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

   1 use crate::utils::{
   2     is_normalizable, last_path_segment, match_def_path, paths, snippet, span_lint, span_lint_and_sugg,
   3     span_lint_and_then, sugg,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_ast::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, Ty};
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use std::borrow::Cow;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for transmutes that can't ever be correct on any
  16     /// architecture.
  17     ///
  18     /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  19     ///
  20     /// **Known problems:** When accessing C, users might want to store pointer
  21     /// sized objects in `extradata` arguments to save an allocation.
  22     ///
  23     /// **Example:**
  24     /// ```ignore
  25     /// let ptr: *const T = core::intrinsics::transmute('x')
  26     /// ```
  27     pub WRONG_TRANSMUTE,
  28     correctness,
  29     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  30 }
  31
  32 // FIXME: Move this to `complexity` again, after #5343 is fixed
  33 declare_clippy_lint! {
  34     /// **What it does:** Checks for transmutes to the original type of the object
  35     /// and transmutes that could be a cast.
  36     ///
  37     /// **Why is this bad?** Readability. The code tricks people into thinking that
  38     /// something complex is going on.
  39     ///
  40     /// **Known problems:** None.
  41     ///
  42     /// **Example:**
  43     /// ```rust,ignore
  44     /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
  45     /// ```
  46     pub USELESS_TRANSMUTE,
  47     nursery,
  48     "transmutes that have the same to and from types or could be a cast/coercion"
  49 }
  50
  51 declare_clippy_lint! {
  52     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  53     ///
  54     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  55     /// pointer to that type.
  56     ///
  57     /// **Known problems:** None.
  58     ///
  59     /// **Example:**
  60     /// ```rust,ignore
  61     /// core::intrinsics::transmute(t) // where the result type is the same as
  62     ///                                // `*t` or `&t`'s
  63     /// ```
  64     pub CROSSPOINTER_TRANSMUTE,
  65     complexity,
  66     "transmutes that have to or from types that are a pointer to the other"
  67 }
  68
  69 declare_clippy_lint! {
  70     /// **What it does:** Checks for transmutes from a pointer to a reference.
  71     ///
  72     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
  73     ///
  74     /// **Known problems:** None.
  75     ///
  76     /// **Example:**
  77     /// ```rust,ignore
  78     /// unsafe {
  79     ///     let _: &T = std::mem::transmute(p); // where p: *const T
  80     /// }
  81     ///
  82     /// // can be written:
  83     /// let _: &T = &*p;
  84     /// ```
  85     pub TRANSMUTE_PTR_TO_REF,
  86     complexity,
  87     "transmutes from a pointer to a reference type"
  88 }
  89
  90 declare_clippy_lint! {
  91     /// **What it does:** Checks for transmutes from an integer to a `char`.
  92     ///
  93     /// **Why is this bad?** Not every integer is a Unicode scalar value.
  94     ///
  95     /// **Known problems:**
  96     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
  97     /// as it needs to validate the input.
  98     /// If you are certain that the input is always a valid Unicode scalar value,
  99     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 100     /// but has a semantically meaningful name.
 101     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 102     ///
 103     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 104     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 105     ///
 106     /// **Example:**
 107     /// ```rust
 108     /// let x = 1_u32;
 109     /// unsafe {
 110     ///     let _: char = std::mem::transmute(x); // where x: u32
 111     /// }
 112     ///
 113     /// // should be:
 114     /// let _ = std::char::from_u32(x).unwrap();
 115     /// ```
 116     pub TRANSMUTE_INT_TO_CHAR,
 117     complexity,
 118     "transmutes from an integer to a `char`"
 119 }
 120
 121 declare_clippy_lint! {
 122     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 123     ///
 124     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 125     ///
 126     /// **Known problems:**
 127     /// - [`from_utf8`] 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 UTF-8,
 130     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 131     /// but has a semantically meaningful name.
 132     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 133     ///
 134     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 135     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 136     ///
 137     /// **Example:**
 138     /// ```rust
 139     /// let b: &[u8] = &[1_u8, 2_u8];
 140     /// unsafe {
 141     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 142     /// }
 143     ///
 144     /// // should be:
 145     /// let _ = std::str::from_utf8(b).unwrap();
 146     /// ```
 147     pub TRANSMUTE_BYTES_TO_STR,
 148     complexity,
 149     "transmutes from a `&[u8]` to a `&str`"
 150 }
 151
 152 declare_clippy_lint! {
 153     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 154     ///
 155     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 156     ///
 157     /// **Known problems:** None.
 158     ///
 159     /// **Example:**
 160     /// ```rust
 161     /// let x = 1_u8;
 162     /// unsafe {
 163     ///     let _: bool = std::mem::transmute(x); // where x: u8
 164     /// }
 165     ///
 166     /// // should be:
 167     /// let _: bool = x != 0;
 168     /// ```
 169     pub TRANSMUTE_INT_TO_BOOL,
 170     complexity,
 171     "transmutes from an integer to a `bool`"
 172 }
 173
 174 declare_clippy_lint! {
 175     /// **What it does:** Checks for transmutes from an integer to a float.
 176     ///
 177     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 178     /// and safe.
 179     ///
 180     /// **Known problems:** None.
 181     ///
 182     /// **Example:**
 183     /// ```rust
 184     /// unsafe {
 185     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 186     /// }
 187     ///
 188     /// // should be:
 189     /// let _: f32 = f32::from_bits(1_u32);
 190     /// ```
 191     pub TRANSMUTE_INT_TO_FLOAT,
 192     complexity,
 193     "transmutes from an integer to a float"
 194 }
 195
 196 declare_clippy_lint! {
 197     /// **What it does:** Checks for transmutes from a float to an integer.
 198     ///
 199     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 200     /// and safe.
 201     ///
 202     /// **Known problems:** None.
 203     ///
 204     /// **Example:**
 205     /// ```rust
 206     /// unsafe {
 207     ///     let _: u32 = std::mem::transmute(1f32);
 208     /// }
 209     ///
 210     /// // should be:
 211     /// let _: u32 = 1f32.to_bits();
 212     /// ```
 213     pub TRANSMUTE_FLOAT_TO_INT,
 214     complexity,
 215     "transmutes from a float to an integer"
 216 }
 217
 218 declare_clippy_lint! {
 219     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 220     /// from a reference to a reference.
 221     ///
 222     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 223     /// written as casts.
 224     ///
 225     /// **Known problems:** None.
 226     ///
 227     /// **Example:**
 228     /// ```rust
 229     /// let ptr = &1u32 as *const u32;
 230     /// unsafe {
 231     ///     // pointer-to-pointer transmute
 232     ///     let _: *const f32 = std::mem::transmute(ptr);
 233     ///     // ref-ref transmute
 234     ///     let _: &f32 = std::mem::transmute(&1u32);
 235     /// }
 236     /// // These can be respectively written:
 237     /// let _ = ptr as *const f32;
 238     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 239     /// ```
 240     pub TRANSMUTE_PTR_TO_PTR,
 241     complexity,
 242     "transmutes from a pointer to a pointer / a reference to a reference"
 243 }
 244
 245 declare_clippy_lint! {
 246     /// **What it does:** Checks for transmutes between collections whose
 247     /// types have different ABI, size or alignment.
 248     ///
 249     /// **Why is this bad?** This is undefined behavior.
 250     ///
 251     /// **Known problems:** Currently, we cannot know whether a type is a
 252     /// collection, so we just lint the ones that come with `std`.
 253     ///
 254     /// **Example:**
 255     /// ```rust
 256     /// // different size, therefore likely out-of-bounds memory access
 257     /// // You absolutely do not want this in your code!
 258     /// unsafe {
 259     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 260     /// };
 261     /// ```
 262     ///
 263     /// You must always iterate, map and collect the values:
 264     ///
 265     /// ```rust
 266     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 267     /// ```
 268     pub UNSOUND_COLLECTION_TRANSMUTE,
 269     correctness,
 270     "transmute between collections of layout-incompatible types"
 271 }
 272 declare_lint_pass!(Transmute => [
 273     CROSSPOINTER_TRANSMUTE,
 274     TRANSMUTE_PTR_TO_REF,
 275     TRANSMUTE_PTR_TO_PTR,
 276     USELESS_TRANSMUTE,
 277     WRONG_TRANSMUTE,
 278     TRANSMUTE_INT_TO_CHAR,
 279     TRANSMUTE_BYTES_TO_STR,
 280     TRANSMUTE_INT_TO_BOOL,
 281     TRANSMUTE_INT_TO_FLOAT,
 282     TRANSMUTE_FLOAT_TO_INT,
 283     UNSOUND_COLLECTION_TRANSMUTE,
 284 ]);
 285
 286 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 287 static COLLECTIONS: &[&[&str]] = &[
 288     &paths::VEC,
 289     &paths::VEC_DEQUE,
 290     &paths::BINARY_HEAP,
 291     &paths::BTREESET,
 292     &paths::BTREEMAP,
 293     &paths::HASHSET,
 294     &paths::HASHMAP,
 295 ];
 296 impl<'tcx> LateLintPass<'tcx> for Transmute {
 297     #[allow(clippy::similar_names, clippy::too_many_lines)]
 298     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 299         if_chain! {
 300             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 301             if let ExprKind::Path(ref qpath) = path_expr.kind;
 302             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 303             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 304             then {
 305                 let from_ty = cx.tables().expr_ty(&args[0]);
 306                 let to_ty = cx.tables().expr_ty(e);
 307
 308                 match (&from_ty.kind, &to_ty.kind) {
 309                     _ if from_ty == to_ty => span_lint(
 310                         cx,
 311                         USELESS_TRANSMUTE,
 312                         e.span,
 313                         &format!("transmute from a type (`{}`) to itself", from_ty),
 314                     ),
 315                     (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => span_lint_and_then(
 316                         cx,
 317                         USELESS_TRANSMUTE,
 318                         e.span,
 319                         "transmute from a reference to a pointer",
 320                         |diag| {
 321                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 322                                 let rty_and_mut = ty::TypeAndMut {
 323                                     ty: rty,
 324                                     mutbl: *rty_mutbl,
 325                                 };
 326
 327                                 let sugg = if *ptr_ty == rty_and_mut {
 328                                     arg.as_ty(to_ty)
 329                                 } else {
 330                                     arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 331                                 };
 332
 333                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 334                             }
 335                         },
 336                     ),
 337                     (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => span_lint_and_then(
 338                         cx,
 339                         USELESS_TRANSMUTE,
 340                         e.span,
 341                         "transmute from an integer to a pointer",
 342                         |diag| {
 343                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 344                                 diag.span_suggestion(
 345                                     e.span,
 346                                     "try",
 347                                     arg.as_ty(&to_ty.to_string()).to_string(),
 348                                     Applicability::Unspecified,
 349                                 );
 350                             }
 351                         },
 352                     ),
 353                     (ty::Float(_) | ty::Char, ty::Ref(..) | ty::RawPtr(_)) => span_lint(
 354                         cx,
 355                         WRONG_TRANSMUTE,
 356                         e.span,
 357                         &format!("transmute from a `{}` to a pointer", from_ty),
 358                     ),
 359                     (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 360                         cx,
 361                         CROSSPOINTER_TRANSMUTE,
 362                         e.span,
 363                         &format!(
 364                             "transmute from a type (`{}`) to the type that it points to (`{}`)",
 365                             from_ty, to_ty
 366                         ),
 367                     ),
 368                     (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 369                         cx,
 370                         CROSSPOINTER_TRANSMUTE,
 371                         e.span,
 372                         &format!(
 373                             "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 374                             from_ty, to_ty
 375                         ),
 376                     ),
 377                     (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 378                         cx,
 379                         TRANSMUTE_PTR_TO_REF,
 380                         e.span,
 381                         &format!(
 382                             "transmute from a pointer type (`{}`) to a reference type \
 383                              (`{}`)",
 384                             from_ty, to_ty
 385                         ),
 386                         |diag| {
 387                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 388                             let (deref, cast) = if *mutbl == Mutability::Mut {
 389                                 ("&mut *", "*mut")
 390                             } else {
 391                                 ("&*", "*const")
 392                             };
 393
 394                             let arg = if from_pty.ty == *to_ref_ty {
 395                                 arg
 396                             } else {
 397                                 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 398                             };
 399
 400                             diag.span_suggestion(
 401                                 e.span,
 402                                 "try",
 403                                 sugg::make_unop(deref, arg).to_string(),
 404                                 Applicability::Unspecified,
 405                             );
 406                         },
 407                     ),
 408                     (ty::Int(ast::IntTy::I32) | ty::Uint(ast::UintTy::U32), &ty::Char) => {
 409                         span_lint_and_then(
 410                             cx,
 411                             TRANSMUTE_INT_TO_CHAR,
 412                             e.span,
 413                             &format!("transmute from a `{}` to a `char`", from_ty),
 414                             |diag| {
 415                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 416                                 let arg = if let ty::Int(_) = from_ty.kind {
 417                                     arg.as_ty(ast::UintTy::U32.name_str())
 418                                 } else {
 419                                     arg
 420                                 };
 421                                 diag.span_suggestion(
 422                                     e.span,
 423                                     "consider using",
 424                                     format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 425                                     Applicability::Unspecified,
 426                                 );
 427                             },
 428                         )
 429                     },
 430                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 431                         if_chain! {
 432                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind, &ty_to.kind);
 433                             if let ty::Uint(ast::UintTy::U8) = slice_ty.kind;
 434                             if from_mutbl == to_mutbl;
 435                             then {
 436                                 let postfix = if *from_mutbl == Mutability::Mut {
 437                                     "_mut"
 438                                 } else {
 439                                     ""
 440                                 };
 441
 442                                 span_lint_and_sugg(
 443                                     cx,
 444                                     TRANSMUTE_BYTES_TO_STR,
 445                                     e.span,
 446                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 447                                     "consider using",
 448                                     format!(
 449                                         "std::str::from_utf8{}({}).unwrap()",
 450                                         postfix,
 451                                         snippet(cx, args[0].span, ".."),
 452                                     ),
 453                                     Applicability::Unspecified,
 454                                 );
 455                             } else {
 456                                 if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
 457                                     span_lint_and_then(
 458                                         cx,
 459                                         TRANSMUTE_PTR_TO_PTR,
 460                                         e.span,
 461                                         "transmute from a reference to a reference",
 462                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 463                                             let ty_from_and_mut = ty::TypeAndMut {
 464                                                 ty: ty_from,
 465                                                 mutbl: *from_mutbl
 466                                             };
 467                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 468                                             let sugg_paren = arg
 469                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 470                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 471                                             let sugg = if *to_mutbl == Mutability::Mut {
 472                                                 sugg_paren.mut_addr_deref()
 473                                             } else {
 474                                                 sugg_paren.addr_deref()
 475                                             };
 476                                             diag.span_suggestion(
 477                                                 e.span,
 478                                                 "try",
 479                                                 sugg.to_string(),
 480                                                 Applicability::Unspecified,
 481                                             );
 482                                         },
 483                                     )
 484                                 }
 485                             }
 486                         }
 487                     },
 488                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 489                         cx,
 490                         TRANSMUTE_PTR_TO_PTR,
 491                         e.span,
 492                         "transmute from a pointer to a pointer",
 493                         |diag| {
 494                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 495                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 496                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 497                             }
 498                         },
 499                     ),
 500                     (ty::Int(ast::IntTy::I8) | ty::Uint(ast::UintTy::U8), ty::Bool) => {
 501                         span_lint_and_then(
 502                             cx,
 503                             TRANSMUTE_INT_TO_BOOL,
 504                             e.span,
 505                             &format!("transmute from a `{}` to a `bool`", from_ty),
 506                             |diag| {
 507                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 508                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 509                                 diag.span_suggestion(
 510                                     e.span,
 511                                     "consider using",
 512                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 513                                     Applicability::Unspecified,
 514                                 );
 515                             },
 516                         )
 517                     },
 518                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) => span_lint_and_then(
 519                         cx,
 520                         TRANSMUTE_INT_TO_FLOAT,
 521                         e.span,
 522                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 523                         |diag| {
 524                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 525                             let arg = if let ty::Int(int_ty) = from_ty.kind {
 526                                 arg.as_ty(format!(
 527                                     "u{}",
 528                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 529                                 ))
 530                             } else {
 531                                 arg
 532                             };
 533                             diag.span_suggestion(
 534                                 e.span,
 535                                 "consider using",
 536                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 537                                 Applicability::Unspecified,
 538                             );
 539                         },
 540                     ),
 541                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) => span_lint_and_then(
 542                         cx,
 543                         TRANSMUTE_FLOAT_TO_INT,
 544                         e.span,
 545                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 546                         |diag| {
 547                             let mut expr = &args[0];
 548                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 549
 550                             if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
 551                                 expr = &inner_expr;
 552                             }
 553
 554                             if_chain! {
 555                                 // if the expression is a float literal and it is unsuffixed then
 556                                 // add a suffix so the suggestion is valid and unambiguous
 557                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 558                                 if let ExprKind::Lit(lit) = &expr.kind;
 559                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 560                                 then {
 561                                     match arg {
 562                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 563                                         _ => arg = sugg::Sugg::NonParen(op)
 564                                     }
 565                                 }
 566                             }
 567
 568                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 569
 570                             // cast the result of `to_bits` if `to_ty` is signed
 571                             arg = if let ty::Int(int_ty) = to_ty.kind {
 572                                 arg.as_ty(int_ty.name_str().to_string())
 573                             } else {
 574                                 arg
 575                             };
 576
 577                             diag.span_suggestion(
 578                                 e.span,
 579                                 "consider using",
 580                                 arg.to_string(),
 581                                 Applicability::Unspecified,
 582                             );
 583                         },
 584                     ),
 585                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 586                         if from_adt.did != to_adt.did ||
 587                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 588                             return;
 589                         }
 590                         if from_substs.types().zip(to_substs.types())
 591                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 592                             span_lint(
 593                                 cx,
 594                                 UNSOUND_COLLECTION_TRANSMUTE,
 595                                 e.span,
 596                                 &format!(
 597                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 598                                     from_ty,
 599                                     to_ty
 600                                 )
 601                             );
 602                         }
 603                     },
 604                     _ => return,
 605                 }
 606             }
 607         }
 608     }
 609 }
 610
 611 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 612 /// not available , use
 613 /// the type's `ToString` implementation. In weird cases it could lead to types
 614 /// with invalid `'_`
 615 /// lifetime, but it should be rare.
 616 fn get_type_snippet(cx: &LateContext<'_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
 617     let seg = last_path_segment(path);
 618     if_chain! {
 619         if let Some(ref params) = seg.args;
 620         if !params.parenthesized;
 621         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 622             GenericArg::Type(ty) => Some(ty),
 623             _ => None,
 624         }).nth(1);
 625         if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
 626         then {
 627             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 628         }
 629     }
 630
 631     to_ref_ty.to_string()
 632 }
 633
 634 // check if the component types of the transmuted collection and the result have different ABI,
 635 // size or alignment
 636 fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
 637     let empty_param_env = ty::ParamEnv::empty();
 638     // check if `from` and `to` are normalizable to avoid ICE (#4968)
 639     if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
 640         return false;
 641     }
 642     let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
 643     let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
 644     if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
 645         from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
 646     } else {
 647         // no idea about layout, so don't lint
 648         false
 649     }
 650 }