src/tools/clippy/clippy_lints/src/misc.rs

   1 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then, span_lint_hir_and_then};
   2 use clippy_utils::source::{snippet, snippet_opt};
   3 use clippy_utils::ty::implements_trait;
   4 use if_chain::if_chain;
   5 use rustc_ast::ast::LitKind;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::intravisit::FnKind;
   8 use rustc_hir::{
   9     self as hir, def, BinOpKind, BindingAnnotation, Body, Expr, ExprKind, FnDecl, HirId, Mutability, PatKind, Stmt,
  10     StmtKind, TyKind, UnOp,
  11 };
  12 use rustc_lint::{LateContext, LateLintPass};
  13 use rustc_middle::lint::in_external_macro;
  14 use rustc_middle::ty::{self, Ty};
  15 use rustc_session::{declare_lint_pass, declare_tool_lint};
  16 use rustc_span::hygiene::DesugaringKind;
  17 use rustc_span::source_map::{ExpnKind, Span};
  18 use rustc_span::symbol::sym;
  19
  20 use clippy_utils::consts::{constant, Constant};
  21 use clippy_utils::sugg::Sugg;
  22 use clippy_utils::{
  23     expr_path_res, get_item_name, get_parent_expr, in_constant, is_diag_trait_item, is_integer_const, iter_input_pats,
  24     last_path_segment, match_any_def_paths, paths, unsext, SpanlessEq,
  25 };
  26
  27 declare_clippy_lint! {
  28     /// ### What it does
  29     /// Checks for function arguments and let bindings denoted as
  30     /// `ref`.
  31     ///
  32     /// ### Why is this bad?
  33     /// The `ref` declaration makes the function take an owned
  34     /// value, but turns the argument into a reference (which means that the value
  35     /// is destroyed when exiting the function). This adds not much value: either
  36     /// take a reference type, or take an owned value and create references in the
  37     /// body.
  38     ///
  39     /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
  40     /// type of `x` is more obvious with the former.
  41     ///
  42     /// ### Known problems
  43     /// If the argument is dereferenced within the function,
  44     /// removing the `ref` will lead to errors. This can be fixed by removing the
  45     /// dereferences, e.g., changing `*x` to `x` within the function.
  46     ///
  47     /// ### Example
  48     /// ```rust,ignore
  49     /// // Bad
  50     /// fn foo(ref x: u8) -> bool {
  51     ///     true
  52     /// }
  53     ///
  54     /// // Good
  55     /// fn foo(x: &u8) -> bool {
  56     ///     true
  57     /// }
  58     /// ```
  59     pub TOPLEVEL_REF_ARG,
  60     style,
  61     "an entire binding declared as `ref`, in a function argument or a `let` statement"
  62 }
  63
  64 declare_clippy_lint! {
  65     /// ### What it does
  66     /// Checks for comparisons to NaN.
  67     ///
  68     /// ### Why is this bad?
  69     /// NaN does not compare meaningfully to anything – not
  70     /// even itself – so those comparisons are simply wrong.
  71     ///
  72     /// ### Example
  73     /// ```rust
  74     /// # let x = 1.0;
  75     ///
  76     /// // Bad
  77     /// if x == f32::NAN { }
  78     ///
  79     /// // Good
  80     /// if x.is_nan() { }
  81     /// ```
  82     pub CMP_NAN,
  83     correctness,
  84     "comparisons to `NAN`, which will always return false, probably not intended"
  85 }
  86
  87 declare_clippy_lint! {
  88     /// ### What it does
  89     /// Checks for (in-)equality comparisons on floating-point
  90     /// values (apart from zero), except in functions called `*eq*` (which probably
  91     /// implement equality for a type involving floats).
  92     ///
  93     /// ### Why is this bad?
  94     /// Floating point calculations are usually imprecise, so
  95     /// asking if two values are *exactly* equal is asking for trouble. For a good
  96     /// guide on what to do, see [the floating point
  97     /// guide](http://www.floating-point-gui.de/errors/comparison).
  98     ///
  99     /// ### Example
 100     /// ```rust
 101     /// let x = 1.2331f64;
 102     /// let y = 1.2332f64;
 103     ///
 104     /// // Bad
 105     /// if y == 1.23f64 { }
 106     /// if y != x {} // where both are floats
 107     ///
 108     /// // Good
 109     /// let error_margin = f64::EPSILON; // Use an epsilon for comparison
 110     /// // Or, if Rust <= 1.42, use `std::f64::EPSILON` constant instead.
 111     /// // let error_margin = std::f64::EPSILON;
 112     /// if (y - 1.23f64).abs() < error_margin { }
 113     /// if (y - x).abs() > error_margin { }
 114     /// ```
 115     pub FLOAT_CMP,
 116     pedantic,
 117     "using `==` or `!=` on float values instead of comparing difference with an epsilon"
 118 }
 119
 120 declare_clippy_lint! {
 121     /// ### What it does
 122     /// Checks for conversions to owned values just for the sake
 123     /// of a comparison.
 124     ///
 125     /// ### Why is this bad?
 126     /// The comparison can operate on a reference, so creating
 127     /// an owned value effectively throws it away directly afterwards, which is
 128     /// needlessly consuming code and heap space.
 129     ///
 130     /// ### Example
 131     /// ```rust
 132     /// # let x = "foo";
 133     /// # let y = String::from("foo");
 134     /// if x.to_owned() == y {}
 135     /// ```
 136     /// Could be written as
 137     /// ```rust
 138     /// # let x = "foo";
 139     /// # let y = String::from("foo");
 140     /// if x == y {}
 141     /// ```
 142     pub CMP_OWNED,
 143     perf,
 144     "creating owned instances for comparing with others, e.g., `x == \"foo\".to_string()`"
 145 }
 146
 147 declare_clippy_lint! {
 148     /// ### What it does
 149     /// Checks for getting the remainder of a division by one or minus
 150     /// one.
 151     ///
 152     /// ### Why is this bad?
 153     /// The result for a divisor of one can only ever be zero; for
 154     /// minus one it can cause panic/overflow (if the left operand is the minimal value of
 155     /// the respective integer type) or results in zero. No one will write such code
 156     /// deliberately, unless trying to win an Underhanded Rust Contest. Even for that
 157     /// contest, it's probably a bad idea. Use something more underhanded.
 158     ///
 159     /// ### Example
 160     /// ```rust
 161     /// # let x = 1;
 162     /// let a = x % 1;
 163     /// let a = x % -1;
 164     /// ```
 165     pub MODULO_ONE,
 166     correctness,
 167     "taking a number modulo +/-1, which can either panic/overflow or always returns 0"
 168 }
 169
 170 declare_clippy_lint! {
 171     /// ### What it does
 172     /// Checks for the use of bindings with a single leading
 173     /// underscore.
 174     ///
 175     /// ### Why is this bad?
 176     /// A single leading underscore is usually used to indicate
 177     /// that a binding will not be used. Using such a binding breaks this
 178     /// expectation.
 179     ///
 180     /// ### Known problems
 181     /// The lint does not work properly with desugaring and
 182     /// macro, it has been allowed in the mean time.
 183     ///
 184     /// ### Example
 185     /// ```rust
 186     /// let _x = 0;
 187     /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
 188     ///                 // underscore. We should rename `_x` to `x`
 189     /// ```
 190     pub USED_UNDERSCORE_BINDING,
 191     pedantic,
 192     "using a binding which is prefixed with an underscore"
 193 }
 194
 195 declare_clippy_lint! {
 196     /// ### What it does
 197     /// Checks for the use of short circuit boolean conditions as
 198     /// a
 199     /// statement.
 200     ///
 201     /// ### Why is this bad?
 202     /// Using a short circuit boolean condition as a statement
 203     /// may hide the fact that the second part is executed or not depending on the
 204     /// outcome of the first part.
 205     ///
 206     /// ### Example
 207     /// ```rust,ignore
 208     /// f() && g(); // We should write `if f() { g(); }`.
 209     /// ```
 210     pub SHORT_CIRCUIT_STATEMENT,
 211     complexity,
 212     "using a short circuit boolean condition as a statement"
 213 }
 214
 215 declare_clippy_lint! {
 216     /// ### What it does
 217     /// Catch casts from `0` to some pointer type
 218     ///
 219     /// ### Why is this bad?
 220     /// This generally means `null` and is better expressed as
 221     /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
 222     ///
 223     /// ### Example
 224     /// ```rust
 225     /// // Bad
 226     /// let a = 0 as *const u32;
 227     ///
 228     /// // Good
 229     /// let a = std::ptr::null::<u32>();
 230     /// ```
 231     pub ZERO_PTR,
 232     style,
 233     "using `0 as *{const, mut} T`"
 234 }
 235
 236 declare_clippy_lint! {
 237     /// ### What it does
 238     /// Checks for (in-)equality comparisons on floating-point
 239     /// value and constant, except in functions called `*eq*` (which probably
 240     /// implement equality for a type involving floats).
 241     ///
 242     /// ### Why is this bad?
 243     /// Floating point calculations are usually imprecise, so
 244     /// asking if two values are *exactly* equal is asking for trouble. For a good
 245     /// guide on what to do, see [the floating point
 246     /// guide](http://www.floating-point-gui.de/errors/comparison).
 247     ///
 248     /// ### Example
 249     /// ```rust
 250     /// let x: f64 = 1.0;
 251     /// const ONE: f64 = 1.00;
 252     ///
 253     /// // Bad
 254     /// if x == ONE { } // where both are floats
 255     ///
 256     /// // Good
 257     /// let error_margin = f64::EPSILON; // Use an epsilon for comparison
 258     /// // Or, if Rust <= 1.42, use `std::f64::EPSILON` constant instead.
 259     /// // let error_margin = std::f64::EPSILON;
 260     /// if (x - ONE).abs() < error_margin { }
 261     /// ```
 262     pub FLOAT_CMP_CONST,
 263     restriction,
 264     "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
 265 }
 266
 267 declare_lint_pass!(MiscLints => [
 268     TOPLEVEL_REF_ARG,
 269     CMP_NAN,
 270     FLOAT_CMP,
 271     CMP_OWNED,
 272     MODULO_ONE,
 273     USED_UNDERSCORE_BINDING,
 274     SHORT_CIRCUIT_STATEMENT,
 275     ZERO_PTR,
 276     FLOAT_CMP_CONST
 277 ]);
 278
 279 impl<'tcx> LateLintPass<'tcx> for MiscLints {
 280     fn check_fn(
 281         &mut self,
 282         cx: &LateContext<'tcx>,
 283         k: FnKind<'tcx>,
 284         decl: &'tcx FnDecl<'_>,
 285         body: &'tcx Body<'_>,
 286         span: Span,
 287         _: HirId,
 288     ) {
 289         if let FnKind::Closure = k {
 290             // Does not apply to closures
 291             return;
 292         }
 293         if in_external_macro(cx.tcx.sess, span) {
 294             return;
 295         }
 296         for arg in iter_input_pats(decl, body) {
 297             if let PatKind::Binding(BindingAnnotation::Ref | BindingAnnotation::RefMut, ..) = arg.pat.kind {
 298                 span_lint(
 299                     cx,
 300                     TOPLEVEL_REF_ARG,
 301                     arg.pat.span,
 302                     "`ref` directly on a function argument is ignored. \
 303                     Consider using a reference type instead",
 304                 );
 305             }
 306         }
 307     }
 308
 309     fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
 310         if_chain! {
 311             if !in_external_macro(cx.tcx.sess, stmt.span);
 312             if let StmtKind::Local(local) = stmt.kind;
 313             if let PatKind::Binding(an, .., name, None) = local.pat.kind;
 314             if let Some(init) = local.init;
 315             if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut;
 316             then {
 317                 // use the macro callsite when the init span (but not the whole local span)
 318                 // comes from an expansion like `vec![1, 2, 3]` in `let ref _ = vec![1, 2, 3];`
 319                 let sugg_init = if init.span.from_expansion() && !local.span.from_expansion() {
 320                     Sugg::hir_with_macro_callsite(cx, init, "..")
 321                 } else {
 322                     Sugg::hir(cx, init, "..")
 323                 };
 324                 let (mutopt, initref) = if an == BindingAnnotation::RefMut {
 325                     ("mut ", sugg_init.mut_addr())
 326                 } else {
 327                     ("", sugg_init.addr())
 328                 };
 329                 let tyopt = if let Some(ty) = local.ty {
 330                     format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, ".."))
 331                 } else {
 332                     String::new()
 333                 };
 334                 span_lint_hir_and_then(
 335                     cx,
 336                     TOPLEVEL_REF_ARG,
 337                     init.hir_id,
 338                     local.pat.span,
 339                     "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
 340                     |diag| {
 341                         diag.span_suggestion(
 342                             stmt.span,
 343                             "try",
 344                             format!(
 345                                 "let {name}{tyopt} = {initref};",
 346                                 name=snippet(cx, name.span, ".."),
 347                                 tyopt=tyopt,
 348                                 initref=initref,
 349                             ),
 350                             Applicability::MachineApplicable,
 351                         );
 352                     }
 353                 );
 354             }
 355         };
 356         if_chain! {
 357             if let StmtKind::Semi(expr) = stmt.kind;
 358             if let ExprKind::Binary(ref binop, a, b) = expr.kind;
 359             if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
 360             if let Some(sugg) = Sugg::hir_opt(cx, a);
 361             then {
 362                 span_lint_hir_and_then(
 363                     cx,
 364                     SHORT_CIRCUIT_STATEMENT,
 365                     expr.hir_id,
 366                     stmt.span,
 367                     "boolean short circuit operator in statement may be clearer using an explicit test",
 368                     |diag| {
 369                         let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
 370                         diag.span_suggestion(
 371                             stmt.span,
 372                             "replace it with",
 373                             format!(
 374                                 "if {} {{ {}; }}",
 375                                 sugg,
 376                                 &snippet(cx, b.span, ".."),
 377                             ),
 378                             Applicability::MachineApplicable, // snippet
 379                         );
 380                     });
 381             }
 382         };
 383     }
 384
 385     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 386         match expr.kind {
 387             ExprKind::Cast(e, ty) => {
 388                 check_cast(cx, expr.span, e, ty);
 389                 return;
 390             },
 391             ExprKind::Binary(ref cmp, left, right) => {
 392                 check_binary(cx, expr, cmp, left, right);
 393                 return;
 394             },
 395             _ => {},
 396         }
 397         if in_attributes_expansion(expr) || expr.span.is_desugaring(DesugaringKind::Await) {
 398             // Don't lint things expanded by #[derive(...)], etc or `await` desugaring
 399             return;
 400         }
 401         let binding = match expr.kind {
 402             ExprKind::Path(ref qpath) if !matches!(qpath, hir::QPath::LangItem(..)) => {
 403                 let binding = last_path_segment(qpath).ident.as_str();
 404                 if binding.starts_with('_') &&
 405                     !binding.starts_with("__") &&
 406                     binding != "_result" && // FIXME: #944
 407                     is_used(cx, expr) &&
 408                     // don't lint if the declaration is in a macro
 409                     non_macro_local(cx, cx.qpath_res(qpath, expr.hir_id))
 410                 {
 411                     Some(binding)
 412                 } else {
 413                     None
 414                 }
 415             },
 416             ExprKind::Field(_, ident) => {
 417                 let name = ident.as_str();
 418                 if name.starts_with('_') && !name.starts_with("__") {
 419                     Some(name)
 420                 } else {
 421                     None
 422                 }
 423             },
 424             _ => None,
 425         };
 426         if let Some(binding) = binding {
 427             span_lint(
 428                 cx,
 429                 USED_UNDERSCORE_BINDING,
 430                 expr.span,
 431                 &format!(
 432                     "used binding `{}` which is prefixed with an underscore. A leading \
 433                      underscore signals that a binding will not be used",
 434                     binding
 435                 ),
 436             );
 437         }
 438     }
 439 }
 440
 441 fn get_lint_and_message(
 442     is_comparing_constants: bool,
 443     is_comparing_arrays: bool,
 444 ) -> (&'static rustc_lint::Lint, &'static str) {
 445     if is_comparing_constants {
 446         (
 447             FLOAT_CMP_CONST,
 448             if is_comparing_arrays {
 449                 "strict comparison of `f32` or `f64` constant arrays"
 450             } else {
 451                 "strict comparison of `f32` or `f64` constant"
 452             },
 453         )
 454     } else {
 455         (
 456             FLOAT_CMP,
 457             if is_comparing_arrays {
 458                 "strict comparison of `f32` or `f64` arrays"
 459             } else {
 460                 "strict comparison of `f32` or `f64`"
 461             },
 462         )
 463     }
 464 }
 465
 466 fn check_nan(cx: &LateContext<'_>, expr: &Expr<'_>, cmp_expr: &Expr<'_>) {
 467     if_chain! {
 468         if !in_constant(cx, cmp_expr.hir_id);
 469         if let Some((value, _)) = constant(cx, cx.typeck_results(), expr);
 470         if match value {
 471             Constant::F32(num) => num.is_nan(),
 472             Constant::F64(num) => num.is_nan(),
 473             _ => false,
 474         };
 475         then {
 476             span_lint(
 477                 cx,
 478                 CMP_NAN,
 479                 cmp_expr.span,
 480                 "doomed comparison with `NAN`, use `{f32,f64}::is_nan()` instead",
 481             );
 482         }
 483     }
 484 }
 485
 486 fn is_named_constant<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 487     if let Some((_, res)) = constant(cx, cx.typeck_results(), expr) {
 488         res
 489     } else {
 490         false
 491     }
 492 }
 493
 494 fn is_allowed<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
 495     match constant(cx, cx.typeck_results(), expr) {
 496         Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
 497         Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
 498         Some((Constant::Vec(vec), _)) => vec.iter().all(|f| match f {
 499             Constant::F32(f) => *f == 0.0 || (*f).is_infinite(),
 500             Constant::F64(f) => *f == 0.0 || (*f).is_infinite(),
 501             _ => false,
 502         }),
 503         _ => false,
 504     }
 505 }
 506
 507 // Return true if `expr` is the result of `signum()` invoked on a float value.
 508 fn is_signum(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 509     // The negation of a signum is still a signum
 510     if let ExprKind::Unary(UnOp::Neg, child_expr) = expr.kind {
 511         return is_signum(cx, child_expr);
 512     }
 513
 514     if_chain! {
 515         if let ExprKind::MethodCall(method_name, _, [ref self_arg, ..], _) = expr.kind;
 516         if sym!(signum) == method_name.ident.name;
 517         // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
 518         // the method call)
 519         then {
 520             return is_float(cx, self_arg);
 521         }
 522     }
 523     false
 524 }
 525
 526 fn is_float(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 527     let value = &cx.typeck_results().expr_ty(expr).peel_refs().kind();
 528
 529     if let ty::Array(arr_ty, _) = value {
 530         return matches!(arr_ty.kind(), ty::Float(_));
 531     };
 532
 533     matches!(value, ty::Float(_))
 534 }
 535
 536 fn is_array(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 537     matches!(&cx.typeck_results().expr_ty(expr).peel_refs().kind(), ty::Array(_, _))
 538 }
 539
 540 fn check_to_owned(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left: bool) {
 541     #[derive(Default)]
 542     struct EqImpl {
 543         ty_eq_other: bool,
 544         other_eq_ty: bool,
 545     }
 546
 547     impl EqImpl {
 548         fn is_implemented(&self) -> bool {
 549             self.ty_eq_other || self.other_eq_ty
 550         }
 551     }
 552
 553     fn symmetric_partial_eq<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> Option<EqImpl> {
 554         cx.tcx.lang_items().eq_trait().map(|def_id| EqImpl {
 555             ty_eq_other: implements_trait(cx, ty, def_id, &[other.into()]),
 556             other_eq_ty: implements_trait(cx, other, def_id, &[ty.into()]),
 557         })
 558     }
 559
 560     let (arg_ty, snip) = match expr.kind {
 561         ExprKind::MethodCall(.., args, _) if args.len() == 1 => {
 562             if_chain!(
 563                 if let Some(expr_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
 564                 if is_diag_trait_item(cx, expr_def_id, sym::ToString)
 565                     || is_diag_trait_item(cx, expr_def_id, sym::ToOwned);
 566                 then {
 567                     (cx.typeck_results().expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
 568                 } else {
 569                     return;
 570                 }
 571             )
 572         },
 573         ExprKind::Call(path, [arg]) => {
 574             if expr_path_res(cx, path)
 575                 .opt_def_id()
 576                 .and_then(|id| match_any_def_paths(cx, id, &[&paths::FROM_STR_METHOD, &paths::FROM_FROM]))
 577                 .is_some()
 578             {
 579                 (cx.typeck_results().expr_ty(arg), snippet(cx, arg.span, ".."))
 580             } else {
 581                 return;
 582             }
 583         },
 584         _ => return,
 585     };
 586
 587     let other_ty = cx.typeck_results().expr_ty(other);
 588
 589     let without_deref = symmetric_partial_eq(cx, arg_ty, other_ty).unwrap_or_default();
 590     let with_deref = arg_ty
 591         .builtin_deref(true)
 592         .and_then(|tam| symmetric_partial_eq(cx, tam.ty, other_ty))
 593         .unwrap_or_default();
 594
 595     if !with_deref.is_implemented() && !without_deref.is_implemented() {
 596         return;
 597     }
 598
 599     let other_gets_derefed = matches!(other.kind, ExprKind::Unary(UnOp::Deref, _));
 600
 601     let lint_span = if other_gets_derefed {
 602         expr.span.to(other.span)
 603     } else {
 604         expr.span
 605     };
 606
 607     span_lint_and_then(
 608         cx,
 609         CMP_OWNED,
 610         lint_span,
 611         "this creates an owned instance just for comparison",
 612         |diag| {
 613             // This also catches `PartialEq` implementations that call `to_owned`.
 614             if other_gets_derefed {
 615                 diag.span_label(lint_span, "try implementing the comparison without allocating");
 616                 return;
 617             }
 618
 619             let expr_snip;
 620             let eq_impl;
 621             if with_deref.is_implemented() {
 622                 expr_snip = format!("*{}", snip);
 623                 eq_impl = with_deref;
 624             } else {
 625                 expr_snip = snip.to_string();
 626                 eq_impl = without_deref;
 627             };
 628
 629             let span;
 630             let hint;
 631             if (eq_impl.ty_eq_other && left) || (eq_impl.other_eq_ty && !left) {
 632                 span = expr.span;
 633                 hint = expr_snip;
 634             } else {
 635                 span = expr.span.to(other.span);
 636                 if eq_impl.ty_eq_other {
 637                     hint = format!("{} == {}", expr_snip, snippet(cx, other.span, ".."));
 638                 } else {
 639                     hint = format!("{} == {}", snippet(cx, other.span, ".."), expr_snip);
 640                 }
 641             }
 642
 643             diag.span_suggestion(
 644                 span,
 645                 "try",
 646                 hint,
 647                 Applicability::MachineApplicable, // snippet
 648             );
 649         },
 650     );
 651 }
 652
 653 /// Heuristic to see if an expression is used. Should be compatible with
 654 /// `unused_variables`'s idea
 655 /// of what it means for an expression to be "used".
 656 fn is_used(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 657     get_parent_expr(cx, expr).map_or(true, |parent| match parent.kind {
 658         ExprKind::Assign(_, rhs, _) | ExprKind::AssignOp(_, _, rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
 659         _ => is_used(cx, parent),
 660     })
 661 }
 662
 663 /// Tests whether an expression is in a macro expansion (e.g., something
 664 /// generated by `#[derive(...)]` or the like).
 665 fn in_attributes_expansion(expr: &Expr<'_>) -> bool {
 666     use rustc_span::hygiene::MacroKind;
 667     if expr.span.from_expansion() {
 668         let data = expr.span.ctxt().outer_expn_data();
 669         matches!(data.kind, ExpnKind::Macro(MacroKind::Attr, _))
 670     } else {
 671         false
 672     }
 673 }
 674
 675 /// Tests whether `res` is a variable defined outside a macro.
 676 fn non_macro_local(cx: &LateContext<'_>, res: def::Res) -> bool {
 677     if let def::Res::Local(id) = res {
 678         !cx.tcx.hir().span(id).from_expansion()
 679     } else {
 680         false
 681     }
 682 }
 683
 684 fn check_cast(cx: &LateContext<'_>, span: Span, e: &Expr<'_>, ty: &hir::Ty<'_>) {
 685     if_chain! {
 686         if let TyKind::Ptr(ref mut_ty) = ty.kind;
 687         if let ExprKind::Lit(ref lit) = e.kind;
 688         if let LitKind::Int(0, _) = lit.node;
 689         if !in_constant(cx, e.hir_id);
 690         then {
 691             let (msg, sugg_fn) = match mut_ty.mutbl {
 692                 Mutability::Mut => ("`0 as *mut _` detected", "std::ptr::null_mut"),
 693                 Mutability::Not => ("`0 as *const _` detected", "std::ptr::null"),
 694             };
 695
 696             let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind {
 697                 (format!("{}()", sugg_fn), Applicability::MachineApplicable)
 698             } else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) {
 699                 (format!("{}::<{}>()", sugg_fn, mut_ty_snip), Applicability::MachineApplicable)
 700             } else {
 701                 // `MaybeIncorrect` as type inference may not work with the suggested code
 702                 (format!("{}()", sugg_fn), Applicability::MaybeIncorrect)
 703             };
 704             span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl);
 705         }
 706     }
 707 }
 708
 709 fn check_binary(
 710     cx: &LateContext<'a>,
 711     expr: &Expr<'_>,
 712     cmp: &rustc_span::source_map::Spanned<rustc_hir::BinOpKind>,
 713     left: &'a Expr<'_>,
 714     right: &'a Expr<'_>,
 715 ) {
 716     let op = cmp.node;
 717     if op.is_comparison() {
 718         check_nan(cx, left, expr);
 719         check_nan(cx, right, expr);
 720         check_to_owned(cx, left, right, true);
 721         check_to_owned(cx, right, left, false);
 722     }
 723     if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
 724         if is_allowed(cx, left) || is_allowed(cx, right) {
 725             return;
 726         }
 727
 728         // Allow comparing the results of signum()
 729         if is_signum(cx, left) && is_signum(cx, right) {
 730             return;
 731         }
 732
 733         if let Some(name) = get_item_name(cx, expr) {
 734             let name = name.as_str();
 735             if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") || name.ends_with("_eq") {
 736                 return;
 737             }
 738         }
 739         let is_comparing_arrays = is_array(cx, left) || is_array(cx, right);
 740         let (lint, msg) = get_lint_and_message(
 741             is_named_constant(cx, left) || is_named_constant(cx, right),
 742             is_comparing_arrays,
 743         );
 744         span_lint_and_then(cx, lint, expr.span, msg, |diag| {
 745             let lhs = Sugg::hir(cx, left, "..");
 746             let rhs = Sugg::hir(cx, right, "..");
 747
 748             if !is_comparing_arrays {
 749                 diag.span_suggestion(
 750                     expr.span,
 751                     "consider comparing them within some margin of error",
 752                     format!(
 753                         "({}).abs() {} error_margin",
 754                         lhs - rhs,
 755                         if op == BinOpKind::Eq { '<' } else { '>' }
 756                     ),
 757                     Applicability::HasPlaceholders, // snippet
 758                 );
 759             }
 760             diag.note("`f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`");
 761         });
 762     } else if op == BinOpKind::Rem {
 763         if is_integer_const(cx, right, 1) {
 764             span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
 765         }
 766
 767         if let ty::Int(ity) = cx.typeck_results().expr_ty(right).kind() {
 768             if is_integer_const(cx, right, unsext(cx.tcx, -1, *ity)) {
 769                 span_lint(
 770                     cx,
 771                     MODULO_ONE,
 772                     expr.span,
 773                     "any number modulo -1 will panic/overflow or result in 0",
 774                 );
 775             }
 776         };
 777     }
 778 }