clippy_lints/src/transmute/mod.rs

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