clippy_lints/src/transmute.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::rustc::hir::*;
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::ty::{self, Ty};
  13 use crate::rustc::{declare_tool_lint, lint_array};
  14 use crate::rustc_errors::Applicability;
  15 use crate::syntax::ast;
  16 use crate::utils::{last_path_segment, match_def_path, paths, snippet, span_lint, span_lint_and_then};
  17 use crate::utils::{opt_def_id, sugg};
  18 use if_chain::if_chain;
  19 use std::borrow::Cow;
  20
  21 /// **What it does:** Checks for transmutes that can't ever be correct on any
  22 /// architecture.
  23 ///
  24 /// **Why is this bad?** It's basically guaranteed to be undefined behaviour.
  25 ///
  26 /// **Known problems:** When accessing C, users might want to store pointer
  27 /// sized objects in `extradata` arguments to save an allocation.
  28 ///
  29 /// **Example:**
  30 /// ```rust
  31 /// let ptr: *const T = core::intrinsics::transmute('x')
  32 /// ```
  33 declare_clippy_lint! {
  34     pub WRONG_TRANSMUTE,
  35     correctness,
  36     "transmutes that are confusing at best, undefined behaviour at worst and always useless"
  37 }
  38
  39 /// **What it does:** Checks for transmutes to the original type of the object
  40 /// and transmutes that could be a cast.
  41 ///
  42 /// **Why is this bad?** Readability. The code tricks people into thinking that
  43 /// something complex is going on.
  44 ///
  45 /// **Known problems:** None.
  46 ///
  47 /// **Example:**
  48 /// ```rust
  49 /// core::intrinsics::transmute(t) // where the result type is the same as `t`'s
  50 /// ```
  51 declare_clippy_lint! {
  52     pub USELESS_TRANSMUTE,
  53     complexity,
  54     "transmutes that have the same to and from types or could be a cast/coercion"
  55 }
  56
  57 /// **What it does:** Checks for transmutes between a type `T` and `*T`.
  58 ///
  59 /// **Why is this bad?** It's easy to mistakenly transmute between a type and a
  60 /// pointer to that type.
  61 ///
  62 /// **Known problems:** None.
  63 ///
  64 /// **Example:**
  65 /// ```rust
  66 /// core::intrinsics::transmute(t) // where the result type is the same as
  67 ///                                // `*t` or `&t`'s
  68 /// ```
  69 declare_clippy_lint! {
  70     pub CROSSPOINTER_TRANSMUTE,
  71     complexity,
  72     "transmutes that have to or from types that are a pointer to the other"
  73 }
  74
  75 /// **What it does:** Checks for transmutes from a pointer to a reference.
  76 ///
  77 /// **Why is this bad?** This can always be rewritten with `&` and `*`.
  78 ///
  79 /// **Known problems:** None.
  80 ///
  81 /// **Example:**
  82 /// ```rust
  83 /// let _: &T = std::mem::transmute(p); // where p: *const T
  84 ///
  85 /// // can be written:
  86 /// let _: &T = &*p;
  87 /// ```
  88 declare_clippy_lint! {
  89     pub TRANSMUTE_PTR_TO_REF,
  90     complexity,
  91     "transmutes from a pointer to a reference type"
  92 }
  93
  94 /// **What it does:** Checks for transmutes from an integer to a `char`.
  95 ///
  96 /// **Why is this bad?** Not every integer is a Unicode scalar value.
  97 ///
  98 /// **Known problems:**
  99 /// - [`from_u32`] which this lint suggests using is slower than `transmute`
 100 /// as it needs to validate the input.
 101 /// If you are certain that the input is always a valid Unicode scalar value,
 102 /// use [`from_u32_unchecked`] which is as fast as `transmute`
 103 /// but has a semantically meaningful name.
 104 /// - You might want to handle `None` returned from [`from_u32`] instead of calling `unwrap`.
 105 ///
 106 /// [`from_u32`]: https://doc.rust-lang.org/std/char/fn.from_u32.html
 107 /// [`from_u32_unchecked`]: https://doc.rust-lang.org/std/char/fn.from_u32_unchecked.html
 108 ///
 109 /// **Example:**
 110 /// ```rust
 111 /// let _: char = std::mem::transmute(x); // where x: u32
 112 ///
 113 /// // should be:
 114 /// let _ = std::char::from_u32(x).unwrap();
 115 /// ```
 116 declare_clippy_lint! {
 117     pub TRANSMUTE_INT_TO_CHAR,
 118     complexity,
 119     "transmutes from an integer to a `char`"
 120 }
 121
 122 /// **What it does:** Checks for transmutes from a `&[u8]` to a `&str`.
 123 ///
 124 /// **Why is this bad?** Not every byte slice is a valid UTF-8 string.
 125 ///
 126 /// **Known problems:**
 127 /// - [`from_utf8`] which this lint suggests using is slower than `transmute`
 128 /// as it needs to validate the input.
 129 /// If you are certain that the input is always a valid UTF-8,
 130 /// use [`from_utf8_unchecked`] which is as fast as `transmute`
 131 /// but has a semantically meaningful name.
 132 /// - You might want to handle errors returned from [`from_utf8`] instead of calling `unwrap`.
 133 ///
 134 /// [`from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
 135 /// [`from_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked.html
 136 ///
 137 /// **Example:**
 138 /// ```rust
 139 /// let _: &str = std::mem::transmute(b); // where b: &[u8]
 140 ///
 141 /// // should be:
 142 /// let _ = std::str::from_utf8(b).unwrap();
 143 /// ```
 144 declare_clippy_lint! {
 145     pub TRANSMUTE_BYTES_TO_STR,
 146     complexity,
 147     "transmutes from a `&[u8]` to a `&str`"
 148 }
 149
 150 /// **What it does:** Checks for transmutes from an integer to a `bool`.
 151 ///
 152 /// **Why is this bad?** This might result in an invalid in-memory representation of a `bool`.
 153 ///
 154 /// **Known problems:** None.
 155 ///
 156 /// **Example:**
 157 /// ```rust
 158 /// let _: bool = std::mem::transmute(x); // where x: u8
 159 ///
 160 /// // should be:
 161 /// let _: bool = x != 0;
 162 /// ```
 163 declare_clippy_lint! {
 164     pub TRANSMUTE_INT_TO_BOOL,
 165     complexity,
 166     "transmutes from an integer to a `bool`"
 167 }
 168
 169 /// **What it does:** Checks for transmutes from an integer to a float.
 170 ///
 171 /// **Why is this bad?** This might result in an invalid in-memory representation of a float.
 172 ///
 173 /// **Known problems:** None.
 174 ///
 175 /// **Example:**
 176 /// ```rust
 177 /// let _: f32 = std::mem::transmute(x); // where x: u32
 178 ///
 179 /// // should be:
 180 /// let _: f32 = f32::from_bits(x);
 181 /// ```
 182 declare_clippy_lint! {
 183     pub TRANSMUTE_INT_TO_FLOAT,
 184     complexity,
 185     "transmutes from an integer to a float"
 186 }
 187
 188 /// **What it does:** Checks for transmutes from a pointer to a pointer, or
 189 /// from a reference to a reference.
 190 ///
 191 /// **Why is this bad?** Transmutes are dangerous, and these can instead be
 192 /// written as casts.
 193 ///
 194 /// **Known problems:** None.
 195 ///
 196 /// **Example:**
 197 /// ```rust
 198 /// let ptr = &1u32 as *const u32;
 199 /// unsafe {
 200 ///     // pointer-to-pointer transmute
 201 ///     let _: *const f32 = std::mem::transmute(ptr);
 202 ///     // ref-ref transmute
 203 ///     let _: &f32 = std::mem::transmute(&1u32);
 204 /// }
 205 /// // These can be respectively written:
 206 /// let _ = ptr as *const f32
 207 /// let _ = unsafe{ &*(&1u32 as *const u32 as *const f32) };
 208 /// ```
 209 declare_clippy_lint! {
 210     pub TRANSMUTE_PTR_TO_PTR,
 211     complexity,
 212     "transmutes from a pointer to a pointer / a reference to a reference"
 213 }
 214
 215 pub struct Transmute;
 216
 217 impl LintPass for Transmute {
 218     fn get_lints(&self) -> LintArray {
 219         lint_array!(
 220             CROSSPOINTER_TRANSMUTE,
 221             TRANSMUTE_PTR_TO_REF,
 222             TRANSMUTE_PTR_TO_PTR,
 223             USELESS_TRANSMUTE,
 224             WRONG_TRANSMUTE,
 225             TRANSMUTE_INT_TO_CHAR,
 226             TRANSMUTE_BYTES_TO_STR,
 227             TRANSMUTE_INT_TO_BOOL,
 228             TRANSMUTE_INT_TO_FLOAT,
 229         )
 230     }
 231 }
 232
 233 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Transmute {
 234     #[allow(clippy::similar_names)]
 235     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 236         if let ExprKind::Call(ref path_expr, ref args) = e.node {
 237             if let ExprKind::Path(ref qpath) = path_expr.node {
 238                 if let Some(def_id) = opt_def_id(cx.tables.qpath_def(qpath, path_expr.hir_id)) {
 239                     if match_def_path(cx.tcx, def_id, &paths::TRANSMUTE) {
 240                         let from_ty = cx.tables.expr_ty(&args[0]);
 241                         let to_ty = cx.tables.expr_ty(e);
 242
 243                         match (&from_ty.sty, &to_ty.sty) {
 244                             _ if from_ty == to_ty => span_lint(
 245                                 cx,
 246                                 USELESS_TRANSMUTE,
 247                                 e.span,
 248                                 &format!("transmute from a type (`{}`) to itself", from_ty),
 249                             ),
 250                             (&ty::Ref(_, rty, rty_mutbl), &ty::RawPtr(ptr_ty)) => span_lint_and_then(
 251                                 cx,
 252                                 USELESS_TRANSMUTE,
 253                                 e.span,
 254                                 "transmute from a reference to a pointer",
 255                                 |db| {
 256                                     if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 257                                         let rty_and_mut = ty::TypeAndMut {
 258                                             ty: rty,
 259                                             mutbl: rty_mutbl,
 260                                         };
 261
 262                                         let sugg = if ptr_ty == rty_and_mut {
 263                                             arg.as_ty(to_ty)
 264                                         } else {
 265                                             arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
 266                                         };
 267
 268                                         db.span_suggestion_with_applicability(
 269                                             e.span,
 270                                             "try",
 271                                             sugg.to_string(),
 272                                             Applicability::Unspecified,
 273                                         );
 274                                     }
 275                                 },
 276                             ),
 277                             (&ty::Int(_), &ty::RawPtr(_)) | (&ty::Uint(_), &ty::RawPtr(_)) => span_lint_and_then(
 278                                 cx,
 279                                 USELESS_TRANSMUTE,
 280                                 e.span,
 281                                 "transmute from an integer to a pointer",
 282                                 |db| {
 283                                     if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 284                                         db.span_suggestion_with_applicability(
 285                                             e.span,
 286                                             "try",
 287                                             arg.as_ty(&to_ty.to_string()).to_string(),
 288                                             Applicability::Unspecified,
 289                                         );
 290                                     }
 291                                 },
 292                             ),
 293                             (&ty::Float(_), &ty::Ref(..))
 294                             | (&ty::Float(_), &ty::RawPtr(_))
 295                             | (&ty::Char, &ty::Ref(..))
 296                             | (&ty::Char, &ty::RawPtr(_)) => span_lint(
 297                                 cx,
 298                                 WRONG_TRANSMUTE,
 299                                 e.span,
 300                                 &format!("transmute from a `{}` to a pointer", from_ty),
 301                             ),
 302                             (&ty::RawPtr(from_ptr), _) if from_ptr.ty == to_ty => span_lint(
 303                                 cx,
 304                                 CROSSPOINTER_TRANSMUTE,
 305                                 e.span,
 306                                 &format!(
 307                                     "transmute from a type (`{}`) to the type that it points to (`{}`)",
 308                                     from_ty, to_ty
 309                                 ),
 310                             ),
 311                             (_, &ty::RawPtr(to_ptr)) if to_ptr.ty == from_ty => span_lint(
 312                                 cx,
 313                                 CROSSPOINTER_TRANSMUTE,
 314                                 e.span,
 315                                 &format!(
 316                                     "transmute from a type (`{}`) to a pointer to that type (`{}`)",
 317                                     from_ty, to_ty
 318                                 ),
 319                             ),
 320                             (&ty::RawPtr(from_pty), &ty::Ref(_, to_ref_ty, mutbl)) => span_lint_and_then(
 321                                 cx,
 322                                 TRANSMUTE_PTR_TO_REF,
 323                                 e.span,
 324                                 &format!(
 325                                     "transmute from a pointer type (`{}`) to a reference type \
 326                                      (`{}`)",
 327                                     from_ty, to_ty
 328                                 ),
 329                                 |db| {
 330                                     let arg = sugg::Sugg::hir(cx, &args[0], "..");
 331                                     let (deref, cast) = if mutbl == Mutability::MutMutable {
 332                                         ("&mut *", "*mut")
 333                                     } else {
 334                                         ("&*", "*const")
 335                                     };
 336
 337                                     let arg = if from_pty.ty == to_ref_ty {
 338                                         arg
 339                                     } else {
 340                                         arg.as_ty(&format!("{} {}", cast, get_type_snippet(cx, qpath, to_ref_ty)))
 341                                     };
 342
 343                                     db.span_suggestion_with_applicability(
 344                                         e.span,
 345                                         "try",
 346                                         sugg::make_unop(deref, arg).to_string(),
 347                                         Applicability::Unspecified,
 348                                     );
 349                                 },
 350                             ),
 351                             (&ty::Int(ast::IntTy::I32), &ty::Char) | (&ty::Uint(ast::UintTy::U32), &ty::Char) => {
 352                                 span_lint_and_then(
 353                                     cx,
 354                                     TRANSMUTE_INT_TO_CHAR,
 355                                     e.span,
 356                                     &format!("transmute from a `{}` to a `char`", from_ty),
 357                                     |db| {
 358                                         let arg = sugg::Sugg::hir(cx, &args[0], "..");
 359                                         let arg = if let ty::Int(_) = from_ty.sty {
 360                                             arg.as_ty(ty::Uint(ast::UintTy::U32))
 361                                         } else {
 362                                             arg
 363                                         };
 364                                         db.span_suggestion_with_applicability(
 365                                             e.span,
 366                                             "consider using",
 367                                             format!("std::char::from_u32({}).unwrap()", arg.to_string()),
 368                                             Applicability::Unspecified,
 369                                         );
 370                                     },
 371                                 )
 372                             },
 373                             (&ty::Ref(_, ty_from, from_mutbl), &ty::Ref(_, ty_to, to_mutbl)) => {
 374                                 if_chain! {
 375                                     if let (&ty::Slice(slice_ty), &ty::Str) = (&ty_from.sty, &ty_to.sty);
 376                                     if let ty::Uint(ast::UintTy::U8) = slice_ty.sty;
 377                                     if from_mutbl == to_mutbl;
 378                                     then {
 379                                         let postfix = if from_mutbl == Mutability::MutMutable {
 380                                             "_mut"
 381                                         } else {
 382                                             ""
 383                                         };
 384
 385                                         span_lint_and_then(
 386                                             cx,
 387                                             TRANSMUTE_BYTES_TO_STR,
 388                                             e.span,
 389                                             &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 390                                             |db| {
 391                                                 db.span_suggestion_with_applicability(
 392                                                     e.span,
 393                                                     "consider using",
 394                                                     format!(
 395                                                         "std::str::from_utf8{}({}).unwrap()",
 396                                                         postfix,
 397                                                         snippet(cx, args[0].span, ".."),
 398                                                     ),
 399                                                     Applicability::Unspecified,
 400                                                 );
 401                                             }
 402                                         )
 403                                     } else {
 404                                         if cx.tcx.erase_regions(&from_ty) != cx.tcx.erase_regions(&to_ty) {
 405                                             span_lint_and_then(
 406                                                 cx,
 407                                                 TRANSMUTE_PTR_TO_PTR,
 408                                                 e.span,
 409                                                 "transmute from a reference to a reference",
 410                                                 |db| if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 411                                                     let ty_from_and_mut = ty::TypeAndMut {
 412                                                         ty: ty_from,
 413                                                         mutbl: from_mutbl
 414                                                     };
 415                                                     let ty_to_and_mut = ty::TypeAndMut { ty: ty_to, mutbl: to_mutbl };
 416                                                     let sugg_paren = arg
 417                                                         .as_ty(cx.tcx.mk_ptr(ty_from_and_mut))
 418                                                         .as_ty(cx.tcx.mk_ptr(ty_to_and_mut));
 419                                                     let sugg = if to_mutbl == Mutability::MutMutable {
 420                                                         sugg_paren.mut_addr_deref()
 421                                                     } else {
 422                                                         sugg_paren.addr_deref()
 423                                                     };
 424                                                     db.span_suggestion_with_applicability(
 425                                                         e.span,
 426                                                         "try",
 427                                                         sugg.to_string(),
 428                                                         Applicability::Unspecified,
 429                                                     );
 430                                                 },
 431                                             )
 432                                         }
 433                                     }
 434                                 }
 435                             },
 436                             (&ty::RawPtr(_), &ty::RawPtr(to_ty)) => span_lint_and_then(
 437                                 cx,
 438                                 TRANSMUTE_PTR_TO_PTR,
 439                                 e.span,
 440                                 "transmute from a pointer to a pointer",
 441                                 |db| {
 442                                     if let Some(arg) = sugg::Sugg::hir_opt(cx, &args[0]) {
 443                                         let sugg = arg.as_ty(cx.tcx.mk_ptr(to_ty));
 444                                         db.span_suggestion_with_applicability(
 445                                             e.span,
 446                                             "try",
 447                                             sugg.to_string(),
 448                                             Applicability::Unspecified,
 449                                         );
 450                                     }
 451                                 },
 452                             ),
 453                             (&ty::Int(ast::IntTy::I8), &ty::Bool) | (&ty::Uint(ast::UintTy::U8), &ty::Bool) => {
 454                                 span_lint_and_then(
 455                                     cx,
 456                                     TRANSMUTE_INT_TO_BOOL,
 457                                     e.span,
 458                                     &format!("transmute from a `{}` to a `bool`", from_ty),
 459                                     |db| {
 460                                         let arg = sugg::Sugg::hir(cx, &args[0], "..");
 461                                         let zero = sugg::Sugg::NonParen(Cow::from("0"));
 462                                         db.span_suggestion_with_applicability(
 463                                             e.span,
 464                                             "consider using",
 465                                             sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
 466                                             Applicability::Unspecified,
 467                                         );
 468                                     },
 469                                 )
 470                             },
 471                             (&ty::Int(_), &ty::Float(_)) | (&ty::Uint(_), &ty::Float(_)) => span_lint_and_then(
 472                                 cx,
 473                                 TRANSMUTE_INT_TO_FLOAT,
 474                                 e.span,
 475                                 &format!("transmute from a `{}` to a `{}`", from_ty, to_ty),
 476                                 |db| {
 477                                     let arg = sugg::Sugg::hir(cx, &args[0], "..");
 478                                     let arg = if let ty::Int(int_ty) = from_ty.sty {
 479                                         arg.as_ty(format!(
 480                                             "u{}",
 481                                             int_ty.bit_width().map_or_else(|| "size".to_string(), |v| v.to_string())
 482                                         ))
 483                                     } else {
 484                                         arg
 485                                     };
 486                                     db.span_suggestion_with_applicability(
 487                                         e.span,
 488                                         "consider using",
 489                                         format!("{}::from_bits({})", to_ty, arg.to_string()),
 490                                         Applicability::Unspecified,
 491                                     );
 492                                 },
 493                             ),
 494                             _ => return,
 495                         };
 496                     }
 497                 }
 498             }
 499         }
 500     }
 501 }
 502
 503 /// Get the snippet of `Bar` in `…::transmute<Foo, &Bar>`. If that snippet is
 504 /// not available , use
 505 /// the type's `ToString` implementation. In weird cases it could lead to types
 506 /// with invalid `'_`
 507 /// lifetime, but it should be rare.
 508 fn get_type_snippet(cx: &LateContext<'_, '_>, path: &QPath, to_ref_ty: Ty<'_>) -> String {
 509     let seg = last_path_segment(path);
 510     if_chain! {
 511         if let Some(ref params) = seg.args;
 512         if !params.parenthesized;
 513         if let Some(to_ty) = params.args.iter().filter_map(|arg| match arg {
 514             GenericArg::Type(ty) => Some(ty),
 515             GenericArg::Lifetime(_) => None,
 516         }).nth(1);
 517         if let TyKind::Rptr(_, ref to_ty) = to_ty.node;
 518         then {
 519             return snippet(cx, to_ty.ty.span, &to_ref_ty.to_string()).to_string();
 520         }
 521     }
 522
 523     to_ref_ty.to_string()
 524 }