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, cast::CastKind, Ty};
  11 use rustc_span::DUMMY_SP;
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  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 declare_clippy_lint! {
  54     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  55     ///
  56     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  57     /// pointer to that type.
  58     ///
  59     /// **Known problems:** None.
  60     ///
  61     /// **Example:**
  62     /// ```rust,ignore
  63     /// core::intrinsics::transmute(t) // where the result type is the same as
  64     ///                                // `*t` or `&t`'s
  65     /// ```
  66     pub CROSSPOINTER_TRANSMUTE,
  67     complexity,
  68     "transmutes that have to or from types that are a pointer to the other"
  69 }
  70
  71 declare_clippy_lint! {
  72     /// **What it does:** Checks for transmutes from a pointer to a reference.
  73     ///
  74     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
  75     ///
  76     /// **Known problems:** None.
  77     ///
  78     /// **Example:**
  79     /// ```rust,ignore
  80     /// unsafe {
  81     ///     let _: &T = std::mem::transmute(p); // where p: *const T
  82     /// }
  83     ///
  84     /// // can be written:
  85     /// let _: &T = &*p;
  86     /// ```
  87     pub TRANSMUTE_PTR_TO_REF,
  88     complexity,
  89     "transmutes from a pointer to a reference type"
  90 }
  91
  92 declare_clippy_lint! {
  93     /// **What it does:** Checks for transmutes from an integer to a `char`.
  94     ///
  95     /// **Why is this bad?** Not every integer is a Unicode scalar value.
  96     ///
  97     /// **Known problems:**
  98     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
  99     /// as it needs to validate the input.
 100     /// If you are certain that the input is always a valid Unicode scalar value,
 101     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 102     /// but has a semantically meaningful name.
 103     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 104     ///
 105     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 106     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 107     ///
 108     /// **Example:**
 109     /// ```rust
 110     /// let x = 1_u32;
 111     /// unsafe {
 112     ///     let _: char = std::mem::transmute(x); // where x: u32
 113     /// }
 114     ///
 115     /// // should be:
 116     /// let _ = std::char::from_u32(x).unwrap();
 117     /// ```
 118     pub TRANSMUTE_INT_TO_CHAR,
 119     complexity,
 120     "transmutes from an integer to a `char`"
 121 }
 122
 123 declare_clippy_lint! {
 124     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 125     ///
 126     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 127     ///
 128     /// **Known problems:**
 129     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 130     /// as it needs to validate the input.
 131     /// If you are certain that the input is always a valid UTF-8,
 132     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 133     /// but has a semantically meaningful name.
 134     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 135     ///
 136     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 137     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 138     ///
 139     /// **Example:**
 140     /// ```rust
 141     /// let b: &[u8] = &[1_u8, 2_u8];
 142     /// unsafe {
 143     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 144     /// }
 145     ///
 146     /// // should be:
 147     /// let _ = std::str::from_utf8(b).unwrap();
 148     /// ```
 149     pub TRANSMUTE_BYTES_TO_STR,
 150     complexity,
 151     "transmutes from a `&[u8]` to a `&str`"
 152 }
 153
 154 declare_clippy_lint! {
 155     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 156     ///
 157     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 158     ///
 159     /// **Known problems:** None.
 160     ///
 161     /// **Example:**
 162     /// ```rust
 163     /// let x = 1_u8;
 164     /// unsafe {
 165     ///     let _: bool = std::mem::transmute(x); // where x: u8
 166     /// }
 167     ///
 168     /// // should be:
 169     /// let _: bool = x != 0;
 170     /// ```
 171     pub TRANSMUTE_INT_TO_BOOL,
 172     complexity,
 173     "transmutes from an integer to a `bool`"
 174 }
 175
 176 declare_clippy_lint! {
 177     /// **What it does:** Checks for transmutes from an integer to a float.
 178     ///
 179     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 180     /// and safe.
 181     ///
 182     /// **Known problems:** None.
 183     ///
 184     /// **Example:**
 185     /// ```rust
 186     /// unsafe {
 187     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 188     /// }
 189     ///
 190     /// // should be:
 191     /// let _: f32 = f32::from_bits(1_u32);
 192     /// ```
 193     pub TRANSMUTE_INT_TO_FLOAT,
 194     complexity,
 195     "transmutes from an integer to a float"
 196 }
 197
 198 declare_clippy_lint! {
 199     /// **What it does:** Checks for transmutes from a float to an integer.
 200     ///
 201     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 202     /// and safe.
 203     ///
 204     /// **Known problems:** None.
 205     ///
 206     /// **Example:**
 207     /// ```rust
 208     /// unsafe {
 209     ///     let _: u32 = std::mem::transmute(1f32);
 210     /// }
 211     ///
 212     /// // should be:
 213     /// let _: u32 = 1f32.to_bits();
 214     /// ```
 215     pub TRANSMUTE_FLOAT_TO_INT,
 216     complexity,
 217     "transmutes from a float to an integer"
 218 }
 219
 220 declare_clippy_lint! {
 221     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 222     /// from a reference to a reference.
 223     ///
 224     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 225     /// written as casts.
 226     ///
 227     /// **Known problems:** None.
 228     ///
 229     /// **Example:**
 230     /// ```rust
 231     /// let ptr = &1u32 as *const u32;
 232     /// unsafe {
 233     ///     // pointer-to-pointer transmute
 234     ///     let _: *const f32 = std::mem::transmute(ptr);
 235     ///     // ref-ref transmute
 236     ///     let _: &f32 = std::mem::transmute(&1u32);
 237     /// }
 238     /// // These can be respectively written:
 239     /// let _ = ptr as *const f32;
 240     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 241     /// ```
 242     pub TRANSMUTE_PTR_TO_PTR,
 243     complexity,
 244     "transmutes from a pointer to a pointer / a reference to a reference"
 245 }
 246
 247 declare_clippy_lint! {
 248     /// **What it does:** Checks for transmutes between collections whose
 249     /// types have different ABI, size or alignment.
 250     ///
 251     /// **Why is this bad?** This is undefined behavior.
 252     ///
 253     /// **Known problems:** Currently, we cannot know whether a type is a
 254     /// collection, so we just lint the ones that come with `std`.
 255     ///
 256     /// **Example:**
 257     /// ```rust
 258     /// // different size, therefore likely out-of-bounds memory access
 259     /// // You absolutely do not want this in your code!
 260     /// unsafe {
 261     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 262     /// };
 263     /// ```
 264     ///
 265     /// You must always iterate, map and collect the values:
 266     ///
 267     /// ```rust
 268     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 269     /// ```
 270     pub UNSOUND_COLLECTION_TRANSMUTE,
 271     correctness,
 272     "transmute between collections of layout-incompatible types"
 273 }
 274
 275 declare_clippy_lint! {
 276     /// **What it does:**
 277     ///
 278     /// **Why is this bad?**
 279     ///
 280     /// **Known problems:** None.
 281     ///
 282     /// **Example:**
 283     ///
 284     /// ```rust
 285     /// // example code where clippy issues a warning
 286     /// ```
 287     /// Use instead:
 288     /// ```rust
 289     /// // example code which does not raise clippy warning
 290     /// ```
 291     pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 292     complexity,
 293     "default lint description"
 294 }
 295
 296 declare_lint_pass!(Transmute => [
 297     CROSSPOINTER_TRANSMUTE,
 298     TRANSMUTE_PTR_TO_REF,
 299     TRANSMUTE_PTR_TO_PTR,
 300     USELESS_TRANSMUTE,
 301     WRONG_TRANSMUTE,
 302     TRANSMUTE_INT_TO_CHAR,
 303     TRANSMUTE_BYTES_TO_STR,
 304     TRANSMUTE_INT_TO_BOOL,
 305     TRANSMUTE_INT_TO_FLOAT,
 306     TRANSMUTE_FLOAT_TO_INT,
 307     UNSOUND_COLLECTION_TRANSMUTE,
 308     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 309 ]);
 310
 311 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 312 static COLLECTIONS: &[&[&str]] = &[
 313     &paths::VEC,
 314     &paths::VEC_DEQUE,
 315     &paths::BINARY_HEAP,
 316     &paths::BTREESET,
 317     &paths::BTREEMAP,
 318     &paths::HASHSET,
 319     &paths::HASHMAP,
 320 ];
 321 impl<'tcx> LateLintPass<'tcx> for Transmute {
 322     #[allow(clippy::similar_names, clippy::too_many_lines)]
 323     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 324         if_chain! {
 325             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 326             if let ExprKind::Path(ref qpath) = path_expr.kind;
 327             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 328             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 329             then {
 330                 let from_ty = cx.typeck_results().expr_ty(&args[0]);
 331                 let to_ty = cx.typeck_results().expr_ty(e);
 332
 333                 match (&from_ty.kind, &to_ty.kind) {
 334                     _ if from_ty == to_ty => span_lint(
 335                         cx,
 336                         USELESS_TRANSMUTE,
 337                         e.span,
 338                         &format!("transmute from a type (`{}`) to itself", from_ty),
 339                     ),
 340                     (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => span_lint_and_then(
 341                         cx,
 342                         USELESS_TRANSMUTE,
 343                         e.span,
 344                         "transmute from a reference to a pointer",
 345                         |diag| {
 346                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 347                                 let rty_and_mut = ty::TypeAndMut {
 348                                     ty: rty,
 349                                     mutbl: *rty_mutbl,
 350                                 };
 351
 352                                 let sugg = if *ptr_ty == rty_and_mut {
 353                                     arg.as_ty(to_ty)
 354                                 } else {
 355                                     arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 356                                 };
 357
 358                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 359                             }
 360                         },
 361                     ),
 362                     (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => span_lint_and_then(
 363                         cx,
 364                         USELESS_TRANSMUTE,
 365                         e.span,
 366                         "transmute from an integer to a pointer",
 367                         |diag| {
 368                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 369                                 diag.span_suggestion(
 370                                     e.span,
 371                                     "try",
 372                                     arg.as_ty(&to_ty.to_string()).to_string(),
 373                                     Applicability::Unspecified,
 374                                 );
 375                             }
 376                         },
 377                     ),
 378                     (ty::Float(_) | ty::Char, ty::Ref(..) | ty::RawPtr(_)) => span_lint(
 379                         cx,
 380                         WRONG_TRANSMUTE,
 381                         e.span,
 382                         &format!("transmute from a `{}` to a pointer", from_ty),
 383                     ),
 384                     (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 385                         cx,
 386                         CROSSPOINTER_TRANSMUTE,
 387                         e.span,
 388                         &format!(
 389                             "transmute from a type (`{}`) to the type that it points to (`{}`)",
 390                             from_ty, to_ty
 391                         ),
 392                     ),
 393                     (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 394                         cx,
 395                         CROSSPOINTER_TRANSMUTE,
 396                         e.span,
 397                         &format!(
 398                             "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 399                             from_ty, to_ty
 400                         ),
 401                     ),
 402                     (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 403                         cx,
 404                         TRANSMUTE_PTR_TO_REF,
 405                         e.span,
 406                         &format!(
 407                             "transmute from a pointer type (`{}`) to a reference type \
 408                              (`{}`)",
 409                             from_ty, to_ty
 410                         ),
 411                         |diag| {
 412                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 413                             let (deref, cast) = if *mutbl == Mutability::Mut {
 414                                 ("&mut *", "*mut")
 415                             } else {
 416                                 ("&*", "*const")
 417                             };
 418
 419                             let arg = if from_pty.ty == *to_ref_ty {
 420                                 arg
 421                             } else {
 422                                 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 423                             };
 424
 425                             diag.span_suggestion(
 426                                 e.span,
 427                                 "try",
 428                                 sugg::make_unop(deref, arg).to_string(),
 429                                 Applicability::Unspecified,
 430                             );
 431                         },
 432                     ),
 433                     (ty::Int(ast::IntTy::I32) | ty::Uint(ast::UintTy::U32), &ty::Char) => {
 434                         span_lint_and_then(
 435                             cx,
 436                             TRANSMUTE_INT_TO_CHAR,
 437                             e.span,
 438                             &format!("transmute from a `{}` to a `char`", from_ty),
 439                             |diag| {
 440                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 441                                 let arg = if let ty::Int(_) = from_ty.kind {
 442                                     arg.as_ty(ast::UintTy::U32.name_str())
 443                                 } else {
 444                                     arg
 445                                 };
 446                                 diag.span_suggestion(
 447                                     e.span,
 448                                     "consider using",
 449                                     format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 450                                     Applicability::Unspecified,
 451                                 );
 452                             },
 453                         )
 454                     },
 455                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 456                         if_chain! {
 457                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind, &ty_to.kind);
 458                             if let ty::Uint(ast::UintTy::U8) = slice_ty.kind;
 459                             if from_mutbl == to_mutbl;
 460                             then {
 461                                 let postfix = if *from_mutbl == Mutability::Mut {
 462                                     "_mut"
 463                                 } else {
 464                                     ""
 465                                 };
 466
 467                                 span_lint_and_sugg(
 468                                     cx,
 469                                     TRANSMUTE_BYTES_TO_STR,
 470                                     e.span,
 471                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 472                                     "consider using",
 473                                     format!(
 474                                         "std::str::from_utf8{}({}).unwrap()",
 475                                         postfix,
 476                                         snippet(cx, args[0].span, ".."),
 477                                     ),
 478                                     Applicability::Unspecified,
 479                                 );
 480                             } else {
 481                                 if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
 482                                     span_lint_and_then(
 483                                         cx,
 484                                         TRANSMUTE_PTR_TO_PTR,
 485                                         e.span,
 486                                         "transmute from a reference to a reference",
 487                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 488                                             let ty_from_and_mut = ty::TypeAndMut {
 489                                                 ty: ty_from,
 490                                                 mutbl: *from_mutbl
 491                                             };
 492                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 493                                             let sugg_paren = arg
 494                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 495                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 496                                             let sugg = if *to_mutbl == Mutability::Mut {
 497                                                 sugg_paren.mut_addr_deref()
 498                                             } else {
 499                                                 sugg_paren.addr_deref()
 500                                             };
 501                                             diag.span_suggestion(
 502                                                 e.span,
 503                                                 "try",
 504                                                 sugg.to_string(),
 505                                                 Applicability::Unspecified,
 506                                             );
 507                                         },
 508                                     )
 509                                 }
 510                             }
 511                         }
 512                     },
 513                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 514                         cx,
 515                         TRANSMUTE_PTR_TO_PTR,
 516                         e.span,
 517                         "transmute from a pointer to a pointer",
 518                         |diag| {
 519                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 520                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 521                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 522                             }
 523                         },
 524                     ),
 525                     (ty::Int(ast::IntTy::I8) | ty::Uint(ast::UintTy::U8), ty::Bool) => {
 526                         span_lint_and_then(
 527                             cx,
 528                             TRANSMUTE_INT_TO_BOOL,
 529                             e.span,
 530                             &format!("transmute from a `{}` to a `bool`", from_ty),
 531                             |diag| {
 532                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 533                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 534                                 diag.span_suggestion(
 535                                     e.span,
 536                                     "consider using",
 537                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 538                                     Applicability::Unspecified,
 539                                 );
 540                             },
 541                         )
 542                     },
 543                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) => span_lint_and_then(
 544                         cx,
 545                         TRANSMUTE_INT_TO_FLOAT,
 546                         e.span,
 547                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 548                         |diag| {
 549                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 550                             let arg = if let ty::Int(int_ty) = from_ty.kind {
 551                                 arg.as_ty(format!(
 552                                     "u{}",
 553                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 554                                 ))
 555                             } else {
 556                                 arg
 557                             };
 558                             diag.span_suggestion(
 559                                 e.span,
 560                                 "consider using",
 561                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 562                                 Applicability::Unspecified,
 563                             );
 564                         },
 565                     ),
 566                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) => span_lint_and_then(
 567                         cx,
 568                         TRANSMUTE_FLOAT_TO_INT,
 569                         e.span,
 570                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 571                         |diag| {
 572                             let mut expr = &args[0];
 573                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 574
 575                             if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
 576                                 expr = &inner_expr;
 577                             }
 578
 579                             if_chain! {
 580                                 // if the expression is a float literal and it is unsuffixed then
 581                                 // add a suffix so the suggestion is valid and unambiguous
 582                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 583                                 if let ExprKind::Lit(lit) = &expr.kind;
 584                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 585                                 then {
 586                                     match arg {
 587                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 588                                         _ => arg = sugg::Sugg::NonParen(op)
 589                                     }
 590                                 }
 591                             }
 592
 593                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 594
 595                             // cast the result of `to_bits` if `to_ty` is signed
 596                             arg = if let ty::Int(int_ty) = to_ty.kind {
 597                                 arg.as_ty(int_ty.name_str().to_string())
 598                             } else {
 599                                 arg
 600                             };
 601
 602                             diag.span_suggestion(
 603                                 e.span,
 604                                 "consider using",
 605                                 arg.to_string(),
 606                                 Applicability::Unspecified,
 607                             );
 608                         },
 609                     ),
 610                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 611                         if from_adt.did != to_adt.did ||
 612                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 613                             return;
 614                         }
 615                         if from_substs.types().zip(to_substs.types())
 616                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 617                             span_lint(
 618                                 cx,
 619                                 UNSOUND_COLLECTION_TRANSMUTE,
 620                                 e.span,
 621                                 &format!(
 622                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 623                                     from_ty,
 624                                     to_ty
 625                                 )
 626                             );
 627                         }
 628                     },
 629                     (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => {
 630                         span_lint(
 631                             cx,
 632                             TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 633                             e.span,
 634                             &format!(
 635                                 "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
 636                                 from_ty,
 637                                 to_ty
 638                             )
 639                         );
 640                     },
 641                     _ => {
 642                         return
 643                     },
 644                 }
 645             }
 646         }
 647     }
 648 }
 649
 650 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 651 /// not available , use
 652 /// the type's `ToString` implementation. In weird cases it could lead to types
 653 /// with invalid `'_`
 654 /// lifetime, but it should be rare.
 655 fn get_type_snippet(cx: &LateContext<'_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
 656     let seg = last_path_segment(path);
 657     if_chain! {
 658         if let Some(ref params) = seg.args;
 659         if !params.parenthesized;
 660         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 661             GenericArg::Type(ty) => Some(ty),
 662             _ => None,
 663         }).nth(1);
 664         if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
 665         then {
 666             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 667         }
 668     }
 669
 670     to_ref_ty.to_string()
 671 }
 672
 673 // check if the component types of the transmuted collection and the result have different ABI,
 674 // size or alignment
 675 fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
 676     let empty_param_env = ty::ParamEnv::empty();
 677     // check if `from` and `to` are normalizable to avoid ICE (#4968)
 678     if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
 679         return false;
 680     }
 681     let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
 682     let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
 683     if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
 684         from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
 685     } else {
 686         // no idea about layout, so don't lint
 687         false
 688     }
 689 }
 690
 691 /// Check if the the type conversion can be expressed as a pointer cast, instead of a transmute.
 692 fn can_be_expressed_as_pointer_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> bool {
 693     use CastKind::*;
 694     matches!(
 695         check_cast(cx, e, from_ty, to_ty),
 696         Some(
 697             PtrPtrCast
 698             | PtrAddrCast
 699             | AddrPtrCast
 700             | ArrayPtrCast
 701             | FnPtrPtrCast
 702             | FnPtrAddrCast
 703         )
 704     )
 705 }
 706
 707 /// If a cast from from_ty to to_ty is valid, returns an Ok containing the kind of the cast.
 708 fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> Option<CastKind> {
 709     let hir_id = e.hir_id;
 710     let local_def_id = hir_id.owner;
 711
 712     Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
 713         let fn_ctxt = FnCtxt::new(
 714             &inherited,
 715             // TODO should we try to get the correct ParamEnv?
 716             ty::ParamEnv::empty(),
 717             hir_id
 718         );
 719
 720         // If we already have errors, we can't be sure we can pointer cast.
 721         if fn_ctxt.errors_reported_since_creation() {
 722             return None;
 723         }
 724
 725         if let Ok(check) = CastCheck::new(
 726             &fn_ctxt,
 727             e,
 728             from_ty,
 729             to_ty,
 730             // We won't show any error to the user, so we don't care what the span is here.
 731             DUMMY_SP,
 732             DUMMY_SP,
 733         ) {
 734             check.do_check(&fn_ctxt)
 735                 .ok()
 736                 // do_check's documentation says that it might return Ok and create
 737                 // errors in the fcx instead of returing Err in some cases.
 738                 .filter(|_| !fn_ctxt.errors_reported_since_creation())
 739         } else {
 740             None
 741         }
 742     })
 743 }