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fix(transmute_ptr_to_ref): don't suggest .cast when to-type is DST #15621

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Merged
merged 2 commits into from
Sep 17, 2025
Merged

fix(transmute_ptr_to_ref): don't suggest .cast when to-type is DST #15621

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d4cb0b4
clean-up a bit
ada4a Sep 5, 2025
1f86679
fix(transmute_ptr_to_ref): don't suggest `.cast` when to-type is DST
ada4a Sep 5, 2025
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44 changes: 31 additions & 13 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 @@ -28,32 +28,50 @@ pub(super) fn check<'tcx>(
format!("transmute from a pointer type (`{from_ty}`) to a reference type (`{to_ty}`)"),
|diag| {
let arg = sugg::Sugg::hir(cx, arg, "..");
let (deref, cast) = if *mutbl == Mutability::Mut {
("&mut *", "*mut")
} else {
("&*", "*const")
let (deref, cast) = match mutbl {
Mutability::Mut => ("&mut *", "*mut"),
Mutability::Not => ("&*", "*const"),
};
let mut app = Applicability::MachineApplicable;

let sugg = if let Some(ty) = get_explicit_type(path) {
let ty_snip = snippet_with_applicability(cx, ty.span, "..", &mut app);
if msrv.meets(cx, msrvs::POINTER_CAST) {
if !to_ref_ty.is_sized(cx.tcx, cx.typing_env()) {
// We can't suggest `.cast()`, because that requires `to_ref_ty` to be Sized.
if from_ptr_ty.has_erased_regions() {
// We can't suggest `as *mut/const () as *mut/const to_ref_ty`, because the former is a
// thin pointer, whereas the latter is a wide pointer, due of its pointee, `to_ref_ty`,
// being !Sized.
//
// The only remaining option is be to skip `*mut/const ()`, but that might not be safe
// to do because of the erased regions in `from_ptr_ty`, so reduce the applicability.
app = Applicability::MaybeIncorrect;
}
sugg::make_unop(deref, arg.as_ty(format!("{cast} {ty_snip}"))).to_string()
} else if msrv.meets(cx, msrvs::POINTER_CAST) {
format!("{deref}{}.cast::<{ty_snip}>()", arg.maybe_paren())
} else if from_ptr_ty.has_erased_regions() {
sugg::make_unop(deref, arg.as_ty(format!("{cast} () as {cast} {ty_snip}"))).to_string()
} else {
sugg::make_unop(deref, arg.as_ty(format!("{cast} {ty_snip}"))).to_string()
}
} else if *from_ptr_ty == *to_ref_ty {
if from_ptr_ty.has_erased_regions() {
if msrv.meets(cx, msrvs::POINTER_CAST) {
format!("{deref}{}.cast::<{to_ref_ty}>()", arg.maybe_paren())
} else {
sugg::make_unop(deref, arg.as_ty(format!("{cast} () as {cast} {to_ref_ty}")))
.to_string()
}
} else {
if !from_ptr_ty.has_erased_regions() {
sugg::make_unop(deref, arg).to_string()
} else if !to_ref_ty.is_sized(cx.tcx, cx.typing_env()) {
// 1. We can't suggest `.cast()`, because that requires `to_ref_ty` to be Sized.
// 2. We can't suggest `as *mut/const () as *mut/const to_ref_ty`, because the former is a
// thin pointer, whereas the latter is a wide pointer, due of its pointee, `to_ref_ty`,
// being !Sized.
//
// The only remaining option is be to skip `*mut/const ()`, but that might not be safe to do
// because of the erased regions in `from_ptr_ty`, so reduce the applicability.
app = Applicability::MaybeIncorrect;
sugg::make_unop(deref, arg.as_ty(format!("{cast} {to_ref_ty}"))).to_string()
} else if msrv.meets(cx, msrvs::POINTER_CAST) {
format!("{deref}{}.cast::<{to_ref_ty}>()", arg.maybe_paren())
} else {
sugg::make_unop(deref, arg.as_ty(format!("{cast} () as {cast} {to_ref_ty}"))).to_string()
}
} else {
sugg::make_unop(deref, arg.as_ty(format!("{cast} {to_ref_ty}"))).to_string()
Expand Down
39 changes: 34 additions & 5 deletions tests/ui/transmute_ptr_to_ref.fixed
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
clippy::missing_transmute_annotations
)]

unsafe fn _ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
fn ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
unsafe {
let _: &T = &*p;
//~^ transmute_ptr_to_ref
Expand Down Expand Up @@ -37,7 +37,7 @@ unsafe fn _ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
}
}

fn _issue1231() {
fn issue1231() {
struct Foo<'a, T> {
bar: &'a T,
}
Expand All @@ -55,7 +55,7 @@ fn _issue1231() {
//~^ transmute_ptr_to_ref
}

unsafe fn _issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'b u32 {
fn issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'b u32 {
unsafe {
match 0 {
0 => &*x.cast::<&u32>(),
Expand All @@ -71,7 +71,7 @@ unsafe fn _issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'
}

#[clippy::msrv = "1.38"]
unsafe fn _meets_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
fn meets_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
unsafe {
let a = 0u32;
let a = &a as *const u32;
Expand All @@ -89,7 +89,7 @@ unsafe fn _meets_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
}

#[clippy::msrv = "1.37"]
unsafe fn _under_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
fn under_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
unsafe {
let a = 0u32;
let a = &a as *const u32;
Expand All @@ -106,4 +106,33 @@ unsafe fn _under_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
}
}

// handle DSTs
fn issue13357(ptr: *const [i32], s_ptr: *const &str, a_s_ptr: *const [&str]) {
unsafe {
// different types, without erased regions
let _ = &*(ptr as *const [u32]);
//~^ transmute_ptr_to_ref
let _: &[u32] = &*(ptr as *const [u32]);
//~^ transmute_ptr_to_ref

// different types, with erased regions
let _ = &*(a_s_ptr as *const [&[u8]]);
//~^ transmute_ptr_to_ref
let _: &[&[u8]] = &*(a_s_ptr as *const [&[u8]]);
//~^ transmute_ptr_to_ref

// same type, without erased regions
let _ = &*(ptr as *const [i32]);
//~^ transmute_ptr_to_ref
let _: &[i32] = &*ptr;
//~^ transmute_ptr_to_ref

// same type, with erased regions
let _ = &*(a_s_ptr as *const [&str]);
//~^ transmute_ptr_to_ref
let _: &[&str] = &*(a_s_ptr as *const [&str]);
//~^ transmute_ptr_to_ref
}
}

fn main() {}
39 changes: 34 additions & 5 deletions tests/ui/transmute_ptr_to_ref.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
clippy::missing_transmute_annotations
)]

unsafe fn _ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
fn ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
unsafe {
let _: &T = std::mem::transmute(p);
//~^ transmute_ptr_to_ref
Expand Down Expand Up @@ -37,7 +37,7 @@ unsafe fn _ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
}
}

fn _issue1231() {
fn issue1231() {
struct Foo<'a, T> {
bar: &'a T,
}
Expand All @@ -55,7 +55,7 @@ fn _issue1231() {
//~^ transmute_ptr_to_ref
}

unsafe fn _issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'b u32 {
fn issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'b u32 {
unsafe {
match 0 {
0 => std::mem::transmute(x),
Expand All @@ -71,7 +71,7 @@ unsafe fn _issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'
}

#[clippy::msrv = "1.38"]
unsafe fn _meets_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
fn meets_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
unsafe {
let a = 0u32;
let a = &a as *const u32;
Expand All @@ -89,7 +89,7 @@ unsafe fn _meets_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
}

#[clippy::msrv = "1.37"]
unsafe fn _under_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
fn under_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
unsafe {
let a = 0u32;
let a = &a as *const u32;
Expand All @@ -106,4 +106,33 @@ unsafe fn _under_msrv<'a, 'b, 'c>(x: *const &'a u32) -> &'c &'b u32 {
}
}

// handle DSTs
fn issue13357(ptr: *const [i32], s_ptr: *const &str, a_s_ptr: *const [&str]) {
unsafe {
// different types, without erased regions
let _ = core::mem::transmute::<_, &[u32]>(ptr);
//~^ transmute_ptr_to_ref
let _: &[u32] = core::mem::transmute(ptr);
//~^ transmute_ptr_to_ref

// different types, with erased regions
let _ = core::mem::transmute::<_, &[&[u8]]>(a_s_ptr);
//~^ transmute_ptr_to_ref
let _: &[&[u8]] = core::mem::transmute(a_s_ptr);
//~^ transmute_ptr_to_ref

// same type, without erased regions
let _ = core::mem::transmute::<_, &[i32]>(ptr);
//~^ transmute_ptr_to_ref
let _: &[i32] = core::mem::transmute(ptr);
//~^ transmute_ptr_to_ref

// same type, with erased regions
let _ = core::mem::transmute::<_, &[&str]>(a_s_ptr);
//~^ transmute_ptr_to_ref
let _: &[&str] = core::mem::transmute(a_s_ptr);
//~^ transmute_ptr_to_ref
}
}

fn main() {}
54 changes: 51 additions & 3 deletions tests/ui/transmute_ptr_to_ref.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -43,13 +43,13 @@ error: transmute from a pointer type (`*mut U`) to a reference type (`&T`)
LL | let _: &T = std::mem::transmute(om);
| ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(om as *const T)`

error: transmute from a pointer type (`*const i32`) to a reference type (`&_issue1231::Foo<'_, u8>`)
error: transmute from a pointer type (`*const i32`) to a reference type (`&issue1231::Foo<'_, u8>`)
--> tests/ui/transmute_ptr_to_ref.rs:46:32
|
LL | let _: &Foo<u8> = unsafe { std::mem::transmute::<_, &Foo<_>>(raw) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*raw.cast::<Foo<_>>()`

error: transmute from a pointer type (`*const i32`) to a reference type (`&_issue1231::Foo<'_, &u8>`)
error: transmute from a pointer type (`*const i32`) to a reference type (`&issue1231::Foo<'_, &u8>`)
--> tests/ui/transmute_ptr_to_ref.rs:49:33
|
LL | let _: &Foo<&u8> = unsafe { std::mem::transmute::<_, &Foo<&_>>(raw) };
Expand Down Expand Up @@ -133,5 +133,53 @@ error: transmute from a pointer type (`*const &u32`) to a reference type (`&&u32
LL | _ => std::mem::transmute::<_, &&'b u32>(x),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(x as *const () as *const &'b u32)`

error: aborting due to 22 previous errors
error: transmute from a pointer type (`*const [i32]`) to a reference type (`&[u32]`)
--> tests/ui/transmute_ptr_to_ref.rs:113:17
|
LL | let _ = core::mem::transmute::<_, &[u32]>(ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(ptr as *const [u32])`

error: transmute from a pointer type (`*const [i32]`) to a reference type (`&[u32]`)
--> tests/ui/transmute_ptr_to_ref.rs:115:25
|
LL | let _: &[u32] = core::mem::transmute(ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(ptr as *const [u32])`

error: transmute from a pointer type (`*const [&str]`) to a reference type (`&[&[u8]]`)
--> tests/ui/transmute_ptr_to_ref.rs:119:17
|
LL | let _ = core::mem::transmute::<_, &[&[u8]]>(a_s_ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(a_s_ptr as *const [&[u8]])`

error: transmute from a pointer type (`*const [&str]`) to a reference type (`&[&[u8]]`)
--> tests/ui/transmute_ptr_to_ref.rs:121:27
|
LL | let _: &[&[u8]] = core::mem::transmute(a_s_ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(a_s_ptr as *const [&[u8]])`

error: transmute from a pointer type (`*const [i32]`) to a reference type (`&[i32]`)
--> tests/ui/transmute_ptr_to_ref.rs:125:17
|
LL | let _ = core::mem::transmute::<_, &[i32]>(ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(ptr as *const [i32])`

error: transmute from a pointer type (`*const [i32]`) to a reference type (`&[i32]`)
--> tests/ui/transmute_ptr_to_ref.rs:127:25
|
LL | let _: &[i32] = core::mem::transmute(ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*ptr`

error: transmute from a pointer type (`*const [&str]`) to a reference type (`&[&str]`)
--> tests/ui/transmute_ptr_to_ref.rs:131:17
|
LL | let _ = core::mem::transmute::<_, &[&str]>(a_s_ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(a_s_ptr as *const [&str])`

error: transmute from a pointer type (`*const [&str]`) to a reference type (`&[&str]`)
--> tests/ui/transmute_ptr_to_ref.rs:133:26
|
LL | let _: &[&str] = core::mem::transmute(a_s_ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&*(a_s_ptr as *const [&str])`

error: aborting due to 30 previous errors