clippy_lints/src/transmute.rs

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