1 use crate::reexport::*;
4 use rustc::hir::intravisit::FnKind;
6 use rustc::{declare_lint, lint_array};
7 use if_chain::if_chain;
9 use syntax::codemap::{ExpnFormat, Span};
10 use crate::utils::{get_item_name, get_parent_expr, implements_trait, in_constant, in_macro, is_integer_literal,
11 iter_input_pats, last_path_segment, match_qpath, match_trait_method, paths, snippet, span_lint,
12 span_lint_and_then, walk_ptrs_ty, SpanlessEq};
13 use crate::utils::sugg::Sugg;
14 use syntax::ast::{LitKind, CRATE_NODE_ID};
15 use crate::consts::{constant, Constant};
17 /// **What it does:** Checks for function arguments and let bindings denoted as
20 /// **Why is this bad?** The `ref` declaration makes the function take an owned
21 /// value, but turns the argument into a reference (which means that the value
22 /// is destroyed when exiting the function). This adds not much value: either
23 /// take a reference type, or take an owned value and create references in the
26 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
27 /// type of `x` is more obvious with the former.
29 /// **Known problems:** If the argument is dereferenced within the function,
30 /// removing the `ref` will lead to errors. This can be fixed by removing the
31 /// dereferences, e.g. changing `*x` to `x` within the function.
35 /// fn foo(ref x: u8) -> bool { .. }
37 declare_clippy_lint! {
40 "an entire binding declared as `ref`, in a function argument or a `let` statement"
43 /// **What it does:** Checks for comparisons to NaN.
45 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
46 /// even itself – so those comparisons are simply wrong.
48 /// **Known problems:** None.
54 declare_clippy_lint! {
57 "comparisons to NAN, which will always return false, probably not intended"
60 /// **What it does:** Checks for (in-)equality comparisons on floating-point
61 /// values (apart from zero), except in functions called `*eq*` (which probably
62 /// implement equality for a type involving floats).
64 /// **Why is this bad?** Floating point calculations are usually imprecise, so
65 /// asking if two values are *exactly* equal is asking for trouble. For a good
66 /// guide on what to do, see [the floating point
67 /// guide](http://www.floating-point-gui.de/errors/comparison).
69 /// **Known problems:** None.
74 /// y != x // where both are floats
76 declare_clippy_lint! {
79 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
82 /// **What it does:** Checks for conversions to owned values just for the sake
85 /// **Why is this bad?** The comparison can operate on a reference, so creating
86 /// an owned value effectively throws it away directly afterwards, which is
87 /// needlessly consuming code and heap space.
89 /// **Known problems:** None.
95 declare_clippy_lint! {
98 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
101 /// **What it does:** Checks for getting the remainder of a division by one.
103 /// **Why is this bad?** The result can only ever be zero. No one will write
104 /// such code deliberately, unless trying to win an Underhanded Rust
105 /// Contest. Even for that contest, it's probably a bad idea. Use something more
108 /// **Known problems:** None.
114 declare_clippy_lint! {
117 "taking a number modulo 1, which always returns 0"
120 /// **What it does:** Checks for patterns in the form `name @ _`.
122 /// **Why is this bad?** It's almost always more readable to just use direct
125 /// **Known problems:** None.
131 /// y @ _ => (), // easier written as `y`,
134 declare_clippy_lint! {
135 pub REDUNDANT_PATTERN,
137 "using `name @ _` in a pattern"
140 /// **What it does:** Checks for the use of bindings with a single leading
143 /// **Why is this bad?** A single leading underscore is usually used to indicate
144 /// that a binding will not be used. Using such a binding breaks this
147 /// **Known problems:** The lint does not work properly with desugaring and
148 /// macro, it has been allowed in the mean time.
153 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
154 /// // underscore. We should rename `_x` to `x`
156 declare_clippy_lint! {
157 pub USED_UNDERSCORE_BINDING,
159 "using a binding which is prefixed with an underscore"
162 /// **What it does:** Checks for the use of short circuit boolean conditions as
166 /// **Why is this bad?** Using a short circuit boolean condition as a statement
167 /// may hide the fact that the second part is executed or not depending on the
168 /// outcome of the first part.
170 /// **Known problems:** None.
174 /// f() && g(); // We should write `if f() { g(); }`.
176 declare_clippy_lint! {
177 pub SHORT_CIRCUIT_STATEMENT,
179 "using a short circuit boolean condition as a statement"
182 /// **What it does:** Catch casts from `0` to some pointer type
184 /// **Why is this bad?** This generally means `null` and is better expressed as
185 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
187 /// **Known problems:** None.
194 declare_clippy_lint! {
197 "using 0 as *{const, mut} T"
200 /// **What it does:** Checks for (in-)equality comparisons on floating-point
201 /// value and constant, except in functions called `*eq*` (which probably
202 /// implement equality for a type involving floats).
204 /// **Why is this bad?** Floating point calculations are usually imprecise, so
205 /// asking if two values are *exactly* equal is asking for trouble. For a good
206 /// guide on what to do, see [the floating point
207 /// guide](http://www.floating-point-gui.de/errors/comparison).
209 /// **Known problems:** None.
213 /// const ONE == 1.00f64
214 /// x == ONE // where both are floats
216 declare_clippy_lint! {
219 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
222 #[derive(Copy, Clone)]
225 impl LintPass for Pass {
226 fn get_lints(&self) -> LintArray {
234 USED_UNDERSCORE_BINDING,
235 SHORT_CIRCUIT_STATEMENT,
242 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
245 cx: &LateContext<'a, 'tcx>,
252 if let FnKind::Closure(_) = k {
253 // Does not apply to closures
256 for arg in iter_input_pats(decl, body) {
258 PatKind::Binding(BindingAnnotation::Ref, _, _, _) |
259 PatKind::Binding(BindingAnnotation::RefMut, _, _, _) => {
264 "`ref` directly on a function argument is ignored. Consider using a reference type \
273 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) {
275 if let StmtKind::Decl(ref d, _) = s.node;
276 if let DeclKind::Local(ref l) = d.node;
277 if let PatKind::Binding(an, _, i, None) = l.pat.node;
278 if let Some(ref init) = l.init;
280 if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
281 let init = Sugg::hir(cx, init, "..");
282 let (mutopt,initref) = if an == BindingAnnotation::RefMut {
283 ("mut ", init.mut_addr())
287 let tyopt = if let Some(ref ty) = l.ty {
288 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
292 span_lint_and_then(cx,
295 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
297 db.span_suggestion(s.span,
299 format!("let {name}{tyopt} = {initref};",
300 name=snippet(cx, i.span, "_"),
309 if let StmtKind::Semi(ref expr, _) = s.node;
310 if let ExprKind::Binary(ref binop, ref a, ref b) = expr.node;
311 if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
312 if let Some(sugg) = Sugg::hir_opt(cx, a);
314 span_lint_and_then(cx,
315 SHORT_CIRCUIT_STATEMENT,
317 "boolean short circuit operator in statement may be clearer using an explicit test",
319 let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
320 db.span_suggestion(s.span, "replace it with",
321 format!("if {} {{ {}; }}", sugg, &snippet(cx, b.span, "..")));
327 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
329 ExprKind::Cast(ref e, ref ty) => {
330 check_cast(cx, expr.span, e, ty);
333 ExprKind::Binary(ref cmp, ref left, ref right) => {
335 if op.is_comparison() {
336 if let ExprKind::Path(QPath::Resolved(_, ref path)) = left.node {
337 check_nan(cx, path, expr);
339 if let ExprKind::Path(QPath::Resolved(_, ref path)) = right.node {
340 check_nan(cx, path, expr);
342 check_to_owned(cx, left, right);
343 check_to_owned(cx, right, left);
345 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
346 if is_allowed(cx, left) || is_allowed(cx, right) {
349 if let Some(name) = get_item_name(cx, expr) {
350 let name = name.as_str();
351 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_")
352 || name.ends_with("_eq")
357 let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
358 (FLOAT_CMP_CONST, "strict comparison of f32 or f64 constant")
360 (FLOAT_CMP, "strict comparison of f32 or f64")
362 span_lint_and_then(cx, lint, expr.span, msg, |db| {
363 let lhs = Sugg::hir(cx, left, "..");
364 let rhs = Sugg::hir(cx, right, "..");
368 "consider comparing them within some error",
369 format!("({}).abs() < error", lhs - rhs),
371 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
373 } else if op == BinOpKind::Rem && is_integer_literal(right, 1) {
374 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
379 if in_attributes_expansion(expr) {
380 // Don't lint things expanded by #[derive(...)], etc
383 let binding = match expr.node {
384 ExprKind::Path(ref qpath) => {
385 let binding = last_path_segment(qpath).ident.as_str();
386 if binding.starts_with('_') &&
387 !binding.starts_with("__") &&
388 binding != "_result" && // FIXME: #944
390 // don't lint if the declaration is in a macro
391 non_macro_local(cx, &cx.tables.qpath_def(qpath, expr.hir_id))
398 ExprKind::Field(_, ident) => {
399 let name = ident.as_str();
400 if name.starts_with('_') && !name.starts_with("__") {
408 if let Some(binding) = binding {
411 USED_UNDERSCORE_BINDING,
414 "used binding `{}` which is prefixed with an underscore. A leading \
415 underscore signals that a binding will not be used.",
422 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
423 if let PatKind::Binding(_, _, ident, Some(ref right)) = pat.node {
424 if let PatKind::Wild = right.node {
429 &format!("the `{} @ _` pattern can be written as just `{}`", ident.name, ident.name),
436 fn check_nan(cx: &LateContext, path: &Path, expr: &Expr) {
437 if !in_constant(cx, expr.id) {
438 if let Some(seg) = path.segments.last() {
439 if seg.ident.name == "NAN" {
444 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead",
451 fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
452 if let Some((_, res)) = constant(cx, cx.tables, expr) {
459 fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
460 match constant(cx, cx.tables, expr) {
461 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
462 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
467 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
468 matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::TyFloat(_))
471 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr) {
472 let (arg_ty, snip) = match expr.node {
473 ExprKind::MethodCall(.., ref args) if args.len() == 1 => {
474 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
475 (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
480 ExprKind::Call(ref path, ref v) if v.len() == 1 => if let ExprKind::Path(ref path) = path.node {
481 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
482 (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
492 let other_ty = cx.tables.expr_ty_adjusted(other);
493 let partial_eq_trait_id = match cx.tcx.lang_items().eq_trait() {
498 // *arg impls PartialEq<other>
501 .map_or(false, |tam| implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty.into()]))
502 // arg impls PartialEq<*other>
505 .map_or(false, |tam| implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty.into()]))
506 // arg impls PartialEq<other>
507 && !implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty.into()])
516 "this creates an owned instance just for comparison",
518 // this is as good as our recursion check can get, we can't prove that the
519 // current function is
521 // PartialEq::eq, but we can at least ensure that this code is not part of it
522 let parent_fn = cx.tcx.hir.get_parent(expr.id);
523 let parent_impl = cx.tcx.hir.get_parent(parent_fn);
524 if parent_impl != CRATE_NODE_ID {
525 if let map::NodeItem(item) = cx.tcx.hir.get(parent_impl) {
526 if let ItemKind::Impl(.., Some(ref trait_ref), _, _) = item.node {
527 if trait_ref.path.def.def_id() == partial_eq_trait_id {
528 // we are implementing PartialEq, don't suggest not doing `to_owned`, otherwise
531 db.span_label(expr.span, "try calling implementing the comparison without allocating");
537 db.span_suggestion(expr.span, "try", snip.to_string());
542 /// Heuristic to see if an expression is used. Should be compatible with
543 /// `unused_variables`'s idea
544 /// of what it means for an expression to be "used".
545 fn is_used(cx: &LateContext, expr: &Expr) -> bool {
546 if let Some(parent) = get_parent_expr(cx, expr) {
548 ExprKind::Assign(_, ref rhs) | ExprKind::AssignOp(_, _, ref rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
549 _ => is_used(cx, parent),
556 /// Test whether an expression is in a macro expansion (e.g. something
558 /// `#[derive(...)`] or the like).
559 fn in_attributes_expansion(expr: &Expr) -> bool {
564 .map_or(false, |info| matches!(info.format, ExpnFormat::MacroAttribute(_)))
567 /// Test whether `def` is a variable defined outside a macro.
568 fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
570 def::Def::Local(id) | def::Def::Upvar(id, _, _) => !in_macro(cx.tcx.hir.span(id)),
575 fn check_cast(cx: &LateContext, span: Span, e: &Expr, ty: &Ty) {
577 if let TyKind::Ptr(MutTy { mutbl, .. }) = ty.node;
578 if let ExprKind::Lit(ref lit) = e.node;
579 if let LitKind::Int(value, ..) = lit.node;
581 if !in_constant(cx, e.id);
583 let msg = match mutbl {
584 Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`",
585 Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`",
587 span_lint(cx, ZERO_PTR, span, msg);