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;
18 in_constant, match_def_path, paths, snippet, span_lint, span_lint_and_sugg, span_lint_and_then, sugg,
20 use if_chain::if_chain;
22 use rustc_errors::Applicability;
23 use rustc_hir::{Expr, ExprKind, Mutability, UnOp};
24 use rustc_lint::{LateContext, LateLintPass};
26 use rustc_session::{declare_lint_pass, declare_tool_lint};
29 declare_clippy_lint! {
30 /// **What it does:** Checks for transmutes that can't ever be correct on any
33 /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
35 /// **Known problems:** When accessing C, users might want to store pointer
36 /// sized objects in `extradata` arguments to save an allocation.
40 /// let ptr: *const T = core::intrinsics::transmute('x')
44 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
47 // FIXME: Move this to `complexity` again, after #5343 is fixed
48 declare_clippy_lint! {
49 /// **What it does:** Checks for transmutes to the original type of the object
50 /// and transmutes that could be a cast.
52 /// **Why is this bad?** Readability. The code tricks people into thinking that
53 /// something complex is going on.
55 /// **Known problems:** None.
59 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
61 pub USELESS_TRANSMUTE,
63 "transmutes that have the same to and from types or could be a cast/coercion"
66 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
67 declare_clippy_lint! {
68 /// **What it does:**Checks for transmutes that could be a pointer cast.
70 /// **Why is this bad?** Readability. The code tricks people into thinking that
71 /// something complex is going on.
73 /// **Known problems:** None.
78 /// # let p: *const [i32] = &[];
79 /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
83 /// # let p: *const [i32] = &[];
84 /// p as *const [u16];
86 pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
88 "transmutes that could be a pointer cast"
91 declare_clippy_lint! {
92 /// **What it does:** Checks for transmutes between a type `T` and `*T`.
94 /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
95 /// pointer to that type.
97 /// **Known problems:** None.
101 /// core::intrinsics::transmute(t) // where the result type is the same as
102 /// // `*t` or `&t`'s
104 pub CROSSPOINTER_TRANSMUTE,
106 "transmutes that have to or from types that are a pointer to the other"
109 declare_clippy_lint! {
110 /// **What it does:** Checks for transmutes from a pointer to a reference.
112 /// **Why is this bad?** This can always be rewritten with `&` and `*`.
114 /// **Known problems:**
115 /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
116 /// while dereferencing raw pointer is not stable yet.
117 /// If you need to do this in those places,
118 /// you would have to use `transmute` instead.
123 /// let _: &T = std::mem::transmute(p); // where p: *const T
126 /// // can be written:
129 pub TRANSMUTE_PTR_TO_REF,
131 "transmutes from a pointer to a reference type"
134 declare_clippy_lint! {
135 /// **What it does:** Checks for transmutes from an integer to a `char`.
137 /// **Why is this bad?** 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! {
166 /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
168 /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
170 /// **Known problems:**
171 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
172 /// as it needs to validate the input.
173 /// If you are certain that the input is always a valid UTF-8,
174 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
175 /// but has a semantically meaningful name.
176 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
178 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
179 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
183 /// let b: &[u8] = &[1_u8, 2_u8];
185 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
189 /// let _ = std::str::from_utf8(b).unwrap();
191 pub TRANSMUTE_BYTES_TO_STR,
193 "transmutes from a `&[u8]` to a `&str`"
196 declare_clippy_lint! {
197 /// **What it does:** Checks for transmutes from an integer to a `bool`.
199 /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
201 /// **Known problems:** None.
207 /// let _: bool = std::mem::transmute(x); // where x: u8
211 /// let _: bool = x != 0;
213 pub TRANSMUTE_INT_TO_BOOL,
215 "transmutes from an integer to a `bool`"
218 declare_clippy_lint! {
219 /// **What it does:** Checks for transmutes from an integer to a float.
221 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
224 /// **Known problems:** None.
229 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
233 /// let _: f32 = f32::from_bits(1_u32);
235 pub TRANSMUTE_INT_TO_FLOAT,
237 "transmutes from an integer to a float"
240 declare_clippy_lint! {
241 /// **What it does:** Checks for transmutes from a float to an integer.
243 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
246 /// **Known problems:** None.
251 /// let _: u32 = std::mem::transmute(1f32);
255 /// let _: u32 = 1f32.to_bits();
257 pub TRANSMUTE_FLOAT_TO_INT,
259 "transmutes from a float to an integer"
262 declare_clippy_lint! {
263 /// **What it does:** Checks for transmutes from a pointer to a pointer, or
264 /// from a reference to a reference.
266 /// **Why is this bad?** Transmutes are dangerous, and these can instead be
267 /// written as casts.
269 /// **Known problems:** None.
273 /// let ptr = &1u32 as *const u32;
275 /// // pointer-to-pointer transmute
276 /// let _: *const f32 = std::mem::transmute(ptr);
277 /// // ref-ref transmute
278 /// let _: &f32 = std::mem::transmute(&1u32);
280 /// // These can be respectively written:
281 /// let _ = ptr as *const f32;
282 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
284 pub TRANSMUTE_PTR_TO_PTR,
286 "transmutes from a pointer to a pointer / a reference to a reference"
289 declare_clippy_lint! {
290 /// **What it does:** Checks for transmutes between collections whose
291 /// types have different ABI, size or alignment.
293 /// **Why is this bad?** This is undefined behavior.
295 /// **Known problems:** Currently, we cannot know whether a type is a
296 /// collection, so we just lint the ones that come with `std`.
300 /// // different size, therefore likely out-of-bounds memory access
301 /// // You absolutely do not want this in your code!
303 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
307 /// You must always iterate, map and collect the values:
310 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
312 pub UNSOUND_COLLECTION_TRANSMUTE,
314 "transmute between collections of layout-incompatible types"
317 declare_lint_pass!(Transmute => [
318 CROSSPOINTER_TRANSMUTE,
319 TRANSMUTE_PTR_TO_REF,
320 TRANSMUTE_PTR_TO_PTR,
323 TRANSMUTE_INT_TO_CHAR,
324 TRANSMUTE_BYTES_TO_STR,
325 TRANSMUTE_INT_TO_BOOL,
326 TRANSMUTE_INT_TO_FLOAT,
327 TRANSMUTE_FLOAT_TO_INT,
328 UNSOUND_COLLECTION_TRANSMUTE,
329 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
332 impl<'tcx> LateLintPass<'tcx> for Transmute {
333 #[allow(clippy::similar_names, clippy::too_many_lines)]
334 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
336 if let ExprKind::Call(ref path_expr, ref args) = e.kind;
337 if let ExprKind::Path(ref qpath) = path_expr.kind;
338 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
339 if match_def_path(cx, def_id, &paths::TRANSMUTE);
341 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
342 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
343 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
344 let const_context = in_constant(cx, e.hir_id);
346 let from_ty = cx.typeck_results().expr_ty(&args[0]);
347 let to_ty = cx.typeck_results().expr_ty(e);
349 let triggered = useless_transmute::check(cx, e, from_ty, to_ty, args);
353 let triggered = wrong_transmute::check(cx, e, from_ty, to_ty);
357 let triggered = crosspointer_transmute::check(cx, e, from_ty, to_ty);
361 let triggered = transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
365 let triggered = transmute_int_to_char::check(cx, e, from_ty, to_ty, args);
369 let triggered = transmute_ref_to_ref::check(cx, e, from_ty, to_ty, args, const_context);
373 let triggered = transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, args);
377 let triggered = transmute_int_to_bool::check(cx, e, from_ty, to_ty, args);
381 let triggered = transmute_int_to_float::check(cx, e, from_ty, to_ty, args, const_context);
385 let triggered = transmute_float_to_int::check(cx, e, from_ty, to_ty, args, const_context);
389 let triggered = unsound_collection_transmute::check(cx, e, from_ty, to_ty);
393 let triggered = transmutes_expressible_as_ptr_casts::check(cx, e, from_ty, to_ty, args);