clippy_lints/src/transmute.rs

   1 use crate::utils::{
   2     in_constant, 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:**
 102     /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
 103     /// while dereferencing raw pointer is not stable yet.
 104     /// If you need to do this in those places,
 105     /// you would have to use `transmute` instead.
 106     ///
 107     /// **Example:**
 108     /// ```rust,ignore
 109     /// unsafe {
 110     ///     let _: &T = std::mem::transmute(p); // where p: *const T
 111     /// }
 112     ///
 113     /// // can be written:
 114     /// let _: &T = &*p;
 115     /// ```
 116     pub TRANSMUTE_PTR_TO_REF,
 117     complexity,
 118     "transmutes from a pointer to a reference type"
 119 }
 120
 121 declare_clippy_lint! {
 122     /// **What it does:** Checks for transmutes from an integer to a `char`.
 123     ///
 124     /// **Why is this bad?** Not every integer is a Unicode scalar value.
 125     ///
 126     /// **Known problems:**
 127     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
 128     /// as it needs to validate the input.
 129     /// If you are certain that the input is always a valid Unicode scalar value,
 130     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 131     /// but has a semantically meaningful name.
 132     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 133     ///
 134     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 135     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 136     ///
 137     /// **Example:**
 138     /// ```rust
 139     /// let x = 1_u32;
 140     /// unsafe {
 141     ///     let _: char = std::mem::transmute(x); // where x: u32
 142     /// }
 143     ///
 144     /// // should be:
 145     /// let _ = std::char::from_u32(x).unwrap();
 146     /// ```
 147     pub TRANSMUTE_INT_TO_CHAR,
 148     complexity,
 149     "transmutes from an integer to a `char`"
 150 }
 151
 152 declare_clippy_lint! {
 153     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 154     ///
 155     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 156     ///
 157     /// **Known problems:**
 158     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 159     /// as it needs to validate the input.
 160     /// If you are certain that the input is always a valid UTF-8,
 161     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 162     /// but has a semantically meaningful name.
 163     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 164     ///
 165     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 166     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 167     ///
 168     /// **Example:**
 169     /// ```rust
 170     /// let b: &[u8] = &[1_u8, 2_u8];
 171     /// unsafe {
 172     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 173     /// }
 174     ///
 175     /// // should be:
 176     /// let _ = std::str::from_utf8(b).unwrap();
 177     /// ```
 178     pub TRANSMUTE_BYTES_TO_STR,
 179     complexity,
 180     "transmutes from a `&[u8]` to a `&str`"
 181 }
 182
 183 declare_clippy_lint! {
 184     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 185     ///
 186     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 187     ///
 188     /// **Known problems:** None.
 189     ///
 190     /// **Example:**
 191     /// ```rust
 192     /// let x = 1_u8;
 193     /// unsafe {
 194     ///     let _: bool = std::mem::transmute(x); // where x: u8
 195     /// }
 196     ///
 197     /// // should be:
 198     /// let _: bool = x != 0;
 199     /// ```
 200     pub TRANSMUTE_INT_TO_BOOL,
 201     complexity,
 202     "transmutes from an integer to a `bool`"
 203 }
 204
 205 declare_clippy_lint! {
 206     /// **What it does:** Checks for transmutes from an integer to a float.
 207     ///
 208     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 209     /// and safe.
 210     ///
 211     /// **Known problems:** None.
 212     ///
 213     /// **Example:**
 214     /// ```rust
 215     /// unsafe {
 216     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 217     /// }
 218     ///
 219     /// // should be:
 220     /// let _: f32 = f32::from_bits(1_u32);
 221     /// ```
 222     pub TRANSMUTE_INT_TO_FLOAT,
 223     complexity,
 224     "transmutes from an integer to a float"
 225 }
 226
 227 declare_clippy_lint! {
 228     /// **What it does:** Checks for transmutes from a float to an integer.
 229     ///
 230     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 231     /// and safe.
 232     ///
 233     /// **Known problems:** None.
 234     ///
 235     /// **Example:**
 236     /// ```rust
 237     /// unsafe {
 238     ///     let _: u32 = std::mem::transmute(1f32);
 239     /// }
 240     ///
 241     /// // should be:
 242     /// let _: u32 = 1f32.to_bits();
 243     /// ```
 244     pub TRANSMUTE_FLOAT_TO_INT,
 245     complexity,
 246     "transmutes from a float to an integer"
 247 }
 248
 249 declare_clippy_lint! {
 250     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 251     /// from a reference to a reference.
 252     ///
 253     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 254     /// written as casts.
 255     ///
 256     /// **Known problems:** None.
 257     ///
 258     /// **Example:**
 259     /// ```rust
 260     /// let ptr = &1u32 as *const u32;
 261     /// unsafe {
 262     ///     // pointer-to-pointer transmute
 263     ///     let _: *const f32 = std::mem::transmute(ptr);
 264     ///     // ref-ref transmute
 265     ///     let _: &f32 = std::mem::transmute(&1u32);
 266     /// }
 267     /// // These can be respectively written:
 268     /// let _ = ptr as *const f32;
 269     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 270     /// ```
 271     pub TRANSMUTE_PTR_TO_PTR,
 272     complexity,
 273     "transmutes from a pointer to a pointer / a reference to a reference"
 274 }
 275
 276 declare_clippy_lint! {
 277     /// **What it does:** Checks for transmutes between collections whose
 278     /// types have different ABI, size or alignment.
 279     ///
 280     /// **Why is this bad?** This is undefined behavior.
 281     ///
 282     /// **Known problems:** Currently, we cannot know whether a type is a
 283     /// collection, so we just lint the ones that come with `std`.
 284     ///
 285     /// **Example:**
 286     /// ```rust
 287     /// // different size, therefore likely out-of-bounds memory access
 288     /// // You absolutely do not want this in your code!
 289     /// unsafe {
 290     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 291     /// };
 292     /// ```
 293     ///
 294     /// You must always iterate, map and collect the values:
 295     ///
 296     /// ```rust
 297     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 298     /// ```
 299     pub UNSOUND_COLLECTION_TRANSMUTE,
 300     correctness,
 301     "transmute between collections of layout-incompatible types"
 302 }
 303
 304 declare_lint_pass!(Transmute => [
 305     CROSSPOINTER_TRANSMUTE,
 306     TRANSMUTE_PTR_TO_REF,
 307     TRANSMUTE_PTR_TO_PTR,
 308     USELESS_TRANSMUTE,
 309     WRONG_TRANSMUTE,
 310     TRANSMUTE_INT_TO_CHAR,
 311     TRANSMUTE_BYTES_TO_STR,
 312     TRANSMUTE_INT_TO_BOOL,
 313     TRANSMUTE_INT_TO_FLOAT,
 314     TRANSMUTE_FLOAT_TO_INT,
 315     UNSOUND_COLLECTION_TRANSMUTE,
 316     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 317 ]);
 318
 319 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 320 static COLLECTIONS: &[&[&str]] = &[
 321     &paths::VEC,
 322     &paths::VEC_DEQUE,
 323     &paths::BINARY_HEAP,
 324     &paths::BTREESET,
 325     &paths::BTREEMAP,
 326     &paths::HASHSET,
 327     &paths::HASHMAP,
 328 ];
 329 impl<'tcx> LateLintPass<'tcx> for Transmute {
 330     #[allow(clippy::similar_names, clippy::too_many_lines)]
 331     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 332         if_chain! {
 333             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 334             if let ExprKind::Path(ref qpath) = path_expr.kind;
 335             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 336             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 337             then {
 338                 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
 339                 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
 340                 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
 341                 let const_context = in_constant(cx, e.hir_id);
 342
 343                 let from_ty = cx.typeck_results().expr_ty(&args[0]);
 344                 let to_ty = cx.typeck_results().expr_ty(e);
 345
 346                 match (&from_ty.kind(), &to_ty.kind()) {
 347                     _ if from_ty == to_ty => span_lint(
 348                         cx,
 349                         USELESS_TRANSMUTE,
 350                         e.span,
 351                         &format!("transmute from a type (`{}`) to itself", from_ty),
 352                     ),
 353                     (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => span_lint_and_then(
 354                         cx,
 355                         USELESS_TRANSMUTE,
 356                         e.span,
 357                         "transmute from a reference to a pointer",
 358                         |diag| {
 359                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 360                                 let rty_and_mut = ty::TypeAndMut {
 361                                     ty: rty,
 362                                     mutbl: *rty_mutbl,
 363                                 };
 364
 365                                 let sugg = if *ptr_ty == rty_and_mut {
 366                                     arg.as_ty(to_ty)
 367                                 } else {
 368                                     arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 369                                 };
 370
 371                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 372                             }
 373                         },
 374                     ),
 375                     (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => span_lint_and_then(
 376                         cx,
 377                         USELESS_TRANSMUTE,
 378                         e.span,
 379                         "transmute from an integer to a pointer",
 380                         |diag| {
 381                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 382                                 diag.span_suggestion(
 383                                     e.span,
 384                                     "try",
 385                                     arg.as_ty(&to_ty.to_string()).to_string(),
 386                                     Applicability::Unspecified,
 387                                 );
 388                             }
 389                         },
 390                     ),
 391                     (ty::Float(_) | ty::Char, ty::Ref(..) | ty::RawPtr(_)) => span_lint(
 392                         cx,
 393                         WRONG_TRANSMUTE,
 394                         e.span,
 395                         &format!("transmute from a `{}` to a pointer", from_ty),
 396                     ),
 397                     (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 398                         cx,
 399                         CROSSPOINTER_TRANSMUTE,
 400                         e.span,
 401                         &format!(
 402                             "transmute from a type (`{}`) to the type that it points to (`{}`)",
 403                             from_ty, to_ty
 404                         ),
 405                     ),
 406                     (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 407                         cx,
 408                         CROSSPOINTER_TRANSMUTE,
 409                         e.span,
 410                         &format!(
 411                             "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 412                             from_ty, to_ty
 413                         ),
 414                     ),
 415                     (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 416                         cx,
 417                         TRANSMUTE_PTR_TO_REF,
 418                         e.span,
 419                         &format!(
 420                             "transmute from a pointer type (`{}`) to a reference type \
 421                              (`{}`)",
 422                             from_ty, to_ty
 423                         ),
 424                         |diag| {
 425                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 426                             let (deref, cast) = if *mutbl == Mutability::Mut {
 427                                 ("&mut *", "*mut")
 428                             } else {
 429                                 ("&*", "*const")
 430                             };
 431
 432                             let arg = if from_pty.ty == *to_ref_ty {
 433                                 arg
 434                             } else {
 435                                 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 436                             };
 437
 438                             diag.span_suggestion(
 439                                 e.span,
 440                                 "try",
 441                                 sugg::make_unop(deref, arg).to_string(),
 442                                 Applicability::Unspecified,
 443                             );
 444                         },
 445                     ),
 446                     (ty::Int(ast::IntTy::I32) | ty::Uint(ast::UintTy::U32), &ty::Char) => {
 447                         span_lint_and_then(
 448                             cx,
 449                             TRANSMUTE_INT_TO_CHAR,
 450                             e.span,
 451                             &format!("transmute from a `{}` to a `char`", from_ty),
 452                             |diag| {
 453                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 454                                 let arg = if let ty::Int(_) = from_ty.kind() {
 455                                     arg.as_ty(ast::UintTy::U32.name_str())
 456                                 } else {
 457                                     arg
 458                                 };
 459                                 diag.span_suggestion(
 460                                     e.span,
 461                                     "consider using",
 462                                     format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 463                                     Applicability::Unspecified,
 464                                 );
 465                             },
 466                         )
 467                     },
 468                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 469                         if_chain! {
 470                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind(), &ty_to.kind());
 471                             if let ty::Uint(ast::UintTy::U8) = slice_ty.kind();
 472                             if from_mutbl == to_mutbl;
 473                             then {
 474                                 let postfix = if *from_mutbl == Mutability::Mut {
 475                                     "_mut"
 476                                 } else {
 477                                     ""
 478                                 };
 479
 480                                 span_lint_and_sugg(
 481                                     cx,
 482                                     TRANSMUTE_BYTES_TO_STR,
 483                                     e.span,
 484                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 485                                     "consider using",
 486                                     format!(
 487                                         "std::str::from_utf8{}({}).unwrap()",
 488                                         postfix,
 489                                         snippet(cx, args[0].span, ".."),
 490                                     ),
 491                                     Applicability::Unspecified,
 492                                 );
 493                             } else {
 494                                 if (cx.tcx.erase_regions(from_ty) != cx.tcx.erase_regions(to_ty))
 495                                     && !const_context {
 496                                     span_lint_and_then(
 497                                         cx,
 498                                         TRANSMUTE_PTR_TO_PTR,
 499                                         e.span,
 500                                         "transmute from a reference to a reference",
 501                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 502                                             let ty_from_and_mut = ty::TypeAndMut {
 503                                                 ty: ty_from,
 504                                                 mutbl: *from_mutbl
 505                                             };
 506                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 507                                             let sugg_paren = arg
 508                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 509                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 510                                             let sugg = if *to_mutbl == Mutability::Mut {
 511                                                 sugg_paren.mut_addr_deref()
 512                                             } else {
 513                                                 sugg_paren.addr_deref()
 514                                             };
 515                                             diag.span_suggestion(
 516                                                 e.span,
 517                                                 "try",
 518                                                 sugg.to_string(),
 519                                                 Applicability::Unspecified,
 520                                             );
 521                                         },
 522                                     )
 523                                 }
 524                             }
 525                         }
 526                     },
 527                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 528                         cx,
 529                         TRANSMUTE_PTR_TO_PTR,
 530                         e.span,
 531                         "transmute from a pointer to a pointer",
 532                         |diag| {
 533                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 534                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 535                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 536                             }
 537                         },
 538                     ),
 539                     (ty::Int(ast::IntTy::I8) | ty::Uint(ast::UintTy::U8), ty::Bool) => {
 540                         span_lint_and_then(
 541                             cx,
 542                             TRANSMUTE_INT_TO_BOOL,
 543                             e.span,
 544                             &format!("transmute from a `{}` to a `bool`", from_ty),
 545                             |diag| {
 546                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 547                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 548                                 diag.span_suggestion(
 549                                     e.span,
 550                                     "consider using",
 551                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 552                                     Applicability::Unspecified,
 553                                 );
 554                             },
 555                         )
 556                     },
 557                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) if !const_context => span_lint_and_then(
 558                         cx,
 559                         TRANSMUTE_INT_TO_FLOAT,
 560                         e.span,
 561                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 562                         |diag| {
 563                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 564                             let arg = if let ty::Int(int_ty) = from_ty.kind() {
 565                                 arg.as_ty(format!(
 566                                     "u{}",
 567                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 568                                 ))
 569                             } else {
 570                                 arg
 571                             };
 572                             diag.span_suggestion(
 573                                 e.span,
 574                                 "consider using",
 575                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 576                                 Applicability::Unspecified,
 577                             );
 578                         },
 579                     ),
 580                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) if !const_context => span_lint_and_then(
 581                         cx,
 582                         TRANSMUTE_FLOAT_TO_INT,
 583                         e.span,
 584                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 585                         |diag| {
 586                             let mut expr = &args[0];
 587                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 588
 589                             if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
 590                                 expr = &inner_expr;
 591                             }
 592
 593                             if_chain! {
 594                                 // if the expression is a float literal and it is unsuffixed then
 595                                 // add a suffix so the suggestion is valid and unambiguous
 596                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 597                                 if let ExprKind::Lit(lit) = &expr.kind;
 598                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 599                                 then {
 600                                     match arg {
 601                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 602                                         _ => arg = sugg::Sugg::NonParen(op)
 603                                     }
 604                                 }
 605                             }
 606
 607                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 608
 609                             // cast the result of `to_bits` if `to_ty` is signed
 610                             arg = if let ty::Int(int_ty) = to_ty.kind() {
 611                                 arg.as_ty(int_ty.name_str().to_string())
 612                             } else {
 613                                 arg
 614                             };
 615
 616                             diag.span_suggestion(
 617                                 e.span,
 618                                 "consider using",
 619                                 arg.to_string(),
 620                                 Applicability::Unspecified,
 621                             );
 622                         },
 623                     ),
 624                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 625                         if from_adt.did != to_adt.did ||
 626                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 627                             return;
 628                         }
 629                         if from_substs.types().zip(to_substs.types())
 630                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 631                             span_lint(
 632                                 cx,
 633                                 UNSOUND_COLLECTION_TRANSMUTE,
 634                                 e.span,
 635                                 &format!(
 636                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 637                                     from_ty,
 638                                     to_ty
 639                                 )
 640                             );
 641                         }
 642                     },
 643                     (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
 644                         cx,
 645                         TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 646                         e.span,
 647                         &format!(
 648                             "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
 649                             from_ty,
 650                             to_ty
 651                         ),
 652                         |diag| {
 653                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 654                                 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
 655                                 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);
 656                             }
 657                         }
 658                     ),
 659                     _ => {
 660                         return;
 661                     },
 662                 }
 663             }
 664         }
 665     }
 666 }
 667
 668 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 669 /// not available , use
 670 /// the type's `ToString` implementation. In weird cases it could lead to types
 671 /// with invalid `'_`
 672 /// lifetime, but it should be rare.
 673 fn get_type_snippet(cx: &LateContext<'_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
 674     let seg = last_path_segment(path);
 675     if_chain! {
 676         if let Some(ref params) = seg.args;
 677         if !params.parenthesized;
 678         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 679             GenericArg::Type(ty) => Some(ty),
 680             _ => None,
 681         }).nth(1);
 682         if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
 683         then {
 684             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 685         }
 686     }
 687
 688     to_ref_ty.to_string()
 689 }
 690
 691 // check if the component types of the transmuted collection and the result have different ABI,
 692 // size or alignment
 693 fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
 694     let empty_param_env = ty::ParamEnv::empty();
 695     // check if `from` and `to` are normalizable to avoid ICE (#4968)
 696     if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
 697         return false;
 698     }
 699     let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
 700     let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
 701     if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
 702         from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
 703     } else {
 704         // no idea about layout, so don't lint
 705         false
 706     }
 707 }
 708
 709 /// Check if the type conversion can be expressed as a pointer cast, instead of
 710 /// a transmute. In certain cases, including some invalid casts from array
 711 /// references to pointers, this may cause additional errors to be emitted and/or
 712 /// ICE error messages. This function will panic if that occurs.
 713 fn can_be_expressed_as_pointer_cast<'tcx>(
 714     cx: &LateContext<'tcx>,
 715     e: &'tcx Expr<'_>,
 716     from_ty: Ty<'tcx>,
 717     to_ty: Ty<'tcx>,
 718 ) -> bool {
 719     use CastKind::{AddrPtrCast, ArrayPtrCast, FnPtrAddrCast, FnPtrPtrCast, PtrAddrCast, PtrPtrCast};
 720     matches!(
 721         check_cast(cx, e, from_ty, to_ty),
 722         Some(PtrPtrCast | PtrAddrCast | AddrPtrCast | ArrayPtrCast | FnPtrPtrCast | FnPtrAddrCast)
 723     )
 724 }
 725
 726 /// If a cast from `from_ty` to `to_ty` is valid, returns an Ok containing the kind of
 727 /// the cast. In certain cases, including some invalid casts from array references
 728 /// to pointers, this may cause additional errors to be emitted and/or ICE error
 729 /// messages. This function will panic if that occurs.
 730 fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> Option<CastKind> {
 731     let hir_id = e.hir_id;
 732     let local_def_id = hir_id.owner;
 733
 734     Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
 735         let fn_ctxt = FnCtxt::new(&inherited, cx.param_env, hir_id);
 736
 737         // If we already have errors, we can't be sure we can pointer cast.
 738         assert!(
 739             !fn_ctxt.errors_reported_since_creation(),
 740             "Newly created FnCtxt contained errors"
 741         );
 742
 743         if let Ok(check) = CastCheck::new(
 744             &fn_ctxt, e, from_ty, to_ty,
 745             // We won't show any error to the user, so we don't care what the span is here.
 746             DUMMY_SP, DUMMY_SP,
 747         ) {
 748             let res = check.do_check(&fn_ctxt);
 749
 750             // do_check's documentation says that it might return Ok and create
 751             // errors in the fcx instead of returing Err in some cases. Those cases
 752             // should be filtered out before getting here.
 753             assert!(
 754                 !fn_ctxt.errors_reported_since_creation(),
 755                 "`fn_ctxt` contained errors after cast check!"
 756             );
 757
 758             res.ok()
 759         } else {
 760             None
 761         }
 762     })
 763 }