clippy_lints/src/transmute.rs

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