2 is_normalizable, last_path_segment, match_def_path, paths, snippet, span_lint, span_lint_and_sugg,
3 span_lint_and_then, sugg,
5 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::{Expr, ExprKind, GenericArg, Mutability, QPath, TyKind, UnOp};
9 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_middle::ty::{self, Ty};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 declare_clippy_lint! {
15 /// **What it does:** Checks for transmutes that can't ever be correct on any
18 /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
20 /// **Known problems:** When accessing C, users might want to store pointer
21 /// sized objects in `extradata` arguments to save an allocation.
25 /// let ptr: *const T = core::intrinsics::transmute('x')
29 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
32 // FIXME: Move this to `complexity` again, after #5343 is fixed
33 declare_clippy_lint! {
34 /// **What it does:** Checks for transmutes to the original type of the object
35 /// and transmutes that could be a cast.
37 /// **Why is this bad?** Readability. The code tricks people into thinking that
38 /// something complex is going on.
40 /// **Known problems:** None.
44 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
46 pub USELESS_TRANSMUTE,
48 "transmutes that have the same to and from types or could be a cast/coercion"
51 declare_clippy_lint! {
52 /// **What it does:** Checks for transmutes between a type `T` and `*T`.
54 /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
55 /// pointer to that type.
57 /// **Known problems:** None.
61 /// core::intrinsics::transmute(t) // where the result type is the same as
64 pub CROSSPOINTER_TRANSMUTE,
66 "transmutes that have to or from types that are a pointer to the other"
69 declare_clippy_lint! {
70 /// **What it does:** Checks for transmutes from a pointer to a reference.
72 /// **Why is this bad?** This can always be rewritten with `&` and `*`.
74 /// **Known problems:** None.
79 /// let _: &T = std::mem::transmute(p); // where p: *const T
82 /// // can be written:
85 pub TRANSMUTE_PTR_TO_REF,
87 "transmutes from a pointer to a reference type"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for transmutes from an integer to a `char`.
93 /// **Why is this bad?** Not every integer is a Unicode scalar value.
95 /// **Known problems:**
96 /// - [`from_u32`] which this lint suggests using is slower than `transmute`
97 /// as it needs to validate the input.
98 /// If you are certain that the input is always a valid Unicode scalar value,
99 /// use [`from_u32_unchecked`] which is as fast as `transmute`
100 /// but has a semantically meaningful name.
101 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
103 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
104 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
110 /// let _: char = std::mem::transmute(x); // where x: u32
114 /// let _ = std::char::from_u32(x).unwrap();
116 pub TRANSMUTE_INT_TO_CHAR,
118 "transmutes from an integer to a `char`"
121 declare_clippy_lint! {
122 /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
124 /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
126 /// **Known problems:**
127 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
128 /// as it needs to validate the input.
129 /// If you are certain that the input is always a valid UTF-8,
130 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
131 /// but has a semantically meaningful name.
132 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
134 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
135 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
139 /// let b: &[u8] = &[1_u8, 2_u8];
141 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
145 /// let _ = std::str::from_utf8(b).unwrap();
147 pub TRANSMUTE_BYTES_TO_STR,
149 "transmutes from a `&[u8]` to a `&str`"
152 declare_clippy_lint! {
153 /// **What it does:** Checks for transmutes from an integer to a `bool`.
155 /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
157 /// **Known problems:** None.
163 /// let _: bool = std::mem::transmute(x); // where x: u8
167 /// let _: bool = x != 0;
169 pub TRANSMUTE_INT_TO_BOOL,
171 "transmutes from an integer to a `bool`"
174 declare_clippy_lint! {
175 /// **What it does:** Checks for transmutes from an integer to a float.
177 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
180 /// **Known problems:** None.
185 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
189 /// let _: f32 = f32::from_bits(1_u32);
191 pub TRANSMUTE_INT_TO_FLOAT,
193 "transmutes from an integer to a float"
196 declare_clippy_lint! {
197 /// **What it does:** Checks for transmutes from a float to an integer.
199 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
202 /// **Known problems:** None.
207 /// let _: u32 = std::mem::transmute(1f32);
211 /// let _: u32 = 1f32.to_bits();
213 pub TRANSMUTE_FLOAT_TO_INT,
215 "transmutes from a float to an integer"
218 declare_clippy_lint! {
219 /// **What it does:** Checks for transmutes from a pointer to a pointer, or
220 /// from a reference to a reference.
222 /// **Why is this bad?** Transmutes are dangerous, and these can instead be
223 /// written as casts.
225 /// **Known problems:** None.
229 /// let ptr = &1u32 as *const u32;
231 /// // pointer-to-pointer transmute
232 /// let _: *const f32 = std::mem::transmute(ptr);
233 /// // ref-ref transmute
234 /// let _: &f32 = std::mem::transmute(&1u32);
236 /// // These can be respectively written:
237 /// let _ = ptr as *const f32;
238 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
240 pub TRANSMUTE_PTR_TO_PTR,
242 "transmutes from a pointer to a pointer / a reference to a reference"
245 declare_clippy_lint! {
246 /// **What it does:** Checks for transmutes between collections whose
247 /// types have different ABI, size or alignment.
249 /// **Why is this bad?** This is undefined behavior.
251 /// **Known problems:** Currently, we cannot know whether a type is a
252 /// collection, so we just lint the ones that come with `std`.
256 /// // different size, therefore likely out-of-bounds memory access
257 /// // You absolutely do not want this in your code!
259 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
263 /// You must always iterate, map and collect the values:
266 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
268 pub UNSOUND_COLLECTION_TRANSMUTE,
270 "transmute between collections of layout-incompatible types"
272 declare_lint_pass!(Transmute => [
273 CROSSPOINTER_TRANSMUTE,
274 TRANSMUTE_PTR_TO_REF,
275 TRANSMUTE_PTR_TO_PTR,
278 TRANSMUTE_INT_TO_CHAR,
279 TRANSMUTE_BYTES_TO_STR,
280 TRANSMUTE_INT_TO_BOOL,
281 TRANSMUTE_INT_TO_FLOAT,
282 TRANSMUTE_FLOAT_TO_INT,
283 UNSOUND_COLLECTION_TRANSMUTE,
286 // used to check for UNSOUND_COLLECTION_TRANSMUTE
287 static COLLECTIONS: &[&[&str]] = &[
296 impl<'tcx> LateLintPass<'tcx> for Transmute {
297 #[allow(clippy::similar_names, clippy::too_many_lines)]
298 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
300 if let ExprKind::Call(ref path_expr, ref args) = e.kind;
301 if let ExprKind::Path(ref qpath) = path_expr.kind;
302 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
303 if match_def_path(cx, def_id, &paths::TRANSMUTE);
305 let from_ty = cx.typeck_results().expr_ty(&args[0]);
306 let to_ty = cx.typeck_results().expr_ty(e);
308 match (&from_ty.kind, &to_ty.kind) {
309 _ if from_ty == to_ty => span_lint(
313 &format!("transmute from a type (`{}`) to itself", from_ty),
315 (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => span_lint_and_then(
319 "transmute from a reference to a pointer",
321 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
322 let rty_and_mut = ty::TypeAndMut {
327 let sugg = if *ptr_ty == rty_and_mut {
330 arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
333 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
337 (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => span_lint_and_then(
341 "transmute from an integer to a pointer",
343 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
344 diag.span_suggestion(
347 arg.as_ty(&to_ty.to_string()).to_string(),
348 Applicability::Unspecified,
353 (ty::Float(_) | ty::Char, ty::Ref(..) | ty::RawPtr(_)) => span_lint(
357 &format!("transmute from a `{}` to a pointer", from_ty),
359 (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
361 CROSSPOINTER_TRANSMUTE,
364 "transmute from a type (`{}`) to the type that it points to (`{}`)",
368 (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
370 CROSSPOINTER_TRANSMUTE,
373 "transmute from a type (`{}`) to a pointer to that type (`{}`)",
377 (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
379 TRANSMUTE_PTR_TO_REF,
382 "transmute from a pointer type (`{}`) to a reference type \
387 let arg = sugg::Sugg::hir(cx, &args[0], "..");
388 let (deref, cast) = if *mutbl == Mutability::Mut {
394 let arg = if from_pty.ty == *to_ref_ty {
397 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
400 diag.span_suggestion(
403 sugg::make_unop(deref, arg).to_string(),
404 Applicability::Unspecified,
408 (ty::Int(ast::IntTy::I32) | ty::Uint(ast::UintTy::U32), &ty::Char) => {
411 TRANSMUTE_INT_TO_CHAR,
413 &format!("transmute from a `{}` to a `char`", from_ty),
415 let arg = sugg::Sugg::hir(cx, &args[0], "..");
416 let arg = if let ty::Int(_) = from_ty.kind {
417 arg.as_ty(ast::UintTy::U32.name_str())
421 diag.span_suggestion(
424 format!("std::char::from_u32({}).unwrap()", arg.to_string()),
425 Applicability::Unspecified,
430 (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
432 if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind, &ty_to.kind);
433 if let ty::Uint(ast::UintTy::U8) = slice_ty.kind;
434 if from_mutbl == to_mutbl;
436 let postfix = if *from_mutbl == Mutability::Mut {
444 TRANSMUTE_BYTES_TO_STR,
446 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
449 "std::str::from_utf8{}({}).unwrap()",
451 snippet(cx, args[0].span, ".."),
453 Applicability::Unspecified,
456 if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
459 TRANSMUTE_PTR_TO_PTR,
461 "transmute from a reference to a reference",
462 |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
463 let ty_from_and_mut = ty::TypeAndMut {
467 let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
469 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
470 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
471 let sugg = if *to_mutbl == Mutability::Mut {
472 sugg_paren.mut_addr_deref()
474 sugg_paren.addr_deref()
476 diag.span_suggestion(
480 Applicability::Unspecified,
488 (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
490 TRANSMUTE_PTR_TO_PTR,
492 "transmute from a pointer to a pointer",
494 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
495 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
496 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
500 (ty::Int(ast::IntTy::I8) | ty::Uint(ast::UintTy::U8), ty::Bool) => {
503 TRANSMUTE_INT_TO_BOOL,
505 &format!("transmute from a `{}` to a `bool`", from_ty),
507 let arg = sugg::Sugg::hir(cx, &args[0], "..");
508 let zero = sugg::Sugg::NonParen(Cow::from("0"));
509 diag.span_suggestion(
512 sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
513 Applicability::Unspecified,
518 (ty::Int(_) | ty::Uint(_), ty::Float(_)) => span_lint_and_then(
520 TRANSMUTE_INT_TO_FLOAT,
522 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
524 let arg = sugg::Sugg::hir(cx, &args[0], "..");
525 let arg = if let ty::Int(int_ty) = from_ty.kind {
528 int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
533 diag.span_suggestion(
536 format!("{}::from_bits({})", to_ty, arg.to_string()),
537 Applicability::Unspecified,
541 (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) => span_lint_and_then(
543 TRANSMUTE_FLOAT_TO_INT,
545 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
547 let mut expr = &args[0];
548 let mut arg = sugg::Sugg::hir(cx, expr, "..");
550 if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
555 // if the expression is a float literal and it is unsuffixed then
556 // add a suffix so the suggestion is valid and unambiguous
557 let op = format!("{}{}", arg, float_ty.name_str()).into();
558 if let ExprKind::Lit(lit) = &expr.kind;
559 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
562 sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
563 _ => arg = sugg::Sugg::NonParen(op)
568 arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
570 // cast the result of `to_bits` if `to_ty` is signed
571 arg = if let ty::Int(int_ty) = to_ty.kind {
572 arg.as_ty(int_ty.name_str().to_string())
577 diag.span_suggestion(
581 Applicability::Unspecified,
585 (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
586 if from_adt.did != to_adt.did ||
587 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
590 if from_substs.types().zip(to_substs.types())
591 .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
594 UNSOUND_COLLECTION_TRANSMUTE,
597 "transmute from `{}` to `{}` with mismatched layout is unsound",
611 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
612 /// not available , use
613 /// the type's `ToString` implementation. In weird cases it could lead to types
614 /// with invalid `'_`
615 /// lifetime, but it should be rare.
616 fn get_type_snippet(cx: &LateContext<'_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
617 let seg = last_path_segment(path);
619 if let Some(ref params) = seg.args;
620 if !params.parenthesized;
621 if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
622 GenericArg::Type(ty) => Some(ty),
625 if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
627 return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
631 to_ref_ty.to_string()
634 // check if the component types of the transmuted collection and the result have different ABI,
636 fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
637 let empty_param_env = ty::ParamEnv::empty();
638 // check if `from` and `to` are normalizable to avoid ICE (#4968)
639 if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
642 let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
643 let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
644 if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
645 from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
647 // no idea about layout, so don't lint