clippy_lints/src/transmute.rs

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