1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution.
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
10 use crate::consts::{constant, Constant};
11 use crate::reexport::*;
12 use crate::utils::sugg::Sugg;
14 get_item_name, get_parent_expr, implements_trait, in_constant, in_macro, is_integer_literal, iter_input_pats,
15 last_path_segment, match_qpath, match_trait_method, paths, snippet, span_lint, span_lint_and_then, walk_ptrs_ty,
18 use if_chain::if_chain;
20 use rustc::hir::intravisit::FnKind;
22 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
24 use rustc::{declare_tool_lint, lint_array};
25 use rustc_errors::Applicability;
26 use syntax::ast::LitKind;
27 use syntax::source_map::{ExpnFormat, Span};
29 /// **What it does:** Checks for function arguments and let bindings denoted as
32 /// **Why is this bad?** The `ref` declaration makes the function take an owned
33 /// value, but turns the argument into a reference (which means that the value
34 /// is destroyed when exiting the function). This adds not much value: either
35 /// take a reference type, or take an owned value and create references in the
38 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
39 /// type of `x` is more obvious with the former.
41 /// **Known problems:** If the argument is dereferenced within the function,
42 /// removing the `ref` will lead to errors. This can be fixed by removing the
43 /// dereferences, e.g. changing `*x` to `x` within the function.
47 /// fn foo(ref x: u8) -> bool {
51 declare_clippy_lint! {
54 "an entire binding declared as `ref`, in a function argument or a `let` statement"
57 /// **What it does:** Checks for comparisons to NaN.
59 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
60 /// even itself – so those comparisons are simply wrong.
62 /// **Known problems:** None.
68 declare_clippy_lint! {
71 "comparisons to NAN, which will always return false, probably not intended"
74 /// **What it does:** Checks for (in-)equality comparisons on floating-point
75 /// values (apart from zero), except in functions called `*eq*` (which probably
76 /// implement equality for a type involving floats).
78 /// **Why is this bad?** Floating point calculations are usually imprecise, so
79 /// asking if two values are *exactly* equal is asking for trouble. For a good
80 /// guide on what to do, see [the floating point
81 /// guide](http://www.floating-point-gui.de/errors/comparison).
83 /// **Known problems:** None.
88 /// y != x // where both are floats
90 declare_clippy_lint! {
93 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
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.
107 /// x.to_owned() == y
109 declare_clippy_lint! {
112 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
115 /// **What it does:** Checks for getting the remainder of a division by one.
117 /// **Why is this bad?** The result can only ever be zero. No one will write
118 /// such code deliberately, unless trying to win an Underhanded Rust
119 /// Contest. Even for that contest, it's probably a bad idea. Use something more
122 /// **Known problems:** None.
128 declare_clippy_lint! {
131 "taking a number modulo 1, which always returns 0"
134 /// **What it does:** Checks for patterns in the form `name @ _`.
136 /// **Why is this bad?** It's almost always more readable to just use direct
139 /// **Known problems:** None.
145 /// y @ _ => (), // easier written as `y`,
148 declare_clippy_lint! {
149 pub REDUNDANT_PATTERN,
151 "using `name @ _` in a pattern"
154 /// **What it does:** Checks for the use of bindings with a single leading
157 /// **Why is this bad?** A single leading underscore is usually used to indicate
158 /// that a binding will not be used. Using such a binding breaks this
161 /// **Known problems:** The lint does not work properly with desugaring and
162 /// macro, it has been allowed in the mean time.
167 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
168 /// // underscore. We should rename `_x` to `x`
170 declare_clippy_lint! {
171 pub USED_UNDERSCORE_BINDING,
173 "using a binding which is prefixed with an underscore"
176 /// **What it does:** Checks for the use of short circuit boolean conditions as
180 /// **Why is this bad?** Using a short circuit boolean condition as a statement
181 /// may hide the fact that the second part is executed or not depending on the
182 /// outcome of the first part.
184 /// **Known problems:** None.
188 /// f() && g(); // We should write `if f() { g(); }`.
190 declare_clippy_lint! {
191 pub SHORT_CIRCUIT_STATEMENT,
193 "using a short circuit boolean condition as a statement"
196 /// **What it does:** Catch casts from `0` to some pointer type
198 /// **Why is this bad?** This generally means `null` and is better expressed as
199 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
201 /// **Known problems:** None.
208 declare_clippy_lint! {
211 "using 0 as *{const, mut} T"
214 /// **What it does:** Checks for (in-)equality comparisons on floating-point
215 /// value and constant, except in functions called `*eq*` (which probably
216 /// implement equality for a type involving floats).
218 /// **Why is this bad?** Floating point calculations are usually imprecise, so
219 /// asking if two values are *exactly* equal is asking for trouble. For a good
220 /// guide on what to do, see [the floating point
221 /// guide](http://www.floating-point-gui.de/errors/comparison).
223 /// **Known problems:** None.
227 /// const ONE == 1.00f64
228 /// x == ONE // where both are floats
230 declare_clippy_lint! {
233 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
236 #[derive(Copy, Clone)]
239 impl LintPass for Pass {
240 fn get_lints(&self) -> LintArray {
248 USED_UNDERSCORE_BINDING,
249 SHORT_CIRCUIT_STATEMENT,
256 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
259 cx: &LateContext<'a, 'tcx>,
266 if let FnKind::Closure(_) = k {
267 // Does not apply to closures
270 for arg in iter_input_pats(decl, body) {
272 PatKind::Binding(BindingAnnotation::Ref, _, _, _)
273 | PatKind::Binding(BindingAnnotation::RefMut, _, _, _) => {
278 "`ref` directly on a function argument is ignored. Consider using a reference type \
287 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) {
289 if let StmtKind::Decl(ref d, _) = s.node;
290 if let DeclKind::Local(ref l) = d.node;
291 if let PatKind::Binding(an, _, i, None) = l.pat.node;
292 if let Some(ref init) = l.init;
294 if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
295 let init = Sugg::hir(cx, init, "..");
296 let (mutopt,initref) = if an == BindingAnnotation::RefMut {
297 ("mut ", init.mut_addr())
301 let tyopt = if let Some(ref ty) = l.ty {
302 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
306 span_lint_and_then(cx,
309 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
311 db.span_suggestion_with_applicability(
315 "let {name}{tyopt} = {initref};",
316 name=snippet(cx, i.span, "_"),
320 Applicability::MachineApplicable, // snippet
328 if let StmtKind::Semi(ref expr, _) = s.node;
329 if let ExprKind::Binary(ref binop, ref a, ref b) = expr.node;
330 if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
331 if let Some(sugg) = Sugg::hir_opt(cx, a);
333 span_lint_and_then(cx,
334 SHORT_CIRCUIT_STATEMENT,
336 "boolean short circuit operator in statement may be clearer using an explicit test",
338 let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
339 db.span_suggestion_with_applicability(
345 &snippet(cx, b.span, ".."),
347 Applicability::MachineApplicable, // snippet
354 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
356 ExprKind::Cast(ref e, ref ty) => {
357 check_cast(cx, expr.span, e, ty);
360 ExprKind::Binary(ref cmp, ref left, ref right) => {
362 if op.is_comparison() {
363 if let ExprKind::Path(QPath::Resolved(_, ref path)) = left.node {
364 check_nan(cx, path, expr);
366 if let ExprKind::Path(QPath::Resolved(_, ref path)) = right.node {
367 check_nan(cx, path, expr);
369 check_to_owned(cx, left, right);
370 check_to_owned(cx, right, left);
372 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
373 if is_allowed(cx, left) || is_allowed(cx, right) {
376 if let Some(name) = get_item_name(cx, expr) {
377 let name = name.as_str();
381 || name.starts_with("eq_")
382 || name.ends_with("_eq")
387 let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
388 (FLOAT_CMP_CONST, "strict comparison of f32 or f64 constant")
390 (FLOAT_CMP, "strict comparison of f32 or f64")
392 span_lint_and_then(cx, lint, expr.span, msg, |db| {
393 let lhs = Sugg::hir(cx, left, "..");
394 let rhs = Sugg::hir(cx, right, "..");
396 db.span_suggestion_with_applicability(
398 "consider comparing them within some error",
399 format!("({}).abs() < error", lhs - rhs),
400 Applicability::MachineApplicable, // snippet
402 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
404 } else if op == BinOpKind::Rem && is_integer_literal(right, 1) {
405 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
410 if in_attributes_expansion(expr) {
411 // Don't lint things expanded by #[derive(...)], etc
414 let binding = match expr.node {
415 ExprKind::Path(ref qpath) => {
416 let binding = last_path_segment(qpath).ident.as_str();
417 if binding.starts_with('_') &&
418 !binding.starts_with("__") &&
419 binding != "_result" && // FIXME: #944
421 // don't lint if the declaration is in a macro
422 non_macro_local(cx, &cx.tables.qpath_def(qpath, expr.hir_id))
429 ExprKind::Field(_, ident) => {
430 let name = ident.as_str();
431 if name.starts_with('_') && !name.starts_with("__") {
439 if let Some(binding) = binding {
442 USED_UNDERSCORE_BINDING,
445 "used binding `{}` which is prefixed with an underscore. A leading \
446 underscore signals that a binding will not be used.",
453 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
454 if let PatKind::Binding(_, _, ident, Some(ref right)) = pat.node {
455 if let PatKind::Wild = right.node {
461 "the `{} @ _` pattern can be written as just `{}`",
462 ident.name, ident.name
470 fn check_nan(cx: &LateContext<'_, '_>, path: &Path, expr: &Expr) {
471 if !in_constant(cx, expr.id) {
472 if let Some(seg) = path.segments.last() {
473 if seg.ident.name == "NAN" {
478 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead",
485 fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
486 if let Some((_, res)) = constant(cx, cx.tables, expr) {
493 fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
494 match constant(cx, cx.tables, expr) {
495 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
496 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
501 fn is_float(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
502 matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::Float(_))
505 fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr, other: &Expr) {
506 let (arg_ty, snip) = match expr.node {
507 ExprKind::MethodCall(.., ref args) if args.len() == 1 => {
508 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
509 (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
514 ExprKind::Call(ref path, ref v) if v.len() == 1 => {
515 if let ExprKind::Path(ref path) = path.node {
516 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
517 (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
528 let other_ty = cx.tables.expr_ty_adjusted(other);
529 let partial_eq_trait_id = match cx.tcx.lang_items().eq_trait() {
534 let deref_arg_impl_partial_eq_other = arg_ty.builtin_deref(true).map_or(false, |tam| {
535 implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty.into()])
537 let arg_impl_partial_eq_deref_other = other_ty.builtin_deref(true).map_or(false, |tam| {
538 implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty.into()])
540 let arg_impl_partial_eq_other = implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty.into()]);
542 if !deref_arg_impl_partial_eq_other && !arg_impl_partial_eq_deref_other && !arg_impl_partial_eq_other {
546 let other_gets_derefed = match other.node {
547 ExprKind::Unary(UnDeref, _) => true,
551 let lint_span = if other_gets_derefed {
552 expr.span.to(other.span)
561 "this creates an owned instance just for comparison",
563 // this also catches PartialEq implementations that call to_owned
564 if other_gets_derefed {
565 db.span_label(lint_span, "try implementing the comparison without allocating");
569 let try_hint = if deref_arg_impl_partial_eq_other {
570 // suggest deref on the left
573 // suggest dropping the to_owned on the left
577 db.span_suggestion_with_applicability(
581 Applicability::MachineApplicable, // snippet
587 /// Heuristic to see if an expression is used. Should be compatible with
588 /// `unused_variables`'s idea
589 /// of what it means for an expression to be "used".
590 fn is_used(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
591 if let Some(parent) = get_parent_expr(cx, expr) {
593 ExprKind::Assign(_, ref rhs) | ExprKind::AssignOp(_, _, ref rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
594 _ => is_used(cx, parent),
601 /// Test whether an expression is in a macro expansion (e.g. something
603 /// `#[derive(...)`] or the like).
604 fn in_attributes_expansion(expr: &Expr) -> bool {
609 .map_or(false, |info| matches!(info.format, ExpnFormat::MacroAttribute(_)))
612 /// Test whether `def` is a variable defined outside a macro.
613 fn non_macro_local(cx: &LateContext<'_, '_>, def: &def::Def) -> bool {
615 def::Def::Local(id) | def::Def::Upvar(id, _, _) => !in_macro(cx.tcx.hir().span(id)),
620 fn check_cast(cx: &LateContext<'_, '_>, span: Span, e: &Expr, ty: &Ty) {
622 if let TyKind::Ptr(MutTy { mutbl, .. }) = ty.node;
623 if let ExprKind::Lit(ref lit) = e.node;
624 if let LitKind::Int(value, ..) = lit.node;
626 if !in_constant(cx, e.id);
628 let msg = match mutbl {
629 Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`",
630 Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`",
632 span_lint(cx, ZERO_PTR, span, msg);