clippy_lints/src/transmute.rs

   1 use crate::utils::{last_path_segment, match_def_path, paths, snippet, span_lint, span_lint_and_then, sugg};
   2 use if_chain::if_chain;
   3 use rustc::hir::*;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc::ty::{self, Ty};
   6 use rustc::{declare_lint_pass, declare_tool_lint};
   7 use rustc_errors::Applicability;
   8 use std::borrow::Cow;
   9 use syntax::ast;
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for transmutes that can't ever be correct on any
  13     /// architecture.
  14     ///
  15     /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  16     ///
  17     /// **Known problems:** When accessing C, users might want to store pointer
  18     /// sized objects in `extradata` arguments to save an allocation.
  19     ///
  20     /// **Example:**
  21     /// ```ignore
  22     /// let ptr: *const T = core::intrinsics::transmute('x')
  23     /// ```
  24     pub WRONG_TRANSMUTE,
  25     correctness,
  26     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  27 }
  28
  29 declare_clippy_lint! {
  30     /// **What it does:** Checks for transmutes to the original type of the object
  31     /// and transmutes that could be a cast.
  32     ///
  33     /// **Why is this bad?** Readability. The code tricks people into thinking that
  34     /// something complex is going on.
  35     ///
  36     /// **Known problems:** None.
  37     ///
  38     /// **Example:**
  39     /// ```rust,ignore
  40     /// core::intrinsics::transmute(t); // where the result type is the same as `t`'s
  41     /// ```
  42     pub USELESS_TRANSMUTE,
  43     complexity,
  44     "transmutes that have the same to and from types or could be a cast/coercion"
  45 }
  46
  47 declare_clippy_lint! {
  48     /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  49     ///
  50     /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  51     /// pointer to that type.
  52     ///
  53     /// **Known problems:** None.
  54     ///
  55     /// **Example:**
  56     /// ```rust,ignore
  57     /// core::intrinsics::transmute(t) // where the result type is the same as
  58     ///                                // `*t` or `&t`'s
  59     /// ```
  60     pub CROSSPOINTER_TRANSMUTE,
  61     complexity,
  62     "transmutes that have to or from types that are a pointer to the other"
  63 }
  64
  65 declare_clippy_lint! {
  66     /// **What it does:** Checks for transmutes from a pointer to a reference.
  67     ///
  68     /// **Why is this bad?** This can always be rewritten with `&` and `*`.
  69     ///
  70     /// **Known problems:** None.
  71     ///
  72     /// **Example:**
  73     /// ```rust,ignore
  74     /// unsafe {
  75     ///     let _: &T = std::mem::transmute(p); // where p: *const T
  76     /// }
  77     ///
  78     /// // can be written:
  79     /// let _: &T = &*p;
  80     /// ```
  81     pub TRANSMUTE_PTR_TO_REF,
  82     complexity,
  83     "transmutes from a pointer to a reference type"
  84 }
  85
  86 declare_clippy_lint! {
  87     /// **What it does:** Checks for transmutes from an integer to a `char`.
  88     ///
  89     /// **Why is this bad?** Not every integer is a Unicode scalar value.
  90     ///
  91     /// **Known problems:**
  92     /// - [`from_u32`] which this lint suggests using is slower than `transmute`
  93     /// as it needs to validate the input.
  94     /// If you are certain that the input is always a valid Unicode scalar value,
  95     /// use [`from_u32_unchecked`] which is as fast as `transmute`
  96     /// but has a semantically meaningful name.
  97     /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
  98     ///
  99     /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 100     /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 101     ///
 102     /// **Example:**
 103     /// ```rust
 104     /// let x = 1_u32;
 105     /// unsafe {
 106     ///     let _: char = std::mem::transmute(x); // where x: u32
 107     /// }
 108     ///
 109     /// // should be:
 110     /// let _ = std::char::from_u32(x).unwrap();
 111     /// ```
 112     pub TRANSMUTE_INT_TO_CHAR,
 113     complexity,
 114     "transmutes from an integer to a `char`"
 115 }
 116
 117 declare_clippy_lint! {
 118     /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 119     ///
 120     /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 121     ///
 122     /// **Known problems:**
 123     /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 124     /// as it needs to validate the input.
 125     /// If you are certain that the input is always a valid UTF-8,
 126     /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 127     /// but has a semantically meaningful name.
 128     /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 129     ///
 130     /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 131     /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 132     ///
 133     /// **Example:**
 134     /// ```rust
 135     /// let b: &[u8] = &[1_u8, 2_u8];
 136     /// unsafe {
 137     ///     let _: &str = std::mem::transmute(b); // where b: &[u8]
 138     /// }
 139     ///
 140     /// // should be:
 141     /// let _ = std::str::from_utf8(b).unwrap();
 142     /// ```
 143     pub TRANSMUTE_BYTES_TO_STR,
 144     complexity,
 145     "transmutes from a `&[u8]` to a `&str`"
 146 }
 147
 148 declare_clippy_lint! {
 149     /// **What it does:** Checks for transmutes from an integer to a `bool`.
 150     ///
 151     /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 152     ///
 153     /// **Known problems:** None.
 154     ///
 155     /// **Example:**
 156     /// ```rust
 157     /// let x = 1_u8;
 158     /// unsafe {
 159     ///     let _: bool = std::mem::transmute(x); // where x: u8
 160     /// }
 161     ///
 162     /// // should be:
 163     /// let _: bool = x != 0;
 164     /// ```
 165     pub TRANSMUTE_INT_TO_BOOL,
 166     complexity,
 167     "transmutes from an integer to a `bool`"
 168 }
 169
 170 declare_clippy_lint! {
 171     /// **What it does:** Checks for transmutes from an integer to a float.
 172     ///
 173     /// **Why is this bad?** Transmutes are dangerous and error-prone, whereas `from_bits` is intuitive
 174     /// and safe.
 175     ///
 176     /// **Known problems:** None.
 177     ///
 178     /// **Example:**
 179     /// ```rust
 180     /// unsafe {
 181     ///     let _: f32 = std::mem::transmute(1_u32); // where x: u32
 182     /// }
 183     ///
 184     /// // should be:
 185     /// let _: f32 = f32::from_bits(1_u32);
 186     /// ```
 187     pub TRANSMUTE_INT_TO_FLOAT,
 188     complexity,
 189     "transmutes from an integer to a float"
 190 }
 191
 192 declare_clippy_lint! {
 193     /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 194     /// from a reference to a reference.
 195     ///
 196     /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 197     /// written as casts.
 198     ///
 199     /// **Known problems:** None.
 200     ///
 201     /// **Example:**
 202     /// ```rust
 203     /// let ptr = &1u32 as *const u32;
 204     /// unsafe {
 205     ///     // pointer-to-pointer transmute
 206     ///     let _: *const f32 = std::mem::transmute(ptr);
 207     ///     // ref-ref transmute
 208     ///     let _: &f32 = std::mem::transmute(&1u32);
 209     /// }
 210     /// // These can be respectively written:
 211     /// let _ = ptr as *const f32;
 212     /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 213     /// ```
 214     pub TRANSMUTE_PTR_TO_PTR,
 215     complexity,
 216     "transmutes from a pointer to a pointer / a reference to a reference"
 217 }
 218
 219 declare_lint_pass!(Transmute => [
 220     CROSSPOINTER_TRANSMUTE,
 221     TRANSMUTE_PTR_TO_REF,
 222     TRANSMUTE_PTR_TO_PTR,
 223     USELESS_TRANSMUTE,
 224     WRONG_TRANSMUTE,
 225     TRANSMUTE_INT_TO_CHAR,
 226     TRANSMUTE_BYTES_TO_STR,
 227     TRANSMUTE_INT_TO_BOOL,
 228     TRANSMUTE_INT_TO_FLOAT,
 229 ]);
 230
 231 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Transmute {
 232     #[allow(clippy::similar_names, clippy::too_many_lines)]
 233     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 234         if let ExprKind::Call(ref path_expr, ref args) = e.node {
 235             if let ExprKind::Path(ref qpath) = path_expr.node {
 236                 if let Some(def_id) = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id() {
 237                     if match_def_path(cx, def_id, &paths::TRANSMUTE) {
 238                         let from_ty = cx.tables.expr_ty(&args[0]);
 239                         let to_ty = cx.tables.expr_ty(e);
 240
 241                         match (&from_ty.sty, &to_ty.sty) {
 242                             _ if from_ty == to_ty => span_lint(
 243                                 cx,
 244                                 USELESS_TRANSMUTE,
 245                                 e.span,
 246                                 &format!("transmute from a type (`{}`) to itself", from_ty),
 247                             ),
 248                             (&ty::Ref(_, rty, rty_mutbl), &ty::RawPtr(ptr_ty)) => span_lint_and_then(
 249                                 cx,
 250                                 USELESS_TRANSMUTE,
 251                                 e.span,
 252                                 "transmute from a reference to a pointer",
 253                                 |db| {
 254                                     if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 255                                         let rty_and_mut = ty::TypeAndMut {
 256                                             ty: rty,
 257                                             mutbl: rty_mutbl,
 258                                         };
 259
 260                                         let sugg = if ptr_ty == rty_and_mut {
 261                                             arg.as_ty(to_ty)
 262                                         } else {
 263                                             arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 264                                         };
 265
 266                                         db.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 267                                     }
 268                                 },
 269                             ),
 270                             (&ty::Int(_), &ty::RawPtr(_)) | (&ty::Uint(_), &ty::RawPtr(_)) => span_lint_and_then(
 271                                 cx,
 272                                 USELESS_TRANSMUTE,
 273                                 e.span,
 274                                 "transmute from an integer to a pointer",
 275                                 |db| {
 276                                     if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 277                                         db.span_suggestion(
 278                                             e.span,
 279                                             "try",
 280                                             arg.as_ty(&to_ty.to_string()).to_string(),
 281                                             Applicability::Unspecified,
 282                                         );
 283                                     }
 284                                 },
 285                             ),
 286                             (&ty::Float(_), &ty::Ref(..))
 287                             | (&ty::Float(_), &ty::RawPtr(_))
 288                             | (&ty::Char, &ty::Ref(..))
 289                             | (&ty::Char, &ty::RawPtr(_)) => span_lint(
 290                                 cx,
 291                                 WRONG_TRANSMUTE,
 292                                 e.span,
 293                                 &format!("transmute from a `{}` to a pointer", from_ty),
 294                             ),
 295                             (&ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 296                                 cx,
 297                                 CROSSPOINTER_TRANSMUTE,
 298                                 e.span,
 299                                 &format!(
 300                                     "transmute from a type (`{}`) to the type that it points to (`{}`)",
 301                                     from_ty, to_ty
 302                                 ),
 303                             ),
 304                             (_, &ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 305                                 cx,
 306                                 CROSSPOINTER_TRANSMUTE,
 307                                 e.span,
 308                                 &format!(
 309                                     "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 310                                     from_ty, to_ty
 311                                 ),
 312                             ),
 313                             (&ty::RawPtr(from_pty), &ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 314                                 cx,
 315                                 TRANSMUTE_PTR_TO_REF,
 316                                 e.span,
 317                                 &format!(
 318                                     "transmute from a pointer type (`{}`) to a reference type \
 319                                      (`{}`)",
 320                                     from_ty, to_ty
 321                                 ),
 322                                 |db| {
 323                                     let arg = sugg::Sugg::hir(cx, &args[0], "..");
 324                                     let (deref, cast) = if mutbl == Mutability::MutMutable {
 325                                         ("&mut *", "*mut")
 326                                     } else {
 327                                         ("&*", "*const")
 328                                     };
 329
 330                                     let arg = if from_pty.ty == to_ref_ty {
 331                                         arg
 332                                     } else {
 333                                         arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 334                                     };
 335
 336                                     db.span_suggestion(
 337                                         e.span,
 338                                         "try",
 339                                         sugg::make_unop(deref, arg).to_string(),
 340                                         Applicability::Unspecified,
 341                                     );
 342                                 },
 343                             ),
 344                             (&ty::Int(ast::IntTy::I32), &ty::Char) | (&ty::Uint(ast::UintTy::U32), &ty::Char) => {
 345                                 span_lint_and_then(
 346                                     cx,
 347                                     TRANSMUTE_INT_TO_CHAR,
 348                                     e.span,
 349                                     &format!("transmute from a `{}` to a `char`", from_ty),
 350                                     |db| {
 351                                         let arg = sugg::Sugg::hir(cx, &args[0], "..");
 352                                         let arg = if let ty::Int(_) = from_ty.sty {
 353                                             arg.as_ty(ast::UintTy::U32)
 354                                         } else {
 355                                             arg
 356                                         };
 357                                         db.span_suggestion(
 358                                             e.span,
 359                                             "consider using",
 360                                             format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 361                                             Applicability::Unspecified,
 362                                         );
 363                                     },
 364                                 )
 365                             },
 366                             (&ty::Ref(_, ty_from, from_mutbl), &ty::Ref(_, ty_to, to_mutbl)) => {
 367                                 if_chain! {
 368                                     if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.sty, &ty_to.sty);
 369                                     if let ty::Uint(ast::UintTy::U8) = slice_ty.sty;
 370                                     if from_mutbl == to_mutbl;
 371                                     then {
 372                                         let postfix = if from_mutbl == Mutability::MutMutable {
 373                                             "_mut"
 374                                         } else {
 375                                             ""
 376                                         };
 377
 378                                         span_lint_and_then(
 379                                             cx,
 380                                             TRANSMUTE_BYTES_TO_STR,
 381                                             e.span,
 382                                             &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 383                                             |db| {
 384                                                 db.span_suggestion(
 385                                                     e.span,
 386                                                     "consider using",
 387                                                     format!(
 388                                                         "std::str::from_utf8{}({}).unwrap()",
 389                                                         postfix,
 390                                                         snippet(cx, args[0].span, ".."),
 391                                                     ),
 392                                                     Applicability::Unspecified,
 393                                                 );
 394                                             }
 395                                         )
 396                                     } else {
 397                                         if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
 398                                             span_lint_and_then(
 399                                                 cx,
 400                                                 TRANSMUTE_PTR_TO_PTR,
 401                                                 e.span,
 402                                                 "transmute from a reference to a reference",
 403                                                 |db| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 404                                                     let ty_from_and_mut = ty::TypeAndMut {
 405                                                         ty: ty_from,
 406                                                         mutbl: from_mutbl
 407                                                     };
 408                                                     let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: to_mutbl };
 409                                                     let sugg_paren = arg
 410                                                         .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 411                                                         .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 412                                                     let sugg = if to_mutbl == Mutability::MutMutable {
 413                                                         sugg_paren.mut_addr_deref()
 414                                                     } else {
 415                                                         sugg_paren.addr_deref()
 416                                                     };
 417                                                     db.span_suggestion(
 418                                                         e.span,
 419                                                         "try",
 420                                                         sugg.to_string(),
 421                                                         Applicability::Unspecified,
 422                                                     );
 423                                                 },
 424                                             )
 425                                         }
 426                                     }
 427                                 }
 428                             },
 429                             (&ty::RawPtr(_), &ty::RawPtr(to_ty)) => span_lint_and_then(
 430                                 cx,
 431                                 TRANSMUTE_PTR_TO_PTR,
 432                                 e.span,
 433                                 "transmute from a pointer to a pointer",
 434                                 |db| {
 435                                     if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 436                                         let sugg = arg.as_ty(cx.tcx.mk_ptr(to_ty));
 437                                         db.span_suggestion(e.span, "try", sugg.to_string(), Applicability::Unspecified);
 438                                     }
 439                                 },
 440                             ),
 441                             (&ty::Int(ast::IntTy::I8), &ty::Bool) | (&ty::Uint(ast::UintTy::U8), &ty::Bool) => {
 442                                 span_lint_and_then(
 443                                     cx,
 444                                     TRANSMUTE_INT_TO_BOOL,
 445                                     e.span,
 446                                     &format!("transmute from a `{}` to a `bool`", from_ty),
 447                                     |db| {
 448                                         let arg = sugg::Sugg::hir(cx, &args[0], "..");
 449                                         let zero = sugg::Sugg::NonParen(Cow::from("0"));
 450                                         db.span_suggestion(
 451                                             e.span,
 452                                             "consider using",
 453                                             sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 454                                             Applicability::Unspecified,
 455                                         );
 456                                     },
 457                                 )
 458                             },
 459                             (&ty::Int(_), &ty::Float(_)) | (&ty::Uint(_), &ty::Float(_)) => span_lint_and_then(
 460                                 cx,
 461                                 TRANSMUTE_INT_TO_FLOAT,
 462                                 e.span,
 463                                 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 464                                 |db| {
 465                                     let arg = sugg::Sugg::hir(cx, &args[0], "..");
 466                                     let arg = if let ty::Int(int_ty) = from_ty.sty {
 467                                         arg.as_ty(format!(
 468                                             "u{}",
 469                                             int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 470                                         ))
 471                                     } else {
 472                                         arg
 473                                     };
 474                                     db.span_suggestion(
 475                                         e.span,
 476                                         "consider using",
 477                                         format!("{}::from_bits({})", to_ty, arg.to_string()),
 478                                         Applicability::Unspecified,
 479                                     );
 480                                 },
 481                             ),
 482                             _ => return,
 483                         };
 484                     }
 485                 }
 486             }
 487         }
 488     }
 489 }
 490
 491 /// Gets the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 492 /// not available , use
 493 /// the type's `ToString` implementation. In weird cases it could lead to types
 494 /// with invalid `'_`
 495 /// lifetime, but it should be rare.
 496 fn get_type_snippet(cx: &LateContext<'_, '_>, path: &QPath, to_ref_ty: Ty<'_>) -> String {
 497     let seg = last_path_segment(path);
 498     if_chain! {
 499         if let Some(ref params) = seg.args;
 500         if !params.parenthesized;
 501         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 502             GenericArg::Type(ty) => Some(ty),
 503             _ => None,
 504         }).nth(1);
 505         if let TyKind::Rptr(_, ref to_ty) = to_ty.node;
 506         then {
 507             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 508         }
 509     }
 510
 511     to_ref_ty.to_string()
 512 }