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