clippy_lints/src/transmute/mod.rs

   1 mod crosspointer_transmute;
   2 mod transmute_ptr_to_ref;
   3 mod useless_transmute;
   4 mod utils;
   5 mod wrong_transmute;
   6
   7 use utils::*;
   8
   9 use crate::utils::{
  10     in_constant, match_def_path, paths, snippet, span_lint, span_lint_and_sugg, span_lint_and_then, sugg,
  11 };
  12 use if_chain::if_chain;
  13 use rustc_ast as ast;
  14 use rustc_errors::Applicability;
  15 use rustc_hir::{Expr, ExprKind, Mutability, UnOp};
  16 use rustc_lint::{LateContext, LateLintPass};
  17 use rustc_middle::ty;
  18 use rustc_session::{declare_lint_pass, declare_tool_lint};
  19 use std::borrow::Cow;
  20
  21 declare_clippy_lint! {
  22     /// **What it does:** Checks for transmutes that can't ever be correct on any
  23     /// architecture.
  24     ///
  25     /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  26     ///
  27     /// **Known problems:** When accessing C, users might want to store pointer
  28     /// sized objects in `extradata` arguments to save an allocation.
  29     ///
  30     /// **Example:**
  31     /// ```ignore
  32     /// let ptr: *const T = core::intrinsics::transmute('x')
  33     /// ```
  34     pub WRONG_TRANSMUTE,
  35     correctness,
  36     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  37 }
  38
  39 // FIXME: Move this to `complexity` again, after #5343 is fixed
  40 declare_clippy_lint! {
  41     /// **What it does:** Checks for transmutes to the original type of the object
  42     /// and transmutes that could be a cast.
  43     ///
  44     /// **Why is this bad?** Readability. The code tricks people into thinking that
  45     /// something complex is going on.
  46     ///
  47     /// **Known problems:** None.
  48     ///
  49     /// **Example:**
  50     /// ```rust,ignore
  51     /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
  52     /// ```
  53     pub USELESS_TRANSMUTE,
  54     nursery,
  55     "transmutes that have the same to and from types or could be a cast/coercion"
  56 }
  57
  58 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
  59 declare_clippy_lint! {
  60     /// **What it does:**Checks for transmutes that could be a pointer cast.
  61     ///
  62     /// **Why is this bad?** Readability. The code tricks people into thinking that
  63     /// something complex is going on.
  64     ///
  65     /// **Known problems:** None.
  66     ///
  67     /// **Example:**
  68     ///
  69     /// ```rust
  70     /// # let p: *const [i32] = &[];
  71     /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
  72     /// ```
  73     /// Use instead:
  74     /// ```rust
  75     /// # let p: *const [i32] = &[];
  76     /// p as *const [u16];
  77     /// ```
  78     pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
  79     complexity,
  80     "transmutes that could be a pointer cast"
  81 }
  82
  83 declare_clippy_lint! {
  84     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  85     ///
  86     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  87     /// pointer to that type.
  88     ///
  89     /// **Known problems:** None.
  90     ///
  91     /// **Example:**
  92     /// ```rust,ignore
  93     /// core::intrinsics::transmute(t) // where the result type is the same as
  94     ///                                // `*t` or `&t`'s
  95     /// ```
  96     pub CROSSPOINTER_TRANSMUTE,
  97     complexity,
  98     "transmutes that have to or from types that are a pointer to the other"
  99 }
 100
 101 declare_clippy_lint! {
 102     /// **What it does:** Checks for transmutes from a pointer to a reference.
 103     ///
 104     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
 105     ///
 106     /// **Known problems:**
 107     /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
 108     /// while dereferencing raw pointer is not stable yet.
 109     /// If you need to do this in those places,
 110     /// you would have to use `transmute` instead.
 111     ///
 112     /// **Example:**
 113     /// ```rust,ignore
 114     /// unsafe {
 115     ///     let _: &T = std::mem::transmute(p); // where p: *const T
 116     /// }
 117     ///
 118     /// // can be written:
 119     /// let _: &T = &*p;
 120     /// ```
 121     pub TRANSMUTE_PTR_TO_REF,
 122     complexity,
 123     "transmutes from a pointer to a reference type"
 124 }
 125
 126 declare_clippy_lint! {
 127     /// **What it does:** Checks for transmutes from an integer to a `char`.
 128     ///
 129     /// **Why is this bad?** Not every integer is a Unicode scalar value.
 130     ///
 131     /// **Known problems:**
 132     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
 133     /// as it needs to validate the input.
 134     /// If you are certain that the input is always a valid Unicode scalar value,
 135     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 136     /// but has a semantically meaningful name.
 137     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 138     ///
 139     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 140     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 141     ///
 142     /// **Example:**
 143     /// ```rust
 144     /// let x = 1_u32;
 145     /// unsafe {
 146     ///     let _: char = std::mem::transmute(x); // where x: u32
 147     /// }
 148     ///
 149     /// // should be:
 150     /// let _ = std::char::from_u32(x).unwrap();
 151     /// ```
 152     pub TRANSMUTE_INT_TO_CHAR,
 153     complexity,
 154     "transmutes from an integer to a `char`"
 155 }
 156
 157 declare_clippy_lint! {
 158     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 159     ///
 160     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 161     ///
 162     /// **Known problems:**
 163     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 164     /// as it needs to validate the input.
 165     /// If you are certain that the input is always a valid UTF-8,
 166     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 167     /// but has a semantically meaningful name.
 168     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 169     ///
 170     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 171     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 172     ///
 173     /// **Example:**
 174     /// ```rust
 175     /// let b: &[u8] = &[1_u8, 2_u8];
 176     /// unsafe {
 177     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 178     /// }
 179     ///
 180     /// // should be:
 181     /// let _ = std::str::from_utf8(b).unwrap();
 182     /// ```
 183     pub TRANSMUTE_BYTES_TO_STR,
 184     complexity,
 185     "transmutes from a `&[u8]` to a `&str`"
 186 }
 187
 188 declare_clippy_lint! {
 189     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 190     ///
 191     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 192     ///
 193     /// **Known problems:** None.
 194     ///
 195     /// **Example:**
 196     /// ```rust
 197     /// let x = 1_u8;
 198     /// unsafe {
 199     ///     let _: bool = std::mem::transmute(x); // where x: u8
 200     /// }
 201     ///
 202     /// // should be:
 203     /// let _: bool = x != 0;
 204     /// ```
 205     pub TRANSMUTE_INT_TO_BOOL,
 206     complexity,
 207     "transmutes from an integer to a `bool`"
 208 }
 209
 210 declare_clippy_lint! {
 211     /// **What it does:** Checks for transmutes from an integer to a float.
 212     ///
 213     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 214     /// and safe.
 215     ///
 216     /// **Known problems:** None.
 217     ///
 218     /// **Example:**
 219     /// ```rust
 220     /// unsafe {
 221     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 222     /// }
 223     ///
 224     /// // should be:
 225     /// let _: f32 = f32::from_bits(1_u32);
 226     /// ```
 227     pub TRANSMUTE_INT_TO_FLOAT,
 228     complexity,
 229     "transmutes from an integer to a float"
 230 }
 231
 232 declare_clippy_lint! {
 233     /// **What it does:** Checks for transmutes from a float to an integer.
 234     ///
 235     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 236     /// and safe.
 237     ///
 238     /// **Known problems:** None.
 239     ///
 240     /// **Example:**
 241     /// ```rust
 242     /// unsafe {
 243     ///     let _: u32 = std::mem::transmute(1f32);
 244     /// }
 245     ///
 246     /// // should be:
 247     /// let _: u32 = 1f32.to_bits();
 248     /// ```
 249     pub TRANSMUTE_FLOAT_TO_INT,
 250     complexity,
 251     "transmutes from a float to an integer"
 252 }
 253
 254 declare_clippy_lint! {
 255     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 256     /// from a reference to a reference.
 257     ///
 258     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 259     /// written as casts.
 260     ///
 261     /// **Known problems:** None.
 262     ///
 263     /// **Example:**
 264     /// ```rust
 265     /// let ptr = &1u32 as *const u32;
 266     /// unsafe {
 267     ///     // pointer-to-pointer transmute
 268     ///     let _: *const f32 = std::mem::transmute(ptr);
 269     ///     // ref-ref transmute
 270     ///     let _: &f32 = std::mem::transmute(&1u32);
 271     /// }
 272     /// // These can be respectively written:
 273     /// let _ = ptr as *const f32;
 274     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 275     /// ```
 276     pub TRANSMUTE_PTR_TO_PTR,
 277     complexity,
 278     "transmutes from a pointer to a pointer / a reference to a reference"
 279 }
 280
 281 declare_clippy_lint! {
 282     /// **What it does:** Checks for transmutes between collections whose
 283     /// types have different ABI, size or alignment.
 284     ///
 285     /// **Why is this bad?** This is undefined behavior.
 286     ///
 287     /// **Known problems:** Currently, we cannot know whether a type is a
 288     /// collection, so we just lint the ones that come with `std`.
 289     ///
 290     /// **Example:**
 291     /// ```rust
 292     /// // different size, therefore likely out-of-bounds memory access
 293     /// // You absolutely do not want this in your code!
 294     /// unsafe {
 295     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 296     /// };
 297     /// ```
 298     ///
 299     /// You must always iterate, map and collect the values:
 300     ///
 301     /// ```rust
 302     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 303     /// ```
 304     pub UNSOUND_COLLECTION_TRANSMUTE,
 305     correctness,
 306     "transmute between collections of layout-incompatible types"
 307 }
 308
 309 declare_lint_pass!(Transmute => [
 310     CROSSPOINTER_TRANSMUTE,
 311     TRANSMUTE_PTR_TO_REF,
 312     TRANSMUTE_PTR_TO_PTR,
 313     USELESS_TRANSMUTE,
 314     WRONG_TRANSMUTE,
 315     TRANSMUTE_INT_TO_CHAR,
 316     TRANSMUTE_BYTES_TO_STR,
 317     TRANSMUTE_INT_TO_BOOL,
 318     TRANSMUTE_INT_TO_FLOAT,
 319     TRANSMUTE_FLOAT_TO_INT,
 320     UNSOUND_COLLECTION_TRANSMUTE,
 321     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 322 ]);
 323
 324 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 325 static COLLECTIONS: &[&[&str]] = &[
 326     &paths::VEC,
 327     &paths::VEC_DEQUE,
 328     &paths::BINARY_HEAP,
 329     &paths::BTREESET,
 330     &paths::BTREEMAP,
 331     &paths::HASHSET,
 332     &paths::HASHMAP,
 333 ];
 334
 335 impl<'tcx> LateLintPass<'tcx> for Transmute {
 336     #[allow(clippy::similar_names, clippy::too_many_lines)]
 337     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 338         if_chain! {
 339             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 340             if let ExprKind::Path(ref qpath) = path_expr.kind;
 341             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 342             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 343             then {
 344                 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
 345                 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
 346                 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
 347                 let const_context = in_constant(cx, e.hir_id);
 348
 349                 let from_ty = cx.typeck_results().expr_ty(&args[0]);
 350                 let to_ty = cx.typeck_results().expr_ty(e);
 351
 352                 let triggered = useless_transmute::check(cx, e, from_ty, to_ty, args);
 353                 if triggered {
 354                     return;
 355                 }
 356                 let triggered = wrong_transmute::check(cx, e, from_ty, to_ty);
 357                 if triggered {
 358                     return;
 359                 }
 360                 let triggered = crosspointer_transmute::check(cx, e, from_ty, to_ty);
 361                 if triggered {
 362                     return;
 363                 }
 364                 let triggered = transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, args, qpath);
 365                 if triggered {
 366                     return;
 367                 }
 368
 369                 match (&from_ty.kind(), &to_ty.kind()) {
 370                     (ty::Int(ty::IntTy::I32) | ty::Uint(ty::UintTy::U32), &ty::Char) => {
 371                         span_lint_and_then(
 372                             cx,
 373                             TRANSMUTE_INT_TO_CHAR,
 374                             e.span,
 375                             &format!("transmute from a `{}` to a `char`", from_ty),
 376                             |diag| {
 377                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 378                                 let arg = if let ty::Int(_) = from_ty.kind() {
 379                                     arg.as_ty(ast::UintTy::U32.name_str())
 380                                 } else {
 381                                     arg
 382                                 };
 383                                 diag.span_suggestion(
 384                                     e.span,
 385                                     "consider using",
 386                                     format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 387                                     Applicability::Unspecified,
 388                                 );
 389                             },
 390                         )
 391                     },
 392                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 393                         if_chain! {
 394                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind(), &ty_to.kind());
 395                             if let ty::Uint(ty::UintTy::U8) = slice_ty.kind();
 396                             if from_mutbl == to_mutbl;
 397                             then {
 398                                 let postfix = if *from_mutbl == Mutability::Mut {
 399                                     "_mut"
 400                                 } else {
 401                                     ""
 402                                 };
 403
 404                                 span_lint_and_sugg(
 405                                     cx,
 406                                     TRANSMUTE_BYTES_TO_STR,
 407                                     e.span,
 408                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 409                                     "consider using",
 410                                     format!(
 411                                         "std::str::from_utf8{}({}).unwrap()",
 412                                         postfix,
 413                                         snippet(cx, args[0].span, ".."),
 414                                     ),
 415                                     Applicability::Unspecified,
 416                                 );
 417                             } else {
 418                                 if (cx.tcx.erase_regions(from_ty) != cx.tcx.erase_regions(to_ty))
 419                                     && !const_context {
 420                                     span_lint_and_then(
 421                                         cx,
 422                                         TRANSMUTE_PTR_TO_PTR,
 423                                         e.span,
 424                                         "transmute from a reference to a reference",
 425                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 426                                             let ty_from_and_mut = ty::TypeAndMut {
 427                                                 ty: ty_from,
 428                                                 mutbl: *from_mutbl
 429                                             };
 430                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 431                                             let sugg_paren = arg
 432                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 433                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 434                                             let sugg = if *to_mutbl == Mutability::Mut {
 435                                                 sugg_paren.mut_addr_deref()
 436                                             } else {
 437                                                 sugg_paren.addr_deref()
 438                                             };
 439                                             diag.span_suggestion(
 440                                                 e.span,
 441                                                 "try",
 442                                                 sugg.to_string(),
 443                                                 Applicability::Unspecified,
 444                                             );
 445                                         },
 446                                     )
 447                                 }
 448                             }
 449                         }
 450                     },
 451                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 452                         cx,
 453                         TRANSMUTE_PTR_TO_PTR,
 454                         e.span,
 455                         "transmute from a pointer to a pointer",
 456                         |diag| {
 457                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 458                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 459                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 460                             }
 461                         },
 462                     ),
 463                     (ty::Int(ty::IntTy::I8) | ty::Uint(ty::UintTy::U8), ty::Bool) => {
 464                         span_lint_and_then(
 465                             cx,
 466                             TRANSMUTE_INT_TO_BOOL,
 467                             e.span,
 468                             &format!("transmute from a `{}` to a `bool`", from_ty),
 469                             |diag| {
 470                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 471                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 472                                 diag.span_suggestion(
 473                                     e.span,
 474                                     "consider using",
 475                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 476                                     Applicability::Unspecified,
 477                                 );
 478                             },
 479                         )
 480                     },
 481                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) if !const_context => span_lint_and_then(
 482                         cx,
 483                         TRANSMUTE_INT_TO_FLOAT,
 484                         e.span,
 485                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 486                         |diag| {
 487                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 488                             let arg = if let ty::Int(int_ty) = from_ty.kind() {
 489                                 arg.as_ty(format!(
 490                                     "u{}",
 491                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 492                                 ))
 493                             } else {
 494                                 arg
 495                             };
 496                             diag.span_suggestion(
 497                                 e.span,
 498                                 "consider using",
 499                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 500                                 Applicability::Unspecified,
 501                             );
 502                         },
 503                     ),
 504                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) if !const_context => span_lint_and_then(
 505                         cx,
 506                         TRANSMUTE_FLOAT_TO_INT,
 507                         e.span,
 508                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 509                         |diag| {
 510                             let mut expr = &args[0];
 511                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 512
 513                             if let ExprKind::Unary(UnOp::Neg, inner_expr) = &expr.kind {
 514                                 expr = &inner_expr;
 515                             }
 516
 517                             if_chain! {
 518                                 // if the expression is a float literal and it is unsuffixed then
 519                                 // add a suffix so the suggestion is valid and unambiguous
 520                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 521                                 if let ExprKind::Lit(lit) = &expr.kind;
 522                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 523                                 then {
 524                                     match arg {
 525                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 526                                         _ => arg = sugg::Sugg::NonParen(op)
 527                                     }
 528                                 }
 529                             }
 530
 531                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 532
 533                             // cast the result of `to_bits` if `to_ty` is signed
 534                             arg = if let ty::Int(int_ty) = to_ty.kind() {
 535                                 arg.as_ty(int_ty.name_str().to_string())
 536                             } else {
 537                                 arg
 538                             };
 539
 540                             diag.span_suggestion(
 541                                 e.span,
 542                                 "consider using",
 543                                 arg.to_string(),
 544                                 Applicability::Unspecified,
 545                             );
 546                         },
 547                     ),
 548                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 549                         if from_adt.did != to_adt.did ||
 550                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 551                             return;
 552                         }
 553                         if from_substs.types().zip(to_substs.types())
 554                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 555                             span_lint(
 556                                 cx,
 557                                 UNSOUND_COLLECTION_TRANSMUTE,
 558                                 e.span,
 559                                 &format!(
 560                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 561                                     from_ty,
 562                                     to_ty
 563                                 )
 564                             );
 565                         }
 566                     },
 567                     (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
 568                         cx,
 569                         TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 570                         e.span,
 571                         &format!(
 572                             "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
 573                             from_ty,
 574                             to_ty
 575                         ),
 576                         |diag| {
 577                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 578                                 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
 579                                 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);
 580                             }
 581                         }
 582                     ),
 583                     _ => {
 584                         return;
 585                     },
 586                 }
 587             }
 588         }
 589     }
 590 }