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 transmutes_expressible_as_ptr_casts;
10 mod unsound_collection_transmute;
11 mod useless_transmute;
15 use clippy_utils::in_constant;
16 use if_chain::if_chain;
17 use rustc_hir::{Expr, ExprKind};
18 use rustc_lint::{LateContext, LateLintPass};
19 use rustc_session::{declare_lint_pass, declare_tool_lint};
20 use rustc_span::symbol::sym;
22 declare_clippy_lint! {
24 /// Checks for transmutes that can't ever be correct on any
27 /// ### Why is this bad?
28 /// It's basically guaranteed to be undefined behaviour.
30 /// ### Known problems
31 /// When accessing C, users might want to store pointer
32 /// sized objects in `extradata` arguments to save an allocation.
36 /// let ptr: *const T = core::intrinsics::transmute('x')
40 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
43 // FIXME: Move this to `complexity` again, after #5343 is fixed
44 declare_clippy_lint! {
46 /// Checks for transmutes to the original type of the object
47 /// and transmutes that could be a cast.
49 /// ### Why is this bad?
50 /// Readability. The code tricks people into thinking that
51 /// something complex is going on.
55 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
57 pub USELESS_TRANSMUTE,
59 "transmutes that have the same to and from types or could be a cast/coercion"
62 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
63 declare_clippy_lint! {
65 ///Checks for transmutes that could be a pointer cast.
67 /// ### Why is this bad?
68 /// Readability. The code tricks people into thinking that
69 /// something complex is going on.
74 /// # let p: *const [i32] = &[];
75 /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
79 /// # let p: *const [i32] = &[];
80 /// p as *const [u16];
82 pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
84 "transmutes that could be a pointer cast"
87 declare_clippy_lint! {
89 /// Checks for transmutes between a type `T` and `*T`.
91 /// ### Why is this bad?
92 /// It's easy to mistakenly transmute between a type and a
93 /// pointer to that type.
97 /// core::intrinsics::transmute(t) // where the result type is the same as
100 pub CROSSPOINTER_TRANSMUTE,
102 "transmutes that have to or from types that are a pointer to the other"
105 declare_clippy_lint! {
107 /// Checks for transmutes from a pointer to a reference.
109 /// ### Why is this bad?
110 /// 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! {
134 /// Checks for transmutes from an integer to a `char`.
136 /// ### Why is this bad?
137 /// Not every integer is a Unicode scalar value.
139 /// ### Known problems
140 /// - [`from_u32`] which this lint suggests using is slower than `transmute`
141 /// as it needs to validate the input.
142 /// If you are certain that the input is always a valid Unicode scalar value,
143 /// use [`from_u32_unchecked`] which is as fast as `transmute`
144 /// but has a semantically meaningful name.
145 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
147 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
148 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
154 /// let _: char = std::mem::transmute(x); // where x: u32
158 /// let _ = std::char::from_u32(x).unwrap();
160 pub TRANSMUTE_INT_TO_CHAR,
162 "transmutes from an integer to a `char`"
165 declare_clippy_lint! {
167 /// Checks for transmutes from a `&[u8]` to a `&str`.
169 /// ### Why is this bad?
170 /// Not every byte slice is a valid UTF-8 string.
172 /// ### Known problems
173 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
174 /// as it needs to validate the input.
175 /// If you are certain that the input is always a valid UTF-8,
176 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
177 /// but has a semantically meaningful name.
178 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
180 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
181 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
185 /// let b: &[u8] = &[1_u8, 2_u8];
187 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
191 /// let _ = std::str::from_utf8(b).unwrap();
193 pub TRANSMUTE_BYTES_TO_STR,
195 "transmutes from a `&[u8]` to a `&str`"
198 declare_clippy_lint! {
200 /// Checks for transmutes from an integer to a `bool`.
202 /// ### Why is this bad?
203 /// This might result in an invalid in-memory representation of a `bool`.
209 /// let _: bool = std::mem::transmute(x); // where x: u8
213 /// let _: bool = x != 0;
215 pub TRANSMUTE_INT_TO_BOOL,
217 "transmutes from an integer to a `bool`"
220 declare_clippy_lint! {
222 /// Checks for transmutes from an integer to a float.
224 /// ### Why is this bad?
225 /// Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
231 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
235 /// let _: f32 = f32::from_bits(1_u32);
237 pub TRANSMUTE_INT_TO_FLOAT,
239 "transmutes from an integer to a float"
242 declare_clippy_lint! {
244 /// Checks for transmutes from a float to an integer.
246 /// ### Why is this bad?
247 /// Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
253 /// let _: u32 = std::mem::transmute(1f32);
257 /// let _: u32 = 1f32.to_bits();
259 pub TRANSMUTE_FLOAT_TO_INT,
261 "transmutes from a float to an integer"
264 declare_clippy_lint! {
266 /// Checks for transmutes from a pointer to a pointer, or
267 /// from a reference to a reference.
269 /// ### Why is this bad?
270 /// Transmutes are dangerous, and these can instead be
271 /// written as casts.
275 /// let ptr = &1u32 as *const u32;
277 /// // pointer-to-pointer transmute
278 /// let _: *const f32 = std::mem::transmute(ptr);
279 /// // ref-ref transmute
280 /// let _: &f32 = std::mem::transmute(&1u32);
282 /// // These can be respectively written:
283 /// let _ = ptr as *const f32;
284 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
286 pub TRANSMUTE_PTR_TO_PTR,
288 "transmutes from a pointer to a pointer / a reference to a reference"
291 declare_clippy_lint! {
293 /// Checks for transmutes between collections whose
294 /// types have different ABI, size or alignment.
296 /// ### Why is this bad?
297 /// This is undefined behavior.
299 /// ### Known problems
300 /// Currently, we cannot know whether a type is a
301 /// collection, so we just lint the ones that come with `std`.
305 /// // different size, therefore likely out-of-bounds memory access
306 /// // You absolutely do not want this in your code!
308 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
312 /// You must always iterate, map and collect the values:
315 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
317 pub UNSOUND_COLLECTION_TRANSMUTE,
319 "transmute between collections of layout-incompatible types"
322 declare_lint_pass!(Transmute => [
323 CROSSPOINTER_TRANSMUTE,
324 TRANSMUTE_PTR_TO_REF,
325 TRANSMUTE_PTR_TO_PTR,
328 TRANSMUTE_INT_TO_CHAR,
329 TRANSMUTE_BYTES_TO_STR,
330 TRANSMUTE_INT_TO_BOOL,
331 TRANSMUTE_INT_TO_FLOAT,
332 TRANSMUTE_FLOAT_TO_INT,
333 UNSOUND_COLLECTION_TRANSMUTE,
334 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
337 impl<'tcx> LateLintPass<'tcx> for Transmute {
338 #[allow(clippy::similar_names, clippy::too_many_lines)]
339 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
341 if let ExprKind::Call(path_expr, args) = e.kind;
342 if let ExprKind::Path(ref qpath) = path_expr.kind;
343 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
344 if cx.tcx.is_diagnostic_item(sym::transmute, def_id);
346 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
347 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
348 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
349 let const_context = in_constant(cx, e.hir_id);
351 let from_ty = cx.typeck_results().expr_ty(&args[0]);
352 let to_ty = cx.typeck_results().expr_ty(e);
354 // If useless_transmute is triggered, the other lints can be skipped.
355 if useless_transmute::check(cx, e, from_ty, to_ty, args) {
359 let mut linted = wrong_transmute::check(cx, e, from_ty, to_ty);
360 linted |= crosspointer_transmute::check(cx, e, from_ty, to_ty);
361 linted |= transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
362 linted |= transmute_int_to_char::check(cx, e, from_ty, to_ty, args);
363 linted |= transmute_ref_to_ref::check(cx, e, from_ty, to_ty, args, const_context);
364 linted |= transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, args);
365 linted |= transmute_int_to_bool::check(cx, e, from_ty, to_ty, args);
366 linted |= transmute_int_to_float::check(cx, e, from_ty, to_ty, args, const_context);
367 linted |= transmute_float_to_int::check(cx, e, from_ty, to_ty, args, const_context);
368 linted |= unsound_collection_transmute::check(cx, e, from_ty, to_ty);
371 transmutes_expressible_as_ptr_casts::check(cx, e, from_ty, to_ty, args);