1 use if_chain::if_chain;
3 use rustc::hir::intravisit::FnKind;
5 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
7 use rustc::{declare_lint_pass, declare_tool_lint};
8 use rustc_errors::Applicability;
9 use syntax::ast::LitKind;
10 use syntax::source_map::{ExpnKind, Span};
12 use crate::consts::{constant, Constant};
13 use crate::utils::sugg::Sugg;
15 get_item_name, get_parent_expr, implements_trait, in_constant, is_integer_literal, iter_input_pats,
16 last_path_segment, match_qpath, match_trait_method, paths, snippet, span_lint, span_lint_and_then,
17 span_lint_hir_and_then, walk_ptrs_ty, SpanlessEq,
20 declare_clippy_lint! {
21 /// **What it does:** Checks for function arguments and let bindings denoted as
24 /// **Why is this bad?** The `ref` declaration makes the function take an owned
25 /// value, but turns the argument into a reference (which means that the value
26 /// is destroyed when exiting the function). This adds not much value: either
27 /// take a reference type, or take an owned value and create references in the
30 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
31 /// type of `x` is more obvious with the former.
33 /// **Known problems:** If the argument is dereferenced within the function,
34 /// removing the `ref` will lead to errors. This can be fixed by removing the
35 /// dereferences, e.g., changing `*x` to `x` within the function.
39 /// fn foo(ref x: u8) -> bool {
45 "an entire binding declared as `ref`, in a function argument or a `let` statement"
48 declare_clippy_lint! {
49 /// **What it does:** Checks for comparisons to NaN.
51 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
52 /// even itself – so those comparisons are simply wrong.
54 /// **Known problems:** None.
58 /// # use core::f32::NAN;
65 "comparisons to NAN, which will always return false, probably not intended"
68 declare_clippy_lint! {
69 /// **What it does:** Checks for (in-)equality comparisons on floating-point
70 /// values (apart from zero), except in functions called `*eq*` (which probably
71 /// implement equality for a type involving floats).
73 /// **Why is this bad?** Floating point calculations are usually imprecise, so
74 /// asking if two values are *exactly* equal is asking for trouble. For a good
75 /// guide on what to do, see [the floating point
76 /// guide](http://www.floating-point-gui.de/errors/comparison).
78 /// **Known problems:** None.
82 /// let x = 1.2331f64;
83 /// let y = 1.2332f64;
84 /// if y == 1.23f64 { }
85 /// if y != x {} // where both are floats
89 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
92 declare_clippy_lint! {
93 /// **What it does:** Checks for conversions to owned values just for the sake
96 /// **Why is this bad?** The comparison can operate on a reference, so creating
97 /// an owned value effectively throws it away directly afterwards, which is
98 /// needlessly consuming code and heap space.
100 /// **Known problems:** None.
105 /// # let y = String::from("foo");
106 /// if x.to_owned() == y {}
108 /// Could be written as
111 /// # let y = String::from("foo");
116 "creating owned instances for comparing with others, e.g., `x == \"foo\".to_string()`"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for getting the remainder of a division by one.
122 /// **Why is this bad?** The result can only ever be zero. No one will write
123 /// such code deliberately, unless trying to win an Underhanded Rust
124 /// Contest. Even for that contest, it's probably a bad idea. Use something more
127 /// **Known problems:** None.
136 "taking a number modulo 1, which always returns 0"
139 declare_clippy_lint! {
140 /// **What it does:** Checks for patterns in the form `name @ _`.
142 /// **Why is this bad?** It's almost always more readable to just use direct
145 /// **Known problems:** None.
149 /// # let v = Some("abc");
153 /// y @ _ => (), // easier written as `y`,
156 pub REDUNDANT_PATTERN,
158 "using `name @ _` in a pattern"
161 declare_clippy_lint! {
162 /// **What it does:** Checks for the use of bindings with a single leading
165 /// **Why is this bad?** A single leading underscore is usually used to indicate
166 /// that a binding will not be used. Using such a binding breaks this
169 /// **Known problems:** The lint does not work properly with desugaring and
170 /// macro, it has been allowed in the mean time.
175 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
176 /// // underscore. We should rename `_x` to `x`
178 pub USED_UNDERSCORE_BINDING,
180 "using a binding which is prefixed with an underscore"
183 declare_clippy_lint! {
184 /// **What it does:** Checks for the use of short circuit boolean conditions as
188 /// **Why is this bad?** Using a short circuit boolean condition as a statement
189 /// may hide the fact that the second part is executed or not depending on the
190 /// outcome of the first part.
192 /// **Known problems:** None.
196 /// f() && g(); // We should write `if f() { g(); }`.
198 pub SHORT_CIRCUIT_STATEMENT,
200 "using a short circuit boolean condition as a statement"
203 declare_clippy_lint! {
204 /// **What it does:** Catch casts from `0` to some pointer type
206 /// **Why is this bad?** This generally means `null` and is better expressed as
207 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
209 /// **Known problems:** None.
214 /// let a = 0 as *const u32;
218 "using 0 as *{const, mut} T"
221 declare_clippy_lint! {
222 /// **What it does:** Checks for (in-)equality comparisons on floating-point
223 /// value and constant, except in functions called `*eq*` (which probably
224 /// implement equality for a type involving floats).
226 /// **Why is this bad?** Floating point calculations are usually imprecise, so
227 /// asking if two values are *exactly* equal is asking for trouble. For a good
228 /// guide on what to do, see [the floating point
229 /// guide](http://www.floating-point-gui.de/errors/comparison).
231 /// **Known problems:** None.
235 /// let x: f64 = 1.0;
236 /// const ONE: f64 = 1.00;
237 /// x == ONE; // where both are floats
241 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
244 declare_lint_pass!(MiscLints => [
251 USED_UNDERSCORE_BINDING,
252 SHORT_CIRCUIT_STATEMENT,
257 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MiscLints {
260 cx: &LateContext<'a, 'tcx>,
267 if let FnKind::Closure(_) = k {
268 // Does not apply to closures
271 for arg in iter_input_pats(decl, body) {
273 PatKind::Binding(BindingAnnotation::Ref, ..) | 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::Local(ref l) = s.node;
290 if let PatKind::Binding(an, .., i, None) = l.pat.node;
291 if let Some(ref init) = l.init;
293 if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
294 let sugg_init = Sugg::hir(cx, init, "..");
295 let (mutopt,initref) = if an == BindingAnnotation::RefMut {
296 ("mut ", sugg_init.mut_addr())
298 ("", sugg_init.addr())
300 let tyopt = if let Some(ref ty) = l.ty {
301 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
305 span_lint_hir_and_then(cx,
309 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
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 };
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) {
377 // Allow comparing the results of signum()
378 if is_signum(cx, left) && is_signum(cx, right) {
382 if let Some(name) = get_item_name(cx, expr) {
383 let name = name.as_str();
387 || name.starts_with("eq_")
388 || name.ends_with("_eq")
393 let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
394 (FLOAT_CMP_CONST, "strict comparison of f32 or f64 constant")
396 (FLOAT_CMP, "strict comparison of f32 or f64")
398 span_lint_and_then(cx, lint, expr.span, msg, |db| {
399 let lhs = Sugg::hir(cx, left, "..");
400 let rhs = Sugg::hir(cx, right, "..");
404 "consider comparing them within some error",
406 "({}).abs() {} error",
408 if op == BinOpKind::Eq { '<' } else { '>' }
410 Applicability::HasPlaceholders, // snippet
412 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
414 } else if op == BinOpKind::Rem && is_integer_literal(right, 1) {
415 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
420 if in_attributes_expansion(expr) {
421 // Don't lint things expanded by #[derive(...)], etc
424 let binding = match expr.node {
425 ExprKind::Path(ref qpath) => {
426 let binding = last_path_segment(qpath).ident.as_str();
427 if binding.starts_with('_') &&
428 !binding.starts_with("__") &&
429 binding != "_result" && // FIXME: #944
431 // don't lint if the declaration is in a macro
432 non_macro_local(cx, cx.tables.qpath_res(qpath, expr.hir_id))
439 ExprKind::Field(_, ident) => {
440 let name = ident.as_str();
441 if name.starts_with('_') && !name.starts_with("__") {
449 if let Some(binding) = binding {
452 USED_UNDERSCORE_BINDING,
455 "used binding `{}` which is prefixed with an underscore. A leading \
456 underscore signals that a binding will not be used.",
463 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
464 if let PatKind::Binding(.., ident, Some(ref right)) = pat.node {
465 if let PatKind::Wild = right.node {
471 "the `{} @ _` pattern can be written as just `{}`",
472 ident.name, ident.name
480 fn check_nan(cx: &LateContext<'_, '_>, path: &Path, expr: &Expr) {
481 if !in_constant(cx, expr.hir_id) {
482 if let Some(seg) = path.segments.last() {
483 if seg.ident.name == sym!(NAN) {
488 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead",
495 fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
496 if let Some((_, res)) = constant(cx, cx.tables, expr) {
503 fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
504 match constant(cx, cx.tables, expr) {
505 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
506 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
511 // Return true if `expr` is the result of `signum()` invoked on a float value.
512 fn is_signum(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
513 // The negation of a signum is still a signum
514 if let ExprKind::Unary(UnNeg, ref child_expr) = expr.node {
515 return is_signum(cx, &child_expr);
519 if let ExprKind::MethodCall(ref method_name, _, ref expressions) = expr.node;
520 if sym!(signum) == method_name.ident.name;
521 // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
524 return is_float(cx, &expressions[0]);
530 fn is_float(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
531 matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::Float(_))
534 fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr, other: &Expr) {
535 let (arg_ty, snip) = match expr.node {
536 ExprKind::MethodCall(.., ref args) if args.len() == 1 => {
537 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
538 (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
543 ExprKind::Call(ref path, ref v) if v.len() == 1 => {
544 if let ExprKind::Path(ref path) = path.node {
545 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
546 (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
557 let other_ty = cx.tables.expr_ty_adjusted(other);
558 let partial_eq_trait_id = match cx.tcx.lang_items().eq_trait() {
563 let deref_arg_impl_partial_eq_other = arg_ty.builtin_deref(true).map_or(false, |tam| {
564 implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty.into()])
566 let arg_impl_partial_eq_deref_other = other_ty.builtin_deref(true).map_or(false, |tam| {
567 implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty.into()])
569 let arg_impl_partial_eq_other = implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty.into()]);
571 if !deref_arg_impl_partial_eq_other && !arg_impl_partial_eq_deref_other && !arg_impl_partial_eq_other {
575 let other_gets_derefed = match other.node {
576 ExprKind::Unary(UnDeref, _) => true,
580 let lint_span = if other_gets_derefed {
581 expr.span.to(other.span)
590 "this creates an owned instance just for comparison",
592 // This also catches `PartialEq` implementations that call `to_owned`.
593 if other_gets_derefed {
594 db.span_label(lint_span, "try implementing the comparison without allocating");
598 let try_hint = if deref_arg_impl_partial_eq_other {
599 // suggest deref on the left
602 // suggest dropping the to_owned on the left
610 Applicability::MachineApplicable, // snippet
616 /// Heuristic to see if an expression is used. Should be compatible with
617 /// `unused_variables`'s idea
618 /// of what it means for an expression to be "used".
619 fn is_used(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
620 if let Some(parent) = get_parent_expr(cx, expr) {
622 ExprKind::Assign(_, ref rhs) | ExprKind::AssignOp(_, _, ref rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
623 _ => is_used(cx, parent),
630 /// Tests whether an expression is in a macro expansion (e.g., something
631 /// generated by `#[derive(...)]` or the like).
632 fn in_attributes_expansion(expr: &Expr) -> bool {
633 use syntax::ext::hygiene::MacroKind;
634 if expr.span.from_expansion() {
635 let data = expr.span.ctxt().outer_expn_data();
637 if let ExpnKind::Macro(MacroKind::Attr, _) = data.kind {
647 /// Tests whether `res` is a variable defined outside a macro.
648 fn non_macro_local(cx: &LateContext<'_, '_>, res: def::Res) -> bool {
649 if let def::Res::Local(id) = res {
650 !cx.tcx.hir().span(id).from_expansion()
656 fn check_cast(cx: &LateContext<'_, '_>, span: Span, e: &Expr, ty: &Ty) {
658 if let TyKind::Ptr(MutTy { mutbl, .. }) = ty.node;
659 if let ExprKind::Lit(ref lit) = e.node;
660 if let LitKind::Int(value, ..) = lit.node;
662 if !in_constant(cx, e.hir_id);
664 let msg = match mutbl {
665 Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`",
666 Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`",
668 span_lint(cx, ZERO_PTR, span, msg);