1 use if_chain::if_chain;
2 use rustc_ast::ast::LitKind;
3 use rustc_errors::Applicability;
4 use rustc_hir::intravisit::FnKind;
6 self as hir, def, BinOpKind, BindingAnnotation, Body, Expr, ExprKind, FnDecl, HirId, Mutability, PatKind, Stmt,
7 StmtKind, TyKind, UnOp,
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};
16 use crate::consts::{constant, Constant};
17 use crate::utils::sugg::Sugg;
19 get_item_name, get_parent_expr, higher, implements_trait, in_constant, is_integer_const, iter_input_pats,
20 last_path_segment, match_qpath, match_trait_method, paths, snippet, snippet_opt, span_lint, span_lint_and_sugg,
21 span_lint_and_then, span_lint_hir_and_then, unsext, SpanlessEq,
24 declare_clippy_lint! {
25 /// **What it does:** Checks for function arguments and let bindings denoted as
28 /// **Why is this bad?** The `ref` declaration makes the function take an owned
29 /// value, but turns the argument into a reference (which means that the value
30 /// is destroyed when exiting the function). This adds not much value: either
31 /// take a reference type, or take an owned value and create references in the
34 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
35 /// type of `x` is more obvious with the former.
37 /// **Known problems:** If the argument is dereferenced within the function,
38 /// removing the `ref` will lead to errors. This can be fixed by removing the
39 /// dereferences, e.g., changing `*x` to `x` within the function.
44 /// fn foo(ref x: u8) -> bool {
49 /// fn foo(x: &u8) -> bool {
55 "an entire binding declared as `ref`, in a function argument or a `let` statement"
58 declare_clippy_lint! {
59 /// **What it does:** Checks for comparisons to NaN.
61 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
62 /// even itself – so those comparisons are simply wrong.
64 /// **Known problems:** None.
71 /// if x == f32::NAN { }
78 "comparisons to `NAN`, which will always return false, probably not intended"
81 declare_clippy_lint! {
82 /// **What it does:** Checks for (in-)equality comparisons on floating-point
83 /// values (apart from zero), except in functions called `*eq*` (which probably
84 /// implement equality for a type involving floats).
86 /// **Why is this bad?** Floating point calculations are usually imprecise, so
87 /// asking if two values are *exactly* equal is asking for trouble. For a good
88 /// guide on what to do, see [the floating point
89 /// guide](http://www.floating-point-gui.de/errors/comparison).
91 /// **Known problems:** None.
95 /// let x = 1.2331f64;
96 /// let y = 1.2332f64;
99 /// if y == 1.23f64 { }
100 /// if y != x {} // where both are floats
103 /// let error_margin = f64::EPSILON; // Use an epsilon for comparison
104 /// // Or, if Rust <= 1.42, use `std::f64::EPSILON` constant instead.
105 /// // let error_margin = std::f64::EPSILON;
106 /// if (y - 1.23f64).abs() < error_margin { }
107 /// if (y - x).abs() > error_margin { }
111 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
114 declare_clippy_lint! {
115 /// **What it does:** Checks for conversions to owned values just for the sake
118 /// **Why is this bad?** The comparison can operate on a reference, so creating
119 /// an owned value effectively throws it away directly afterwards, which is
120 /// needlessly consuming code and heap space.
122 /// **Known problems:** None.
127 /// # let y = String::from("foo");
128 /// if x.to_owned() == y {}
130 /// Could be written as
133 /// # let y = String::from("foo");
138 "creating owned instances for comparing with others, e.g., `x == \"foo\".to_string()`"
141 declare_clippy_lint! {
142 /// **What it does:** Checks for getting the remainder of a division by one or minus
145 /// **Why is this bad?** The result for a divisor of one can only ever be zero; for
146 /// minus one it can cause panic/overflow (if the left operand is the minimal value of
147 /// the respective integer type) or results in zero. No one will write such code
148 /// deliberately, unless trying to win an Underhanded Rust Contest. Even for that
149 /// contest, it's probably a bad idea. Use something more underhanded.
151 /// **Known problems:** None.
161 "taking a number modulo +/-1, which can either panic/overflow or always returns 0"
164 declare_clippy_lint! {
165 /// **What it does:** Checks for the use of bindings with a single leading
168 /// **Why is this bad?** A single leading underscore is usually used to indicate
169 /// that a binding will not be used. Using such a binding breaks this
172 /// **Known problems:** The lint does not work properly with desugaring and
173 /// macro, it has been allowed in the mean time.
178 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
179 /// // underscore. We should rename `_x` to `x`
181 pub USED_UNDERSCORE_BINDING,
183 "using a binding which is prefixed with an underscore"
186 declare_clippy_lint! {
187 /// **What it does:** Checks for the use of short circuit boolean conditions as
191 /// **Why is this bad?** Using a short circuit boolean condition as a statement
192 /// may hide the fact that the second part is executed or not depending on the
193 /// outcome of the first part.
195 /// **Known problems:** None.
199 /// f() && g(); // We should write `if f() { g(); }`.
201 pub SHORT_CIRCUIT_STATEMENT,
203 "using a short circuit boolean condition as a statement"
206 declare_clippy_lint! {
207 /// **What it does:** Catch casts from `0` to some pointer type
209 /// **Why is this bad?** This generally means `null` and is better expressed as
210 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
212 /// **Known problems:** None.
218 /// let a = 0 as *const u32;
221 /// let a = std::ptr::null::<u32>();
225 "using `0 as *{const, mut} T`"
228 declare_clippy_lint! {
229 /// **What it does:** Checks for (in-)equality comparisons on floating-point
230 /// value and constant, except in functions called `*eq*` (which probably
231 /// implement equality for a type involving floats).
233 /// **Why is this bad?** Floating point calculations are usually imprecise, so
234 /// asking if two values are *exactly* equal is asking for trouble. For a good
235 /// guide on what to do, see [the floating point
236 /// guide](http://www.floating-point-gui.de/errors/comparison).
238 /// **Known problems:** None.
242 /// let x: f64 = 1.0;
243 /// const ONE: f64 = 1.00;
246 /// if x == ONE { } // where both are floats
249 /// let error_margin = f64::EPSILON; // Use an epsilon for comparison
250 /// // Or, if Rust <= 1.42, use `std::f64::EPSILON` constant instead.
251 /// // let error_margin = std::f64::EPSILON;
252 /// if (x - ONE).abs() < error_margin { }
256 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
259 declare_lint_pass!(MiscLints => [
265 USED_UNDERSCORE_BINDING,
266 SHORT_CIRCUIT_STATEMENT,
271 impl<'tcx> LateLintPass<'tcx> for MiscLints {
274 cx: &LateContext<'tcx>,
276 decl: &'tcx FnDecl<'_>,
277 body: &'tcx Body<'_>,
281 if let FnKind::Closure(_) = k {
282 // Does not apply to closures
285 if in_external_macro(cx.tcx.sess, span) {
288 for arg in iter_input_pats(decl, body) {
289 if let PatKind::Binding(BindingAnnotation::Ref | BindingAnnotation::RefMut, ..) = arg.pat.kind {
294 "`ref` directly on a function argument is ignored. \
295 Consider using a reference type instead.",
301 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
303 if !in_external_macro(cx.tcx.sess, stmt.span);
304 if let StmtKind::Local(ref local) = stmt.kind;
305 if let PatKind::Binding(an, .., name, None) = local.pat.kind;
306 if let Some(ref init) = local.init;
307 if !higher::is_from_for_desugar(local);
309 if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
310 // use the macro callsite when the init span (but not the whole local span)
311 // comes from an expansion like `vec![1, 2, 3]` in `let ref _ = vec![1, 2, 3];`
312 let sugg_init = if init.span.from_expansion() && !local.span.from_expansion() {
313 Sugg::hir_with_macro_callsite(cx, init, "..")
315 Sugg::hir(cx, init, "..")
317 let (mutopt, initref) = if an == BindingAnnotation::RefMut {
318 ("mut ", sugg_init.mut_addr())
320 ("", sugg_init.addr())
322 let tyopt = if let Some(ref ty) = local.ty {
323 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, ".."))
327 span_lint_hir_and_then(
332 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
334 diag.span_suggestion(
338 "let {name}{tyopt} = {initref};",
339 name=snippet(cx, name.span, ".."),
343 Applicability::MachineApplicable,
351 if let StmtKind::Semi(ref expr) = stmt.kind;
352 if let ExprKind::Binary(ref binop, ref a, ref b) = expr.kind;
353 if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
354 if let Some(sugg) = Sugg::hir_opt(cx, a);
356 span_lint_and_then(cx,
357 SHORT_CIRCUIT_STATEMENT,
359 "boolean short circuit operator in statement may be clearer using an explicit test",
361 let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
362 diag.span_suggestion(
368 &snippet(cx, b.span, ".."),
370 Applicability::MachineApplicable, // snippet
377 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
379 ExprKind::Cast(ref e, ref ty) => {
380 check_cast(cx, expr.span, e, ty);
383 ExprKind::Binary(ref cmp, ref left, ref right) => {
384 check_binary(cx, expr, cmp, left, right);
389 if in_attributes_expansion(expr) || expr.span.is_desugaring(DesugaringKind::Await) {
390 // Don't lint things expanded by #[derive(...)], etc or `await` desugaring
393 let binding = match expr.kind {
394 ExprKind::Path(ref qpath) if !matches!(qpath, hir::QPath::LangItem(..)) => {
395 let binding = last_path_segment(qpath).ident.as_str();
396 if binding.starts_with('_') &&
397 !binding.starts_with("__") &&
398 binding != "_result" && // FIXME: #944
400 // don't lint if the declaration is in a macro
401 non_macro_local(cx, cx.qpath_res(qpath, expr.hir_id))
408 ExprKind::Field(_, ident) => {
409 let name = ident.as_str();
410 if name.starts_with('_') && !name.starts_with("__") {
418 if let Some(binding) = binding {
421 USED_UNDERSCORE_BINDING,
424 "used binding `{}` which is prefixed with an underscore. A leading \
425 underscore signals that a binding will not be used.",
433 fn get_lint_and_message(
434 is_comparing_constants: bool,
435 is_comparing_arrays: bool,
436 ) -> (&'static rustc_lint::Lint, &'static str) {
437 if is_comparing_constants {
440 if is_comparing_arrays {
441 "strict comparison of `f32` or `f64` constant arrays"
443 "strict comparison of `f32` or `f64` constant"
449 if is_comparing_arrays {
450 "strict comparison of `f32` or `f64` arrays"
452 "strict comparison of `f32` or `f64`"
458 fn check_nan(cx: &LateContext<'_>, expr: &Expr<'_>, cmp_expr: &Expr<'_>) {
460 if !in_constant(cx, cmp_expr.hir_id);
461 if let Some((value, _)) = constant(cx, cx.typeck_results(), expr);
463 let needs_lint = match value {
464 Constant::F32(num) => num.is_nan(),
465 Constant::F64(num) => num.is_nan(),
474 "doomed comparison with `NAN`, use `{f32,f64}::is_nan()` instead",
481 fn is_named_constant<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
482 if let Some((_, res)) = constant(cx, cx.typeck_results(), expr) {
489 fn is_allowed<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
490 match constant(cx, cx.typeck_results(), expr) {
491 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
492 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
493 Some((Constant::Vec(vec), _)) => vec.iter().all(|f| match f {
494 Constant::F32(f) => *f == 0.0 || (*f).is_infinite(),
495 Constant::F64(f) => *f == 0.0 || (*f).is_infinite(),
502 // Return true if `expr` is the result of `signum()` invoked on a float value.
503 fn is_signum(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
504 // The negation of a signum is still a signum
505 if let ExprKind::Unary(UnOp::UnNeg, ref child_expr) = expr.kind {
506 return is_signum(cx, &child_expr);
510 if let ExprKind::MethodCall(ref method_name, _, ref expressions, _) = expr.kind;
511 if sym!(signum) == method_name.ident.name;
512 // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
515 return is_float(cx, &expressions[0]);
521 fn is_float(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
522 let value = &cx.typeck_results().expr_ty(expr).peel_refs().kind();
524 if let ty::Array(arr_ty, _) = value {
525 return matches!(arr_ty.kind(), ty::Float(_));
528 matches!(value, ty::Float(_))
531 fn is_array(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
532 matches!(&cx.typeck_results().expr_ty(expr).peel_refs().kind(), ty::Array(_, _))
535 fn check_to_owned(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left: bool) {
543 fn is_implemented(&self) -> bool {
544 self.ty_eq_other || self.other_eq_ty
548 fn symmetric_partial_eq<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> Option<EqImpl> {
549 cx.tcx.lang_items().eq_trait().map(|def_id| EqImpl {
550 ty_eq_other: implements_trait(cx, ty, def_id, &[other.into()]),
551 other_eq_ty: implements_trait(cx, other, def_id, &[ty.into()]),
555 let (arg_ty, snip) = match expr.kind {
556 ExprKind::MethodCall(.., ref args, _) if args.len() == 1 => {
557 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
558 (cx.typeck_results().expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
563 ExprKind::Call(ref path, ref v) if v.len() == 1 => {
564 if let ExprKind::Path(ref path) = path.kind {
565 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
566 (cx.typeck_results().expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
577 let other_ty = cx.typeck_results().expr_ty(other);
579 let without_deref = symmetric_partial_eq(cx, arg_ty, other_ty).unwrap_or_default();
580 let with_deref = arg_ty
582 .and_then(|tam| symmetric_partial_eq(cx, tam.ty, other_ty))
583 .unwrap_or_default();
585 if !with_deref.is_implemented() && !without_deref.is_implemented() {
589 let other_gets_derefed = matches!(other.kind, ExprKind::Unary(UnOp::UnDeref, _));
591 let lint_span = if other_gets_derefed {
592 expr.span.to(other.span)
601 "this creates an owned instance just for comparison",
603 // This also catches `PartialEq` implementations that call `to_owned`.
604 if other_gets_derefed {
605 diag.span_label(lint_span, "try implementing the comparison without allocating");
611 if with_deref.is_implemented() {
612 expr_snip = format!("*{}", snip);
613 eq_impl = with_deref;
615 expr_snip = snip.to_string();
616 eq_impl = without_deref;
621 if (eq_impl.ty_eq_other && left) || (eq_impl.other_eq_ty && !left) {
625 span = expr.span.to(other.span);
626 if eq_impl.ty_eq_other {
627 hint = format!("{} == {}", expr_snip, snippet(cx, other.span, ".."));
629 hint = format!("{} == {}", snippet(cx, other.span, ".."), expr_snip);
633 diag.span_suggestion(
637 Applicability::MachineApplicable, // snippet
643 /// Heuristic to see if an expression is used. Should be compatible with
644 /// `unused_variables`'s idea
645 /// of what it means for an expression to be "used".
646 fn is_used(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
647 get_parent_expr(cx, expr).map_or(true, |parent| match parent.kind {
648 ExprKind::Assign(_, ref rhs, _) | ExprKind::AssignOp(_, _, ref rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
649 _ => is_used(cx, parent),
653 /// Tests whether an expression is in a macro expansion (e.g., something
654 /// generated by `#[derive(...)]` or the like).
655 fn in_attributes_expansion(expr: &Expr<'_>) -> bool {
656 use rustc_span::hygiene::MacroKind;
657 if expr.span.from_expansion() {
658 let data = expr.span.ctxt().outer_expn_data();
659 matches!(data.kind, ExpnKind::Macro(MacroKind::Attr, _))
665 /// Tests whether `res` is a variable defined outside a macro.
666 fn non_macro_local(cx: &LateContext<'_>, res: def::Res) -> bool {
667 if let def::Res::Local(id) = res {
668 !cx.tcx.hir().span(id).from_expansion()
674 fn check_cast(cx: &LateContext<'_>, span: Span, e: &Expr<'_>, ty: &hir::Ty<'_>) {
676 if let TyKind::Ptr(ref mut_ty) = ty.kind;
677 if let ExprKind::Lit(ref lit) = e.kind;
678 if let LitKind::Int(0, _) = lit.node;
679 if !in_constant(cx, e.hir_id);
681 let (msg, sugg_fn) = match mut_ty.mutbl {
682 Mutability::Mut => ("`0 as *mut _` detected", "std::ptr::null_mut"),
683 Mutability::Not => ("`0 as *const _` detected", "std::ptr::null"),
686 let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind {
687 (format!("{}()", sugg_fn), Applicability::MachineApplicable)
688 } else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) {
689 (format!("{}::<{}>()", sugg_fn, mut_ty_snip), Applicability::MachineApplicable)
691 // `MaybeIncorrect` as type inference may not work with the suggested code
692 (format!("{}()", sugg_fn), Applicability::MaybeIncorrect)
694 span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl);
700 cx: &LateContext<'a>,
702 cmp: &rustc_span::source_map::Spanned<rustc_hir::BinOpKind>,
707 if op.is_comparison() {
708 check_nan(cx, left, expr);
709 check_nan(cx, right, expr);
710 check_to_owned(cx, left, right, true);
711 check_to_owned(cx, right, left, false);
713 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
714 if is_allowed(cx, left) || is_allowed(cx, right) {
718 // Allow comparing the results of signum()
719 if is_signum(cx, left) && is_signum(cx, right) {
723 if let Some(name) = get_item_name(cx, expr) {
724 let name = name.as_str();
725 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") || name.ends_with("_eq") {
729 let is_comparing_arrays = is_array(cx, left) || is_array(cx, right);
730 let (lint, msg) = get_lint_and_message(
731 is_named_constant(cx, left) || is_named_constant(cx, right),
734 span_lint_and_then(cx, lint, expr.span, msg, |diag| {
735 let lhs = Sugg::hir(cx, left, "..");
736 let rhs = Sugg::hir(cx, right, "..");
738 if !is_comparing_arrays {
739 diag.span_suggestion(
741 "consider comparing them within some margin of error",
743 "({}).abs() {} error_margin",
745 if op == BinOpKind::Eq { '<' } else { '>' }
747 Applicability::HasPlaceholders, // snippet
750 diag.note("`f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`");
752 } else if op == BinOpKind::Rem {
753 if is_integer_const(cx, right, 1) {
754 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
757 if let ty::Int(ity) = cx.typeck_results().expr_ty(right).kind() {
758 if is_integer_const(cx, right, unsext(cx.tcx, -1, *ity)) {
763 "any number modulo -1 will panic/overflow or result in 0",