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Reenable linting on UFCS deref calls #14808

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May 16, 2025
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Reenable linting on UFCS deref calls #14808

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67 changes: 28 additions & 39 deletions clippy_lints/src/dereference.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt, TypeckResults};
use rustc_session::impl_lint_pass;
use rustc_span::symbol::sym;
use rustc_span::{Span, Symbol};
use std::borrow::Cow;

declare_clippy_lint! {
/// ### What it does
Expand Down Expand Up @@ -252,13 +253,14 @@ impl<'tcx> LateLintPass<'tcx> for Dereferencing<'tcx> {
}

let typeck = cx.typeck_results();
let Some((kind, sub_expr)) = try_parse_ref_op(cx.tcx, typeck, expr) else {
let Some((kind, sub_expr, skip_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;
};
self.skip_expr = skip_expr;

match (self.state.take(), kind) {
(None, kind) => {
Expand Down Expand Up @@ -671,42 +673,38 @@ 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),
) -> Option<(RefOp, &'tcx Expr<'tcx>, Option<HirId>)> {
let (call_path_id, def_id, arg) = match expr.kind {
ExprKind::MethodCall(_, arg, [], _) => (None, typeck.type_dependent_def_id(expr.hir_id)?, arg),
ExprKind::Call(
Expr {
kind: ExprKind::Path(path),
&Expr {
kind: ExprKind::Path(QPath::Resolved(None, path)),
hir_id,
..
},
[arg],
) => (true, typeck.qpath_res(path, *hir_id).opt_def_id()?, arg),
) => (Some(hir_id), path.res.opt_def_id()?, arg),
ExprKind::Unary(UnOp::Deref, sub_expr) if !typeck.expr_ty(sub_expr).is_raw_ptr() => {
return Some((RefOp::Deref, sub_expr));
return Some((RefOp::Deref, sub_expr, None));
},
ExprKind::AddrOf(BorrowKind::Ref, mutability, sub_expr) => {
return Some((RefOp::AddrOf(mutability), sub_expr, None));
},
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
}
let mutbl = match tcx.get_diagnostic_name(def_id) {
Some(sym::deref_method) => Mutability::Not,
Some(sym::deref_mut_method) => Mutability::Mut,
_ => return None,
};
Some((
RefOp::Method {
mutbl,
is_ufcs: call_path_id.is_some(),
},
arg,
call_path_id,
))
}

// Checks if the adjustments contains a deref of `ManuallyDrop<_>`
Expand Down Expand Up @@ -944,7 +942,7 @@ fn report<'tcx>(
mutbl,
} => {
let mut app = Applicability::MachineApplicable;
let (expr_str, _expr_is_macro_call) =
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_middle_ty_refs(ty);
Expand All @@ -968,20 +966,11 @@ fn report<'tcx>(
"&"
};

// 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() < ExprPrecedence::Prefix {
let expr_str = if !expr_is_macro_call && is_ufcs && expr.precedence() < ExprPrecedence::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,
Expand Down
11 changes: 7 additions & 4 deletions tests/ui/explicit_deref_methods.fixed
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,8 @@
clippy::needless_borrow,
clippy::no_effect,
clippy::uninlined_format_args,
clippy::unnecessary_literal_unwrap
clippy::unnecessary_literal_unwrap,
clippy::deref_addrof
)]

use std::ops::{Deref, DerefMut};
Expand Down Expand Up @@ -87,9 +88,6 @@ fn main() {
let b = &*opt_a.unwrap();
//~^ explicit_deref_methods

// make sure `Aaa::deref` instead of `aaa.deref()` is not linted, as well as fully qualified
// syntax

Aaa::deref(&Aaa);
Aaa::deref_mut(&mut Aaa);
<Aaa as Deref>::deref(&Aaa);
Expand Down Expand Up @@ -139,4 +137,9 @@ fn main() {
let no_lint = NoLint(42);
let b = no_lint.deref();
let b = no_lint.deref_mut();

let _ = &*&"foo"; //~ explicit_deref_methods
let mut x = String::new();
let _ = &&mut **&mut x; //~ explicit_deref_methods
let _ = &&mut ***(&mut &mut x); //~ explicit_deref_methods
}
11 changes: 7 additions & 4 deletions tests/ui/explicit_deref_methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,8 @@
clippy::needless_borrow,
clippy::no_effect,
clippy::uninlined_format_args,
clippy::unnecessary_literal_unwrap
clippy::unnecessary_literal_unwrap,
clippy::deref_addrof
)]

use std::ops::{Deref, DerefMut};
Expand Down Expand Up @@ -87,9 +88,6 @@ fn main() {
let b = opt_a.unwrap().deref();
//~^ explicit_deref_methods

// make sure `Aaa::deref` instead of `aaa.deref()` is not linted, as well as fully qualified
// syntax

Aaa::deref(&Aaa);
Aaa::deref_mut(&mut Aaa);
<Aaa as Deref>::deref(&Aaa);
Expand Down Expand Up @@ -139,4 +137,9 @@ fn main() {
let no_lint = NoLint(42);
let b = no_lint.deref();
let b = no_lint.deref_mut();

let _ = &Deref::deref(&"foo"); //~ explicit_deref_methods
let mut x = String::new();
let _ = &DerefMut::deref_mut(&mut x); //~ explicit_deref_methods
let _ = &DerefMut::deref_mut((&mut &mut x).deref_mut()); //~ explicit_deref_methods
}
44 changes: 31 additions & 13 deletions tests/ui/explicit_deref_methods.stderr
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:54:19
--> tests/ui/explicit_deref_methods.rs:55:19
|
LL | let b: &str = a.deref();
| ^^^^^^^^^ help: try: `&*a`
Expand All @@ -8,70 +8,88 @@ LL | let b: &str = a.deref();
= help: to override `-D warnings` add `#[allow(clippy::explicit_deref_methods)]`

error: explicit `deref_mut` method call
--> tests/ui/explicit_deref_methods.rs:57:23
--> tests/ui/explicit_deref_methods.rs:58:23
|
LL | let b: &mut str = a.deref_mut();
| ^^^^^^^^^^^^^ help: try: `&mut **a`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:61:39
--> tests/ui/explicit_deref_methods.rs:62:39
|
LL | let b: String = format!("{}, {}", a.deref(), a.deref());
| ^^^^^^^^^ help: try: `&*a`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:61:50
--> tests/ui/explicit_deref_methods.rs:62:50
|
LL | let b: String = format!("{}, {}", a.deref(), a.deref());
| ^^^^^^^^^ help: try: `&*a`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:65:20
--> tests/ui/explicit_deref_methods.rs:66:20
|
LL | println!("{}", a.deref());
| ^^^^^^^^^ help: try: `&*a`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:69:11
--> tests/ui/explicit_deref_methods.rs:70:11
|
LL | match a.deref() {
| ^^^^^^^^^ help: try: `&*a`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:74:28
--> tests/ui/explicit_deref_methods.rs:75:28
|
LL | let b: String = concat(a.deref());
| ^^^^^^^^^ help: try: `&*a`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:77:13
--> tests/ui/explicit_deref_methods.rs:78:13
|
LL | let b = just_return(a).deref();
| ^^^^^^^^^^^^^^^^^^^^^^ help: try: `just_return(a)`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:80:28
--> tests/ui/explicit_deref_methods.rs:81:28
|
LL | let b: String = concat(just_return(a).deref());
| ^^^^^^^^^^^^^^^^^^^^^^ help: try: `just_return(a)`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:83:19
--> tests/ui/explicit_deref_methods.rs:84:19
|
LL | let b: &str = a.deref().deref();
| ^^^^^^^^^^^^^^^^^ help: try: `&**a`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:87:13
--> tests/ui/explicit_deref_methods.rs:88:13
|
LL | let b = opt_a.unwrap().deref();
| ^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*opt_a.unwrap()`

error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:125:31
--> tests/ui/explicit_deref_methods.rs:123:31
|
LL | let b: &str = expr_deref!(a.deref());
| ^^^^^^^^^ help: try: `&*a`

error: aborting due to 12 previous errors
error: explicit `deref` method call
--> tests/ui/explicit_deref_methods.rs:141:14
|
LL | let _ = &Deref::deref(&"foo");
| ^^^^^^^^^^^^^^^^^^^^ help: try: `*&"foo"`

error: explicit `deref_mut` method call
--> tests/ui/explicit_deref_methods.rs:143:14
|
LL | let _ = &DerefMut::deref_mut(&mut x);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&mut **&mut x`

error: explicit `deref_mut` method call
--> tests/ui/explicit_deref_methods.rs:144:14
|
LL | let _ = &DerefMut::deref_mut((&mut &mut x).deref_mut());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&mut ***(&mut &mut x)`

error: aborting due to 15 previous errors