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_then, sugg,
   3 };
   4 use if_chain::if_chain;
   5 use rustc::ty::{self, Ty};
   6 use rustc_ast::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_session::{declare_lint_pass, declare_tool_lint};
  11 use std::borrow::Cow;
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for transmutes that can't ever be correct on any
  15     /// architecture.
  16     ///
  17     /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  18     ///
  19     /// **Known problems:** When accessing C, users might want to store pointer
  20     /// sized objects in `extradata` arguments to save an allocation.
  21     ///
  22     /// **Example:**
  23     /// ```ignore
  24     /// let ptr: *const T = core::intrinsics::transmute('x')
  25     /// ```
  26     pub WRONG_TRANSMUTE,
  27     correctness,
  28     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  29 }
  30
  31 declare_clippy_lint! {
  32     /// **What it does:** Checks for transmutes to the original type of the object
  33     /// and transmutes that could be a cast.
  34     ///
  35     /// **Why is this bad?** Readability. The code tricks people into thinking that
  36     /// something complex is going on.
  37     ///
  38     /// **Known problems:** None.
  39     ///
  40     /// **Example:**
  41     /// ```rust,ignore
  42     /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
  43     /// ```
  44     pub USELESS_TRANSMUTE,
  45     complexity,
  46     "transmutes that have the same to and from types or could be a cast/coercion"
  47 }
  48
  49 declare_clippy_lint! {
  50     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  51     ///
  52     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  53     /// pointer to that type.
  54     ///
  55     /// **Known problems:** None.
  56     ///
  57     /// **Example:**
  58     /// ```rust,ignore
  59     /// core::intrinsics::transmute(t) // where the result type is the same as
  60     ///                                // `*t` or `&t`'s
  61     /// ```
  62     pub CROSSPOINTER_TRANSMUTE,
  63     complexity,
  64     "transmutes that have to or from types that are a pointer to the other"
  65 }
  66
  67 declare_clippy_lint! {
  68     /// **What it does:** Checks for transmutes from a pointer to a reference.
  69     ///
  70     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
  71     ///
  72     /// **Known problems:** None.
  73     ///
  74     /// **Example:**
  75     /// ```rust,ignore
  76     /// unsafe {
  77     ///     let _: &T = std::mem::transmute(p); // where p: *const T
  78     /// }
  79     ///
  80     /// // can be written:
  81     /// let _: &T = &*p;
  82     /// ```
  83     pub TRANSMUTE_PTR_TO_REF,
  84     complexity,
  85     "transmutes from a pointer to a reference type"
  86 }
  87
  88 declare_clippy_lint! {
  89     /// **What it does:** Checks for transmutes from an integer to a `char`.
  90     ///
  91     /// **Why is this bad?** Not every integer is a Unicode scalar value.
  92     ///
  93     /// **Known problems:**
  94     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
  95     /// as it needs to validate the input.
  96     /// If you are certain that the input is always a valid Unicode scalar value,
  97     /// use [`from_u32_unchecked`] which is as fast as `transmute`
  98     /// but has a semantically meaningful name.
  99     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 100     ///
 101     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 102     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 103     ///
 104     /// **Example:**
 105     /// ```rust
 106     /// let x = 1_u32;
 107     /// unsafe {
 108     ///     let _: char = std::mem::transmute(x); // where x: u32
 109     /// }
 110     ///
 111     /// // should be:
 112     /// let _ = std::char::from_u32(x).unwrap();
 113     /// ```
 114     pub TRANSMUTE_INT_TO_CHAR,
 115     complexity,
 116     "transmutes from an integer to a `char`"
 117 }
 118
 119 declare_clippy_lint! {
 120     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 121     ///
 122     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 123     ///
 124     /// **Known problems:**
 125     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 126     /// as it needs to validate the input.
 127     /// If you are certain that the input is always a valid UTF-8,
 128     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 129     /// but has a semantically meaningful name.
 130     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 131     ///
 132     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 133     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 134     ///
 135     /// **Example:**
 136     /// ```rust
 137     /// let b: &[u8] = &[1_u8, 2_u8];
 138     /// unsafe {
 139     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 140     /// }
 141     ///
 142     /// // should be:
 143     /// let _ = std::str::from_utf8(b).unwrap();
 144     /// ```
 145     pub TRANSMUTE_BYTES_TO_STR,
 146     complexity,
 147     "transmutes from a `&[u8]` to a `&str`"
 148 }
 149
 150 declare_clippy_lint! {
 151     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 152     ///
 153     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 154     ///
 155     /// **Known problems:** None.
 156     ///
 157     /// **Example:**
 158     /// ```rust
 159     /// let x = 1_u8;
 160     /// unsafe {
 161     ///     let _: bool = std::mem::transmute(x); // where x: u8
 162     /// }
 163     ///
 164     /// // should be:
 165     /// let _: bool = x != 0;
 166     /// ```
 167     pub TRANSMUTE_INT_TO_BOOL,
 168     complexity,
 169     "transmutes from an integer to a `bool`"
 170 }
 171
 172 declare_clippy_lint! {
 173     /// **What it does:** Checks for transmutes from an integer to a float.
 174     ///
 175     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 176     /// and safe.
 177     ///
 178     /// **Known problems:** None.
 179     ///
 180     /// **Example:**
 181     /// ```rust
 182     /// unsafe {
 183     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 184     /// }
 185     ///
 186     /// // should be:
 187     /// let _: f32 = f32::from_bits(1_u32);
 188     /// ```
 189     pub TRANSMUTE_INT_TO_FLOAT,
 190     complexity,
 191     "transmutes from an integer to a float"
 192 }
 193
 194 declare_clippy_lint! {
 195     /// **What it does:** Checks for transmutes from a float to an integer.
 196     ///
 197     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 198     /// and safe.
 199     ///
 200     /// **Known problems:** None.
 201     ///
 202     /// **Example:**
 203     /// ```rust
 204     /// unsafe {
 205     ///     let _: u32 = std::mem::transmute(1f32);
 206     /// }
 207     ///
 208     /// // should be:
 209     /// let _: u32 = 1f32.to_bits();
 210     /// ```
 211     pub TRANSMUTE_FLOAT_TO_INT,
 212     complexity,
 213     "transmutes from a float to an integer"
 214 }
 215
 216 declare_clippy_lint! {
 217     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 218     /// from a reference to a reference.
 219     ///
 220     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 221     /// written as casts.
 222     ///
 223     /// **Known problems:** None.
 224     ///
 225     /// **Example:**
 226     /// ```rust
 227     /// let ptr = &1u32 as *const u32;
 228     /// unsafe {
 229     ///     // pointer-to-pointer transmute
 230     ///     let _: *const f32 = std::mem::transmute(ptr);
 231     ///     // ref-ref transmute
 232     ///     let _: &f32 = std::mem::transmute(&1u32);
 233     /// }
 234     /// // These can be respectively written:
 235     /// let _ = ptr as *const f32;
 236     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 237     /// ```
 238     pub TRANSMUTE_PTR_TO_PTR,
 239     complexity,
 240     "transmutes from a pointer to a pointer / a reference to a reference"
 241 }
 242
 243 declare_clippy_lint! {
 244     /// **What it does:** Checks for transmutes between collections whose
 245     /// types have different ABI, size or alignment.
 246     ///
 247     /// **Why is this bad?** This is undefined behavior.
 248     ///
 249     /// **Known problems:** Currently, we cannot know whether a type is a
 250     /// collection, so we just lint the ones that come with `std`.
 251     ///
 252     /// **Example:**
 253     /// ```rust
 254     /// // different size, therefore likely out-of-bounds memory access
 255     /// // You absolutely do not want this in your code!
 256     /// unsafe {
 257     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 258     /// };
 259     /// ```
 260     ///
 261     /// You must always iterate, map and collect the values:
 262     ///
 263     /// ```rust
 264     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 265     /// ```
 266     pub UNSOUND_COLLECTION_TRANSMUTE,
 267     correctness,
 268     "transmute between collections of layout-incompatible types"
 269 }
 270 declare_lint_pass!(Transmute => [
 271     CROSSPOINTER_TRANSMUTE,
 272     TRANSMUTE_PTR_TO_REF,
 273     TRANSMUTE_PTR_TO_PTR,
 274     USELESS_TRANSMUTE,
 275     WRONG_TRANSMUTE,
 276     TRANSMUTE_INT_TO_CHAR,
 277     TRANSMUTE_BYTES_TO_STR,
 278     TRANSMUTE_INT_TO_BOOL,
 279     TRANSMUTE_INT_TO_FLOAT,
 280     TRANSMUTE_FLOAT_TO_INT,
 281     UNSOUND_COLLECTION_TRANSMUTE,
 282 ]);
 283
 284 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 285 static COLLECTIONS: &[&[&str]] = &[
 286     &paths::VEC,
 287     &paths::VEC_DEQUE,
 288     &paths::BINARY_HEAP,
 289     &paths::BTREESET,
 290     &paths::BTREEMAP,
 291     &paths::HASHSET,
 292     &paths::HASHMAP,
 293 ];
 294 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Transmute {
 295     #[allow(clippy::similar_names, clippy::too_many_lines)]
 296     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
 297         if_chain! {
 298             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 299             if let ExprKind::Path(ref qpath) = path_expr.kind;
 300             if let Some(def_id) = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 301             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 302             then {
 303                 let from_ty = cx.tables.expr_ty(&args[0]);
 304                 let to_ty = cx.tables.expr_ty(e);
 305
 306                 match (&from_ty.kind, &to_ty.kind) {
 307                     _ if from_ty == to_ty => span_lint(
 308                         cx,
 309                         USELESS_TRANSMUTE,
 310                         e.span,
 311                         &format!("transmute from a type (`{}`) to itself", from_ty),
 312                     ),
 313                     (&ty::Ref(_, rty, rty_mutbl), &ty::RawPtr(ptr_ty)) => span_lint_and_then(
 314                         cx,
 315                         USELESS_TRANSMUTE,
 316                         e.span,
 317                         "transmute from a reference to a pointer",
 318                         |db| {
 319                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 320                                 let rty_and_mut = ty::TypeAndMut {
 321                                     ty: rty,
 322                                     mutbl: rty_mutbl,
 323                                 };
 324
 325                                 let sugg = if ptr_ty == rty_and_mut {
 326                                     arg.as_ty(to_ty)
 327                                 } else {
 328                                     arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 329                                 };
 330
 331                                 db.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 332                             }
 333                         },
 334                     ),
 335                     (&ty::Int(_), &ty::RawPtr(_)) | (&ty::Uint(_), &ty::RawPtr(_)) => span_lint_and_then(
 336                         cx,
 337                         USELESS_TRANSMUTE,
 338                         e.span,
 339                         "transmute from an integer to a pointer",
 340                         |db| {
 341                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 342                                 db.span_suggestion(
 343                                     e.span,
 344                                     "try",
 345                                     arg.as_ty(&to_ty.to_string()).to_string(),
 346                                     Applicability::Unspecified,
 347                                 );
 348                             }
 349                         },
 350                     ),
 351                     (&ty::Float(_), &ty::Ref(..))
 352                     | (&ty::Float(_), &ty::RawPtr(_))
 353                     | (&ty::Char, &ty::Ref(..))
 354                     | (&ty::Char, &ty::RawPtr(_)) => span_lint(
 355                         cx,
 356                         WRONG_TRANSMUTE,
 357                         e.span,
 358                         &format!("transmute from a `{}` to a pointer", from_ty),
 359                     ),
 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                         |db| {
 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                             db.span_suggestion(
 402                                 e.span,
 403                                 "try",
 404                                 sugg::make_unop(deref, arg).to_string(),
 405                                 Applicability::Unspecified,
 406                             );
 407                         },
 408                     ),
 409                     (&ty::Int(ast::IntTy::I32), &ty::Char) | (&ty::Uint(ast::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                             |db| {
 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                                 db.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(ast::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_then(
 444                                     cx,
 445                                     TRANSMUTE_BYTES_TO_STR,
 446                                     e.span,
 447                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 448                                     |db| {
 449                                         db.span_suggestion(
 450                                             e.span,
 451                                             "consider using",
 452                                             format!(
 453                                                 "std::str::from_utf8{}({}).unwrap()",
 454                                                 postfix,
 455                                                 snippet(cx, args[0].span, ".."),
 456                                             ),
 457                                             Applicability::Unspecified,
 458                                         );
 459                                     }
 460                                 )
 461                             } else {
 462                                 if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
 463                                     span_lint_and_then(
 464                                         cx,
 465                                         TRANSMUTE_PTR_TO_PTR,
 466                                         e.span,
 467                                         "transmute from a reference to a reference",
 468                                         |db| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 469                                             let ty_from_and_mut = ty::TypeAndMut {
 470                                                 ty: ty_from,
 471                                                 mutbl: from_mutbl
 472                                             };
 473                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: to_mutbl };
 474                                             let sugg_paren = arg
 475                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 476                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 477                                             let sugg = if to_mutbl == Mutability::Mut {
 478                                                 sugg_paren.mut_addr_deref()
 479                                             } else {
 480                                                 sugg_paren.addr_deref()
 481                                             };
 482                                             db.span_suggestion(
 483                                                 e.span,
 484                                                 "try",
 485                                                 sugg.to_string(),
 486                                                 Applicability::Unspecified,
 487                                             );
 488                                         },
 489                                     )
 490                                 }
 491                             }
 492                         }
 493                     },
 494                     (&ty::RawPtr(_), &ty::RawPtr(to_ty)) => span_lint_and_then(
 495                         cx,
 496                         TRANSMUTE_PTR_TO_PTR,
 497                         e.span,
 498                         "transmute from a pointer to a pointer",
 499                         |db| {
 500                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 501                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(to_ty));
 502                                 db.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 503                             }
 504                         },
 505                     ),
 506                     (&ty::Int(ast::IntTy::I8), &ty::Bool) | (&ty::Uint(ast::UintTy::U8), &ty::Bool) => {
 507                         span_lint_and_then(
 508                             cx,
 509                             TRANSMUTE_INT_TO_BOOL,
 510                             e.span,
 511                             &format!("transmute from a `{}` to a `bool`", from_ty),
 512                             |db| {
 513                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 514                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 515                                 db.span_suggestion(
 516                                     e.span,
 517                                     "consider using",
 518                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 519                                     Applicability::Unspecified,
 520                                 );
 521                             },
 522                         )
 523                     },
 524                     (&ty::Int(_), &ty::Float(_)) | (&ty::Uint(_), &ty::Float(_)) => span_lint_and_then(
 525                         cx,
 526                         TRANSMUTE_INT_TO_FLOAT,
 527                         e.span,
 528                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 529                         |db| {
 530                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 531                             let arg = if let ty::Int(int_ty) = from_ty.kind {
 532                                 arg.as_ty(format!(
 533                                     "u{}",
 534                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 535                                 ))
 536                             } else {
 537                                 arg
 538                             };
 539                             db.span_suggestion(
 540                                 e.span,
 541                                 "consider using",
 542                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 543                                 Applicability::Unspecified,
 544                             );
 545                         },
 546                     ),
 547                     (&ty::Float(float_ty), &ty::Int(_)) | (&ty::Float(float_ty), &ty::Uint(_)) => span_lint_and_then(
 548                         cx,
 549                         TRANSMUTE_FLOAT_TO_INT,
 550                         e.span,
 551                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 552                         |db| {
 553                             let mut expr = &args[0];
 554                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 555
 556                             if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
 557                                 expr = &inner_expr;
 558                             }
 559
 560                             if_chain! {
 561                                 // if the expression is a float literal and it is unsuffixed then
 562                                 // add a suffix so the suggestion is valid and unambiguous
 563                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 564                                 if let ExprKind::Lit(lit) = &expr.kind;
 565                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 566                                 then {
 567                                     match arg {
 568                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 569                                         _ => arg = sugg::Sugg::NonParen(op)
 570                                     }
 571                                 }
 572                             }
 573
 574                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 575
 576                             // cast the result of `to_bits` if `to_ty` is signed
 577                             arg = if let ty::Int(int_ty) = to_ty.kind {
 578                                 arg.as_ty(int_ty.name_str().to_string())
 579                             } else {
 580                                 arg
 581                             };
 582
 583                             db.span_suggestion(
 584                                 e.span,
 585                                 "consider using",
 586                                 arg.to_string(),
 587                                 Applicability::Unspecified,
 588                             );
 589                         },
 590                     ),
 591                     (&ty::Adt(ref from_adt, ref from_substs), &ty::Adt(ref to_adt, ref to_substs)) => {
 592                         if from_adt.did != to_adt.did ||
 593                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 594                             return;
 595                         }
 596                         if from_substs.types().zip(to_substs.types())
 597                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 598                             span_lint(
 599                                 cx,
 600                                 UNSOUND_COLLECTION_TRANSMUTE,
 601                                 e.span,
 602                                 &format!(
 603                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 604                                     from_ty,
 605                                     to_ty
 606                                 )
 607                             );
 608                         }
 609                     },
 610                     _ => return,
 611                 }
 612             }
 613         }
 614     }
 615 }
 616
 617 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 618 /// not available , use
 619 /// the type's `ToString` implementation. In weird cases it could lead to types
 620 /// with invalid `'_`
 621 /// lifetime, but it should be rare.
 622 fn get_type_snippet(cx: &LateContext<'_, '_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
 623     let seg = last_path_segment(path);
 624     if_chain! {
 625         if let Some(ref params) = seg.args;
 626         if !params.parenthesized;
 627         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 628             GenericArg::Type(ty) => Some(ty),
 629             _ => None,
 630         }).nth(1);
 631         if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
 632         then {
 633             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 634         }
 635     }
 636
 637     to_ref_ty.to_string()
 638 }
 639
 640 // check if the component types of the transmuted collection and the result have different ABI,
 641 // size or alignment
 642 fn is_layout_incompatible<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
 643     let empty_param_env = ty::ParamEnv::empty();
 644     // check if `from` and `to` are normalizable to avoid ICE (#4968)
 645     if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
 646         return false;
 647     }
 648     let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
 649     let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
 650     if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
 651         from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
 652     } else {
 653         // no idea about layout, so don't lint
 654         false
 655     }
 656 }