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_num_to_bytes;
7 mod transmute_ptr_to_ptr;
8 mod transmute_ptr_to_ref;
9 mod transmute_ref_to_ref;
10 mod transmutes_expressible_as_ptr_casts;
11 mod unsound_collection_transmute;
12 mod useless_transmute;
16 use clippy_utils::in_constant;
17 use if_chain::if_chain;
18 use rustc_hir::{Expr, ExprKind};
19 use rustc_lint::{LateContext, LateLintPass};
20 use rustc_session::{declare_lint_pass, declare_tool_lint};
21 use rustc_span::symbol::sym;
23 declare_clippy_lint! {
25 /// Checks for transmutes that can't ever be correct on any
28 /// ### Why is this bad?
29 /// It's basically guaranteed to be undefined behaviour.
31 /// ### Known problems
32 /// When accessing C, users might want to store pointer
33 /// sized objects in `extradata` arguments to save an allocation.
37 /// let ptr: *const T = core::intrinsics::transmute('x')
41 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
44 // FIXME: Move this to `complexity` again, after #5343 is fixed
45 declare_clippy_lint! {
47 /// Checks for transmutes to the original type of the object
48 /// and transmutes that could be a cast.
50 /// ### Why is this bad?
51 /// Readability. The code tricks people into thinking that
52 /// something complex is going on.
56 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
58 pub USELESS_TRANSMUTE,
60 "transmutes that have the same to and from types or could be a cast/coercion"
63 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
64 declare_clippy_lint! {
66 ///Checks for transmutes that could be a pointer cast.
68 /// ### Why is this bad?
69 /// Readability. The code tricks people into thinking that
70 /// something complex is going on.
75 /// # let p: *const [i32] = &[];
76 /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
80 /// # let p: *const [i32] = &[];
81 /// p as *const [u16];
83 pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
85 "transmutes that could be a pointer cast"
88 declare_clippy_lint! {
90 /// Checks for transmutes between a type `T` and `*T`.
92 /// ### Why is this bad?
93 /// It's easy to mistakenly transmute between a type and a
94 /// pointer to that type.
98 /// core::intrinsics::transmute(t) // where the result type is the same as
101 pub CROSSPOINTER_TRANSMUTE,
103 "transmutes that have to or from types that are a pointer to the other"
106 declare_clippy_lint! {
108 /// Checks for transmutes from a pointer to a reference.
110 /// ### Why is this bad?
111 /// 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! {
135 /// Checks for transmutes from an integer to a `char`.
137 /// ### Why is this bad?
138 /// Not every integer is a Unicode scalar value.
140 /// ### Known problems
141 /// - [`from_u32`] which this lint suggests using is slower than `transmute`
142 /// as it needs to validate the input.
143 /// If you are certain that the input is always a valid Unicode scalar value,
144 /// use [`from_u32_unchecked`] which is as fast as `transmute`
145 /// but has a semantically meaningful name.
146 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
148 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
149 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
155 /// let _: char = std::mem::transmute(x); // where x: u32
159 /// let _ = std::char::from_u32(x).unwrap();
161 pub TRANSMUTE_INT_TO_CHAR,
163 "transmutes from an integer to a `char`"
166 declare_clippy_lint! {
168 /// Checks for transmutes from a `&[u8]` to a `&str`.
170 /// ### Why is this bad?
171 /// Not every byte slice is a valid UTF-8 string.
173 /// ### Known problems
174 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
175 /// as it needs to validate the input.
176 /// If you are certain that the input is always a valid UTF-8,
177 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
178 /// but has a semantically meaningful name.
179 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
181 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
182 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
186 /// let b: &[u8] = &[1_u8, 2_u8];
188 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
192 /// let _ = std::str::from_utf8(b).unwrap();
194 pub TRANSMUTE_BYTES_TO_STR,
196 "transmutes from a `&[u8]` to a `&str`"
199 declare_clippy_lint! {
201 /// Checks for transmutes from an integer to a `bool`.
203 /// ### Why is this bad?
204 /// This might result in an invalid in-memory representation of a `bool`.
210 /// let _: bool = std::mem::transmute(x); // where x: u8
214 /// let _: bool = x != 0;
216 pub TRANSMUTE_INT_TO_BOOL,
218 "transmutes from an integer to a `bool`"
221 declare_clippy_lint! {
223 /// Checks for transmutes from an integer to a float.
225 /// ### Why is this bad?
226 /// Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
232 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
236 /// let _: f32 = f32::from_bits(1_u32);
238 pub TRANSMUTE_INT_TO_FLOAT,
240 "transmutes from an integer to a float"
243 declare_clippy_lint! {
245 /// Checks for transmutes from a float to an integer.
247 /// ### Why is this bad?
248 /// Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
254 /// let _: u32 = std::mem::transmute(1f32);
258 /// let _: u32 = 1f32.to_bits();
260 pub TRANSMUTE_FLOAT_TO_INT,
262 "transmutes from a float to an integer"
265 declare_clippy_lint! {
267 /// Checks for transmutes from a number to an array of `u8`
269 /// ### Why this is bad?
270 /// Transmutes are dangerous and error-prone, whereas `to_ne_bytes`
271 /// is intuitive and safe.
276 /// let x: [u8; 8] = std::mem::transmute(1i64);
280 /// let x: [u8; 8] = 0i64.to_ne_bytes();
282 pub TRANSMUTE_NUM_TO_BYTES,
284 "transmutes from a number to an array of `u8`"
287 declare_clippy_lint! {
289 /// Checks for transmutes from a pointer to a pointer, or
290 /// from a reference to a reference.
292 /// ### Why is this bad?
293 /// Transmutes are dangerous, and these can instead be
294 /// written as casts.
298 /// let ptr = &1u32 as *const u32;
300 /// // pointer-to-pointer transmute
301 /// let _: *const f32 = std::mem::transmute(ptr);
302 /// // ref-ref transmute
303 /// let _: &f32 = std::mem::transmute(&1u32);
305 /// // These can be respectively written:
306 /// let _ = ptr as *const f32;
307 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
309 pub TRANSMUTE_PTR_TO_PTR,
311 "transmutes from a pointer to a pointer / a reference to a reference"
314 declare_clippy_lint! {
316 /// Checks for transmutes between collections whose
317 /// types have different ABI, size or alignment.
319 /// ### Why is this bad?
320 /// This is undefined behavior.
322 /// ### Known problems
323 /// Currently, we cannot know whether a type is a
324 /// collection, so we just lint the ones that come with `std`.
328 /// // different size, therefore likely out-of-bounds memory access
329 /// // You absolutely do not want this in your code!
331 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
335 /// You must always iterate, map and collect the values:
338 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
340 pub UNSOUND_COLLECTION_TRANSMUTE,
342 "transmute between collections of layout-incompatible types"
345 declare_lint_pass!(Transmute => [
346 CROSSPOINTER_TRANSMUTE,
347 TRANSMUTE_PTR_TO_REF,
348 TRANSMUTE_PTR_TO_PTR,
351 TRANSMUTE_INT_TO_CHAR,
352 TRANSMUTE_BYTES_TO_STR,
353 TRANSMUTE_INT_TO_BOOL,
354 TRANSMUTE_INT_TO_FLOAT,
355 TRANSMUTE_FLOAT_TO_INT,
356 TRANSMUTE_NUM_TO_BYTES,
357 UNSOUND_COLLECTION_TRANSMUTE,
358 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
361 impl<'tcx> LateLintPass<'tcx> for Transmute {
362 #[allow(clippy::similar_names, clippy::too_many_lines)]
363 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
365 if let ExprKind::Call(path_expr, args) = e.kind;
366 if let ExprKind::Path(ref qpath) = path_expr.kind;
367 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
368 if cx.tcx.is_diagnostic_item(sym::transmute, def_id);
370 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
371 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
372 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
373 let const_context = in_constant(cx, e.hir_id);
375 let from_ty = cx.typeck_results().expr_ty(&args[0]);
376 let to_ty = cx.typeck_results().expr_ty(e);
378 // If useless_transmute is triggered, the other lints can be skipped.
379 if useless_transmute::check(cx, e, from_ty, to_ty, args) {
383 let mut linted = wrong_transmute::check(cx, e, from_ty, to_ty);
384 linted |= crosspointer_transmute::check(cx, e, from_ty, to_ty);
385 linted |= transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
386 linted |= transmute_int_to_char::check(cx, e, from_ty, to_ty, args);
387 linted |= transmute_ref_to_ref::check(cx, e, from_ty, to_ty, args, const_context);
388 linted |= transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, args);
389 linted |= transmute_int_to_bool::check(cx, e, from_ty, to_ty, args);
390 linted |= transmute_int_to_float::check(cx, e, from_ty, to_ty, args, const_context);
391 linted |= transmute_float_to_int::check(cx, e, from_ty, to_ty, args, const_context);
392 linted |= transmute_num_to_bytes::check(cx, e, from_ty, to_ty, args, const_context);
393 linted |= unsound_collection_transmute::check(cx, e, from_ty, to_ty);
396 transmutes_expressible_as_ptr_casts::check(cx, e, from_ty, to_ty, args);