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

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