clippy_lints/src/transmute/mod.rs

   1 mod useless_transmute;
   2 mod utils;
   3 mod wrong_transmute;
   4
   5 use utils::*;
   6
   7 use crate::utils::{
   8     in_constant, match_def_path, paths, snippet, span_lint, span_lint_and_sugg, span_lint_and_then, sugg,
   9 };
  10 use if_chain::if_chain;
  11 use rustc_ast as ast;
  12 use rustc_errors::Applicability;
  13 use rustc_hir::{Expr, ExprKind, Mutability, UnOp};
  14 use rustc_lint::{LateContext, LateLintPass};
  15 use rustc_middle::ty;
  16 use rustc_session::{declare_lint_pass, declare_tool_lint};
  17 use std::borrow::Cow;
  18
  19 declare_clippy_lint! {
  20     /// **What it does:** Checks for transmutes that can't ever be correct on any
  21     /// architecture.
  22     ///
  23     /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  24     ///
  25     /// **Known problems:** When accessing C, users might want to store pointer
  26     /// sized objects in `extradata` arguments to save an allocation.
  27     ///
  28     /// **Example:**
  29     /// ```ignore
  30     /// let ptr: *const T = core::intrinsics::transmute('x')
  31     /// ```
  32     pub WRONG_TRANSMUTE,
  33     correctness,
  34     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  35 }
  36
  37 // FIXME: Move this to `complexity` again, after #5343 is fixed
  38 declare_clippy_lint! {
  39     /// **What it does:** Checks for transmutes to the original type of the object
  40     /// and transmutes that could be a cast.
  41     ///
  42     /// **Why is this bad?** Readability. The code tricks people into thinking that
  43     /// something complex is going on.
  44     ///
  45     /// **Known problems:** None.
  46     ///
  47     /// **Example:**
  48     /// ```rust,ignore
  49     /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
  50     /// ```
  51     pub USELESS_TRANSMUTE,
  52     nursery,
  53     "transmutes that have the same to and from types or could be a cast/coercion"
  54 }
  55
  56 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
  57 declare_clippy_lint! {
  58     /// **What it does:**Checks for transmutes that could be a pointer cast.
  59     ///
  60     /// **Why is this bad?** Readability. The code tricks people into thinking that
  61     /// something complex is going on.
  62     ///
  63     /// **Known problems:** None.
  64     ///
  65     /// **Example:**
  66     ///
  67     /// ```rust
  68     /// # let p: *const [i32] = &[];
  69     /// unsafe { std::mem::transmute::<*const [i32], *const [u16]>(p) };
  70     /// ```
  71     /// Use instead:
  72     /// ```rust
  73     /// # let p: *const [i32] = &[];
  74     /// p as *const [u16];
  75     /// ```
  76     pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
  77     complexity,
  78     "transmutes that could be a pointer cast"
  79 }
  80
  81 declare_clippy_lint! {
  82     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  83     ///
  84     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  85     /// pointer to that type.
  86     ///
  87     /// **Known problems:** None.
  88     ///
  89     /// **Example:**
  90     /// ```rust,ignore
  91     /// core::intrinsics::transmute(t) // where the result type is the same as
  92     ///                                // `*t` or `&t`'s
  93     /// ```
  94     pub CROSSPOINTER_TRANSMUTE,
  95     complexity,
  96     "transmutes that have to or from types that are a pointer to the other"
  97 }
  98
  99 declare_clippy_lint! {
 100     /// **What it does:** Checks for transmutes from a pointer to a reference.
 101     ///
 102     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
 103     ///
 104     /// **Known problems:**
 105     /// - `mem::transmute` in statics and constants is stable from Rust 1.46.0,
 106     /// while dereferencing raw pointer is not stable yet.
 107     /// If you need to do this in those places,
 108     /// you would have to use `transmute` instead.
 109     ///
 110     /// **Example:**
 111     /// ```rust,ignore
 112     /// unsafe {
 113     ///     let _: &T = std::mem::transmute(p); // where p: *const T
 114     /// }
 115     ///
 116     /// // can be written:
 117     /// let _: &T = &*p;
 118     /// ```
 119     pub TRANSMUTE_PTR_TO_REF,
 120     complexity,
 121     "transmutes from a pointer to a reference type"
 122 }
 123
 124 declare_clippy_lint! {
 125     /// **What it does:** Checks for transmutes from an integer to a `char`.
 126     ///
 127     /// **Why is this bad?** Not every integer is a Unicode scalar value.
 128     ///
 129     /// **Known problems:**
 130     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
 131     /// as it needs to validate the input.
 132     /// If you are certain that the input is always a valid Unicode scalar value,
 133     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 134     /// but has a semantically meaningful name.
 135     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 136     ///
 137     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 138     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 139     ///
 140     /// **Example:**
 141     /// ```rust
 142     /// let x = 1_u32;
 143     /// unsafe {
 144     ///     let _: char = std::mem::transmute(x); // where x: u32
 145     /// }
 146     ///
 147     /// // should be:
 148     /// let _ = std::char::from_u32(x).unwrap();
 149     /// ```
 150     pub TRANSMUTE_INT_TO_CHAR,
 151     complexity,
 152     "transmutes from an integer to a `char`"
 153 }
 154
 155 declare_clippy_lint! {
 156     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 157     ///
 158     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 159     ///
 160     /// **Known problems:**
 161     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 162     /// as it needs to validate the input.
 163     /// If you are certain that the input is always a valid UTF-8,
 164     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 165     /// but has a semantically meaningful name.
 166     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 167     ///
 168     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 169     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 170     ///
 171     /// **Example:**
 172     /// ```rust
 173     /// let b: &[u8] = &[1_u8, 2_u8];
 174     /// unsafe {
 175     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 176     /// }
 177     ///
 178     /// // should be:
 179     /// let _ = std::str::from_utf8(b).unwrap();
 180     /// ```
 181     pub TRANSMUTE_BYTES_TO_STR,
 182     complexity,
 183     "transmutes from a `&[u8]` to a `&str`"
 184 }
 185
 186 declare_clippy_lint! {
 187     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 188     ///
 189     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 190     ///
 191     /// **Known problems:** None.
 192     ///
 193     /// **Example:**
 194     /// ```rust
 195     /// let x = 1_u8;
 196     /// unsafe {
 197     ///     let _: bool = std::mem::transmute(x); // where x: u8
 198     /// }
 199     ///
 200     /// // should be:
 201     /// let _: bool = x != 0;
 202     /// ```
 203     pub TRANSMUTE_INT_TO_BOOL,
 204     complexity,
 205     "transmutes from an integer to a `bool`"
 206 }
 207
 208 declare_clippy_lint! {
 209     /// **What it does:** Checks for transmutes from an integer to a float.
 210     ///
 211     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 212     /// and safe.
 213     ///
 214     /// **Known problems:** None.
 215     ///
 216     /// **Example:**
 217     /// ```rust
 218     /// unsafe {
 219     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 220     /// }
 221     ///
 222     /// // should be:
 223     /// let _: f32 = f32::from_bits(1_u32);
 224     /// ```
 225     pub TRANSMUTE_INT_TO_FLOAT,
 226     complexity,
 227     "transmutes from an integer to a float"
 228 }
 229
 230 declare_clippy_lint! {
 231     /// **What it does:** Checks for transmutes from a float to an integer.
 232     ///
 233     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 234     /// and safe.
 235     ///
 236     /// **Known problems:** None.
 237     ///
 238     /// **Example:**
 239     /// ```rust
 240     /// unsafe {
 241     ///     let _: u32 = std::mem::transmute(1f32);
 242     /// }
 243     ///
 244     /// // should be:
 245     /// let _: u32 = 1f32.to_bits();
 246     /// ```
 247     pub TRANSMUTE_FLOAT_TO_INT,
 248     complexity,
 249     "transmutes from a float to an integer"
 250 }
 251
 252 declare_clippy_lint! {
 253     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 254     /// from a reference to a reference.
 255     ///
 256     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 257     /// written as casts.
 258     ///
 259     /// **Known problems:** None.
 260     ///
 261     /// **Example:**
 262     /// ```rust
 263     /// let ptr = &1u32 as *const u32;
 264     /// unsafe {
 265     ///     // pointer-to-pointer transmute
 266     ///     let _: *const f32 = std::mem::transmute(ptr);
 267     ///     // ref-ref transmute
 268     ///     let _: &f32 = std::mem::transmute(&1u32);
 269     /// }
 270     /// // These can be respectively written:
 271     /// let _ = ptr as *const f32;
 272     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 273     /// ```
 274     pub TRANSMUTE_PTR_TO_PTR,
 275     complexity,
 276     "transmutes from a pointer to a pointer / a reference to a reference"
 277 }
 278
 279 declare_clippy_lint! {
 280     /// **What it does:** Checks for transmutes between collections whose
 281     /// types have different ABI, size or alignment.
 282     ///
 283     /// **Why is this bad?** This is undefined behavior.
 284     ///
 285     /// **Known problems:** Currently, we cannot know whether a type is a
 286     /// collection, so we just lint the ones that come with `std`.
 287     ///
 288     /// **Example:**
 289     /// ```rust
 290     /// // different size, therefore likely out-of-bounds memory access
 291     /// // You absolutely do not want this in your code!
 292     /// unsafe {
 293     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 294     /// };
 295     /// ```
 296     ///
 297     /// You must always iterate, map and collect the values:
 298     ///
 299     /// ```rust
 300     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 301     /// ```
 302     pub UNSOUND_COLLECTION_TRANSMUTE,
 303     correctness,
 304     "transmute between collections of layout-incompatible types"
 305 }
 306
 307 declare_lint_pass!(Transmute => [
 308     CROSSPOINTER_TRANSMUTE,
 309     TRANSMUTE_PTR_TO_REF,
 310     TRANSMUTE_PTR_TO_PTR,
 311     USELESS_TRANSMUTE,
 312     WRONG_TRANSMUTE,
 313     TRANSMUTE_INT_TO_CHAR,
 314     TRANSMUTE_BYTES_TO_STR,
 315     TRANSMUTE_INT_TO_BOOL,
 316     TRANSMUTE_INT_TO_FLOAT,
 317     TRANSMUTE_FLOAT_TO_INT,
 318     UNSOUND_COLLECTION_TRANSMUTE,
 319     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 320 ]);
 321
 322 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 323 static COLLECTIONS: &[&[&str]] = &[
 324     &paths::VEC,
 325     &paths::VEC_DEQUE,
 326     &paths::BINARY_HEAP,
 327     &paths::BTREESET,
 328     &paths::BTREEMAP,
 329     &paths::HASHSET,
 330     &paths::HASHMAP,
 331 ];
 332
 333 impl<'tcx> LateLintPass<'tcx> for Transmute {
 334     #[allow(clippy::similar_names, clippy::too_many_lines)]
 335     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 336         if_chain! {
 337             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 338             if let ExprKind::Path(ref qpath) = path_expr.kind;
 339             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 340             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 341             then {
 342                 // Avoid suggesting from/to bits and dereferencing raw pointers in const contexts.
 343                 // See https://github.com/rust-lang/rust/issues/73736 for progress on making them `const fn`.
 344                 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
 345                 let const_context = in_constant(cx, e.hir_id);
 346
 347                 let from_ty = cx.typeck_results().expr_ty(&args[0]);
 348                 let to_ty = cx.typeck_results().expr_ty(e);
 349
 350                 let triggered = useless_transmute::check(cx, e, from_ty, to_ty, args);
 351                 if triggered {
 352                     return;
 353                 }
 354                 let triggered = wrong_transmute::check(cx, e, from_ty, to_ty);
 355                 if triggered {
 356                     return;
 357                 }
 358
 359                 match (&from_ty.kind(), &to_ty.kind()) {
 360                     (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 361                         cx,
 362                         CROSSPOINTER_TRANSMUTE,
 363                         e.span,
 364                         &format!(
 365                             "transmute from a type (`{}`) to the type that it points to (`{}`)",
 366                             from_ty, to_ty
 367                         ),
 368                     ),
 369                     (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 370                         cx,
 371                         CROSSPOINTER_TRANSMUTE,
 372                         e.span,
 373                         &format!(
 374                             "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 375                             from_ty, to_ty
 376                         ),
 377                     ),
 378                     (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 379                         cx,
 380                         TRANSMUTE_PTR_TO_REF,
 381                         e.span,
 382                         &format!(
 383                             "transmute from a pointer type (`{}`) to a reference type \
 384                              (`{}`)",
 385                             from_ty, to_ty
 386                         ),
 387                         |diag| {
 388                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 389                             let (deref, cast) = if *mutbl == Mutability::Mut {
 390                                 ("&mut *", "*mut")
 391                             } else {
 392                                 ("&*", "*const")
 393                             };
 394
 395                             let arg = if from_pty.ty == *to_ref_ty {
 396                                 arg
 397                             } else {
 398                                 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 399                             };
 400
 401                             diag.span_suggestion(
 402                                 e.span,
 403                                 "try",
 404                                 sugg::make_unop(deref, arg).to_string(),
 405                                 Applicability::Unspecified,
 406                             );
 407                         },
 408                     ),
 409                     (ty::Int(ty::IntTy::I32) | ty::Uint(ty::UintTy::U32), &ty::Char) => {
 410                         span_lint_and_then(
 411                             cx,
 412                             TRANSMUTE_INT_TO_CHAR,
 413                             e.span,
 414                             &format!("transmute from a `{}` to a `char`", from_ty),
 415                             |diag| {
 416                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 417                                 let arg = if let ty::Int(_) = from_ty.kind() {
 418                                     arg.as_ty(ast::UintTy::U32.name_str())
 419                                 } else {
 420                                     arg
 421                                 };
 422                                 diag.span_suggestion(
 423                                     e.span,
 424                                     "consider using",
 425                                     format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 426                                     Applicability::Unspecified,
 427                                 );
 428                             },
 429                         )
 430                     },
 431                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 432                         if_chain! {
 433                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind(), &ty_to.kind());
 434                             if let ty::Uint(ty::UintTy::U8) = slice_ty.kind();
 435                             if from_mutbl == to_mutbl;
 436                             then {
 437                                 let postfix = if *from_mutbl == Mutability::Mut {
 438                                     "_mut"
 439                                 } else {
 440                                     ""
 441                                 };
 442
 443                                 span_lint_and_sugg(
 444                                     cx,
 445                                     TRANSMUTE_BYTES_TO_STR,
 446                                     e.span,
 447                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 448                                     "consider using",
 449                                     format!(
 450                                         "std::str::from_utf8{}({}).unwrap()",
 451                                         postfix,
 452                                         snippet(cx, args[0].span, ".."),
 453                                     ),
 454                                     Applicability::Unspecified,
 455                                 );
 456                             } else {
 457                                 if (cx.tcx.erase_regions(from_ty) != cx.tcx.erase_regions(to_ty))
 458                                     && !const_context {
 459                                     span_lint_and_then(
 460                                         cx,
 461                                         TRANSMUTE_PTR_TO_PTR,
 462                                         e.span,
 463                                         "transmute from a reference to a reference",
 464                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 465                                             let ty_from_and_mut = ty::TypeAndMut {
 466                                                 ty: ty_from,
 467                                                 mutbl: *from_mutbl
 468                                             };
 469                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 470                                             let sugg_paren = arg
 471                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 472                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 473                                             let sugg = if *to_mutbl == Mutability::Mut {
 474                                                 sugg_paren.mut_addr_deref()
 475                                             } else {
 476                                                 sugg_paren.addr_deref()
 477                                             };
 478                                             diag.span_suggestion(
 479                                                 e.span,
 480                                                 "try",
 481                                                 sugg.to_string(),
 482                                                 Applicability::Unspecified,
 483                                             );
 484                                         },
 485                                     )
 486                                 }
 487                             }
 488                         }
 489                     },
 490                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 491                         cx,
 492                         TRANSMUTE_PTR_TO_PTR,
 493                         e.span,
 494                         "transmute from a pointer to a pointer",
 495                         |diag| {
 496                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 497                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 498                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 499                             }
 500                         },
 501                     ),
 502                     (ty::Int(ty::IntTy::I8) | ty::Uint(ty::UintTy::U8), ty::Bool) => {
 503                         span_lint_and_then(
 504                             cx,
 505                             TRANSMUTE_INT_TO_BOOL,
 506                             e.span,
 507                             &format!("transmute from a `{}` to a `bool`", from_ty),
 508                             |diag| {
 509                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 510                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 511                                 diag.span_suggestion(
 512                                     e.span,
 513                                     "consider using",
 514                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 515                                     Applicability::Unspecified,
 516                                 );
 517                             },
 518                         )
 519                     },
 520                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) if !const_context => span_lint_and_then(
 521                         cx,
 522                         TRANSMUTE_INT_TO_FLOAT,
 523                         e.span,
 524                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 525                         |diag| {
 526                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 527                             let arg = if let ty::Int(int_ty) = from_ty.kind() {
 528                                 arg.as_ty(format!(
 529                                     "u{}",
 530                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 531                                 ))
 532                             } else {
 533                                 arg
 534                             };
 535                             diag.span_suggestion(
 536                                 e.span,
 537                                 "consider using",
 538                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 539                                 Applicability::Unspecified,
 540                             );
 541                         },
 542                     ),
 543                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) if !const_context => span_lint_and_then(
 544                         cx,
 545                         TRANSMUTE_FLOAT_TO_INT,
 546                         e.span,
 547                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 548                         |diag| {
 549                             let mut expr = &args[0];
 550                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 551
 552                             if let ExprKind::Unary(UnOp::Neg, inner_expr) = &expr.kind {
 553                                 expr = &inner_expr;
 554                             }
 555
 556                             if_chain! {
 557                                 // if the expression is a float literal and it is unsuffixed then
 558                                 // add a suffix so the suggestion is valid and unambiguous
 559                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 560                                 if let ExprKind::Lit(lit) = &expr.kind;
 561                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 562                                 then {
 563                                     match arg {
 564                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 565                                         _ => arg = sugg::Sugg::NonParen(op)
 566                                     }
 567                                 }
 568                             }
 569
 570                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 571
 572                             // cast the result of `to_bits` if `to_ty` is signed
 573                             arg = if let ty::Int(int_ty) = to_ty.kind() {
 574                                 arg.as_ty(int_ty.name_str().to_string())
 575                             } else {
 576                                 arg
 577                             };
 578
 579                             diag.span_suggestion(
 580                                 e.span,
 581                                 "consider using",
 582                                 arg.to_string(),
 583                                 Applicability::Unspecified,
 584                             );
 585                         },
 586                     ),
 587                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 588                         if from_adt.did != to_adt.did ||
 589                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 590                             return;
 591                         }
 592                         if from_substs.types().zip(to_substs.types())
 593                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 594                             span_lint(
 595                                 cx,
 596                                 UNSOUND_COLLECTION_TRANSMUTE,
 597                                 e.span,
 598                                 &format!(
 599                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 600                                     from_ty,
 601                                     to_ty
 602                                 )
 603                             );
 604                         }
 605                     },
 606                     (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
 607                         cx,
 608                         TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 609                         e.span,
 610                         &format!(
 611                             "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
 612                             from_ty,
 613                             to_ty
 614                         ),
 615                         |diag| {
 616                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 617                                 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
 618                                 diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);
 619                             }
 620                         }
 621                     ),
 622                     _ => {
 623                         return;
 624                     },
 625                 }
 626             }
 627         }
 628     }
 629 }