2 is_normalizable, last_path_segment, match_def_path, paths, snippet, span_lint, span_lint_and_then, sugg,
4 use if_chain::if_chain;
5 use rustc::ty::{self, Ty};
6 use rustc_errors::Applicability;
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 declare_clippy_lint! {
14 /// **What it does:** Checks for transmutes that can't ever be correct on any
17 /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
19 /// **Known problems:** When accessing C, users might want to store pointer
20 /// sized objects in `extradata` arguments to save an allocation.
24 /// let ptr: *const T = core::intrinsics::transmute('x')
28 "transmutes that are confusing at best, undefined behaviour at worst and always useless"
31 declare_clippy_lint! {
32 /// **What it does:** Checks for transmutes to the original type of the object
33 /// and transmutes that could be a cast.
35 /// **Why is this bad?** Readability. The code tricks people into thinking that
36 /// something complex is going on.
38 /// **Known problems:** None.
42 /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
44 pub USELESS_TRANSMUTE,
46 "transmutes that have the same to and from types or could be a cast/coercion"
49 declare_clippy_lint! {
50 /// **What it does:** Checks for transmutes between a type `T` and `*T`.
52 /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
53 /// pointer to that type.
55 /// **Known problems:** None.
59 /// core::intrinsics::transmute(t) // where the result type is the same as
62 pub CROSSPOINTER_TRANSMUTE,
64 "transmutes that have to or from types that are a pointer to the other"
67 declare_clippy_lint! {
68 /// **What it does:** Checks for transmutes from a pointer to a reference.
70 /// **Why is this bad?** This can always be rewritten with `&` and `*`.
72 /// **Known problems:** None.
77 /// let _: &T = std::mem::transmute(p); // where p: *const T
80 /// // can be written:
83 pub TRANSMUTE_PTR_TO_REF,
85 "transmutes from a pointer to a reference type"
88 declare_clippy_lint! {
89 /// **What it does:** Checks for transmutes from an integer to a `char`.
91 /// **Why is this bad?** Not every integer is a Unicode scalar value.
93 /// **Known problems:**
94 /// - [`from_u32`] which this lint suggests using is slower than `transmute`
95 /// as it needs to validate the input.
96 /// If you are certain that the input is always a valid Unicode scalar value,
97 /// use [`from_u32_unchecked`] which is as fast as `transmute`
98 /// but has a semantically meaningful name.
99 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
101 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
102 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
108 /// let _: char = std::mem::transmute(x); // where x: u32
112 /// let _ = std::char::from_u32(x).unwrap();
114 pub TRANSMUTE_INT_TO_CHAR,
116 "transmutes from an integer to a `char`"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
122 /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
124 /// **Known problems:**
125 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
126 /// as it needs to validate the input.
127 /// If you are certain that the input is always a valid UTF-8,
128 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
129 /// but has a semantically meaningful name.
130 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
132 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
133 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
137 /// let b: &[u8] = &[1_u8, 2_u8];
139 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
143 /// let _ = std::str::from_utf8(b).unwrap();
145 pub TRANSMUTE_BYTES_TO_STR,
147 "transmutes from a `&[u8]` to a `&str`"
150 declare_clippy_lint! {
151 /// **What it does:** Checks for transmutes from an integer to a `bool`.
153 /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
155 /// **Known problems:** None.
161 /// let _: bool = std::mem::transmute(x); // where x: u8
165 /// let _: bool = x != 0;
167 pub TRANSMUTE_INT_TO_BOOL,
169 "transmutes from an integer to a `bool`"
172 declare_clippy_lint! {
173 /// **What it does:** Checks for transmutes from an integer to a float.
175 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
178 /// **Known problems:** None.
183 /// let _: f32 = std::mem::transmute(1_u32); // where x: u32
187 /// let _: f32 = f32::from_bits(1_u32);
189 pub TRANSMUTE_INT_TO_FLOAT,
191 "transmutes from an integer to a float"
194 declare_clippy_lint! {
195 /// **What it does:** Checks for transmutes from a float to an integer.
197 /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
200 /// **Known problems:** None.
205 /// let _: u32 = std::mem::transmute(1f32);
209 /// let _: u32 = 1f32.to_bits();
211 pub TRANSMUTE_FLOAT_TO_INT,
213 "transmutes from a float to an integer"
216 declare_clippy_lint! {
217 /// **What it does:** Checks for transmutes from a pointer to a pointer, or
218 /// from a reference to a reference.
220 /// **Why is this bad?** Transmutes are dangerous, and these can instead be
221 /// written as casts.
223 /// **Known problems:** None.
227 /// let ptr = &1u32 as *const u32;
229 /// // pointer-to-pointer transmute
230 /// let _: *const f32 = std::mem::transmute(ptr);
231 /// // ref-ref transmute
232 /// let _: &f32 = std::mem::transmute(&1u32);
234 /// // These can be respectively written:
235 /// let _ = ptr as *const f32;
236 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
238 pub TRANSMUTE_PTR_TO_PTR,
240 "transmutes from a pointer to a pointer / a reference to a reference"
243 declare_clippy_lint! {
244 /// **What it does:** Checks for transmutes between collections whose
245 /// types have different ABI, size or alignment.
247 /// **Why is this bad?** This is undefined behavior.
249 /// **Known problems:** Currently, we cannot know whether a type is a
250 /// collection, so we just lint the ones that come with `std`.
254 /// // different size, therefore likely out-of-bounds memory access
255 /// // You absolutely do not want this in your code!
257 /// std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
261 /// You must always iterate, map and collect the values:
264 /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
266 pub UNSOUND_COLLECTION_TRANSMUTE,
268 "transmute between collections of layout-incompatible types"
270 declare_lint_pass!(Transmute => [
271 CROSSPOINTER_TRANSMUTE,
272 TRANSMUTE_PTR_TO_REF,
273 TRANSMUTE_PTR_TO_PTR,
276 TRANSMUTE_INT_TO_CHAR,
277 TRANSMUTE_BYTES_TO_STR,
278 TRANSMUTE_INT_TO_BOOL,
279 TRANSMUTE_INT_TO_FLOAT,
280 TRANSMUTE_FLOAT_TO_INT,
281 UNSOUND_COLLECTION_TRANSMUTE,
284 // used to check for UNSOUND_COLLECTION_TRANSMUTE
285 static COLLECTIONS: &[&[&str]] = &[
294 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Transmute {
295 #[allow(clippy::similar_names, clippy::too_many_lines)]
296 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
298 if let ExprKind::Call(ref path_expr, ref args) = e.kind;
299 if let ExprKind::Path(ref qpath) = path_expr.kind;
300 if let Some(def_id) = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id();
301 if match_def_path(cx, def_id, &paths::TRANSMUTE);
303 let from_ty = cx.tables.expr_ty(&args[0]);
304 let to_ty = cx.tables.expr_ty(e);
306 match (&from_ty.kind, &to_ty.kind) {
307 _ if from_ty == to_ty => span_lint(
311 &format!("transmute from a type (`{}`) to itself", from_ty),
313 (&ty::Ref(_, rty, rty_mutbl), &ty::RawPtr(ptr_ty)) => span_lint_and_then(
317 "transmute from a reference to a pointer",
319 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
320 let rty_and_mut = ty::TypeAndMut {
325 let sugg = if ptr_ty == rty_and_mut {
328 arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
331 db.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
335 (&ty::Int(_), &ty::RawPtr(_)) | (&ty::Uint(_), &ty::RawPtr(_)) => span_lint_and_then(
339 "transmute from an integer to a pointer",
341 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
345 arg.as_ty(&to_ty.to_string()).to_string(),
346 Applicability::Unspecified,
351 (&ty::Float(_), &ty::Ref(..))
352 | (&ty::Float(_), &ty::RawPtr(_))
353 | (&ty::Char, &ty::Ref(..))
354 | (&ty::Char, &ty::RawPtr(_)) => span_lint(
358 &format!("transmute from a `{}` to a pointer", from_ty),
360 (&ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
362 CROSSPOINTER_TRANSMUTE,
365 "transmute from a type (`{}`) to the type that it points to (`{}`)",
369 (_, &ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
371 CROSSPOINTER_TRANSMUTE,
374 "transmute from a type (`{}`) to a pointer to that type (`{}`)",
378 (&ty::RawPtr(from_pty), &ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
380 TRANSMUTE_PTR_TO_REF,
383 "transmute from a pointer type (`{}`) to a reference type \
388 let arg = sugg::Sugg::hir(cx, &args[0], "..");
389 let (deref, cast) = if mutbl == Mutability::Mut {
395 let arg = if from_pty.ty == to_ref_ty {
398 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
404 sugg::make_unop(deref, arg).to_string(),
405 Applicability::Unspecified,
409 (&ty::Int(ast::IntTy::I32), &ty::Char) | (&ty::Uint(ast::UintTy::U32), &ty::Char) => {
412 TRANSMUTE_INT_TO_CHAR,
414 &format!("transmute from a `{}` to a `char`", from_ty),
416 let arg = sugg::Sugg::hir(cx, &args[0], "..");
417 let arg = if let ty::Int(_) = from_ty.kind {
418 arg.as_ty(ast::UintTy::U32.name_str())
425 format!("std::char::from_u32({}).unwrap()", arg.to_string()),
426 Applicability::Unspecified,
431 (&ty::Ref(_, ty_from, from_mutbl), &ty::Ref(_, ty_to, to_mutbl)) => {
433 if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind, &ty_to.kind);
434 if let ty::Uint(ast::UintTy::U8) = slice_ty.kind;
435 if from_mutbl == to_mutbl;
437 let postfix = if from_mutbl == Mutability::Mut {
445 TRANSMUTE_BYTES_TO_STR,
447 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
453 "std::str::from_utf8{}({}).unwrap()",
455 snippet(cx, args[0].span, ".."),
457 Applicability::Unspecified,
462 if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
465 TRANSMUTE_PTR_TO_PTR,
467 "transmute from a reference to a reference",
468 |db| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
469 let ty_from_and_mut = ty::TypeAndMut {
473 let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: to_mutbl };
475 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
476 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
477 let sugg = if to_mutbl == Mutability::Mut {
478 sugg_paren.mut_addr_deref()
480 sugg_paren.addr_deref()
486 Applicability::Unspecified,
494 (&ty::RawPtr(_), &ty::RawPtr(to_ty)) => span_lint_and_then(
496 TRANSMUTE_PTR_TO_PTR,
498 "transmute from a pointer to a pointer",
500 if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
501 let sugg = arg.as_ty(cx.tcx.mk_ptr(to_ty));
502 db.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
506 (&ty::Int(ast::IntTy::I8), &ty::Bool) | (&ty::Uint(ast::UintTy::U8), &ty::Bool) => {
509 TRANSMUTE_INT_TO_BOOL,
511 &format!("transmute from a `{}` to a `bool`", from_ty),
513 let arg = sugg::Sugg::hir(cx, &args[0], "..");
514 let zero = sugg::Sugg::NonParen(Cow::from("0"));
518 sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
519 Applicability::Unspecified,
524 (&ty::Int(_), &ty::Float(_)) | (&ty::Uint(_), &ty::Float(_)) => span_lint_and_then(
526 TRANSMUTE_INT_TO_FLOAT,
528 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
530 let arg = sugg::Sugg::hir(cx, &args[0], "..");
531 let arg = if let ty::Int(int_ty) = from_ty.kind {
534 int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
542 format!("{}::from_bits({})", to_ty, arg.to_string()),
543 Applicability::Unspecified,
547 (&ty::Float(float_ty), &ty::Int(_)) | (&ty::Float(float_ty), &ty::Uint(_)) => span_lint_and_then(
549 TRANSMUTE_FLOAT_TO_INT,
551 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
553 let mut expr = &args[0];
554 let mut arg = sugg::Sugg::hir(cx, expr, "..");
556 if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
561 // if the expression is a float literal and it is unsuffixed then
562 // add a suffix so the suggestion is valid and unambiguous
563 let op = format!("{}{}", arg, float_ty.name_str()).into();
564 if let ExprKind::Lit(lit) = &expr.kind;
565 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
568 sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
569 _ => arg = sugg::Sugg::NonParen(op)
574 arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
576 // cast the result of `to_bits` if `to_ty` is signed
577 arg = if let ty::Int(int_ty) = to_ty.kind {
578 arg.as_ty(int_ty.name_str().to_string())
587 Applicability::Unspecified,
591 (&ty::Adt(ref from_adt, ref from_substs), &ty::Adt(ref to_adt, ref to_substs)) => {
592 if from_adt.did != to_adt.did ||
593 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
596 if from_substs.types().zip(to_substs.types())
597 .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
600 UNSOUND_COLLECTION_TRANSMUTE,
603 "transmute from `{}` to `{}` with mismatched layout is unsound",
617 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
618 /// not available , use
619 /// the type's `ToString` implementation. In weird cases it could lead to types
620 /// with invalid `'_`
621 /// lifetime, but it should be rare.
622 fn get_type_snippet(cx: &LateContext<'_, '_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
623 let seg = last_path_segment(path);
625 if let Some(ref params) = seg.args;
626 if !params.parenthesized;
627 if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
628 GenericArg::Type(ty) => Some(ty),
631 if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
633 return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
637 to_ref_ty.to_string()
640 // check if the component types of the transmuted collection and the result have different ABI,
642 fn is_layout_incompatible<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
643 let empty_param_env = ty::ParamEnv::empty();
644 // check if `from` and `to` are normalizable to avoid ICE (#4968)
645 if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
648 let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
649 let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
650 if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
651 from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
653 // no idea about layout, so don't lint