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::ty::{self, Ty};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use rustc_span::hygiene::DesugaringKind;
13 use rustc_span::source_map::{ExpnKind, Span};
15 use crate::consts::{constant, Constant};
16 use crate::utils::sugg::Sugg;
18 get_item_name, get_parent_expr, higher, implements_trait, in_constant, is_integer_const, iter_input_pats,
19 last_path_segment, match_qpath, match_trait_method, paths, snippet, snippet_opt, span_lint, span_lint_and_sugg,
20 span_lint_and_then, span_lint_hir_and_then, SpanlessEq,
23 declare_clippy_lint! {
24 /// **What it does:** Checks for function arguments and let bindings denoted as
27 /// **Why is this bad?** The `ref` declaration makes the function take an owned
28 /// value, but turns the argument into a reference (which means that the value
29 /// is destroyed when exiting the function). This adds not much value: either
30 /// take a reference type, or take an owned value and create references in the
33 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
34 /// type of `x` is more obvious with the former.
36 /// **Known problems:** If the argument is dereferenced within the function,
37 /// removing the `ref` will lead to errors. This can be fixed by removing the
38 /// dereferences, e.g., changing `*x` to `x` within the function.
43 /// fn foo(ref x: u8) -> bool {
48 /// fn foo(x: &u8) -> bool {
54 "an entire binding declared as `ref`, in a function argument or a `let` statement"
57 declare_clippy_lint! {
58 /// **What it does:** Checks for comparisons to NaN.
60 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
61 /// even itself – so those comparisons are simply wrong.
63 /// **Known problems:** None.
70 /// if x == f32::NAN { }
77 "comparisons to `NAN`, which will always return false, probably not intended"
80 declare_clippy_lint! {
81 /// **What it does:** Checks for (in-)equality comparisons on floating-point
82 /// values (apart from zero), except in functions called `*eq*` (which probably
83 /// implement equality for a type involving floats).
85 /// **Why is this bad?** Floating point calculations are usually imprecise, so
86 /// asking if two values are *exactly* equal is asking for trouble. For a good
87 /// guide on what to do, see [the floating point
88 /// guide](http://www.floating-point-gui.de/errors/comparison).
90 /// **Known problems:** None.
94 /// let x = 1.2331f64;
95 /// let y = 1.2332f64;
98 /// if y == 1.23f64 { }
99 /// if y != x {} // where both are floats
102 /// let error_margin = f64::EPSILON; // Use an epsilon for comparison
103 /// // Or, if Rust <= 1.42, use `std::f64::EPSILON` constant instead.
104 /// // let error_margin = std::f64::EPSILON;
105 /// if (y - 1.23f64).abs() < error_margin { }
106 /// if (y - x).abs() > error_margin { }
110 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
113 declare_clippy_lint! {
114 /// **What it does:** Checks for conversions to owned values just for the sake
117 /// **Why is this bad?** The comparison can operate on a reference, so creating
118 /// an owned value effectively throws it away directly afterwards, which is
119 /// needlessly consuming code and heap space.
121 /// **Known problems:** None.
126 /// # let y = String::from("foo");
127 /// if x.to_owned() == y {}
129 /// Could be written as
132 /// # let y = String::from("foo");
137 "creating owned instances for comparing with others, e.g., `x == \"foo\".to_string()`"
140 declare_clippy_lint! {
141 /// **What it does:** Checks for getting the remainder of a division by one.
143 /// **Why is this bad?** The result can only ever be zero. No one will write
144 /// such code deliberately, unless trying to win an Underhanded Rust
145 /// Contest. Even for that contest, it's probably a bad idea. Use something more
148 /// **Known problems:** None.
157 "taking a number modulo 1, which always returns 0"
160 declare_clippy_lint! {
161 /// **What it does:** Checks for the use of bindings with a single leading
164 /// **Why is this bad?** A single leading underscore is usually used to indicate
165 /// that a binding will not be used. Using such a binding breaks this
168 /// **Known problems:** The lint does not work properly with desugaring and
169 /// macro, it has been allowed in the mean time.
174 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
175 /// // underscore. We should rename `_x` to `x`
177 pub USED_UNDERSCORE_BINDING,
179 "using a binding which is prefixed with an underscore"
182 declare_clippy_lint! {
183 /// **What it does:** Checks for the use of short circuit boolean conditions as
187 /// **Why is this bad?** Using a short circuit boolean condition as a statement
188 /// may hide the fact that the second part is executed or not depending on the
189 /// outcome of the first part.
191 /// **Known problems:** None.
195 /// f() && g(); // We should write `if f() { g(); }`.
197 pub SHORT_CIRCUIT_STATEMENT,
199 "using a short circuit boolean condition as a statement"
202 declare_clippy_lint! {
203 /// **What it does:** Catch casts from `0` to some pointer type
205 /// **Why is this bad?** This generally means `null` and is better expressed as
206 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
208 /// **Known problems:** None.
214 /// let a = 0 as *const u32;
217 /// let a = std::ptr::null::<u32>();
221 "using `0 as *{const, mut} T`"
224 declare_clippy_lint! {
225 /// **What it does:** Checks for (in-)equality comparisons on floating-point
226 /// value and constant, except in functions called `*eq*` (which probably
227 /// implement equality for a type involving floats).
229 /// **Why is this bad?** Floating point calculations are usually imprecise, so
230 /// asking if two values are *exactly* equal is asking for trouble. For a good
231 /// guide on what to do, see [the floating point
232 /// guide](http://www.floating-point-gui.de/errors/comparison).
234 /// **Known problems:** None.
238 /// let x: f64 = 1.0;
239 /// const ONE: f64 = 1.00;
242 /// if x == ONE { } // where both are floats
245 /// let error_margin = f64::EPSILON; // Use an epsilon for comparison
246 /// // Or, if Rust <= 1.42, use `std::f64::EPSILON` constant instead.
247 /// // let error_margin = std::f64::EPSILON;
248 /// if (x - ONE).abs() < error_margin { }
252 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
255 declare_lint_pass!(MiscLints => [
261 USED_UNDERSCORE_BINDING,
262 SHORT_CIRCUIT_STATEMENT,
267 impl<'tcx> LateLintPass<'tcx> for MiscLints {
270 cx: &LateContext<'tcx>,
272 decl: &'tcx FnDecl<'_>,
273 body: &'tcx Body<'_>,
277 if let FnKind::Closure(_) = k {
278 // Does not apply to closures
281 for arg in iter_input_pats(decl, body) {
282 if let PatKind::Binding(BindingAnnotation::Ref | BindingAnnotation::RefMut, ..) = arg.pat.kind {
287 "`ref` directly on a function argument is ignored. \
288 Consider using a reference type instead.",
294 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
296 if let StmtKind::Local(ref local) = stmt.kind;
297 if let PatKind::Binding(an, .., name, None) = local.pat.kind;
298 if let Some(ref init) = local.init;
299 if !higher::is_from_for_desugar(local);
301 if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
302 let sugg_init = if init.span.from_expansion() {
303 Sugg::hir_with_macro_callsite(cx, init, "..")
305 Sugg::hir(cx, init, "..")
307 let (mutopt, initref) = if an == BindingAnnotation::RefMut {
308 ("mut ", sugg_init.mut_addr())
310 ("", sugg_init.addr())
312 let tyopt = if let Some(ref ty) = local.ty {
313 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
317 span_lint_hir_and_then(
322 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
324 diag.span_suggestion(
328 "let {name}{tyopt} = {initref};",
329 name=snippet(cx, name.span, "_"),
333 Applicability::MachineApplicable,
341 if let StmtKind::Semi(ref expr) = stmt.kind;
342 if let ExprKind::Binary(ref binop, ref a, ref b) = expr.kind;
343 if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
344 if let Some(sugg) = Sugg::hir_opt(cx, a);
346 span_lint_and_then(cx,
347 SHORT_CIRCUIT_STATEMENT,
349 "boolean short circuit operator in statement may be clearer using an explicit test",
351 let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
352 diag.span_suggestion(
358 &snippet(cx, b.span, ".."),
360 Applicability::MachineApplicable, // snippet
367 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
369 ExprKind::Cast(ref e, ref ty) => {
370 check_cast(cx, expr.span, e, ty);
373 ExprKind::Binary(ref cmp, ref left, ref right) => {
375 if op.is_comparison() {
376 check_nan(cx, left, expr);
377 check_nan(cx, right, expr);
378 check_to_owned(cx, left, right, true);
379 check_to_owned(cx, right, left, false);
381 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
382 if is_allowed(cx, left) || is_allowed(cx, right) {
386 // Allow comparing the results of signum()
387 if is_signum(cx, left) && is_signum(cx, right) {
391 if let Some(name) = get_item_name(cx, expr) {
392 let name = name.as_str();
396 || name.starts_with("eq_")
397 || name.ends_with("_eq")
402 let is_comparing_arrays = is_array(cx, left) || is_array(cx, right);
403 let (lint, msg) = get_lint_and_message(
404 is_named_constant(cx, left) || is_named_constant(cx, right),
407 span_lint_and_then(cx, lint, expr.span, msg, |diag| {
408 let lhs = Sugg::hir(cx, left, "..");
409 let rhs = Sugg::hir(cx, right, "..");
411 if !is_comparing_arrays {
412 diag.span_suggestion(
414 "consider comparing them within some margin of error",
416 "({}).abs() {} error_margin",
418 if op == BinOpKind::Eq { '<' } else { '>' }
420 Applicability::HasPlaceholders, // snippet
423 diag.note("`f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`");
425 } else if op == BinOpKind::Rem && is_integer_const(cx, right, 1) {
426 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
431 if in_attributes_expansion(expr) || expr.span.is_desugaring(DesugaringKind::Await) {
432 // Don't lint things expanded by #[derive(...)], etc or `await` desugaring
435 let binding = match expr.kind {
436 ExprKind::Path(ref qpath) if !matches!(qpath, hir::QPath::LangItem(..)) => {
437 let binding = last_path_segment(qpath).ident.as_str();
438 if binding.starts_with('_') &&
439 !binding.starts_with("__") &&
440 binding != "_result" && // FIXME: #944
442 // don't lint if the declaration is in a macro
443 non_macro_local(cx, cx.qpath_res(qpath, expr.hir_id))
450 ExprKind::Field(_, ident) => {
451 let name = ident.as_str();
452 if name.starts_with('_') && !name.starts_with("__") {
460 if let Some(binding) = binding {
463 USED_UNDERSCORE_BINDING,
466 "used binding `{}` which is prefixed with an underscore. A leading \
467 underscore signals that a binding will not be used.",
475 fn get_lint_and_message(
476 is_comparing_constants: bool,
477 is_comparing_arrays: bool,
478 ) -> (&'static rustc_lint::Lint, &'static str) {
479 if is_comparing_constants {
482 if is_comparing_arrays {
483 "strict comparison of `f32` or `f64` constant arrays"
485 "strict comparison of `f32` or `f64` constant"
491 if is_comparing_arrays {
492 "strict comparison of `f32` or `f64` arrays"
494 "strict comparison of `f32` or `f64`"
500 fn check_nan(cx: &LateContext<'_>, expr: &Expr<'_>, cmp_expr: &Expr<'_>) {
502 if !in_constant(cx, cmp_expr.hir_id);
503 if let Some((value, _)) = constant(cx, cx.typeck_results(), expr);
505 let needs_lint = match value {
506 Constant::F32(num) => num.is_nan(),
507 Constant::F64(num) => num.is_nan(),
516 "doomed comparison with `NAN`, use `{f32,f64}::is_nan()` instead",
523 fn is_named_constant<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
524 if let Some((_, res)) = constant(cx, cx.typeck_results(), expr) {
531 fn is_allowed<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
532 match constant(cx, cx.typeck_results(), expr) {
533 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
534 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
535 Some((Constant::Vec(vec), _)) => vec.iter().all(|f| match f {
536 Constant::F32(f) => *f == 0.0 || (*f).is_infinite(),
537 Constant::F64(f) => *f == 0.0 || (*f).is_infinite(),
544 // Return true if `expr` is the result of `signum()` invoked on a float value.
545 fn is_signum(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
546 // The negation of a signum is still a signum
547 if let ExprKind::Unary(UnOp::UnNeg, ref child_expr) = expr.kind {
548 return is_signum(cx, &child_expr);
552 if let ExprKind::MethodCall(ref method_name, _, ref expressions, _) = expr.kind;
553 if sym!(signum) == method_name.ident.name;
554 // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
557 return is_float(cx, &expressions[0]);
563 fn is_float(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
564 let value = &cx.typeck_results().expr_ty(expr).peel_refs().kind();
566 if let ty::Array(arr_ty, _) = value {
567 return matches!(arr_ty.kind(), ty::Float(_));
570 matches!(value, ty::Float(_))
573 fn is_array(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
574 matches!(&cx.typeck_results().expr_ty(expr).peel_refs().kind(), ty::Array(_, _))
577 fn check_to_owned(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left: bool) {
585 fn is_implemented(&self) -> bool {
586 self.ty_eq_other || self.other_eq_ty
590 fn symmetric_partial_eq<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> Option<EqImpl> {
591 cx.tcx.lang_items().eq_trait().map(|def_id| EqImpl {
592 ty_eq_other: implements_trait(cx, ty, def_id, &[other.into()]),
593 other_eq_ty: implements_trait(cx, other, def_id, &[ty.into()]),
597 let (arg_ty, snip) = match expr.kind {
598 ExprKind::MethodCall(.., ref args, _) if args.len() == 1 => {
599 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
600 (cx.typeck_results().expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
605 ExprKind::Call(ref path, ref v) if v.len() == 1 => {
606 if let ExprKind::Path(ref path) = path.kind {
607 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
608 (cx.typeck_results().expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
619 let other_ty = cx.typeck_results().expr_ty(other);
621 let without_deref = symmetric_partial_eq(cx, arg_ty, other_ty).unwrap_or_default();
622 let with_deref = arg_ty
624 .and_then(|tam| symmetric_partial_eq(cx, tam.ty, other_ty))
625 .unwrap_or_default();
627 if !with_deref.is_implemented() && !without_deref.is_implemented() {
631 let other_gets_derefed = matches!(other.kind, ExprKind::Unary(UnOp::UnDeref, _));
633 let lint_span = if other_gets_derefed {
634 expr.span.to(other.span)
643 "this creates an owned instance just for comparison",
645 // This also catches `PartialEq` implementations that call `to_owned`.
646 if other_gets_derefed {
647 diag.span_label(lint_span, "try implementing the comparison without allocating");
653 if with_deref.is_implemented() {
654 expr_snip = format!("*{}", snip);
655 eq_impl = with_deref;
657 expr_snip = snip.to_string();
658 eq_impl = without_deref;
663 if (eq_impl.ty_eq_other && left) || (eq_impl.other_eq_ty && !left) {
667 span = expr.span.to(other.span);
668 if eq_impl.ty_eq_other {
669 hint = format!("{} == {}", expr_snip, snippet(cx, other.span, ".."));
671 hint = format!("{} == {}", snippet(cx, other.span, ".."), expr_snip);
675 diag.span_suggestion(
679 Applicability::MachineApplicable, // snippet
685 /// Heuristic to see if an expression is used. Should be compatible with
686 /// `unused_variables`'s idea
687 /// of what it means for an expression to be "used".
688 fn is_used(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
689 get_parent_expr(cx, expr).map_or(true, |parent| match parent.kind {
690 ExprKind::Assign(_, ref rhs, _) | ExprKind::AssignOp(_, _, ref rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
691 _ => is_used(cx, parent),
695 /// Tests whether an expression is in a macro expansion (e.g., something
696 /// generated by `#[derive(...)]` or the like).
697 fn in_attributes_expansion(expr: &Expr<'_>) -> bool {
698 use rustc_span::hygiene::MacroKind;
699 if expr.span.from_expansion() {
700 let data = expr.span.ctxt().outer_expn_data();
701 matches!(data.kind, ExpnKind::Macro(MacroKind::Attr, _))
707 /// Tests whether `res` is a variable defined outside a macro.
708 fn non_macro_local(cx: &LateContext<'_>, res: def::Res) -> bool {
709 if let def::Res::Local(id) = res {
710 !cx.tcx.hir().span(id).from_expansion()
716 fn check_cast(cx: &LateContext<'_>, span: Span, e: &Expr<'_>, ty: &hir::Ty<'_>) {
718 if let TyKind::Ptr(ref mut_ty) = ty.kind;
719 if let ExprKind::Lit(ref lit) = e.kind;
720 if let LitKind::Int(0, _) = lit.node;
721 if !in_constant(cx, e.hir_id);
723 let (msg, sugg_fn) = match mut_ty.mutbl {
724 Mutability::Mut => ("`0 as *mut _` detected", "std::ptr::null_mut"),
725 Mutability::Not => ("`0 as *const _` detected", "std::ptr::null"),
728 let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind {
729 (format!("{}()", sugg_fn), Applicability::MachineApplicable)
730 } else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) {
731 (format!("{}::<{}>()", sugg_fn, mut_ty_snip), Applicability::MachineApplicable)
733 // `MaybeIncorrect` as type inference may not work with the suggested code
734 (format!("{}()", sugg_fn), Applicability::MaybeIncorrect)
736 span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl);