1 mod crosspointer_transmute;
2 mod transmute_float_to_int;
3 mod transmute_int_to_bool;
4 mod transmute_int_to_char;
5 mod transmute_int_to_float;
6 mod transmute_ptr_to_ptr;
7 mod transmute_ptr_to_ref;
8 mod transmute_ref_to_ref;
16 in_constant, match_def_path, paths, snippet, span_lint, span_lint_and_sugg, span_lint_and_then, sugg,
18 use if_chain::if_chain;
20 use rustc_errors::Applicability;
21 use rustc_hir::{Expr, ExprKind, Mutability, UnOp};
22 use rustc_lint::{LateContext, LateLintPass};
24 use rustc_session::{declare_lint_pass, declare_tool_lint};
27 declare_clippy_lint! {
28 /// **What it does:** Checks for transmutes that can't ever be correct on any
31 /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
33 /// **Known problems:** When accessing C, users might want to store pointer
34 /// sized objects in `extradata` arguments to save an allocation.
38 /// let ptr: *const T = core::intrinsics::transmute('x')
42 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
45 // FIXME: Move this to `complexity` again, after #5343 is fixed
46 declare_clippy_lint! {
47 /// **What it does:** Checks for transmutes to the original type of the object
48 /// and transmutes that could be a cast.
50 /// **Why is this bad?** Readability. The code tricks people into thinking that
51 /// something complex is going on.
53 /// **Known problems:** None.
57 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
59 pub USELESS_TRANSMUTE,
61 "transmutes that have the same to and from types or could be a cast/coercion"
64 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
65 declare_clippy_lint! {
66 /// **What it does:**Checks for transmutes that could be a pointer cast.
68 /// **Why is this bad?** Readability. The code tricks people into thinking that
69 /// something complex is going on.
71 /// **Known problems:** None.
76 /// # let p: *const [i32] = &[];
77 /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
81 /// # let p: *const [i32] = &[];
82 /// p as *const [u16];
84 pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
86 "transmutes that could be a pointer cast"
89 declare_clippy_lint! {
90 /// **What it does:** Checks for transmutes between a type `T` and `*T`.
92 /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
93 /// pointer to that type.
95 /// **Known problems:** None.
99 /// core::intrinsics::transmute(t) // where the result type is the same as
100 /// // `*t` or `&t`'s
102 pub CROSSPOINTER_TRANSMUTE,
104 "transmutes that have to or from types that are a pointer to the other"
107 declare_clippy_lint! {
108 /// **What it does:** Checks for transmutes from a pointer to a reference.
110 /// **Why is this bad?** This can always be rewritten with `&` and `*`.
112 /// **Known problems:**
113 /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
114 /// while dereferencing raw pointer is not stable yet.
115 /// If you need to do this in those places,
116 /// you would have to use `transmute` instead.
121 /// let _: &T = std::mem::transmute(p); // where p: *const T
124 /// // can be written:
127 pub TRANSMUTE_PTR_TO_REF,
129 "transmutes from a pointer to a reference type"
132 declare_clippy_lint! {
133 /// **What it does:** Checks for transmutes from an integer to a `char`.
135 /// **Why is this bad?** Not every integer is a Unicode scalar value.
137 /// **Known problems:**
138 /// - [`from_u32`] which this lint suggests using is slower than `transmute`
139 /// as it needs to validate the input.
140 /// If you are certain that the input is always a valid Unicode scalar value,
141 /// use [`from_u32_unchecked`] which is as fast as `transmute`
142 /// but has a semantically meaningful name.
143 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
145 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
146 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
152 /// let _: char = std::mem::transmute(x); // where x: u32
156 /// let _ = std::char::from_u32(x).unwrap();
158 pub TRANSMUTE_INT_TO_CHAR,
160 "transmutes from an integer to a `char`"
163 declare_clippy_lint! {
164 /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
166 /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
168 /// **Known problems:**
169 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
170 /// as it needs to validate the input.
171 /// If you are certain that the input is always a valid UTF-8,
172 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
173 /// but has a semantically meaningful name.
174 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
176 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
177 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
181 /// let b: &[u8] = &[1_u8, 2_u8];
183 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
187 /// let _ = std::str::from_utf8(b).unwrap();
189 pub TRANSMUTE_BYTES_TO_STR,
191 "transmutes from a `&[u8]` to a `&str`"
194 declare_clippy_lint! {
195 /// **What it does:** Checks for transmutes from an integer to a `bool`.
197 /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
199 /// **Known problems:** None.
205 /// let _: bool = std::mem::transmute(x); // where x: u8
209 /// let _: bool = x != 0;
211 pub TRANSMUTE_INT_TO_BOOL,
213 "transmutes from an integer to a `bool`"
216 declare_clippy_lint! {
217 /// **What it does:** Checks for transmutes from an integer to a float.
219 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
222 /// **Known problems:** None.
227 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
231 /// let _: f32 = f32::from_bits(1_u32);
233 pub TRANSMUTE_INT_TO_FLOAT,
235 "transmutes from an integer to a float"
238 declare_clippy_lint! {
239 /// **What it does:** Checks for transmutes from a float to an integer.
241 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
244 /// **Known problems:** None.
249 /// let _: u32 = std::mem::transmute(1f32);
253 /// let _: u32 = 1f32.to_bits();
255 pub TRANSMUTE_FLOAT_TO_INT,
257 "transmutes from a float to an integer"
260 declare_clippy_lint! {
261 /// **What it does:** Checks for transmutes from a pointer to a pointer, or
262 /// from a reference to a reference.
264 /// **Why is this bad?** Transmutes are dangerous, and these can instead be
265 /// written as casts.
267 /// **Known problems:** None.
271 /// let ptr = &1u32 as *const u32;
273 /// // pointer-to-pointer transmute
274 /// let _: *const f32 = std::mem::transmute(ptr);
275 /// // ref-ref transmute
276 /// let _: &f32 = std::mem::transmute(&1u32);
278 /// // These can be respectively written:
279 /// let _ = ptr as *const f32;
280 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
282 pub TRANSMUTE_PTR_TO_PTR,
284 "transmutes from a pointer to a pointer / a reference to a reference"
287 declare_clippy_lint! {
288 /// **What it does:** Checks for transmutes between collections whose
289 /// types have different ABI, size or alignment.
291 /// **Why is this bad?** This is undefined behavior.
293 /// **Known problems:** Currently, we cannot know whether a type is a
294 /// collection, so we just lint the ones that come with `std`.
298 /// // different size, therefore likely out-of-bounds memory access
299 /// // You absolutely do not want this in your code!
301 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
305 /// You must always iterate, map and collect the values:
308 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
310 pub UNSOUND_COLLECTION_TRANSMUTE,
312 "transmute between collections of layout-incompatible types"
315 declare_lint_pass!(Transmute => [
316 CROSSPOINTER_TRANSMUTE,
317 TRANSMUTE_PTR_TO_REF,
318 TRANSMUTE_PTR_TO_PTR,
321 TRANSMUTE_INT_TO_CHAR,
322 TRANSMUTE_BYTES_TO_STR,
323 TRANSMUTE_INT_TO_BOOL,
324 TRANSMUTE_INT_TO_FLOAT,
325 TRANSMUTE_FLOAT_TO_INT,
326 UNSOUND_COLLECTION_TRANSMUTE,
327 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
330 // used to check for UNSOUND_COLLECTION_TRANSMUTE
331 static COLLECTIONS: &[&[&str]] = &[
341 impl<'tcx> LateLintPass<'tcx> for Transmute {
342 #[allow(clippy::similar_names, clippy::too_many_lines)]
343 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
345 if let ExprKind::Call(ref path_expr, ref args) = e.kind;
346 if let ExprKind::Path(ref qpath) = path_expr.kind;
347 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
348 if match_def_path(cx, def_id, &paths::TRANSMUTE);
350 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
351 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
352 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
353 let const_context = in_constant(cx, e.hir_id);
355 let from_ty = cx.typeck_results().expr_ty(&args[0]);
356 let to_ty = cx.typeck_results().expr_ty(e);
358 let triggered = useless_transmute::check(cx, e, from_ty, to_ty, args);
362 let triggered = wrong_transmute::check(cx, e, from_ty, to_ty);
366 let triggered = crosspointer_transmute::check(cx, e, from_ty, to_ty);
370 let triggered = transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
374 let triggered = transmute_int_to_char::check(cx, e, from_ty, to_ty, args);
378 let triggered = transmute_ref_to_ref::check(cx, e, from_ty, to_ty, args, const_context);
382 let triggered = transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, args);
386 let triggered = transmute_int_to_bool::check(cx, e, from_ty, to_ty, args);
390 let triggered = transmute_int_to_float::check(cx, e, from_ty, to_ty, args, const_context);
394 let triggered = transmute_float_to_int::check(cx, e, from_ty, to_ty, args, const_context);
399 match (&from_ty.kind(), &to_ty.kind()) {
400 (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
401 if from_adt.did != to_adt.did ||
402 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
405 if from_substs.types().zip(to_substs.types())
406 .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
409 UNSOUND_COLLECTION_TRANSMUTE,
412 "transmute from `{}` to `{}` with mismatched layout is unsound",
419 (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
421 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
424 "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
429 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
430 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
431 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);