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;
9 mod unsound_collection_transmute;
10 mod useless_transmute;
17 in_constant, match_def_path, paths, snippet, span_lint, span_lint_and_sugg, span_lint_and_then, sugg,
19 use if_chain::if_chain;
21 use rustc_errors::Applicability;
22 use rustc_hir::{Expr, ExprKind, Mutability, UnOp};
23 use rustc_lint::{LateContext, LateLintPass};
25 use rustc_session::{declare_lint_pass, declare_tool_lint};
28 declare_clippy_lint! {
29 /// **What it does:** Checks for transmutes that can't ever be correct on any
32 /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
34 /// **Known problems:** When accessing C, users might want to store pointer
35 /// sized objects in `extradata` arguments to save an allocation.
39 /// let ptr: *const T = core::intrinsics::transmute('x')
43 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
46 // FIXME: Move this to `complexity` again, after #5343 is fixed
47 declare_clippy_lint! {
48 /// **What it does:** Checks for transmutes to the original type of the object
49 /// and transmutes that could be a cast.
51 /// **Why is this bad?** Readability. The code tricks people into thinking that
52 /// something complex is going on.
54 /// **Known problems:** None.
58 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
60 pub USELESS_TRANSMUTE,
62 "transmutes that have the same to and from types or could be a cast/coercion"
65 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
66 declare_clippy_lint! {
67 /// **What it does:**Checks for transmutes that could be a pointer cast.
69 /// **Why is this bad?** Readability. The code tricks people into thinking that
70 /// something complex is going on.
72 /// **Known problems:** None.
77 /// # let p: *const [i32] = &[];
78 /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
82 /// # let p: *const [i32] = &[];
83 /// p as *const [u16];
85 pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
87 "transmutes that could be a pointer cast"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for transmutes between a type `T` and `*T`.
93 /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
94 /// pointer to that type.
96 /// **Known problems:** None.
100 /// core::intrinsics::transmute(t) // where the result type is the same as
101 /// // `*t` or `&t`'s
103 pub CROSSPOINTER_TRANSMUTE,
105 "transmutes that have to or from types that are a pointer to the other"
108 declare_clippy_lint! {
109 /// **What it does:** Checks for transmutes from a pointer to a reference.
111 /// **Why is this bad?** This can always be rewritten with `&` and `*`.
113 /// **Known problems:**
114 /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
115 /// while dereferencing raw pointer is not stable yet.
116 /// If you need to do this in those places,
117 /// you would have to use `transmute` instead.
122 /// let _: &T = std::mem::transmute(p); // where p: *const T
125 /// // can be written:
128 pub TRANSMUTE_PTR_TO_REF,
130 "transmutes from a pointer to a reference type"
133 declare_clippy_lint! {
134 /// **What it does:** Checks for transmutes from an integer to a `char`.
136 /// **Why is this bad?** Not every integer is a Unicode scalar value.
138 /// **Known problems:**
139 /// - [`from_u32`] which this lint suggests using is slower than `transmute`
140 /// as it needs to validate the input.
141 /// If you are certain that the input is always a valid Unicode scalar value,
142 /// use [`from_u32_unchecked`] which is as fast as `transmute`
143 /// but has a semantically meaningful name.
144 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
146 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
147 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
153 /// let _: char = std::mem::transmute(x); // where x: u32
157 /// let _ = std::char::from_u32(x).unwrap();
159 pub TRANSMUTE_INT_TO_CHAR,
161 "transmutes from an integer to a `char`"
164 declare_clippy_lint! {
165 /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
167 /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
169 /// **Known problems:**
170 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
171 /// as it needs to validate the input.
172 /// If you are certain that the input is always a valid UTF-8,
173 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
174 /// but has a semantically meaningful name.
175 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
177 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
178 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
182 /// let b: &[u8] = &[1_u8, 2_u8];
184 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
188 /// let _ = std::str::from_utf8(b).unwrap();
190 pub TRANSMUTE_BYTES_TO_STR,
192 "transmutes from a `&[u8]` to a `&str`"
195 declare_clippy_lint! {
196 /// **What it does:** Checks for transmutes from an integer to a `bool`.
198 /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
200 /// **Known problems:** None.
206 /// let _: bool = std::mem::transmute(x); // where x: u8
210 /// let _: bool = x != 0;
212 pub TRANSMUTE_INT_TO_BOOL,
214 "transmutes from an integer to a `bool`"
217 declare_clippy_lint! {
218 /// **What it does:** Checks for transmutes from an integer to a float.
220 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
223 /// **Known problems:** None.
228 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
232 /// let _: f32 = f32::from_bits(1_u32);
234 pub TRANSMUTE_INT_TO_FLOAT,
236 "transmutes from an integer to a float"
239 declare_clippy_lint! {
240 /// **What it does:** Checks for transmutes from a float to an integer.
242 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
245 /// **Known problems:** None.
250 /// let _: u32 = std::mem::transmute(1f32);
254 /// let _: u32 = 1f32.to_bits();
256 pub TRANSMUTE_FLOAT_TO_INT,
258 "transmutes from a float to an integer"
261 declare_clippy_lint! {
262 /// **What it does:** Checks for transmutes from a pointer to a pointer, or
263 /// from a reference to a reference.
265 /// **Why is this bad?** Transmutes are dangerous, and these can instead be
266 /// written as casts.
268 /// **Known problems:** None.
272 /// let ptr = &1u32 as *const u32;
274 /// // pointer-to-pointer transmute
275 /// let _: *const f32 = std::mem::transmute(ptr);
276 /// // ref-ref transmute
277 /// let _: &f32 = std::mem::transmute(&1u32);
279 /// // These can be respectively written:
280 /// let _ = ptr as *const f32;
281 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
283 pub TRANSMUTE_PTR_TO_PTR,
285 "transmutes from a pointer to a pointer / a reference to a reference"
288 declare_clippy_lint! {
289 /// **What it does:** Checks for transmutes between collections whose
290 /// types have different ABI, size or alignment.
292 /// **Why is this bad?** This is undefined behavior.
294 /// **Known problems:** Currently, we cannot know whether a type is a
295 /// collection, so we just lint the ones that come with `std`.
299 /// // different size, therefore likely out-of-bounds memory access
300 /// // You absolutely do not want this in your code!
302 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
306 /// You must always iterate, map and collect the values:
309 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
311 pub UNSOUND_COLLECTION_TRANSMUTE,
313 "transmute between collections of layout-incompatible types"
316 declare_lint_pass!(Transmute => [
317 CROSSPOINTER_TRANSMUTE,
318 TRANSMUTE_PTR_TO_REF,
319 TRANSMUTE_PTR_TO_PTR,
322 TRANSMUTE_INT_TO_CHAR,
323 TRANSMUTE_BYTES_TO_STR,
324 TRANSMUTE_INT_TO_BOOL,
325 TRANSMUTE_INT_TO_FLOAT,
326 TRANSMUTE_FLOAT_TO_INT,
327 UNSOUND_COLLECTION_TRANSMUTE,
328 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
331 impl<'tcx> LateLintPass<'tcx> for Transmute {
332 #[allow(clippy::similar_names, clippy::too_many_lines)]
333 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
335 if let ExprKind::Call(ref path_expr, ref args) = e.kind;
336 if let ExprKind::Path(ref qpath) = path_expr.kind;
337 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
338 if match_def_path(cx, def_id, &paths::TRANSMUTE);
340 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
341 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
342 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
343 let const_context = in_constant(cx, e.hir_id);
345 let from_ty = cx.typeck_results().expr_ty(&args[0]);
346 let to_ty = cx.typeck_results().expr_ty(e);
348 let triggered = useless_transmute::check(cx, e, from_ty, to_ty, args);
352 let triggered = wrong_transmute::check(cx, e, from_ty, to_ty);
356 let triggered = crosspointer_transmute::check(cx, e, from_ty, to_ty);
360 let triggered = transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
364 let triggered = transmute_int_to_char::check(cx, e, from_ty, to_ty, args);
368 let triggered = transmute_ref_to_ref::check(cx, e, from_ty, to_ty, args, const_context);
372 let triggered = transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, args);
376 let triggered = transmute_int_to_bool::check(cx, e, from_ty, to_ty, args);
380 let triggered = transmute_int_to_float::check(cx, e, from_ty, to_ty, args, const_context);
384 let triggered = transmute_float_to_int::check(cx, e, from_ty, to_ty, args, const_context);
388 let triggered = unsound_collection_transmute::check(cx, e, from_ty, to_ty);
393 match (&from_ty.kind(), &to_ty.kind()) {
394 (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
396 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
399 "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
404 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
405 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
406 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);