clippy_lints/src/transmute.rs

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