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feat(transmute_ptr_to_ref): Handle a pointer wrapped in a struct #15948

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5d02b59
feat(transmute_ptr_to_ref): Handle a pointer wrapped in a struct
Oct 24, 2025
e5b5f8d
feat(transmute_ptr_to_ptr): Handle a pointer wrapped in a struct
Oct 24, 2025
a9b4078
Avoid private fields
Oct 27, 2025
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33 changes: 31 additions & 2 deletions clippy_lints/src/transmute/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,10 @@ mod wrong_transmute;
use clippy_config::Conf;
use clippy_utils::is_in_const_context;
use clippy_utils::msrvs::Msrv;
use clippy_utils::sugg::Sugg;
use rustc_hir::{Expr, ExprKind, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, Ty};
use rustc_session::impl_lint_pass;
use rustc_span::symbol::sym;

Expand Down Expand Up @@ -465,6 +467,30 @@ declare_clippy_lint! {
"warns if a transmute call doesn't have all generics specified"
}

/// When transmuting, a struct containing a single field works like the field.
/// This function extracts the field type and the expression to get the field.
fn extract_struct_field<'tcx>(
cx: &LateContext<'tcx>,
outer_type: Ty<'tcx>,
outer: &'tcx Expr<'tcx>,
) -> (Ty<'tcx>, Option<Sugg<'tcx>>) {
let outer_sugg = Sugg::hir_opt(cx, outer);
if let ty::Adt(struct_def, struct_args) = *outer_type.kind()
&& struct_def.is_struct()
&& let mut fields = struct_def.all_fields()
&& let Some(first) = fields.next()
&& fields.next().is_none()
&& first.vis.is_accessible_from(cx.tcx.parent_module(outer.hir_id), cx.tcx)
{
(
first.ty(cx.tcx, struct_args),
outer_sugg.map(|outer| Sugg::NonParen(format!("{}.{}", outer.maybe_paren(), first.name).into())),
)
} else {
(outer_type, outer_sugg)
}
}

pub struct Transmute {
msrv: Msrv,
}
Expand Down Expand Up @@ -515,14 +541,17 @@ impl<'tcx> LateLintPass<'tcx> for Transmute {
return;
}

// A struct having a single pointer can be treated like a pointer.
let (from_field_ty, from_field_expr) = extract_struct_field(cx, from_ty, arg);

let linted = wrong_transmute::check(cx, e, from_ty, to_ty)
| crosspointer_transmute::check(cx, e, from_ty, to_ty)
| transmuting_null::check(cx, e, arg, to_ty)
| transmute_null_to_fn::check(cx, e, arg, to_ty)
| transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, arg, path, self.msrv)
| transmute_ptr_to_ref::check(cx, e, from_field_ty, to_ty, from_field_expr.clone(), path, self.msrv)
| missing_transmute_annotations::check(cx, path, arg, from_ty, to_ty, e.hir_id)
| transmute_ref_to_ref::check(cx, e, from_ty, to_ty, arg, const_context)
| transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, arg, self.msrv)
| transmute_ptr_to_ptr::check(cx, e, from_field_ty, to_ty, from_field_expr, self.msrv)
| transmute_int_to_bool::check(cx, e, from_ty, to_ty, arg)
| transmute_int_to_non_zero::check(cx, e, from_ty, to_ty, arg)
| (unsound_collection_transmute::check(cx, e, from_ty, to_ty)
Expand Down
4 changes: 2 additions & 2 deletions clippy_lints/src/transmute/transmute_ptr_to_ptr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ pub(super) fn check<'tcx>(
e: &'tcx Expr<'_>,
from_ty: Ty<'tcx>,
to_ty: Ty<'tcx>,
arg: &'tcx Expr<'_>,
arg: Option<sugg::Sugg<'_>>,
msrv: Msrv,
) -> bool {
match (from_ty.kind(), to_ty.kind()) {
Expand All @@ -25,7 +25,7 @@ pub(super) fn check<'tcx>(
e.span,
"transmute from a pointer to a pointer",
|diag| {
if let Some(arg) = sugg::Sugg::hir_opt(cx, arg) {
if let Some(arg) = arg {
if from_mutbl == to_mutbl
&& to_pointee_ty.is_sized(cx.tcx, cx.typing_env())
&& msrv.meets(cx, msrvs::POINTER_CAST)
Expand Down
4 changes: 2 additions & 2 deletions clippy_lints/src/transmute/transmute_ptr_to_ref.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ pub(super) fn check<'tcx>(
e: &'tcx Expr<'_>,
from_ty: Ty<'tcx>,
to_ty: Ty<'tcx>,
arg: &'tcx Expr<'_>,
arg: Option<sugg::Sugg<'_>>,
path: &'tcx Path<'_>,
msrv: Msrv,
) -> bool {
Expand All @@ -27,7 +27,7 @@ pub(super) fn check<'tcx>(
e.span,
format!("transmute from a pointer type (`{from_ty}`) to a reference type (`{to_ty}`)"),
|diag| {
let arg = sugg::Sugg::hir(cx, arg, "..");
let arg = arg.unwrap_or(sugg::Sugg::NonParen("..".into()));
let (deref, cast) = match mutbl {
Mutability::Mut => ("&mut *", "*mut"),
Mutability::Not => ("&*", "*const"),
Expand Down
16 changes: 16 additions & 0 deletions tests/ui/transmute_ptr_to_ptr.fixed
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Original file line number Diff line number Diff line change
Expand Up @@ -24,13 +24,23 @@ struct GenericParam<T> {
t: T,
}

#[derive(Clone, Copy)]
struct PtrNamed {
ptr: *const u32,
}
#[derive(Clone, Copy)]
struct Ptr(*const u32);
fn transmute_ptr_to_ptr() {
let ptr = &1u32 as *const u32;
let mut_ptr = &mut 1u32 as *mut u32;
unsafe {
// pointer-to-pointer transmutes; bad
let _: *const f32 = Ptr(ptr).0.cast::<f32>();
//~^ transmute_ptr_to_ptr
let _: *const f32 = ptr.cast::<f32>();
//~^ transmute_ptr_to_ptr
let _: *const f32 = PtrNamed { ptr }.ptr.cast::<f32>();
//~^ transmute_ptr_to_ptr

let _: *mut f32 = mut_ptr.cast::<f32>();
//~^ transmute_ptr_to_ptr
Expand Down Expand Up @@ -59,6 +69,8 @@ fn transmute_ptr_to_ptr() {

let _: *mut u32 = ptr.cast_mut();
//~^ transmute_ptr_to_ptr
let _: *mut u32 = Ptr(ptr).0.cast_mut();
//~^ transmute_ptr_to_ptr
}

// transmute internal lifetimes, should not lint
Expand All @@ -81,9 +93,13 @@ const _: &() = {
unsafe { transmute::<&'static Zst, &'static ()>(zst) }
};

#[derive(Clone, Copy)]
struct Ptr8(*const u8);
#[clippy::msrv = "1.37"]
fn msrv_1_37(ptr: *const u8) {
unsafe {
let _: *const i8 = Ptr8(ptr).0 as *const i8;
//~^ transmute_ptr_to_ptr
let _: *const i8 = ptr as *const i8;
//~^ transmute_ptr_to_ptr
}
Expand Down
16 changes: 16 additions & 0 deletions tests/ui/transmute_ptr_to_ptr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,13 +24,23 @@ struct GenericParam<T> {
t: T,
}

#[derive(Clone, Copy)]
struct PtrNamed {
ptr: *const u32,
}
#[derive(Clone, Copy)]
struct Ptr(*const u32);
fn transmute_ptr_to_ptr() {
let ptr = &1u32 as *const u32;
let mut_ptr = &mut 1u32 as *mut u32;
unsafe {
// pointer-to-pointer transmutes; bad
let _: *const f32 = transmute(Ptr(ptr));
//~^ transmute_ptr_to_ptr
let _: *const f32 = transmute(ptr);
//~^ transmute_ptr_to_ptr
let _: *const f32 = transmute(PtrNamed { ptr });
//~^ transmute_ptr_to_ptr

let _: *mut f32 = transmute(mut_ptr);
//~^ transmute_ptr_to_ptr
Expand Down Expand Up @@ -59,6 +69,8 @@ fn transmute_ptr_to_ptr() {

let _: *mut u32 = transmute(ptr);
//~^ transmute_ptr_to_ptr
let _: *mut u32 = transmute(Ptr(ptr));
//~^ transmute_ptr_to_ptr
}

// transmute internal lifetimes, should not lint
Expand All @@ -81,9 +93,13 @@ const _: &() = {
unsafe { transmute::<&'static Zst, &'static ()>(zst) }
};

#[derive(Clone, Copy)]
struct Ptr8(*const u8);
#[clippy::msrv = "1.37"]
fn msrv_1_37(ptr: *const u8) {
unsafe {
let _: *const i8 = transmute(Ptr8(ptr));
//~^ transmute_ptr_to_ptr
let _: *const i8 = transmute(ptr);
//~^ transmute_ptr_to_ptr
}
Expand Down
86 changes: 67 additions & 19 deletions tests/ui/transmute_ptr_to_ptr.stderr
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Original file line number Diff line number Diff line change
@@ -1,19 +1,43 @@
error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:32:29
--> tests/ui/transmute_ptr_to_ptr.rs:38:29
|
LL | let _: *const f32 = transmute(ptr);
| ^^^^^^^^^^^^^^
LL | let _: *const f32 = transmute(Ptr(ptr));
| ^^^^^^^^^^^^^^^^^^^
|
= note: `-D clippy::transmute-ptr-to-ptr` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::transmute_ptr_to_ptr)]`
help: use `pointer::cast` instead
|
LL - let _: *const f32 = transmute(Ptr(ptr));
LL + let _: *const f32 = Ptr(ptr).0.cast::<f32>();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:40:29
|
LL | let _: *const f32 = transmute(ptr);
| ^^^^^^^^^^^^^^
|
help: use `pointer::cast` instead
|
LL - let _: *const f32 = transmute(ptr);
LL + let _: *const f32 = ptr.cast::<f32>();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:35:27
--> tests/ui/transmute_ptr_to_ptr.rs:42:29
|
LL | let _: *const f32 = transmute(PtrNamed { ptr });
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: use `pointer::cast` instead
|
LL - let _: *const f32 = transmute(PtrNamed { ptr });
LL + let _: *const f32 = PtrNamed { ptr }.ptr.cast::<f32>();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:45:27
|
LL | let _: *mut f32 = transmute(mut_ptr);
| ^^^^^^^^^^^^^^^^^^
Expand All @@ -25,37 +49,37 @@ LL + let _: *mut f32 = mut_ptr.cast::<f32>();
|

error: transmute from a reference to a reference
--> tests/ui/transmute_ptr_to_ptr.rs:39:23
--> tests/ui/transmute_ptr_to_ptr.rs:49:23
|
LL | let _: &f32 = transmute(&1u32);
| ^^^^^^^^^^^^^^^^ help: try: `&*(&1u32 as *const u32 as *const f32)`

error: transmute from a reference to a reference
--> tests/ui/transmute_ptr_to_ptr.rs:42:23
--> tests/ui/transmute_ptr_to_ptr.rs:52:23
|
LL | let _: &f32 = transmute(&1f64);
| ^^^^^^^^^^^^^^^^ help: try: `&*(&1f64 as *const f64 as *const f32)`

error: transmute from a reference to a reference
--> tests/ui/transmute_ptr_to_ptr.rs:47:27
--> tests/ui/transmute_ptr_to_ptr.rs:57:27
|
LL | let _: &mut f32 = transmute(&mut 1u32);
| ^^^^^^^^^^^^^^^^^^^^ help: try: `&mut *(&mut 1u32 as *mut u32 as *mut f32)`

error: transmute from a reference to a reference
--> tests/ui/transmute_ptr_to_ptr.rs:50:37
--> tests/ui/transmute_ptr_to_ptr.rs:60:37
|
LL | let _: &GenericParam<f32> = transmute(&GenericParam { t: 1u32 });
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(&GenericParam { t: 1u32 } as *const GenericParam<u32> as *const GenericParam<f32>)`

error: transmute from a reference to a reference
--> tests/ui/transmute_ptr_to_ptr.rs:54:27
--> tests/ui/transmute_ptr_to_ptr.rs:64:27
|
LL | let u8_ref: &u8 = transmute(u64_ref);
| ^^^^^^^^^^^^^^^^^^ help: try: `&*(u64_ref as *const u64 as *const u8)`

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:57:29
--> tests/ui/transmute_ptr_to_ptr.rs:67:29
|
LL | let _: *const u32 = transmute(mut_ptr);
| ^^^^^^^^^^^^^^^^^^
Expand All @@ -67,7 +91,7 @@ LL + let _: *const u32 = mut_ptr.cast_const();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:60:27
--> tests/ui/transmute_ptr_to_ptr.rs:70:27
|
LL | let _: *mut u32 = transmute(ptr);
| ^^^^^^^^^^^^^^
Expand All @@ -79,7 +103,19 @@ LL + let _: *mut u32 = ptr.cast_mut();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:72:14
--> tests/ui/transmute_ptr_to_ptr.rs:72:27
|
LL | let _: *mut u32 = transmute(Ptr(ptr));
| ^^^^^^^^^^^^^^^^^^^
|
help: use `pointer::cast_mut` instead
|
LL - let _: *mut u32 = transmute(Ptr(ptr));
LL + let _: *mut u32 = Ptr(ptr).0.cast_mut();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:84:14
|
LL | unsafe { transmute(v) }
| ^^^^^^^^^^^^
Expand All @@ -91,7 +127,19 @@ LL + unsafe { v as *const &() }
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:87:28
--> tests/ui/transmute_ptr_to_ptr.rs:101:28
|
LL | let _: *const i8 = transmute(Ptr8(ptr));
| ^^^^^^^^^^^^^^^^^^^^
|
help: use an `as` cast instead
|
LL - let _: *const i8 = transmute(Ptr8(ptr));
LL + let _: *const i8 = Ptr8(ptr).0 as *const i8;
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:103:28
|
LL | let _: *const i8 = transmute(ptr);
| ^^^^^^^^^^^^^^
Expand All @@ -103,7 +151,7 @@ LL + let _: *const i8 = ptr as *const i8;
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:95:28
--> tests/ui/transmute_ptr_to_ptr.rs:111:28
|
LL | let _: *const i8 = transmute(ptr);
| ^^^^^^^^^^^^^^
Expand All @@ -115,7 +163,7 @@ LL + let _: *const i8 = ptr.cast::<i8>();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:103:26
--> tests/ui/transmute_ptr_to_ptr.rs:119:26
|
LL | let _: *mut u8 = transmute(ptr);
| ^^^^^^^^^^^^^^
Expand All @@ -127,7 +175,7 @@ LL + let _: *mut u8 = ptr as *mut u8;
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:105:28
--> tests/ui/transmute_ptr_to_ptr.rs:121:28
|
LL | let _: *const u8 = transmute(mut_ptr);
| ^^^^^^^^^^^^^^^^^^
Expand All @@ -139,7 +187,7 @@ LL + let _: *const u8 = mut_ptr as *const u8;
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:113:26
--> tests/ui/transmute_ptr_to_ptr.rs:129:26
|
LL | let _: *mut u8 = transmute(ptr);
| ^^^^^^^^^^^^^^
Expand All @@ -151,7 +199,7 @@ LL + let _: *mut u8 = ptr.cast_mut();
|

error: transmute from a pointer to a pointer
--> tests/ui/transmute_ptr_to_ptr.rs:115:28
--> tests/ui/transmute_ptr_to_ptr.rs:131:28
|
LL | let _: *const u8 = transmute(mut_ptr);
| ^^^^^^^^^^^^^^^^^^
Expand All @@ -162,5 +210,5 @@ LL - let _: *const u8 = transmute(mut_ptr);
LL + let _: *const u8 = mut_ptr.cast_const();
|

error: aborting due to 16 previous errors
error: aborting due to 20 previous errors

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