clippy_lints/src/transmute/mod.rs

   1 mod crosspointer_transmute;
   2 mod transmute_int_to_char;
   3 mod transmute_ptr_to_ref;
   4 mod useless_transmute;
   5 mod utils;
   6 mod wrong_transmute;
   7
   8 use utils::*;
   9
  10 use crate::utils::{
  11     in_constant, match_def_path, paths, snippet, span_lint, span_lint_and_sugg, span_lint_and_then, sugg,
  12 };
  13 use if_chain::if_chain;
  14 use rustc_ast as ast;
  15 use rustc_errors::Applicability;
  16 use rustc_hir::{Expr, ExprKind, Mutability, UnOp};
  17 use rustc_lint::{LateContext, LateLintPass};
  18 use rustc_middle::ty;
  19 use rustc_session::{declare_lint_pass, declare_tool_lint};
  20 use std::borrow::Cow;
  21
  22 declare_clippy_lint! {
  23     /// **What it does:** Checks for transmutes that can't ever be correct on any
  24     /// architecture.
  25     ///
  26     /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  27     ///
  28     /// **Known problems:** When accessing C, users might want to store pointer
  29     /// sized objects in `extradata` arguments to save an allocation.
  30     ///
  31     /// **Example:**
  32     /// ```ignore
  33     /// let ptr: *const T = core::intrinsics::transmute('x')
  34     /// ```
  35     pub WRONG_TRANSMUTE,
  36     correctness,
  37     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  38 }
  39
  40 // FIXME: Move this to `complexity` again, after #5343 is fixed
  41 declare_clippy_lint! {
  42     /// **What it does:** Checks for transmutes to the original type of the object
  43     /// and transmutes that could be a cast.
  44     ///
  45     /// **Why is this bad?** Readability. The code tricks people into thinking that
  46     /// something complex is going on.
  47     ///
  48     /// **Known problems:** None.
  49     ///
  50     /// **Example:**
  51     /// ```rust,ignore
  52     /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
  53     /// ```
  54     pub USELESS_TRANSMUTE,
  55     nursery,
  56     "transmutes that have the same to and from types or could be a cast/coercion"
  57 }
  58
  59 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
  60 declare_clippy_lint! {
  61     /// **What it does:**Checks for transmutes that could be a pointer cast.
  62     ///
  63     /// **Why is this bad?** Readability. The code tricks people into thinking that
  64     /// something complex is going on.
  65     ///
  66     /// **Known problems:** None.
  67     ///
  68     /// **Example:**
  69     ///
  70     /// ```rust
  71     /// # let p: *const [i32] = &[];
  72     /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
  73     /// ```
  74     /// Use instead:
  75     /// ```rust
  76     /// # let p: *const [i32] = &[];
  77     /// p as *const [u16];
  78     /// ```
  79     pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
  80     complexity,
  81     "transmutes that could be a pointer cast"
  82 }
  83
  84 declare_clippy_lint! {
  85     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  86     ///
  87     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  88     /// pointer to that type.
  89     ///
  90     /// **Known problems:** None.
  91     ///
  92     /// **Example:**
  93     /// ```rust,ignore
  94     /// core::intrinsics::transmute(t) // where the result type is the same as
  95     ///                                // `*t` or `&t`'s
  96     /// ```
  97     pub CROSSPOINTER_TRANSMUTE,
  98     complexity,
  99     "transmutes that have to or from types that are a pointer to the other"
 100 }
 101
 102 declare_clippy_lint! {
 103     /// **What it does:** Checks for transmutes from a pointer to a reference.
 104     ///
 105     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
 106     ///
 107     /// **Known problems:**
 108     /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
 109     /// while dereferencing raw pointer is not stable yet.
 110     /// If you need to do this in those places,
 111     /// you would have to use `transmute` instead.
 112     ///
 113     /// **Example:**
 114     /// ```rust,ignore
 115     /// unsafe {
 116     ///     let _: &T = std::mem::transmute(p); // where p: *const T
 117     /// }
 118     ///
 119     /// // can be written:
 120     /// let _: &T = &*p;
 121     /// ```
 122     pub TRANSMUTE_PTR_TO_REF,
 123     complexity,
 124     "transmutes from a pointer to a reference type"
 125 }
 126
 127 declare_clippy_lint! {
 128     /// **What it does:** Checks for transmutes from an integer to a `char`.
 129     ///
 130     /// **Why is this bad?** Not every integer is a Unicode scalar value.
 131     ///
 132     /// **Known problems:**
 133     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
 134     /// as it needs to validate the input.
 135     /// If you are certain that the input is always a valid Unicode scalar value,
 136     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 137     /// but has a semantically meaningful name.
 138     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 139     ///
 140     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 141     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 142     ///
 143     /// **Example:**
 144     /// ```rust
 145     /// let x = 1_u32;
 146     /// unsafe {
 147     ///     let _: char = std::mem::transmute(x); // where x: u32
 148     /// }
 149     ///
 150     /// // should be:
 151     /// let _ = std::char::from_u32(x).unwrap();
 152     /// ```
 153     pub TRANSMUTE_INT_TO_CHAR,
 154     complexity,
 155     "transmutes from an integer to a `char`"
 156 }
 157
 158 declare_clippy_lint! {
 159     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 160     ///
 161     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 162     ///
 163     /// **Known problems:**
 164     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 165     /// as it needs to validate the input.
 166     /// If you are certain that the input is always a valid UTF-8,
 167     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 168     /// but has a semantically meaningful name.
 169     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 170     ///
 171     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 172     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 173     ///
 174     /// **Example:**
 175     /// ```rust
 176     /// let b: &[u8] = &[1_u8, 2_u8];
 177     /// unsafe {
 178     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 179     /// }
 180     ///
 181     /// // should be:
 182     /// let _ = std::str::from_utf8(b).unwrap();
 183     /// ```
 184     pub TRANSMUTE_BYTES_TO_STR,
 185     complexity,
 186     "transmutes from a `&[u8]` to a `&str`"
 187 }
 188
 189 declare_clippy_lint! {
 190     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 191     ///
 192     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 193     ///
 194     /// **Known problems:** None.
 195     ///
 196     /// **Example:**
 197     /// ```rust
 198     /// let x = 1_u8;
 199     /// unsafe {
 200     ///     let _: bool = std::mem::transmute(x); // where x: u8
 201     /// }
 202     ///
 203     /// // should be:
 204     /// let _: bool = x != 0;
 205     /// ```
 206     pub TRANSMUTE_INT_TO_BOOL,
 207     complexity,
 208     "transmutes from an integer to a `bool`"
 209 }
 210
 211 declare_clippy_lint! {
 212     /// **What it does:** Checks for transmutes from an integer to a float.
 213     ///
 214     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 215     /// and safe.
 216     ///
 217     /// **Known problems:** None.
 218     ///
 219     /// **Example:**
 220     /// ```rust
 221     /// unsafe {
 222     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 223     /// }
 224     ///
 225     /// // should be:
 226     /// let _: f32 = f32::from_bits(1_u32);
 227     /// ```
 228     pub TRANSMUTE_INT_TO_FLOAT,
 229     complexity,
 230     "transmutes from an integer to a float"
 231 }
 232
 233 declare_clippy_lint! {
 234     /// **What it does:** Checks for transmutes from a float to an integer.
 235     ///
 236     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 237     /// and safe.
 238     ///
 239     /// **Known problems:** None.
 240     ///
 241     /// **Example:**
 242     /// ```rust
 243     /// unsafe {
 244     ///     let _: u32 = std::mem::transmute(1f32);
 245     /// }
 246     ///
 247     /// // should be:
 248     /// let _: u32 = 1f32.to_bits();
 249     /// ```
 250     pub TRANSMUTE_FLOAT_TO_INT,
 251     complexity,
 252     "transmutes from a float to an integer"
 253 }
 254
 255 declare_clippy_lint! {
 256     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 257     /// from a reference to a reference.
 258     ///
 259     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 260     /// written as casts.
 261     ///
 262     /// **Known problems:** None.
 263     ///
 264     /// **Example:**
 265     /// ```rust
 266     /// let ptr = &1u32 as *const u32;
 267     /// unsafe {
 268     ///     // pointer-to-pointer transmute
 269     ///     let _: *const f32 = std::mem::transmute(ptr);
 270     ///     // ref-ref transmute
 271     ///     let _: &f32 = std::mem::transmute(&1u32);
 272     /// }
 273     /// // These can be respectively written:
 274     /// let _ = ptr as *const f32;
 275     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 276     /// ```
 277     pub TRANSMUTE_PTR_TO_PTR,
 278     complexity,
 279     "transmutes from a pointer to a pointer / a reference to a reference"
 280 }
 281
 282 declare_clippy_lint! {
 283     /// **What it does:** Checks for transmutes between collections whose
 284     /// types have different ABI, size or alignment.
 285     ///
 286     /// **Why is this bad?** This is undefined behavior.
 287     ///
 288     /// **Known problems:** Currently, we cannot know whether a type is a
 289     /// collection, so we just lint the ones that come with `std`.
 290     ///
 291     /// **Example:**
 292     /// ```rust
 293     /// // different size, therefore likely out-of-bounds memory access
 294     /// // You absolutely do not want this in your code!
 295     /// unsafe {
 296     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 297     /// };
 298     /// ```
 299     ///
 300     /// You must always iterate, map and collect the values:
 301     ///
 302     /// ```rust
 303     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 304     /// ```
 305     pub UNSOUND_COLLECTION_TRANSMUTE,
 306     correctness,
 307     "transmute between collections of layout-incompatible types"
 308 }
 309
 310 declare_lint_pass!(Transmute => [
 311     CROSSPOINTER_TRANSMUTE,
 312     TRANSMUTE_PTR_TO_REF,
 313     TRANSMUTE_PTR_TO_PTR,
 314     USELESS_TRANSMUTE,
 315     WRONG_TRANSMUTE,
 316     TRANSMUTE_INT_TO_CHAR,
 317     TRANSMUTE_BYTES_TO_STR,
 318     TRANSMUTE_INT_TO_BOOL,
 319     TRANSMUTE_INT_TO_FLOAT,
 320     TRANSMUTE_FLOAT_TO_INT,
 321     UNSOUND_COLLECTION_TRANSMUTE,
 322     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 323 ]);
 324
 325 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 326 static COLLECTIONS: &[&[&str]] = &[
 327     &paths::VEC,
 328     &paths::VEC_DEQUE,
 329     &paths::BINARY_HEAP,
 330     &paths::BTREESET,
 331     &paths::BTREEMAP,
 332     &paths::HASHSET,
 333     &paths::HASHMAP,
 334 ];
 335
 336 impl<'tcx> LateLintPass<'tcx> for Transmute {
 337     #[allow(clippy::similar_names, clippy::too_many_lines)]
 338     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 339         if_chain! {
 340             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 341             if let ExprKind::Path(ref qpath) = path_expr.kind;
 342             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 343             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 344             then {
 345                 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
 346                 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
 347                 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
 348                 let const_context = in_constant(cx, e.hir_id);
 349
 350                 let from_ty = cx.typeck_results().expr_ty(&args[0]);
 351                 let to_ty = cx.typeck_results().expr_ty(e);
 352
 353                 let triggered = useless_transmute::check(cx, e, from_ty, to_ty, args);
 354                 if triggered {
 355                     return;
 356                 }
 357                 let triggered = wrong_transmute::check(cx, e, from_ty, to_ty);
 358                 if triggered {
 359                     return;
 360                 }
 361                 let triggered = crosspointer_transmute::check(cx, e, from_ty, to_ty);
 362                 if triggered {
 363                     return;
 364                 }
 365                 let triggered = transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
 366                 if triggered {
 367                     return;
 368                 }
 369                 let triggered = transmute_int_to_char::check(cx, e, from_ty, to_ty, args);
 370                 if triggered {
 371                     return;
 372                 }
 373
 374                 match (&from_ty.kind(), &to_ty.kind()) {
 375                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 376                         if_chain! {
 377                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind(), &ty_to.kind());
 378                             if let ty::Uint(ty::UintTy::U8) = slice_ty.kind();
 379                             if from_mutbl == to_mutbl;
 380                             then {
 381                                 let postfix = if *from_mutbl == Mutability::Mut {
 382                                     "_mut"
 383                                 } else {
 384                                     ""
 385                                 };
 386
 387                                 span_lint_and_sugg(
 388                                     cx,
 389                                     TRANSMUTE_BYTES_TO_STR,
 390                                     e.span,
 391                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 392                                     "consider using",
 393                                     format!(
 394                                         "std::str::from_utf8{}({}).unwrap()",
 395                                         postfix,
 396                                         snippet(cx, args[0].span, ".."),
 397                                     ),
 398                                     Applicability::Unspecified,
 399                                 );
 400                             } else {
 401                                 if (cx.tcx.erase_regions(from_ty) != cx.tcx.erase_regions(to_ty))
 402                                     && !const_context {
 403                                     span_lint_and_then(
 404                                         cx,
 405                                         TRANSMUTE_PTR_TO_PTR,
 406                                         e.span,
 407                                         "transmute from a reference to a reference",
 408                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 409                                             let ty_from_and_mut = ty::TypeAndMut {
 410                                                 ty: ty_from,
 411                                                 mutbl: *from_mutbl
 412                                             };
 413                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 414                                             let sugg_paren = arg
 415                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 416                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 417                                             let sugg = if *to_mutbl == Mutability::Mut {
 418                                                 sugg_paren.mut_addr_deref()
 419                                             } else {
 420                                                 sugg_paren.addr_deref()
 421                                             };
 422                                             diag.span_suggestion(
 423                                                 e.span,
 424                                                 "try",
 425                                                 sugg.to_string(),
 426                                                 Applicability::Unspecified,
 427                                             );
 428                                         },
 429                                     )
 430                                 }
 431                             }
 432                         }
 433                     },
 434                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 435                         cx,
 436                         TRANSMUTE_PTR_TO_PTR,
 437                         e.span,
 438                         "transmute from a pointer to a pointer",
 439                         |diag| {
 440                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 441                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 442                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 443                             }
 444                         },
 445                     ),
 446                     (ty::Int(ty::IntTy::I8) | ty::Uint(ty::UintTy::U8), ty::Bool) => {
 447                         span_lint_and_then(
 448                             cx,
 449                             TRANSMUTE_INT_TO_BOOL,
 450                             e.span,
 451                             &format!("transmute from a `{}` to a `bool`", from_ty),
 452                             |diag| {
 453                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 454                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 455                                 diag.span_suggestion(
 456                                     e.span,
 457                                     "consider using",
 458                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 459                                     Applicability::Unspecified,
 460                                 );
 461                             },
 462                         )
 463                     },
 464                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) if !const_context => span_lint_and_then(
 465                         cx,
 466                         TRANSMUTE_INT_TO_FLOAT,
 467                         e.span,
 468                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 469                         |diag| {
 470                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 471                             let arg = if let ty::Int(int_ty) = from_ty.kind() {
 472                                 arg.as_ty(format!(
 473                                     "u{}",
 474                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 475                                 ))
 476                             } else {
 477                                 arg
 478                             };
 479                             diag.span_suggestion(
 480                                 e.span,
 481                                 "consider using",
 482                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 483                                 Applicability::Unspecified,
 484                             );
 485                         },
 486                     ),
 487                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) if !const_context => span_lint_and_then(
 488                         cx,
 489                         TRANSMUTE_FLOAT_TO_INT,
 490                         e.span,
 491                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 492                         |diag| {
 493                             let mut expr = &args[0];
 494                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 495
 496                             if let ExprKind::Unary(UnOp::Neg, inner_expr) = &expr.kind {
 497                                 expr = &inner_expr;
 498                             }
 499
 500                             if_chain! {
 501                                 // if the expression is a float literal and it is unsuffixed then
 502                                 // add a suffix so the suggestion is valid and unambiguous
 503                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 504                                 if let ExprKind::Lit(lit) = &expr.kind;
 505                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 506                                 then {
 507                                     match arg {
 508                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 509                                         _ => arg = sugg::Sugg::NonParen(op)
 510                                     }
 511                                 }
 512                             }
 513
 514                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 515
 516                             // cast the result of `to_bits` if `to_ty` is signed
 517                             arg = if let ty::Int(int_ty) = to_ty.kind() {
 518                                 arg.as_ty(int_ty.name_str().to_string())
 519                             } else {
 520                                 arg
 521                             };
 522
 523                             diag.span_suggestion(
 524                                 e.span,
 525                                 "consider using",
 526                                 arg.to_string(),
 527                                 Applicability::Unspecified,
 528                             );
 529                         },
 530                     ),
 531                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 532                         if from_adt.did != to_adt.did ||
 533                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 534                             return;
 535                         }
 536                         if from_substs.types().zip(to_substs.types())
 537                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 538                             span_lint(
 539                                 cx,
 540                                 UNSOUND_COLLECTION_TRANSMUTE,
 541                                 e.span,
 542                                 &format!(
 543                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 544                                     from_ty,
 545                                     to_ty
 546                                 )
 547                             );
 548                         }
 549                     },
 550                     (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
 551                         cx,
 552                         TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 553                         e.span,
 554                         &format!(
 555                             "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
 556                             from_ty,
 557                             to_ty
 558                         ),
 559                         |diag| {
 560                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 561                                 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
 562                                 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);
 563                             }
 564                         }
 565                     ),
 566                     _ => {
 567                         return;
 568                     },
 569                 }
 570             }
 571         }
 572     }
 573 }