice.len();
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//~^ needless_borrow
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let slice = slice as *const [T];
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let _ = unsafe { (&*slice).len() };
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// Check that rustc would actually warn if Clippy had suggested removing the reference
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#[expect(dangerous_implicit_autorefs)]
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let _ = unsafe { (*slice).len() };
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}

‎tests/ui/needless_borrow.rs

Lines changed: 12 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -107,9 +107,6 @@ fn main() {
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let x = (1, 2);
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let _ = (&x).0;
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//~^ needless_borrow
110-
let x = &x as *const (i32, i32);
111-
let _ = unsafe { (&*x).0 };
112-
//~^ needless_borrow
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114111
// Issue #8367
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trait Foo {
@@ -289,3 +286,15 @@ fn issue_12268() {
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// compiler
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}
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fn issue_14743<T>(slice: &[T]) {
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let _ = (&slice).len();
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//~^ needless_borrow
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let slice = slice as *const [T];
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let _ = unsafe { (&*slice).len() };
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// Check that rustc would actually warn if Clippy had suggested removing the reference
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#[expect(dangerous_implicit_autorefs)]
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let _ = unsafe { (*slice).len() };
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}

‎tests/ui/needless_borrow.stderr

Lines changed: 16 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -103,71 +103,71 @@ error: this expression borrows a value the compiler would automatically borrow
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LL | let _ = (&x).0;
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| ^^^^ help: change this to: `x`
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106-
error: this expression borrows a value the compiler would automatically borrow
107-
--> tests/ui/needless_borrow.rs:111:22
108-
|
109-
LL | let _ = unsafe { (&*x).0 };
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| ^^^^^ help: change this to: `(*x)`
111-
112106
error: this expression creates a reference which is immediately dereferenced by the compiler
113-
--> tests/ui/needless_borrow.rs:122:5
107+
--> tests/ui/needless_borrow.rs:119:5
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|
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LL | (&&()).foo();
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| ^^^^^^ help: change this to: `(&())`
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118112
error: this expression creates a reference which is immediately dereferenced by the compiler
119-
--> tests/ui/needless_borrow.rs:132:5
113+
--> tests/ui/needless_borrow.rs:129:5
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|
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LL | (&&5).foo();
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| ^^^^^ help: change this to: `(&5)`
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124118
error: this expression creates a reference which is immediately dereferenced by the compiler
125-
--> tests/ui/needless_borrow.rs:159:23
119+
--> tests/ui/needless_borrow.rs:156:23
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|
127121
LL | let x: (&str,) = (&"",);
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| ^^^ help: change this to: `""`
129123

130124
error: this expression borrows a value the compiler would automatically borrow
131-
--> tests/ui/needless_borrow.rs:202:13
125+
--> tests/ui/needless_borrow.rs:199:13
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|
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LL | (&self.f)()
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| ^^^^^^^^^ help: change this to: `(self.f)`
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136130
error: this expression borrows a value the compiler would automatically borrow
137-
--> tests/ui/needless_borrow.rs:212:13
131+
--> tests/ui/needless_borrow.rs:209:13
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|
139133
LL | (&mut self.f)()
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| ^^^^^^^^^^^^^ help: change this to: `(self.f)`
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142136
error: this expression borrows a value the compiler would automatically borrow
143-
--> tests/ui/needless_borrow.rs:250:22
137+
--> tests/ui/needless_borrow.rs:247:22
144138
|
145139
LL | let _ = &mut (&mut { x.u }).x;
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| ^^^^^^^^^^^^^^ help: change this to: `{ x.u }`
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148142
error: this expression borrows a value the compiler would automatically borrow
149-
--> tests/ui/needless_borrow.rs:258:22
143+
--> tests/ui/needless_borrow.rs:255:22
150144
|
151145
LL | let _ = &mut (&mut { x.u }).x;
152146
| ^^^^^^^^^^^^^^ help: change this to: `{ x.u }`
153147

154148
error: this expression borrows a value the compiler would automatically borrow
155-
--> tests/ui/needless_borrow.rs:263:22
149+
--> tests/ui/needless_borrow.rs:260:22
156150
|
157151
LL | let _ = &mut (&mut x.u).x;
158152
| ^^^^^^^^^^ help: change this to: `x.u`
159153

160154
error: this expression borrows a value the compiler would automatically borrow
161-
--> tests/ui/needless_borrow.rs:265:22
155+
--> tests/ui/needless_borrow.rs:262:22
162156
|
163157
LL | let _ = &mut (&mut { x.u }).x;
164158
| ^^^^^^^^^^^^^^ help: change this to: `{ x.u }`
165159

166160
error: this expression creates a reference which is immediately dereferenced by the compiler
167-
--> tests/ui/needless_borrow.rs:287:23
161+
--> tests/ui/needless_borrow.rs:284:23
168162
|
169163
LL | option.unwrap_or((&x.0,));
170164
| ^^^^ help: change this to: `x.0`
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166+
error: this expression creates a reference which is immediately dereferenced by the compiler
167+
--> tests/ui/needless_borrow.rs:291:13
168+
|
169+
LL | let _ = (&slice).len();
170+
| ^^^^^^^^ help: change this to: `slice`
171+
172172
error: aborting due to 28 previous errors
173173

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