clippy_lints/src/transmute/mod.rs

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