clippy_lints/src/transmute.rs

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