1 use if_chain::if_chain;
4 use rustc_ast::ast::LitKind;
5 use rustc_errors::Applicability;
6 use rustc_hir::intravisit::FnKind;
8 def, BinOpKind, BindingAnnotation, Body, Expr, ExprKind, FnDecl, HirId, Mutability, PatKind, Stmt, StmtKind, Ty,
11 use rustc_lint::{LateContext, LateLintPass};
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
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, 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, walk_ptrs_ty, 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.
42 /// fn foo(ref x: u8) -> bool {
48 "an entire binding declared as `ref`, in a function argument or a `let` statement"
51 declare_clippy_lint! {
52 /// **What it does:** Checks for comparisons to NaN.
54 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
55 /// even itself – so those comparisons are simply wrong.
57 /// **Known problems:** None.
61 /// # use core::f32::NAN;
68 "comparisons to `NAN`, which will always return false, probably not intended"
71 declare_clippy_lint! {
72 /// **What it does:** Checks for (in-)equality comparisons on floating-point
73 /// values (apart from zero), except in functions called `*eq*` (which probably
74 /// implement equality for a type involving floats).
76 /// **Why is this bad?** Floating point calculations are usually imprecise, so
77 /// asking if two values are *exactly* equal is asking for trouble. For a good
78 /// guide on what to do, see [the floating point
79 /// guide](http://www.floating-point-gui.de/errors/comparison).
81 /// **Known problems:** None.
85 /// let x = 1.2331f64;
86 /// let y = 1.2332f64;
87 /// if y == 1.23f64 { }
88 /// if y != x {} // where both are floats
92 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
95 declare_clippy_lint! {
96 /// **What it does:** Checks for conversions to owned values just for the sake
99 /// **Why is this bad?** The comparison can operate on a reference, so creating
100 /// an owned value effectively throws it away directly afterwards, which is
101 /// needlessly consuming code and heap space.
103 /// **Known problems:** None.
108 /// # let y = String::from("foo");
109 /// if x.to_owned() == y {}
111 /// Could be written as
114 /// # let y = String::from("foo");
119 "creating owned instances for comparing with others, e.g., `x == \"foo\".to_string()`"
122 declare_clippy_lint! {
123 /// **What it does:** Checks for getting the remainder of a division by one.
125 /// **Why is this bad?** The result can only ever be zero. No one will write
126 /// such code deliberately, unless trying to win an Underhanded Rust
127 /// Contest. Even for that contest, it's probably a bad idea. Use something more
130 /// **Known problems:** None.
139 "taking a number modulo 1, which always returns 0"
142 declare_clippy_lint! {
143 /// **What it does:** Checks for the use of bindings with a single leading
146 /// **Why is this bad?** A single leading underscore is usually used to indicate
147 /// that a binding will not be used. Using such a binding breaks this
150 /// **Known problems:** The lint does not work properly with desugaring and
151 /// macro, it has been allowed in the mean time.
156 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
157 /// // underscore. We should rename `_x` to `x`
159 pub USED_UNDERSCORE_BINDING,
161 "using a binding which is prefixed with an underscore"
164 declare_clippy_lint! {
165 /// **What it does:** Checks for the use of short circuit boolean conditions as
169 /// **Why is this bad?** Using a short circuit boolean condition as a statement
170 /// may hide the fact that the second part is executed or not depending on the
171 /// outcome of the first part.
173 /// **Known problems:** None.
177 /// f() && g(); // We should write `if f() { g(); }`.
179 pub SHORT_CIRCUIT_STATEMENT,
181 "using a short circuit boolean condition as a statement"
184 declare_clippy_lint! {
185 /// **What it does:** Catch casts from `0` to some pointer type
187 /// **Why is this bad?** This generally means `null` and is better expressed as
188 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
190 /// **Known problems:** None.
195 /// let a = 0 as *const u32;
199 "using `0 as *{const, mut} T`"
202 declare_clippy_lint! {
203 /// **What it does:** Checks for (in-)equality comparisons on floating-point
204 /// value and constant, except in functions called `*eq*` (which probably
205 /// implement equality for a type involving floats).
207 /// **Why is this bad?** Floating point calculations are usually imprecise, so
208 /// asking if two values are *exactly* equal is asking for trouble. For a good
209 /// guide on what to do, see [the floating point
210 /// guide](http://www.floating-point-gui.de/errors/comparison).
212 /// **Known problems:** None.
216 /// let x: f64 = 1.0;
217 /// const ONE: f64 = 1.00;
218 /// x == ONE; // where both are floats
222 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
225 declare_lint_pass!(MiscLints => [
231 USED_UNDERSCORE_BINDING,
232 SHORT_CIRCUIT_STATEMENT,
237 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MiscLints {
240 cx: &LateContext<'a, 'tcx>,
242 decl: &'tcx FnDecl<'_>,
243 body: &'tcx Body<'_>,
247 if let FnKind::Closure(_) = k {
248 // Does not apply to closures
251 for arg in iter_input_pats(decl, body) {
253 PatKind::Binding(BindingAnnotation::Ref, ..) | PatKind::Binding(BindingAnnotation::RefMut, ..) => {
258 "`ref` directly on a function argument is ignored. Consider using a reference type \
267 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt<'_>) {
269 if let StmtKind::Local(ref local) = stmt.kind;
270 if let PatKind::Binding(an, .., name, None) = local.pat.kind;
271 if let Some(ref init) = local.init;
273 if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
274 let sugg_init = if init.span.from_expansion() {
275 Sugg::hir_with_macro_callsite(cx, init, "..")
277 Sugg::hir(cx, init, "..")
279 let (mutopt, initref) = if an == BindingAnnotation::RefMut {
280 ("mut ", sugg_init.mut_addr())
282 ("", sugg_init.addr())
284 let tyopt = if let Some(ref ty) = local.ty {
285 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
289 span_lint_hir_and_then(
294 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
300 "let {name}{tyopt} = {initref};",
301 name=snippet(cx, name.span, "_"),
305 Applicability::MachineApplicable,
313 if let StmtKind::Semi(ref expr) = stmt.kind;
314 if let ExprKind::Binary(ref binop, ref a, ref b) = expr.kind;
315 if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
316 if let Some(sugg) = Sugg::hir_opt(cx, a);
318 span_lint_and_then(cx,
319 SHORT_CIRCUIT_STATEMENT,
321 "boolean short circuit operator in statement may be clearer using an explicit test",
323 let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
330 &snippet(cx, b.span, ".."),
332 Applicability::MachineApplicable, // snippet
339 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
341 ExprKind::Cast(ref e, ref ty) => {
342 check_cast(cx, expr.span, e, ty);
345 ExprKind::Binary(ref cmp, ref left, ref right) => {
347 if op.is_comparison() {
348 check_nan(cx, left, expr);
349 check_nan(cx, right, expr);
350 check_to_owned(cx, left, right);
351 check_to_owned(cx, right, left);
353 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
354 if is_allowed(cx, left) || is_allowed(cx, right) {
358 // Allow comparing the results of signum()
359 if is_signum(cx, left) && is_signum(cx, right) {
363 if let Some(name) = get_item_name(cx, expr) {
364 let name = name.as_str();
368 || name.starts_with("eq_")
369 || name.ends_with("_eq")
374 let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
375 (FLOAT_CMP_CONST, "strict comparison of `f32` or `f64` constant")
377 (FLOAT_CMP, "strict comparison of `f32` or `f64`")
379 span_lint_and_then(cx, lint, expr.span, msg, |db| {
380 let lhs = Sugg::hir(cx, left, "..");
381 let rhs = Sugg::hir(cx, right, "..");
385 "consider comparing them within some error",
387 "({}).abs() {} error",
389 if op == BinOpKind::Eq { '<' } else { '>' }
391 Applicability::HasPlaceholders, // snippet
393 db.span_note(expr.span, "`std::f32::EPSILON` and `std::f64::EPSILON` are available.");
395 } else if op == BinOpKind::Rem && is_integer_const(cx, right, 1) {
396 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
401 if in_attributes_expansion(expr) {
402 // Don't lint things expanded by #[derive(...)], etc
405 let binding = match expr.kind {
406 ExprKind::Path(ref qpath) => {
407 let binding = last_path_segment(qpath).ident.as_str();
408 if binding.starts_with('_') &&
409 !binding.starts_with("__") &&
410 binding != "_result" && // FIXME: #944
412 // don't lint if the declaration is in a macro
413 non_macro_local(cx, cx.tables.qpath_res(qpath, expr.hir_id))
420 ExprKind::Field(_, ident) => {
421 let name = ident.as_str();
422 if name.starts_with('_') && !name.starts_with("__") {
430 if let Some(binding) = binding {
433 USED_UNDERSCORE_BINDING,
436 "used binding `{}` which is prefixed with an underscore. A leading \
437 underscore signals that a binding will not be used.",
445 fn check_nan(cx: &LateContext<'_, '_>, expr: &Expr<'_>, cmp_expr: &Expr<'_>) {
447 if !in_constant(cx, cmp_expr.hir_id);
448 if let Some((value, _)) = constant(cx, cx.tables, expr);
450 let needs_lint = match value {
451 Constant::F32(num) => num.is_nan(),
452 Constant::F64(num) => num.is_nan(),
461 "doomed comparison with `NAN`, use `std::{f32,f64}::is_nan()` instead",
468 fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) -> bool {
469 if let Some((_, res)) = constant(cx, cx.tables, expr) {
476 fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) -> bool {
477 match constant(cx, cx.tables, expr) {
478 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
479 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
484 // Return true if `expr` is the result of `signum()` invoked on a float value.
485 fn is_signum(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
486 // The negation of a signum is still a signum
487 if let ExprKind::Unary(UnOp::UnNeg, ref child_expr) = expr.kind {
488 return is_signum(cx, &child_expr);
492 if let ExprKind::MethodCall(ref method_name, _, ref expressions) = expr.kind;
493 if sym!(signum) == method_name.ident.name;
494 // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
497 return is_float(cx, &expressions[0]);
503 fn is_float(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
504 matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).kind, ty::Float(_))
507 fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr<'_>, other: &Expr<'_>) {
508 let (arg_ty, snip) = match expr.kind {
509 ExprKind::MethodCall(.., ref args) if args.len() == 1 => {
510 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
511 (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
516 ExprKind::Call(ref path, ref v) if v.len() == 1 => {
517 if let ExprKind::Path(ref path) = path.kind {
518 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
519 (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
530 let other_ty = cx.tables.expr_ty_adjusted(other);
531 let partial_eq_trait_id = match cx.tcx.lang_items().eq_trait() {
536 let deref_arg_impl_partial_eq_other = arg_ty.builtin_deref(true).map_or(false, |tam| {
537 implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty.into()])
539 let arg_impl_partial_eq_deref_other = other_ty.builtin_deref(true).map_or(false, |tam| {
540 implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty.into()])
542 let arg_impl_partial_eq_other = implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty.into()]);
544 if !deref_arg_impl_partial_eq_other && !arg_impl_partial_eq_deref_other && !arg_impl_partial_eq_other {
548 let other_gets_derefed = match other.kind {
549 ExprKind::Unary(UnOp::UnDeref, _) => true,
553 let lint_span = if other_gets_derefed {
554 expr.span.to(other.span)
563 "this creates an owned instance just for comparison",
565 // This also catches `PartialEq` implementations that call `to_owned`.
566 if other_gets_derefed {
567 db.span_label(lint_span, "try implementing the comparison without allocating");
571 let try_hint = if deref_arg_impl_partial_eq_other {
572 // suggest deref on the left
575 // suggest dropping the to_owned on the left
583 Applicability::MachineApplicable, // snippet
589 /// Heuristic to see if an expression is used. Should be compatible with
590 /// `unused_variables`'s idea
591 /// of what it means for an expression to be "used".
592 fn is_used(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
593 if let Some(parent) = get_parent_expr(cx, expr) {
595 ExprKind::Assign(_, ref rhs, _) | ExprKind::AssignOp(_, _, ref rhs) => {
596 SpanlessEq::new(cx).eq_expr(rhs, expr)
598 _ => is_used(cx, parent),
605 /// Tests whether an expression is in a macro expansion (e.g., something
606 /// generated by `#[derive(...)]` or the like).
607 fn in_attributes_expansion(expr: &Expr<'_>) -> bool {
608 use rustc_span::hygiene::MacroKind;
609 if expr.span.from_expansion() {
610 let data = expr.span.ctxt().outer_expn_data();
612 if let ExpnKind::Macro(MacroKind::Attr, _) = data.kind {
622 /// Tests whether `res` is a variable defined outside a macro.
623 fn non_macro_local(cx: &LateContext<'_, '_>, res: def::Res) -> bool {
624 if let def::Res::Local(id) = res {
625 !cx.tcx.hir().span(id).from_expansion()
631 fn check_cast(cx: &LateContext<'_, '_>, span: Span, e: &Expr<'_>, ty: &Ty<'_>) {
633 if let TyKind::Ptr(ref mut_ty) = ty.kind;
634 if let ExprKind::Lit(ref lit) = e.kind;
635 if let LitKind::Int(0, _) = lit.node;
636 if !in_constant(cx, e.hir_id);
638 let (msg, sugg_fn) = match mut_ty.mutbl {
639 Mutability::Mut => ("`0 as *mut _` detected", "std::ptr::null_mut"),
640 Mutability::Not => ("`0 as *const _` detected", "std::ptr::null"),
643 let (sugg, appl) = if let TyKind::Infer = mut_ty.ty.kind {
644 (format!("{}()", sugg_fn), Applicability::MachineApplicable)
645 } else if let Some(mut_ty_snip) = snippet_opt(cx, mut_ty.ty.span) {
646 (format!("{}::<{}>()", sugg_fn, mut_ty_snip), Applicability::MachineApplicable)
648 // `MaybeIncorrect` as type inference may not work with the suggested code
649 (format!("{}()", sugg_fn), Applicability::MaybeIncorrect)
651 span_lint_and_sugg(cx, ZERO_PTR, span, msg, "try", sugg, appl);