src/tools/clippy/clippy_lints/src/transmute.rs

   1 use crate::utils::{
   2     is_normalizable, last_path_segment, match_def_path, paths, snippet, span_lint, span_lint_and_sugg,
   3     span_lint_and_then, sugg,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_ast as ast;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{Expr, ExprKind, GenericArg, Mutability, QPath, TyKind, UnOp};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_middle::ty::{self, cast::CastKind, Ty};
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::DUMMY_SP;
  13 use rustc_typeck::check::{cast::CastCheck, FnCtxt, Inherited};
  14 use std::borrow::Cow;
  15
  16 declare_clippy_lint! {
  17     /// **What it does:** Checks for transmutes that can't ever be correct on any
  18     /// architecture.
  19     ///
  20     /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  21     ///
  22     /// **Known problems:** When accessing C, users might want to store pointer
  23     /// sized objects in `extradata` arguments to save an allocation.
  24     ///
  25     /// **Example:**
  26     /// ```ignore
  27     /// let ptr: *const T = core::intrinsics::transmute('x')
  28     /// ```
  29     pub WRONG_TRANSMUTE,
  30     correctness,
  31     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  32 }
  33
  34 // FIXME: Move this to `complexity` again, after #5343 is fixed
  35 declare_clippy_lint! {
  36     /// **What it does:** Checks for transmutes to the original type of the object
  37     /// and transmutes that could be a cast.
  38     ///
  39     /// **Why is this bad?** Readability. The code tricks people into thinking that
  40     /// something complex is going on.
  41     ///
  42     /// **Known problems:** None.
  43     ///
  44     /// **Example:**
  45     /// ```rust,ignore
  46     /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
  47     /// ```
  48     pub USELESS_TRANSMUTE,
  49     nursery,
  50     "transmutes that have the same to and from types or could be a cast/coercion"
  51 }
  52
  53 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
  54 declare_clippy_lint! {
  55     /// **What it does:**Checks for transmutes that could be a pointer cast.
  56     ///
  57     /// **Why is this bad?** Readability. The code tricks people into thinking that
  58     /// something complex is going on.
  59     ///
  60     /// **Known problems:** None.
  61     ///
  62     /// **Example:**
  63     ///
  64     /// ```rust
  65     /// # let p: *const [i32] = &[];
  66     /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
  67     /// ```
  68     /// Use instead:
  69     /// ```rust
  70     /// # let p: *const [i32] = &[];
  71     /// p as *const [u16];
  72     /// ```
  73     pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
  74     complexity,
  75     "transmutes that could be a pointer cast"
  76 }
  77
  78 declare_clippy_lint! {
  79     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  80     ///
  81     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  82     /// pointer to that type.
  83     ///
  84     /// **Known problems:** None.
  85     ///
  86     /// **Example:**
  87     /// ```rust,ignore
  88     /// core::intrinsics::transmute(t) // where the result type is the same as
  89     ///                                // `*t` or `&t`'s
  90     /// ```
  91     pub CROSSPOINTER_TRANSMUTE,
  92     complexity,
  93     "transmutes that have to or from types that are a pointer to the other"
  94 }
  95
  96 declare_clippy_lint! {
  97     /// **What it does:** Checks for transmutes from a pointer to a reference.
  98     ///
  99     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
 100     ///
 101     /// **Known problems:** None.
 102     ///
 103     /// **Example:**
 104     /// ```rust,ignore
 105     /// unsafe {
 106     ///     let _: &T = std::mem::transmute(p); // where p: *const T
 107     /// }
 108     ///
 109     /// // can be written:
 110     /// let _: &T = &*p;
 111     /// ```
 112     pub TRANSMUTE_PTR_TO_REF,
 113     complexity,
 114     "transmutes from a pointer to a reference type"
 115 }
 116
 117 declare_clippy_lint! {
 118     /// **What it does:** Checks for transmutes from an integer to a `char`.
 119     ///
 120     /// **Why is this bad?** Not every integer is a Unicode scalar value.
 121     ///
 122     /// **Known problems:**
 123     /// - [`from_u32`] 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 Unicode scalar value,
 126     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 127     /// but has a semantically meaningful name.
 128     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 129     ///
 130     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 131     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 132     ///
 133     /// **Example:**
 134     /// ```rust
 135     /// let x = 1_u32;
 136     /// unsafe {
 137     ///     let _: char = std::mem::transmute(x); // where x: u32
 138     /// }
 139     ///
 140     /// // should be:
 141     /// let _ = std::char::from_u32(x).unwrap();
 142     /// ```
 143     pub TRANSMUTE_INT_TO_CHAR,
 144     complexity,
 145     "transmutes from an integer to a `char`"
 146 }
 147
 148 declare_clippy_lint! {
 149     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 150     ///
 151     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 152     ///
 153     /// **Known problems:**
 154     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 155     /// as it needs to validate the input.
 156     /// If you are certain that the input is always a valid UTF-8,
 157     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 158     /// but has a semantically meaningful name.
 159     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 160     ///
 161     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 162     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 163     ///
 164     /// **Example:**
 165     /// ```rust
 166     /// let b: &[u8] = &[1_u8, 2_u8];
 167     /// unsafe {
 168     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 169     /// }
 170     ///
 171     /// // should be:
 172     /// let _ = std::str::from_utf8(b).unwrap();
 173     /// ```
 174     pub TRANSMUTE_BYTES_TO_STR,
 175     complexity,
 176     "transmutes from a `&[u8]` to a `&str`"
 177 }
 178
 179 declare_clippy_lint! {
 180     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 181     ///
 182     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 183     ///
 184     /// **Known problems:** None.
 185     ///
 186     /// **Example:**
 187     /// ```rust
 188     /// let x = 1_u8;
 189     /// unsafe {
 190     ///     let _: bool = std::mem::transmute(x); // where x: u8
 191     /// }
 192     ///
 193     /// // should be:
 194     /// let _: bool = x != 0;
 195     /// ```
 196     pub TRANSMUTE_INT_TO_BOOL,
 197     complexity,
 198     "transmutes from an integer to a `bool`"
 199 }
 200
 201 declare_clippy_lint! {
 202     /// **What it does:** Checks for transmutes from an integer to a float.
 203     ///
 204     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 205     /// and safe.
 206     ///
 207     /// **Known problems:** None.
 208     ///
 209     /// **Example:**
 210     /// ```rust
 211     /// unsafe {
 212     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 213     /// }
 214     ///
 215     /// // should be:
 216     /// let _: f32 = f32::from_bits(1_u32);
 217     /// ```
 218     pub TRANSMUTE_INT_TO_FLOAT,
 219     complexity,
 220     "transmutes from an integer to a float"
 221 }
 222
 223 declare_clippy_lint! {
 224     /// **What it does:** Checks for transmutes from a float to an integer.
 225     ///
 226     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 227     /// and safe.
 228     ///
 229     /// **Known problems:** None.
 230     ///
 231     /// **Example:**
 232     /// ```rust
 233     /// unsafe {
 234     ///     let _: u32 = std::mem::transmute(1f32);
 235     /// }
 236     ///
 237     /// // should be:
 238     /// let _: u32 = 1f32.to_bits();
 239     /// ```
 240     pub TRANSMUTE_FLOAT_TO_INT,
 241     complexity,
 242     "transmutes from a float to an integer"
 243 }
 244
 245 declare_clippy_lint! {
 246     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 247     /// from a reference to a reference.
 248     ///
 249     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 250     /// written as casts.
 251     ///
 252     /// **Known problems:** None.
 253     ///
 254     /// **Example:**
 255     /// ```rust
 256     /// let ptr = &1u32 as *const u32;
 257     /// unsafe {
 258     ///     // pointer-to-pointer transmute
 259     ///     let _: *const f32 = std::mem::transmute(ptr);
 260     ///     // ref-ref transmute
 261     ///     let _: &f32 = std::mem::transmute(&1u32);
 262     /// }
 263     /// // These can be respectively written:
 264     /// let _ = ptr as *const f32;
 265     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 266     /// ```
 267     pub TRANSMUTE_PTR_TO_PTR,
 268     complexity,
 269     "transmutes from a pointer to a pointer / a reference to a reference"
 270 }
 271
 272 declare_clippy_lint! {
 273     /// **What it does:** Checks for transmutes between collections whose
 274     /// types have different ABI, size or alignment.
 275     ///
 276     /// **Why is this bad?** This is undefined behavior.
 277     ///
 278     /// **Known problems:** Currently, we cannot know whether a type is a
 279     /// collection, so we just lint the ones that come with `std`.
 280     ///
 281     /// **Example:**
 282     /// ```rust
 283     /// // different size, therefore likely out-of-bounds memory access
 284     /// // You absolutely do not want this in your code!
 285     /// unsafe {
 286     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 287     /// };
 288     /// ```
 289     ///
 290     /// You must always iterate, map and collect the values:
 291     ///
 292     /// ```rust
 293     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 294     /// ```
 295     pub UNSOUND_COLLECTION_TRANSMUTE,
 296     correctness,
 297     "transmute between collections of layout-incompatible types"
 298 }
 299
 300 declare_lint_pass!(Transmute => [
 301     CROSSPOINTER_TRANSMUTE,
 302     TRANSMUTE_PTR_TO_REF,
 303     TRANSMUTE_PTR_TO_PTR,
 304     USELESS_TRANSMUTE,
 305     WRONG_TRANSMUTE,
 306     TRANSMUTE_INT_TO_CHAR,
 307     TRANSMUTE_BYTES_TO_STR,
 308     TRANSMUTE_INT_TO_BOOL,
 309     TRANSMUTE_INT_TO_FLOAT,
 310     TRANSMUTE_FLOAT_TO_INT,
 311     UNSOUND_COLLECTION_TRANSMUTE,
 312     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 313 ]);
 314
 315 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 316 static COLLECTIONS: &[&[&str]] = &[
 317     &paths::VEC,
 318     &paths::VEC_DEQUE,
 319     &paths::BINARY_HEAP,
 320     &paths::BTREESET,
 321     &paths::BTREEMAP,
 322     &paths::HASHSET,
 323     &paths::HASHMAP,
 324 ];
 325 impl<'tcx> LateLintPass<'tcx> for Transmute {
 326     #[allow(clippy::similar_names, clippy::too_many_lines)]
 327     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 328         if_chain! {
 329             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 330             if let ExprKind::Path(ref qpath) = path_expr.kind;
 331             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 332             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 333             then {
 334                 let from_ty = cx.typeck_results().expr_ty(&args[0]);
 335                 let to_ty = cx.typeck_results().expr_ty(e);
 336
 337                 match (&from_ty.kind, &to_ty.kind) {
 338                     _ if from_ty == to_ty => span_lint(
 339                         cx,
 340                         USELESS_TRANSMUTE,
 341                         e.span,
 342                         &format!("transmute from a type (`{}`) to itself", from_ty),
 343                     ),
 344                     (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => span_lint_and_then(
 345                         cx,
 346                         USELESS_TRANSMUTE,
 347                         e.span,
 348                         "transmute from a reference to a pointer",
 349                         |diag| {
 350                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 351                                 let rty_and_mut = ty::TypeAndMut {
 352                                     ty: rty,
 353                                     mutbl: *rty_mutbl,
 354                                 };
 355
 356                                 let sugg = if *ptr_ty == rty_and_mut {
 357                                     arg.as_ty(to_ty)
 358                                 } else {
 359                                     arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 360                                 };
 361
 362                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 363                             }
 364                         },
 365                     ),
 366                     (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => span_lint_and_then(
 367                         cx,
 368                         USELESS_TRANSMUTE,
 369                         e.span,
 370                         "transmute from an integer to a pointer",
 371                         |diag| {
 372                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 373                                 diag.span_suggestion(
 374                                     e.span,
 375                                     "try",
 376                                     arg.as_ty(&to_ty.to_string()).to_string(),
 377                                     Applicability::Unspecified,
 378                                 );
 379                             }
 380                         },
 381                     ),
 382                     (ty::Float(_) | ty::Char, ty::Ref(..) | ty::RawPtr(_)) => span_lint(
 383                         cx,
 384                         WRONG_TRANSMUTE,
 385                         e.span,
 386                         &format!("transmute from a `{}` to a pointer", from_ty),
 387                     ),
 388                     (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 389                         cx,
 390                         CROSSPOINTER_TRANSMUTE,
 391                         e.span,
 392                         &format!(
 393                             "transmute from a type (`{}`) to the type that it points to (`{}`)",
 394                             from_ty, to_ty
 395                         ),
 396                     ),
 397                     (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 398                         cx,
 399                         CROSSPOINTER_TRANSMUTE,
 400                         e.span,
 401                         &format!(
 402                             "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 403                             from_ty, to_ty
 404                         ),
 405                     ),
 406                     (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 407                         cx,
 408                         TRANSMUTE_PTR_TO_REF,
 409                         e.span,
 410                         &format!(
 411                             "transmute from a pointer type (`{}`) to a reference type \
 412                              (`{}`)",
 413                             from_ty, to_ty
 414                         ),
 415                         |diag| {
 416                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 417                             let (deref, cast) = if *mutbl == Mutability::Mut {
 418                                 ("&mut *", "*mut")
 419                             } else {
 420                                 ("&*", "*const")
 421                             };
 422
 423                             let arg = if from_pty.ty == *to_ref_ty {
 424                                 arg
 425                             } else {
 426                                 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 427                             };
 428
 429                             diag.span_suggestion(
 430                                 e.span,
 431                                 "try",
 432                                 sugg::make_unop(deref, arg).to_string(),
 433                                 Applicability::Unspecified,
 434                             );
 435                         },
 436                     ),
 437                     (ty::Int(ast::IntTy::I32) | ty::Uint(ast::UintTy::U32), &ty::Char) => {
 438                         span_lint_and_then(
 439                             cx,
 440                             TRANSMUTE_INT_TO_CHAR,
 441                             e.span,
 442                             &format!("transmute from a `{}` to a `char`", from_ty),
 443                             |diag| {
 444                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 445                                 let arg = if let ty::Int(_) = from_ty.kind {
 446                                     arg.as_ty(ast::UintTy::U32.name_str())
 447                                 } else {
 448                                     arg
 449                                 };
 450                                 diag.span_suggestion(
 451                                     e.span,
 452                                     "consider using",
 453                                     format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 454                                     Applicability::Unspecified,
 455                                 );
 456                             },
 457                         )
 458                     },
 459                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 460                         if_chain! {
 461                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind, &ty_to.kind);
 462                             if let ty::Uint(ast::UintTy::U8) = slice_ty.kind;
 463                             if from_mutbl == to_mutbl;
 464                             then {
 465                                 let postfix = if *from_mutbl == Mutability::Mut {
 466                                     "_mut"
 467                                 } else {
 468                                     ""
 469                                 };
 470
 471                                 span_lint_and_sugg(
 472                                     cx,
 473                                     TRANSMUTE_BYTES_TO_STR,
 474                                     e.span,
 475                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 476                                     "consider using",
 477                                     format!(
 478                                         "std::str::from_utf8{}({}).unwrap()",
 479                                         postfix,
 480                                         snippet(cx, args[0].span, ".."),
 481                                     ),
 482                                     Applicability::Unspecified,
 483                                 );
 484                             } else {
 485                                 if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
 486                                     span_lint_and_then(
 487                                         cx,
 488                                         TRANSMUTE_PTR_TO_PTR,
 489                                         e.span,
 490                                         "transmute from a reference to a reference",
 491                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 492                                             let ty_from_and_mut = ty::TypeAndMut {
 493                                                 ty: ty_from,
 494                                                 mutbl: *from_mutbl
 495                                             };
 496                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 497                                             let sugg_paren = arg
 498                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 499                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 500                                             let sugg = if *to_mutbl == Mutability::Mut {
 501                                                 sugg_paren.mut_addr_deref()
 502                                             } else {
 503                                                 sugg_paren.addr_deref()
 504                                             };
 505                                             diag.span_suggestion(
 506                                                 e.span,
 507                                                 "try",
 508                                                 sugg.to_string(),
 509                                                 Applicability::Unspecified,
 510                                             );
 511                                         },
 512                                     )
 513                                 }
 514                             }
 515                         }
 516                     },
 517                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 518                         cx,
 519                         TRANSMUTE_PTR_TO_PTR,
 520                         e.span,
 521                         "transmute from a pointer to a pointer",
 522                         |diag| {
 523                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 524                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 525                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 526                             }
 527                         },
 528                     ),
 529                     (ty::Int(ast::IntTy::I8) | ty::Uint(ast::UintTy::U8), ty::Bool) => {
 530                         span_lint_and_then(
 531                             cx,
 532                             TRANSMUTE_INT_TO_BOOL,
 533                             e.span,
 534                             &format!("transmute from a `{}` to a `bool`", from_ty),
 535                             |diag| {
 536                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 537                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 538                                 diag.span_suggestion(
 539                                     e.span,
 540                                     "consider using",
 541                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 542                                     Applicability::Unspecified,
 543                                 );
 544                             },
 545                         )
 546                     },
 547                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) => span_lint_and_then(
 548                         cx,
 549                         TRANSMUTE_INT_TO_FLOAT,
 550                         e.span,
 551                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 552                         |diag| {
 553                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 554                             let arg = if let ty::Int(int_ty) = from_ty.kind {
 555                                 arg.as_ty(format!(
 556                                     "u{}",
 557                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 558                                 ))
 559                             } else {
 560                                 arg
 561                             };
 562                             diag.span_suggestion(
 563                                 e.span,
 564                                 "consider using",
 565                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 566                                 Applicability::Unspecified,
 567                             );
 568                         },
 569                     ),
 570                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) => span_lint_and_then(
 571                         cx,
 572                         TRANSMUTE_FLOAT_TO_INT,
 573                         e.span,
 574                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 575                         |diag| {
 576                             let mut expr = &args[0];
 577                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 578
 579                             if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
 580                                 expr = &inner_expr;
 581                             }
 582
 583                             if_chain! {
 584                                 // if the expression is a float literal and it is unsuffixed then
 585                                 // add a suffix so the suggestion is valid and unambiguous
 586                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 587                                 if let ExprKind::Lit(lit) = &expr.kind;
 588                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 589                                 then {
 590                                     match arg {
 591                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 592                                         _ => arg = sugg::Sugg::NonParen(op)
 593                                     }
 594                                 }
 595                             }
 596
 597                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 598
 599                             // cast the result of `to_bits` if `to_ty` is signed
 600                             arg = if let ty::Int(int_ty) = to_ty.kind {
 601                                 arg.as_ty(int_ty.name_str().to_string())
 602                             } else {
 603                                 arg
 604                             };
 605
 606                             diag.span_suggestion(
 607                                 e.span,
 608                                 "consider using",
 609                                 arg.to_string(),
 610                                 Applicability::Unspecified,
 611                             );
 612                         },
 613                     ),
 614                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 615                         if from_adt.did != to_adt.did ||
 616                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 617                             return;
 618                         }
 619                         if from_substs.types().zip(to_substs.types())
 620                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 621                             span_lint(
 622                                 cx,
 623                                 UNSOUND_COLLECTION_TRANSMUTE,
 624                                 e.span,
 625                                 &format!(
 626                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 627                                     from_ty,
 628                                     to_ty
 629                                 )
 630                             );
 631                         }
 632                     },
 633                     (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
 634                         cx,
 635                         TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 636                         e.span,
 637                         &format!(
 638                             "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
 639                             from_ty,
 640                             to_ty
 641                         ),
 642                         |diag| {
 643                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 644                                 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
 645                                 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);
 646                             }
 647                         }
 648                     ),
 649                     _ => {
 650                         return;
 651                     },
 652                 }
 653             }
 654         }
 655     }
 656 }
 657
 658 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 659 /// not available , use
 660 /// the type's `ToString` implementation. In weird cases it could lead to types
 661 /// with invalid `'_`
 662 /// lifetime, but it should be rare.
 663 fn get_type_snippet(cx: &LateContext<'_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
 664     let seg = last_path_segment(path);
 665     if_chain! {
 666         if let Some(ref params) = seg.args;
 667         if !params.parenthesized;
 668         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 669             GenericArg::Type(ty) => Some(ty),
 670             _ => None,
 671         }).nth(1);
 672         if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
 673         then {
 674             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 675         }
 676     }
 677
 678     to_ref_ty.to_string()
 679 }
 680
 681 // check if the component types of the transmuted collection and the result have different ABI,
 682 // size or alignment
 683 fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
 684     let empty_param_env = ty::ParamEnv::empty();
 685     // check if `from` and `to` are normalizable to avoid ICE (#4968)
 686     if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
 687         return false;
 688     }
 689     let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
 690     let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
 691     if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
 692         from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
 693     } else {
 694         // no idea about layout, so don't lint
 695         false
 696     }
 697 }
 698
 699 /// Check if the type conversion can be expressed as a pointer cast, instead of
 700 /// a transmute. In certain cases, including some invalid casts from array
 701 /// references to pointers, this may cause additional errors to be emitted and/or
 702 /// ICE error messages. This function will panic if that occurs.
 703 fn can_be_expressed_as_pointer_cast<'tcx>(
 704     cx: &LateContext<'tcx>,
 705     e: &'tcx Expr<'_>,
 706     from_ty: Ty<'tcx>,
 707     to_ty: Ty<'tcx>,
 708 ) -> bool {
 709     use CastKind::{AddrPtrCast, ArrayPtrCast, FnPtrAddrCast, FnPtrPtrCast, PtrAddrCast, PtrPtrCast};
 710     matches!(
 711         check_cast(cx, e, from_ty, to_ty),
 712         Some(PtrPtrCast | PtrAddrCast | AddrPtrCast | ArrayPtrCast | FnPtrPtrCast | FnPtrAddrCast)
 713     )
 714 }
 715
 716 /// If a cast from `from_ty` to `to_ty` is valid, returns an Ok containing the kind of
 717 /// the cast. In certain cases, including some invalid casts from array references
 718 /// to pointers, this may cause additional errors to be emitted and/or ICE error
 719 /// messages. This function will panic if that occurs.
 720 fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> Option<CastKind> {
 721     let hir_id = e.hir_id;
 722     let local_def_id = hir_id.owner;
 723
 724     Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
 725         let fn_ctxt = FnCtxt::new(&inherited, cx.param_env, hir_id);
 726
 727         // If we already have errors, we can't be sure we can pointer cast.
 728         assert!(
 729             !fn_ctxt.errors_reported_since_creation(),
 730             "Newly created FnCtxt contained errors"
 731         );
 732
 733         if let Ok(check) = CastCheck::new(
 734             &fn_ctxt, e, from_ty, to_ty,
 735             // We won't show any error to the user, so we don't care what the span is here.
 736             DUMMY_SP, DUMMY_SP,
 737         ) {
 738             let res = check.do_check(&fn_ctxt);
 739
 740             // do_check's documentation says that it might return Ok and create
 741             // errors in the fcx instead of returing Err in some cases. Those cases
 742             // should be filtered out before getting here.
 743             assert!(
 744                 !fn_ctxt.errors_reported_since_creation(),
 745                 "`fn_ctxt` contained errors after cast check!"
 746             );
 747
 748             res.ok()
 749         } else {
 750             None
 751         }
 752     })
 753 }