clippy_lints/src/transmute/mod.rs

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