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