2 in_constant, 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, cast::CastKind, Ty};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use rustc_span::DUMMY_SP;
13 use rustc_typeck::check::{cast::CastCheck, FnCtxt, Inherited};
16 declare_clippy_lint! {
17 /// **What it does:** Checks for transmutes that can't ever be correct on any
20 /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
22 /// **Known problems:** When accessing C, users might want to store pointer
23 /// sized objects in `extradata` arguments to save an allocation.
27 /// let ptr: *const T = core::intrinsics::transmute('x')
31 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
34 // FIXME: Move this to `complexity` again, after #5343 is fixed
35 declare_clippy_lint! {
36 /// **What it does:** Checks for transmutes to the original type of the object
37 /// and transmutes that could be a cast.
39 /// **Why is this bad?** Readability. The code tricks people into thinking that
40 /// something complex is going on.
42 /// **Known problems:** None.
46 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
48 pub USELESS_TRANSMUTE,
50 "transmutes that have the same to and from types or could be a cast/coercion"
53 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
54 declare_clippy_lint! {
55 /// **What it does:**Checks for transmutes that could be a pointer cast.
57 /// **Why is this bad?** Readability. The code tricks people into thinking that
58 /// something complex is going on.
60 /// **Known problems:** None.
65 /// # let p: *const [i32] = &[];
66 /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
70 /// # let p: *const [i32] = &[];
71 /// p as *const [u16];
73 pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
75 "transmutes that could be a pointer cast"
78 declare_clippy_lint! {
79 /// **What it does:** Checks for transmutes between a type `T` and `*T`.
81 /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
82 /// pointer to that type.
84 /// **Known problems:** None.
88 /// core::intrinsics::transmute(t) // where the result type is the same as
91 pub CROSSPOINTER_TRANSMUTE,
93 "transmutes that have to or from types that are a pointer to the other"
96 declare_clippy_lint! {
97 /// **What it does:** Checks for transmutes from a pointer to a reference.
99 /// **Why is this bad?** This can always be rewritten with `&` and `*`.
101 /// **Known problems:**
102 /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
103 /// while dereferencing raw pointer is not stable yet.
104 /// If you need to do this in those places,
105 /// you would have to use `transmute` instead.
110 /// let _: &T = std::mem::transmute(p); // where p: *const T
113 /// // can be written:
116 pub TRANSMUTE_PTR_TO_REF,
118 "transmutes from a pointer to a reference type"
121 declare_clippy_lint! {
122 /// **What it does:** Checks for transmutes from an integer to a `char`.
124 /// **Why is this bad?** Not every integer is a Unicode scalar value.
126 /// **Known problems:**
127 /// - [`from_u32`] 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 Unicode scalar value,
130 /// use [`from_u32_unchecked`] which is as fast as `transmute`
131 /// but has a semantically meaningful name.
132 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
134 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
135 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
141 /// let _: char = std::mem::transmute(x); // where x: u32
145 /// let _ = std::char::from_u32(x).unwrap();
147 pub TRANSMUTE_INT_TO_CHAR,
149 "transmutes from an integer to a `char`"
152 declare_clippy_lint! {
153 /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
155 /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
157 /// **Known problems:**
158 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
159 /// as it needs to validate the input.
160 /// If you are certain that the input is always a valid UTF-8,
161 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
162 /// but has a semantically meaningful name.
163 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
165 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
166 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
170 /// let b: &[u8] = &[1_u8, 2_u8];
172 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
176 /// let _ = std::str::from_utf8(b).unwrap();
178 pub TRANSMUTE_BYTES_TO_STR,
180 "transmutes from a `&[u8]` to a `&str`"
183 declare_clippy_lint! {
184 /// **What it does:** Checks for transmutes from an integer to a `bool`.
186 /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
188 /// **Known problems:** None.
194 /// let _: bool = std::mem::transmute(x); // where x: u8
198 /// let _: bool = x != 0;
200 pub TRANSMUTE_INT_TO_BOOL,
202 "transmutes from an integer to a `bool`"
205 declare_clippy_lint! {
206 /// **What it does:** Checks for transmutes from an integer to a float.
208 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
211 /// **Known problems:** None.
216 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
220 /// let _: f32 = f32::from_bits(1_u32);
222 pub TRANSMUTE_INT_TO_FLOAT,
224 "transmutes from an integer to a float"
227 declare_clippy_lint! {
228 /// **What it does:** Checks for transmutes from a float to an integer.
230 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
233 /// **Known problems:** None.
238 /// let _: u32 = std::mem::transmute(1f32);
242 /// let _: u32 = 1f32.to_bits();
244 pub TRANSMUTE_FLOAT_TO_INT,
246 "transmutes from a float to an integer"
249 declare_clippy_lint! {
250 /// **What it does:** Checks for transmutes from a pointer to a pointer, or
251 /// from a reference to a reference.
253 /// **Why is this bad?** Transmutes are dangerous, and these can instead be
254 /// written as casts.
256 /// **Known problems:** None.
260 /// let ptr = &1u32 as *const u32;
262 /// // pointer-to-pointer transmute
263 /// let _: *const f32 = std::mem::transmute(ptr);
264 /// // ref-ref transmute
265 /// let _: &f32 = std::mem::transmute(&1u32);
267 /// // These can be respectively written:
268 /// let _ = ptr as *const f32;
269 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
271 pub TRANSMUTE_PTR_TO_PTR,
273 "transmutes from a pointer to a pointer / a reference to a reference"
276 declare_clippy_lint! {
277 /// **What it does:** Checks for transmutes between collections whose
278 /// types have different ABI, size or alignment.
280 /// **Why is this bad?** This is undefined behavior.
282 /// **Known problems:** Currently, we cannot know whether a type is a
283 /// collection, so we just lint the ones that come with `std`.
287 /// // different size, therefore likely out-of-bounds memory access
288 /// // You absolutely do not want this in your code!
290 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
294 /// You must always iterate, map and collect the values:
297 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
299 pub UNSOUND_COLLECTION_TRANSMUTE,
301 "transmute between collections of layout-incompatible types"
304 declare_lint_pass!(Transmute => [
305 CROSSPOINTER_TRANSMUTE,
306 TRANSMUTE_PTR_TO_REF,
307 TRANSMUTE_PTR_TO_PTR,
310 TRANSMUTE_INT_TO_CHAR,
311 TRANSMUTE_BYTES_TO_STR,
312 TRANSMUTE_INT_TO_BOOL,
313 TRANSMUTE_INT_TO_FLOAT,
314 TRANSMUTE_FLOAT_TO_INT,
315 UNSOUND_COLLECTION_TRANSMUTE,
316 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
319 // used to check for UNSOUND_COLLECTION_TRANSMUTE
320 static COLLECTIONS: &[&[&str]] = &[
329 impl<'tcx> LateLintPass<'tcx> for Transmute {
330 #[allow(clippy::similar_names, clippy::too_many_lines)]
331 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
333 if let ExprKind::Call(ref path_expr, ref args) = e.kind;
334 if let ExprKind::Path(ref qpath) = path_expr.kind;
335 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
336 if match_def_path(cx, def_id, &paths::TRANSMUTE);
338 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
339 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
340 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
341 let const_context = in_constant(cx, e.hir_id);
343 let from_ty = cx.typeck_results().expr_ty(&args[0]);
344 let to_ty = cx.typeck_results().expr_ty(e);
346 match (&from_ty.kind(), &to_ty.kind()) {
347 _ if from_ty == to_ty => span_lint(
351 &format!("transmute from a type (`{}`) to itself", from_ty),
353 (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => span_lint_and_then(
357 "transmute from a reference to a pointer",
359 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
360 let rty_and_mut = ty::TypeAndMut {
365 let sugg = if *ptr_ty == rty_and_mut {
368 arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
371 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
375 (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => span_lint_and_then(
379 "transmute from an integer to a pointer",
381 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
382 diag.span_suggestion(
385 arg.as_ty(&to_ty.to_string()).to_string(),
386 Applicability::Unspecified,
391 (ty::Float(_) | ty::Char, ty::Ref(..) | ty::RawPtr(_)) => span_lint(
395 &format!("transmute from a `{}` to a pointer", from_ty),
397 (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
399 CROSSPOINTER_TRANSMUTE,
402 "transmute from a type (`{}`) to the type that it points to (`{}`)",
406 (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
408 CROSSPOINTER_TRANSMUTE,
411 "transmute from a type (`{}`) to a pointer to that type (`{}`)",
415 (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
417 TRANSMUTE_PTR_TO_REF,
420 "transmute from a pointer type (`{}`) to a reference type \
425 let arg = sugg::Sugg::hir(cx, &args[0], "..");
426 let (deref, cast) = if *mutbl == Mutability::Mut {
432 let arg = if from_pty.ty == *to_ref_ty {
435 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
438 diag.span_suggestion(
441 sugg::make_unop(deref, arg).to_string(),
442 Applicability::Unspecified,
446 (ty::Int(ty::IntTy::I32) | ty::Uint(ty::UintTy::U32), &ty::Char) => {
449 TRANSMUTE_INT_TO_CHAR,
451 &format!("transmute from a `{}` to a `char`", from_ty),
453 let arg = sugg::Sugg::hir(cx, &args[0], "..");
454 let arg = if let ty::Int(_) = from_ty.kind() {
455 arg.as_ty(ast::UintTy::U32.name_str())
459 diag.span_suggestion(
462 format!("std::char::from_u32({}).unwrap()", arg.to_string()),
463 Applicability::Unspecified,
468 (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
470 if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind(), &ty_to.kind());
471 if let ty::Uint(ty::UintTy::U8) = slice_ty.kind();
472 if from_mutbl == to_mutbl;
474 let postfix = if *from_mutbl == Mutability::Mut {
482 TRANSMUTE_BYTES_TO_STR,
484 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
487 "std::str::from_utf8{}({}).unwrap()",
489 snippet(cx, args[0].span, ".."),
491 Applicability::Unspecified,
494 if (cx.tcx.erase_regions(from_ty) != cx.tcx.erase_regions(to_ty))
498 TRANSMUTE_PTR_TO_PTR,
500 "transmute from a reference to a reference",
501 |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
502 let ty_from_and_mut = ty::TypeAndMut {
506 let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
508 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
509 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
510 let sugg = if *to_mutbl == Mutability::Mut {
511 sugg_paren.mut_addr_deref()
513 sugg_paren.addr_deref()
515 diag.span_suggestion(
519 Applicability::Unspecified,
527 (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
529 TRANSMUTE_PTR_TO_PTR,
531 "transmute from a pointer to a pointer",
533 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
534 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
535 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
539 (ty::Int(ty::IntTy::I8) | ty::Uint(ty::UintTy::U8), ty::Bool) => {
542 TRANSMUTE_INT_TO_BOOL,
544 &format!("transmute from a `{}` to a `bool`", from_ty),
546 let arg = sugg::Sugg::hir(cx, &args[0], "..");
547 let zero = sugg::Sugg::NonParen(Cow::from("0"));
548 diag.span_suggestion(
551 sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
552 Applicability::Unspecified,
557 (ty::Int(_) | ty::Uint(_), ty::Float(_)) if !const_context => span_lint_and_then(
559 TRANSMUTE_INT_TO_FLOAT,
561 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
563 let arg = sugg::Sugg::hir(cx, &args[0], "..");
564 let arg = if let ty::Int(int_ty) = from_ty.kind() {
567 int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
572 diag.span_suggestion(
575 format!("{}::from_bits({})", to_ty, arg.to_string()),
576 Applicability::Unspecified,
580 (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) if !const_context => span_lint_and_then(
582 TRANSMUTE_FLOAT_TO_INT,
584 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
586 let mut expr = &args[0];
587 let mut arg = sugg::Sugg::hir(cx, expr, "..");
589 if let ExprKind::Unary(UnOp::Neg, inner_expr) = &expr.kind {
594 // if the expression is a float literal and it is unsuffixed then
595 // add a suffix so the suggestion is valid and unambiguous
596 let op = format!("{}{}", arg, float_ty.name_str()).into();
597 if let ExprKind::Lit(lit) = &expr.kind;
598 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
601 sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
602 _ => arg = sugg::Sugg::NonParen(op)
607 arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
609 // cast the result of `to_bits` if `to_ty` is signed
610 arg = if let ty::Int(int_ty) = to_ty.kind() {
611 arg.as_ty(int_ty.name_str().to_string())
616 diag.span_suggestion(
620 Applicability::Unspecified,
624 (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
625 if from_adt.did != to_adt.did ||
626 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
629 if from_substs.types().zip(to_substs.types())
630 .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
633 UNSOUND_COLLECTION_TRANSMUTE,
636 "transmute from `{}` to `{}` with mismatched layout is unsound",
643 (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
645 TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
648 "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
653 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
654 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
655 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);
668 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
669 /// not available , use
670 /// the type's `ToString` implementation. In weird cases it could lead to types
671 /// with invalid `'_`
672 /// lifetime, but it should be rare.
673 fn get_type_snippet(cx: &LateContext<'_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
674 let seg = last_path_segment(path);
676 if let Some(ref params) = seg.args;
677 if !params.parenthesized;
678 if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
679 GenericArg::Type(ty) => Some(ty),
682 if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
684 return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
688 to_ref_ty.to_string()
691 // check if the component types of the transmuted collection and the result have different ABI,
693 fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
694 let empty_param_env = ty::ParamEnv::empty();
695 // check if `from` and `to` are normalizable to avoid ICE (#4968)
696 if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
699 let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
700 let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
701 if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
702 from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
704 // no idea about layout, so don't lint
709 /// Check if the type conversion can be expressed as a pointer cast, instead of
710 /// a transmute. In certain cases, including some invalid casts from array
711 /// references to pointers, this may cause additional errors to be emitted and/or
712 /// ICE error messages. This function will panic if that occurs.
713 fn can_be_expressed_as_pointer_cast<'tcx>(
714 cx: &LateContext<'tcx>,
719 use CastKind::{AddrPtrCast, ArrayPtrCast, FnPtrAddrCast, FnPtrPtrCast, PtrAddrCast, PtrPtrCast};
721 check_cast(cx, e, from_ty, to_ty),
722 Some(PtrPtrCast | PtrAddrCast | AddrPtrCast | ArrayPtrCast | FnPtrPtrCast | FnPtrAddrCast)
726 /// If a cast from `from_ty` to `to_ty` is valid, returns an Ok containing the kind of
727 /// the cast. In certain cases, including some invalid casts from array references
728 /// to pointers, this may cause additional errors to be emitted and/or ICE error
729 /// messages. This function will panic if that occurs.
730 fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> Option<CastKind> {
731 let hir_id = e.hir_id;
732 let local_def_id = hir_id.owner;
734 Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
735 let fn_ctxt = FnCtxt::new(&inherited, cx.param_env, hir_id);
737 // If we already have errors, we can't be sure we can pointer cast.
739 !fn_ctxt.errors_reported_since_creation(),
740 "Newly created FnCtxt contained errors"
743 if let Ok(check) = CastCheck::new(
744 &fn_ctxt, e, from_ty, to_ty,
745 // We won't show any error to the user, so we don't care what the span is here.
748 let res = check.do_check(&fn_ctxt);
750 // do_check's documentation says that it might return Ok and create
751 // errors in the fcx instead of returing Err in some cases. Those cases
752 // should be filtered out before getting here.
754 !fn_ctxt.errors_reported_since_creation(),
755 "`fn_ctxt` contained errors after cast check!"