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 // FIXME: Merge this lint with USELESS_TRANSMUTE once that is out of the nursery.
  54 declare_clippy_lint! {
  55     /// **What it does:**Checks for transmutes that could be a pointer cast.
  56     ///
  57     /// **Why is this bad?** Readability. The code tricks people into thinking that
  58     /// something complex is going on.
  59     ///
  60     /// **Known problems:** None.
  61     ///
  62     /// **Example:**
  63     ///
  64     /// ```rust,ignore
  65     /// core::intrinsics::transmute::<*const [i32], *const [u16]>(p)
  66     /// ```
  67     /// Use instead:
  68     /// ```rust
  69     /// p as *const [u16]
  70     /// ```
  71     pub TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
  72     complexity,
  73     "transmutes that could be a pointer cast"
  74 }
  75
  76 declare_clippy_lint! {
  77     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  78     ///
  79     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  80     /// pointer to that type.
  81     ///
  82     /// **Known problems:** None.
  83     ///
  84     /// **Example:**
  85     /// ```rust,ignore
  86     /// core::intrinsics::transmute(t) // where the result type is the same as
  87     ///                                // `*t` or `&t`'s
  88     /// ```
  89     pub CROSSPOINTER_TRANSMUTE,
  90     complexity,
  91     "transmutes that have to or from types that are a pointer to the other"
  92 }
  93
  94 declare_clippy_lint! {
  95     /// **What it does:** Checks for transmutes from a pointer to a reference.
  96     ///
  97     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
  98     ///
  99     /// **Known problems:** None.
 100     ///
 101     /// **Example:**
 102     /// ```rust,ignore
 103     /// unsafe {
 104     ///     let _: &T = std::mem::transmute(p); // where p: *const T
 105     /// }
 106     ///
 107     /// // can be written:
 108     /// let _: &T = &*p;
 109     /// ```
 110     pub TRANSMUTE_PTR_TO_REF,
 111     complexity,
 112     "transmutes from a pointer to a reference type"
 113 }
 114
 115 declare_clippy_lint! {
 116     /// **What it does:** Checks for transmutes from an integer to a `char`.
 117     ///
 118     /// **Why is this bad?** Not every integer is a Unicode scalar value.
 119     ///
 120     /// **Known problems:**
 121     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
 122     /// as it needs to validate the input.
 123     /// If you are certain that the input is always a valid Unicode scalar value,
 124     /// use [`from_u32_unchecked`] which is as fast as `transmute`
 125     /// but has a semantically meaningful name.
 126     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 127     ///
 128     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 129     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 130     ///
 131     /// **Example:**
 132     /// ```rust
 133     /// let x = 1_u32;
 134     /// unsafe {
 135     ///     let _: char = std::mem::transmute(x); // where x: u32
 136     /// }
 137     ///
 138     /// // should be:
 139     /// let _ = std::char::from_u32(x).unwrap();
 140     /// ```
 141     pub TRANSMUTE_INT_TO_CHAR,
 142     complexity,
 143     "transmutes from an integer to a `char`"
 144 }
 145
 146 declare_clippy_lint! {
 147     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 148     ///
 149     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 150     ///
 151     /// **Known problems:**
 152     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 153     /// as it needs to validate the input.
 154     /// If you are certain that the input is always a valid UTF-8,
 155     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 156     /// but has a semantically meaningful name.
 157     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 158     ///
 159     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 160     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 161     ///
 162     /// **Example:**
 163     /// ```rust
 164     /// let b: &[u8] = &[1_u8, 2_u8];
 165     /// unsafe {
 166     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 167     /// }
 168     ///
 169     /// // should be:
 170     /// let _ = std::str::from_utf8(b).unwrap();
 171     /// ```
 172     pub TRANSMUTE_BYTES_TO_STR,
 173     complexity,
 174     "transmutes from a `&[u8]` to a `&str`"
 175 }
 176
 177 declare_clippy_lint! {
 178     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 179     ///
 180     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 181     ///
 182     /// **Known problems:** None.
 183     ///
 184     /// **Example:**
 185     /// ```rust
 186     /// let x = 1_u8;
 187     /// unsafe {
 188     ///     let _: bool = std::mem::transmute(x); // where x: u8
 189     /// }
 190     ///
 191     /// // should be:
 192     /// let _: bool = x != 0;
 193     /// ```
 194     pub TRANSMUTE_INT_TO_BOOL,
 195     complexity,
 196     "transmutes from an integer to a `bool`"
 197 }
 198
 199 declare_clippy_lint! {
 200     /// **What it does:** Checks for transmutes from an integer to a float.
 201     ///
 202     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 203     /// and safe.
 204     ///
 205     /// **Known problems:** None.
 206     ///
 207     /// **Example:**
 208     /// ```rust
 209     /// unsafe {
 210     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 211     /// }
 212     ///
 213     /// // should be:
 214     /// let _: f32 = f32::from_bits(1_u32);
 215     /// ```
 216     pub TRANSMUTE_INT_TO_FLOAT,
 217     complexity,
 218     "transmutes from an integer to a float"
 219 }
 220
 221 declare_clippy_lint! {
 222     /// **What it does:** Checks for transmutes from a float to an integer.
 223     ///
 224     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `to_bits` is intuitive
 225     /// and safe.
 226     ///
 227     /// **Known problems:** None.
 228     ///
 229     /// **Example:**
 230     /// ```rust
 231     /// unsafe {
 232     ///     let _: u32 = std::mem::transmute(1f32);
 233     /// }
 234     ///
 235     /// // should be:
 236     /// let _: u32 = 1f32.to_bits();
 237     /// ```
 238     pub TRANSMUTE_FLOAT_TO_INT,
 239     complexity,
 240     "transmutes from a float to an integer"
 241 }
 242
 243 declare_clippy_lint! {
 244     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 245     /// from a reference to a reference.
 246     ///
 247     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 248     /// written as casts.
 249     ///
 250     /// **Known problems:** None.
 251     ///
 252     /// **Example:**
 253     /// ```rust
 254     /// let ptr = &1u32 as *const u32;
 255     /// unsafe {
 256     ///     // pointer-to-pointer transmute
 257     ///     let _: *const f32 = std::mem::transmute(ptr);
 258     ///     // ref-ref transmute
 259     ///     let _: &f32 = std::mem::transmute(&1u32);
 260     /// }
 261     /// // These can be respectively written:
 262     /// let _ = ptr as *const f32;
 263     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 264     /// ```
 265     pub TRANSMUTE_PTR_TO_PTR,
 266     complexity,
 267     "transmutes from a pointer to a pointer / a reference to a reference"
 268 }
 269
 270 declare_clippy_lint! {
 271     /// **What it does:** Checks for transmutes between collections whose
 272     /// types have different ABI, size or alignment.
 273     ///
 274     /// **Why is this bad?** This is undefined behavior.
 275     ///
 276     /// **Known problems:** Currently, we cannot know whether a type is a
 277     /// collection, so we just lint the ones that come with `std`.
 278     ///
 279     /// **Example:**
 280     /// ```rust
 281     /// // different size, therefore likely out-of-bounds memory access
 282     /// // You absolutely do not want this in your code!
 283     /// unsafe {
 284     ///     std::mem::transmute::<_, Vec<u32>>(vec![2_u16])
 285     /// };
 286     /// ```
 287     ///
 288     /// You must always iterate, map and collect the values:
 289     ///
 290     /// ```rust
 291     /// vec![2_u16].into_iter().map(u32::from).collect::<Vec<_>>();
 292     /// ```
 293     pub UNSOUND_COLLECTION_TRANSMUTE,
 294     correctness,
 295     "transmute between collections of layout-incompatible types"
 296 }
 297
 298 declare_lint_pass!(Transmute => [
 299     CROSSPOINTER_TRANSMUTE,
 300     TRANSMUTE_PTR_TO_REF,
 301     TRANSMUTE_PTR_TO_PTR,
 302     USELESS_TRANSMUTE,
 303     WRONG_TRANSMUTE,
 304     TRANSMUTE_INT_TO_CHAR,
 305     TRANSMUTE_BYTES_TO_STR,
 306     TRANSMUTE_INT_TO_BOOL,
 307     TRANSMUTE_INT_TO_FLOAT,
 308     TRANSMUTE_FLOAT_TO_INT,
 309     UNSOUND_COLLECTION_TRANSMUTE,
 310     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 311 ]);
 312
 313 // used to check for UNSOUND_COLLECTION_TRANSMUTE
 314 static COLLECTIONS: &[&[&str]] = &[
 315     &paths::VEC,
 316     &paths::VEC_DEQUE,
 317     &paths::BINARY_HEAP,
 318     &paths::BTREESET,
 319     &paths::BTREEMAP,
 320     &paths::HASHSET,
 321     &paths::HASHMAP,
 322 ];
 323 impl<'tcx> LateLintPass<'tcx> for Transmute {
 324     #[allow(clippy::similar_names, clippy::too_many_lines)]
 325     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 326         if_chain! {
 327             if let ExprKind::Call(ref path_expr, ref args) = e.kind;
 328             if let ExprKind::Path(ref qpath) = path_expr.kind;
 329             if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id();
 330             if match_def_path(cx, def_id, &paths::TRANSMUTE);
 331             then {
 332                 let from_ty = cx.typeck_results().expr_ty(&args[0]);
 333                 let to_ty = cx.typeck_results().expr_ty(e);
 334
 335                 match (&from_ty.kind, &to_ty.kind) {
 336                     _ if from_ty == to_ty => span_lint(
 337                         cx,
 338                         USELESS_TRANSMUTE,
 339                         e.span,
 340                         &format!("transmute from a type (`{}`) to itself", from_ty),
 341                     ),
 342                     (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => span_lint_and_then(
 343                         cx,
 344                         USELESS_TRANSMUTE,
 345                         e.span,
 346                         "transmute from a reference to a pointer",
 347                         |diag| {
 348                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 349                                 let rty_and_mut = ty::TypeAndMut {
 350                                     ty: rty,
 351                                     mutbl: *rty_mutbl,
 352                                 };
 353
 354                                 let sugg = if *ptr_ty == rty_and_mut {
 355                                     arg.as_ty(to_ty)
 356                                 } else {
 357                                     arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 358                                 };
 359
 360                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 361                             }
 362                         },
 363                     ),
 364                     (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => span_lint_and_then(
 365                         cx,
 366                         USELESS_TRANSMUTE,
 367                         e.span,
 368                         "transmute from an integer to a pointer",
 369                         |diag| {
 370                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 371                                 diag.span_suggestion(
 372                                     e.span,
 373                                     "try",
 374                                     arg.as_ty(&to_ty.to_string()).to_string(),
 375                                     Applicability::Unspecified,
 376                                 );
 377                             }
 378                         },
 379                     ),
 380                     (ty::Float(_) | ty::Char, ty::Ref(..) | ty::RawPtr(_)) => span_lint(
 381                         cx,
 382                         WRONG_TRANSMUTE,
 383                         e.span,
 384                         &format!("transmute from a `{}` to a pointer", from_ty),
 385                     ),
 386                     (ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 387                         cx,
 388                         CROSSPOINTER_TRANSMUTE,
 389                         e.span,
 390                         &format!(
 391                             "transmute from a type (`{}`) to the type that it points to (`{}`)",
 392                             from_ty, to_ty
 393                         ),
 394                     ),
 395                     (_, ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 396                         cx,
 397                         CROSSPOINTER_TRANSMUTE,
 398                         e.span,
 399                         &format!(
 400                             "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 401                             from_ty, to_ty
 402                         ),
 403                     ),
 404                     (ty::RawPtr(from_pty), ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 405                         cx,
 406                         TRANSMUTE_PTR_TO_REF,
 407                         e.span,
 408                         &format!(
 409                             "transmute from a pointer type (`{}`) to a reference type \
 410                              (`{}`)",
 411                             from_ty, to_ty
 412                         ),
 413                         |diag| {
 414                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 415                             let (deref, cast) = if *mutbl == Mutability::Mut {
 416                                 ("&mut *", "*mut")
 417                             } else {
 418                                 ("&*", "*const")
 419                             };
 420
 421                             let arg = if from_pty.ty == *to_ref_ty {
 422                                 arg
 423                             } else {
 424                                 arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 425                             };
 426
 427                             diag.span_suggestion(
 428                                 e.span,
 429                                 "try",
 430                                 sugg::make_unop(deref, arg).to_string(),
 431                                 Applicability::Unspecified,
 432                             );
 433                         },
 434                     ),
 435                     (ty::Int(ast::IntTy::I32) | ty::Uint(ast::UintTy::U32), &ty::Char) => {
 436                         span_lint_and_then(
 437                             cx,
 438                             TRANSMUTE_INT_TO_CHAR,
 439                             e.span,
 440                             &format!("transmute from a `{}` to a `char`", from_ty),
 441                             |diag| {
 442                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 443                                 let arg = if let ty::Int(_) = from_ty.kind {
 444                                     arg.as_ty(ast::UintTy::U32.name_str())
 445                                 } else {
 446                                     arg
 447                                 };
 448                                 diag.span_suggestion(
 449                                     e.span,
 450                                     "consider using",
 451                                     format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 452                                     Applicability::Unspecified,
 453                                 );
 454                             },
 455                         )
 456                     },
 457                     (ty::Ref(_, ty_from, from_mutbl), ty::Ref(_, ty_to, to_mutbl)) => {
 458                         if_chain! {
 459                             if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.kind, &ty_to.kind);
 460                             if let ty::Uint(ast::UintTy::U8) = slice_ty.kind;
 461                             if from_mutbl == to_mutbl;
 462                             then {
 463                                 let postfix = if *from_mutbl == Mutability::Mut {
 464                                     "_mut"
 465                                 } else {
 466                                     ""
 467                                 };
 468
 469                                 span_lint_and_sugg(
 470                                     cx,
 471                                     TRANSMUTE_BYTES_TO_STR,
 472                                     e.span,
 473                                     &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 474                                     "consider using",
 475                                     format!(
 476                                         "std::str::from_utf8{}({}).unwrap()",
 477                                         postfix,
 478                                         snippet(cx, args[0].span, ".."),
 479                                     ),
 480                                     Applicability::Unspecified,
 481                                 );
 482                             } else {
 483                                 if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
 484                                     span_lint_and_then(
 485                                         cx,
 486                                         TRANSMUTE_PTR_TO_PTR,
 487                                         e.span,
 488                                         "transmute from a reference to a reference",
 489                                         |diag| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 490                                             let ty_from_and_mut = ty::TypeAndMut {
 491                                                 ty: ty_from,
 492                                                 mutbl: *from_mutbl
 493                                             };
 494                                             let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: *to_mutbl };
 495                                             let sugg_paren = arg
 496                                                 .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 497                                                 .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 498                                             let sugg = if *to_mutbl == Mutability::Mut {
 499                                                 sugg_paren.mut_addr_deref()
 500                                             } else {
 501                                                 sugg_paren.addr_deref()
 502                                             };
 503                                             diag.span_suggestion(
 504                                                 e.span,
 505                                                 "try",
 506                                                 sugg.to_string(),
 507                                                 Applicability::Unspecified,
 508                                             );
 509                                         },
 510                                     )
 511                                 }
 512                             }
 513                         }
 514                     },
 515                     (ty::RawPtr(_), ty::RawPtr(to_ty)) => span_lint_and_then(
 516                         cx,
 517                         TRANSMUTE_PTR_TO_PTR,
 518                         e.span,
 519                         "transmute from a pointer to a pointer",
 520                         |diag| {
 521                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 522                                 let sugg = arg.as_ty(cx.tcx.mk_ptr(*to_ty));
 523                                 diag.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 524                             }
 525                         },
 526                     ),
 527                     (ty::Int(ast::IntTy::I8) | ty::Uint(ast::UintTy::U8), ty::Bool) => {
 528                         span_lint_and_then(
 529                             cx,
 530                             TRANSMUTE_INT_TO_BOOL,
 531                             e.span,
 532                             &format!("transmute from a `{}` to a `bool`", from_ty),
 533                             |diag| {
 534                                 let arg = sugg::Sugg::hir(cx, &args[0], "..");
 535                                 let zero = sugg::Sugg::NonParen(Cow::from("0"));
 536                                 diag.span_suggestion(
 537                                     e.span,
 538                                     "consider using",
 539                                     sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 540                                     Applicability::Unspecified,
 541                                 );
 542                             },
 543                         )
 544                     },
 545                     (ty::Int(_) | ty::Uint(_), ty::Float(_)) => span_lint_and_then(
 546                         cx,
 547                         TRANSMUTE_INT_TO_FLOAT,
 548                         e.span,
 549                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 550                         |diag| {
 551                             let arg = sugg::Sugg::hir(cx, &args[0], "..");
 552                             let arg = if let ty::Int(int_ty) = from_ty.kind {
 553                                 arg.as_ty(format!(
 554                                     "u{}",
 555                                     int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 556                                 ))
 557                             } else {
 558                                 arg
 559                             };
 560                             diag.span_suggestion(
 561                                 e.span,
 562                                 "consider using",
 563                                 format!("{}::from_bits({})", to_ty, arg.to_string()),
 564                                 Applicability::Unspecified,
 565                             );
 566                         },
 567                     ),
 568                     (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) => span_lint_and_then(
 569                         cx,
 570                         TRANSMUTE_FLOAT_TO_INT,
 571                         e.span,
 572                         &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 573                         |diag| {
 574                             let mut expr = &args[0];
 575                             let mut arg = sugg::Sugg::hir(cx, expr, "..");
 576
 577                             if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
 578                                 expr = &inner_expr;
 579                             }
 580
 581                             if_chain! {
 582                                 // if the expression is a float literal and it is unsuffixed then
 583                                 // add a suffix so the suggestion is valid and unambiguous
 584                                 let op = format!("{}{}", arg, float_ty.name_str()).into();
 585                                 if let ExprKind::Lit(lit) = &expr.kind;
 586                                 if let ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) = lit.node;
 587                                 then {
 588                                     match arg {
 589                                         sugg::Sugg::MaybeParen(_) => arg = sugg::Sugg::MaybeParen(op),
 590                                         _ => arg = sugg::Sugg::NonParen(op)
 591                                     }
 592                                 }
 593                             }
 594
 595                             arg = sugg::Sugg::NonParen(format!("{}.to_bits()", arg.maybe_par()).into());
 596
 597                             // cast the result of `to_bits` if `to_ty` is signed
 598                             arg = if let ty::Int(int_ty) = to_ty.kind {
 599                                 arg.as_ty(int_ty.name_str().to_string())
 600                             } else {
 601                                 arg
 602                             };
 603
 604                             diag.span_suggestion(
 605                                 e.span,
 606                                 "consider using",
 607                                 arg.to_string(),
 608                                 Applicability::Unspecified,
 609                             );
 610                         },
 611                     ),
 612                     (ty::Adt(from_adt, from_substs), ty::Adt(to_adt, to_substs)) => {
 613                         if from_adt.did != to_adt.did ||
 614                                 !COLLECTIONS.iter().any(|path| match_def_path(cx, to_adt.did, path)) {
 615                             return;
 616                         }
 617                         if from_substs.types().zip(to_substs.types())
 618                                               .any(|(from_ty, to_ty)| is_layout_incompatible(cx, from_ty, to_ty)) {
 619                             span_lint(
 620                                 cx,
 621                                 UNSOUND_COLLECTION_TRANSMUTE,
 622                                 e.span,
 623                                 &format!(
 624                                     "transmute from `{}` to `{}` with mismatched layout is unsound",
 625                                     from_ty,
 626                                     to_ty
 627                                 )
 628                             );
 629                         }
 630                     },
 631                     (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => span_lint_and_then(
 632                         cx,
 633                         TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
 634                         e.span,
 635                         &format!(
 636                             "transmute from `{}` to `{}` which could be expressed as a pointer cast instead",
 637                             from_ty,
 638                             to_ty
 639                         ),
 640                         |diag| {
 641                             if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 642                                 let sugg = arg.as_ty(&to_ty.to_string()).to_string();
 643                                 diag.span_suggestion(e.span, "try", sugg, Applicability::Unspecified);
 644                             }
 645                         }
 646                     ),
 647                     _ => {
 648                         return;
 649                     },
 650                 }
 651             }
 652         }
 653     }
 654 }
 655
 656 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 657 /// not available , use
 658 /// the type's `ToString` implementation. In weird cases it could lead to types
 659 /// with invalid `'_`
 660 /// lifetime, but it should be rare.
 661 fn get_type_snippet(cx: &LateContext<'_>, path: &QPath<'_>, to_ref_ty: Ty<'_>) -> String {
 662     let seg = last_path_segment(path);
 663     if_chain! {
 664         if let Some(ref params) = seg.args;
 665         if !params.parenthesized;
 666         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 667             GenericArg::Type(ty) => Some(ty),
 668             _ => None,
 669         }).nth(1);
 670         if let TyKind::Rptr(_, ref to_ty) = to_ty.kind;
 671         then {
 672             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 673         }
 674     }
 675
 676     to_ref_ty.to_string()
 677 }
 678
 679 // check if the component types of the transmuted collection and the result have different ABI,
 680 // size or alignment
 681 fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
 682     let empty_param_env = ty::ParamEnv::empty();
 683     // check if `from` and `to` are normalizable to avoid ICE (#4968)
 684     if !(is_normalizable(cx, empty_param_env, from) && is_normalizable(cx, empty_param_env, to)) {
 685         return false;
 686     }
 687     let from_ty_layout = cx.tcx.layout_of(empty_param_env.and(from));
 688     let to_ty_layout = cx.tcx.layout_of(empty_param_env.and(to));
 689     if let (Ok(from_layout), Ok(to_layout)) = (from_ty_layout, to_ty_layout) {
 690         from_layout.size != to_layout.size || from_layout.align != to_layout.align || from_layout.abi != to_layout.abi
 691     } else {
 692         // no idea about layout, so don't lint
 693         false
 694     }
 695 }
 696
 697 /// Check if the the type conversion can be expressed as a pointer cast, instead of a transmute.
 698 fn can_be_expressed_as_pointer_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> bool {
 699     use CastKind::*;
 700     matches!(
 701         check_cast(cx, e, from_ty, to_ty),
 702         Some(
 703             PtrPtrCast
 704             | PtrAddrCast
 705             | AddrPtrCast
 706             | ArrayPtrCast
 707             | FnPtrPtrCast
 708             | FnPtrAddrCast
 709         )
 710     )
 711 }
 712
 713 /// If a cast from from_ty to to_ty is valid, returns an Ok containing the kind of the cast.
 714 fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> Option<CastKind> {
 715     let hir_id = e.hir_id;
 716     let local_def_id = hir_id.owner;
 717
 718     Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
 719         let fn_ctxt = FnCtxt::new(
 720             &inherited,
 721             // TODO should we try to get the correct ParamEnv?
 722             ty::ParamEnv::empty(),
 723             hir_id
 724         );
 725
 726         // If we already have errors, we can't be sure we can pointer cast.
 727         if fn_ctxt.errors_reported_since_creation() {
 728             return None;
 729         }
 730
 731         if let Ok(check) = CastCheck::new(
 732             &fn_ctxt,
 733             e,
 734             from_ty,
 735             to_ty,
 736             // We won't show any error to the user, so we don't care what the span is here.
 737             DUMMY_SP,
 738             DUMMY_SP,
 739         ) {
 740             check.do_check(&fn_ctxt)
 741                 .ok()
 742                 // do_check's documentation says that it might return Ok and create
 743                 // errors in the fcx instead of returing Err in some cases.
 744                 .filter(|_| !fn_ctxt.errors_reported_since_creation())
 745         } else {
 746             None
 747         }
 748     })
 749 }