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, in_macro_or_desugar, is_integer_literal,
16 iter_input_pats, 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 {}
110 "creating owned instances for comparing with others, e.g., `x == \"foo\".to_string()`"
113 declare_clippy_lint! {
114 /// **What it does:** Checks for getting the remainder of a division by one.
116 /// **Why is this bad?** The result can only ever be zero. No one will write
117 /// such code deliberately, unless trying to win an Underhanded Rust
118 /// Contest. Even for that contest, it's probably a bad idea. Use something more
121 /// **Known problems:** None.
130 "taking a number modulo 1, which always returns 0"
133 declare_clippy_lint! {
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.
143 /// # let v = Some("abc");
147 /// y @ _ => (), // easier written as `y`,
150 pub REDUNDANT_PATTERN,
152 "using `name @ _` in a pattern"
155 declare_clippy_lint! {
156 /// **What it does:** Checks for the use of bindings with a single leading
159 /// **Why is this bad?** A single leading underscore is usually used to indicate
160 /// that a binding will not be used. Using such a binding breaks this
163 /// **Known problems:** The lint does not work properly with desugaring and
164 /// macro, it has been allowed in the mean time.
169 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
170 /// // underscore. We should rename `_x` to `x`
172 pub USED_UNDERSCORE_BINDING,
174 "using a binding which is prefixed with an underscore"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for the use of short circuit boolean conditions as
182 /// **Why is this bad?** Using a short circuit boolean condition as a statement
183 /// may hide the fact that the second part is executed or not depending on the
184 /// outcome of the first part.
186 /// **Known problems:** None.
190 /// f() && g(); // We should write `if f() { g(); }`.
192 pub SHORT_CIRCUIT_STATEMENT,
194 "using a short circuit boolean condition as a statement"
197 declare_clippy_lint! {
198 /// **What it does:** Catch casts from `0` to some pointer type
200 /// **Why is this bad?** This generally means `null` and is better expressed as
201 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
203 /// **Known problems:** None.
208 /// let a = 0 as *const u32;
212 "using 0 as *{const, mut} T"
215 declare_clippy_lint! {
216 /// **What it does:** Checks for (in-)equality comparisons on floating-point
217 /// value and constant, except in functions called `*eq*` (which probably
218 /// implement equality for a type involving floats).
220 /// **Why is this bad?** Floating point calculations are usually imprecise, so
221 /// asking if two values are *exactly* equal is asking for trouble. For a good
222 /// guide on what to do, see [the floating point
223 /// guide](http://www.floating-point-gui.de/errors/comparison).
225 /// **Known problems:** None.
229 /// const ONE = 1.00f64;
230 /// x == ONE // where both are floats
234 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
237 declare_lint_pass!(MiscLints => [
244 USED_UNDERSCORE_BINDING,
245 SHORT_CIRCUIT_STATEMENT,
250 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MiscLints {
253 cx: &LateContext<'a, 'tcx>,
260 if let FnKind::Closure(_) = k {
261 // Does not apply to closures
264 for arg in iter_input_pats(decl, body) {
266 PatKind::Binding(BindingAnnotation::Ref, ..) | PatKind::Binding(BindingAnnotation::RefMut, ..) => {
271 "`ref` directly on a function argument is ignored. Consider using a reference type \
280 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) {
282 if let StmtKind::Local(ref l) = s.node;
283 if let PatKind::Binding(an, .., i, None) = l.pat.node;
284 if let Some(ref init) = l.init;
286 if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut {
287 let sugg_init = Sugg::hir(cx, init, "..");
288 let (mutopt,initref) = if an == BindingAnnotation::RefMut {
289 ("mut ", sugg_init.mut_addr())
291 ("", sugg_init.addr())
293 let tyopt = if let Some(ref ty) = l.ty {
294 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
298 span_lint_hir_and_then(cx,
302 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
308 "let {name}{tyopt} = {initref};",
309 name=snippet(cx, i.span, "_"),
313 Applicability::MachineApplicable, // snippet
321 if let StmtKind::Semi(ref expr) = s.node;
322 if let ExprKind::Binary(ref binop, ref a, ref b) = expr.node;
323 if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
324 if let Some(sugg) = Sugg::hir_opt(cx, a);
326 span_lint_and_then(cx,
327 SHORT_CIRCUIT_STATEMENT,
329 "boolean short circuit operator in statement may be clearer using an explicit test",
331 let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
338 &snippet(cx, b.span, ".."),
340 Applicability::MachineApplicable, // snippet
347 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
349 ExprKind::Cast(ref e, ref ty) => {
350 check_cast(cx, expr.span, e, ty);
353 ExprKind::Binary(ref cmp, ref left, ref right) => {
355 if op.is_comparison() {
356 if let ExprKind::Path(QPath::Resolved(_, ref path)) = left.node {
357 check_nan(cx, path, expr);
359 if let ExprKind::Path(QPath::Resolved(_, ref path)) = right.node {
360 check_nan(cx, path, expr);
362 check_to_owned(cx, left, right);
363 check_to_owned(cx, right, left);
365 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
366 if is_allowed(cx, left) || is_allowed(cx, right) {
370 // Allow comparing the results of signum()
371 if is_signum(cx, left) && is_signum(cx, right) {
375 if let Some(name) = get_item_name(cx, expr) {
376 let name = name.as_str();
380 || name.starts_with("eq_")
381 || name.ends_with("_eq")
386 let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
387 (FLOAT_CMP_CONST, "strict comparison of f32 or f64 constant")
389 (FLOAT_CMP, "strict comparison of f32 or f64")
391 span_lint_and_then(cx, lint, expr.span, msg, |db| {
392 let lhs = Sugg::hir(cx, left, "..");
393 let rhs = Sugg::hir(cx, right, "..");
397 "consider comparing them within some error",
399 "({}).abs() {} error",
401 if op == BinOpKind::Eq { '<' } else { '>' }
403 Applicability::MachineApplicable, // snippet
405 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
407 } else if op == BinOpKind::Rem && is_integer_literal(right, 1) {
408 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
413 if in_attributes_expansion(expr) {
414 // Don't lint things expanded by #[derive(...)], etc
417 let binding = match expr.node {
418 ExprKind::Path(ref qpath) => {
419 let binding = last_path_segment(qpath).ident.as_str();
420 if binding.starts_with('_') &&
421 !binding.starts_with("__") &&
422 binding != "_result" && // FIXME: #944
424 // don't lint if the declaration is in a macro
425 non_macro_local(cx, cx.tables.qpath_res(qpath, expr.hir_id))
432 ExprKind::Field(_, ident) => {
433 let name = ident.as_str();
434 if name.starts_with('_') && !name.starts_with("__") {
442 if let Some(binding) = binding {
445 USED_UNDERSCORE_BINDING,
448 "used binding `{}` which is prefixed with an underscore. A leading \
449 underscore signals that a binding will not be used.",
456 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
457 if let PatKind::Binding(.., ident, Some(ref right)) = pat.node {
458 if let PatKind::Wild = right.node {
464 "the `{} @ _` pattern can be written as just `{}`",
465 ident.name, ident.name
473 fn check_nan(cx: &LateContext<'_, '_>, path: &Path, expr: &Expr) {
474 if !in_constant(cx, expr.hir_id) {
475 if let Some(seg) = path.segments.last() {
476 if seg.ident.name == sym!(NAN) {
481 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead",
488 fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
489 if let Some((_, res)) = constant(cx, cx.tables, expr) {
496 fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
497 match constant(cx, cx.tables, expr) {
498 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
499 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
504 // Return true if `expr` is the result of `signum()` invoked on a float value.
505 fn is_signum(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
506 // The negation of a signum is still a signum
507 if let ExprKind::Unary(UnNeg, ref child_expr) = expr.node {
508 return is_signum(cx, &child_expr);
512 if let ExprKind::MethodCall(ref method_name, _, ref expressions) = expr.node;
513 if sym!(signum) == method_name.ident.name;
514 // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
517 return is_float(cx, &expressions[0]);
523 fn is_float(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
524 matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::Float(_))
527 fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr, other: &Expr) {
528 let (arg_ty, snip) = match expr.node {
529 ExprKind::MethodCall(.., ref args) if args.len() == 1 => {
530 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
531 (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
536 ExprKind::Call(ref path, ref v) if v.len() == 1 => {
537 if let ExprKind::Path(ref path) = path.node {
538 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
539 (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
550 let other_ty = cx.tables.expr_ty_adjusted(other);
551 let partial_eq_trait_id = match cx.tcx.lang_items().eq_trait() {
556 let deref_arg_impl_partial_eq_other = arg_ty.builtin_deref(true).map_or(false, |tam| {
557 implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty.into()])
559 let arg_impl_partial_eq_deref_other = other_ty.builtin_deref(true).map_or(false, |tam| {
560 implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty.into()])
562 let arg_impl_partial_eq_other = implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty.into()]);
564 if !deref_arg_impl_partial_eq_other && !arg_impl_partial_eq_deref_other && !arg_impl_partial_eq_other {
568 let other_gets_derefed = match other.node {
569 ExprKind::Unary(UnDeref, _) => true,
573 let lint_span = if other_gets_derefed {
574 expr.span.to(other.span)
583 "this creates an owned instance just for comparison",
585 // This also catches `PartialEq` implementations that call `to_owned`.
586 if other_gets_derefed {
587 db.span_label(lint_span, "try implementing the comparison without allocating");
591 let try_hint = if deref_arg_impl_partial_eq_other {
592 // suggest deref on the left
595 // suggest dropping the to_owned on the left
603 Applicability::MachineApplicable, // snippet
609 /// Heuristic to see if an expression is used. Should be compatible with
610 /// `unused_variables`'s idea
611 /// of what it means for an expression to be "used".
612 fn is_used(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
613 if let Some(parent) = get_parent_expr(cx, expr) {
615 ExprKind::Assign(_, ref rhs) | ExprKind::AssignOp(_, _, ref rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
616 _ => is_used(cx, parent),
623 /// Tests whether an expression is in a macro expansion (e.g., something
624 /// generated by `#[derive(...)]` or the like).
625 fn in_attributes_expansion(expr: &Expr) -> bool {
626 use syntax::ext::hygiene::MacroKind;
627 expr.span.ctxt().outer_expn_info().map_or(false, |info| {
628 if let ExpnKind::Macro(MacroKind::Attr, _) = info.kind {
636 /// Tests whether `res` is a variable defined outside a macro.
637 fn non_macro_local(cx: &LateContext<'_, '_>, res: def::Res) -> bool {
638 if let def::Res::Local(id) = res {
639 !in_macro_or_desugar(cx.tcx.hir().span(id))
645 fn check_cast(cx: &LateContext<'_, '_>, span: Span, e: &Expr, ty: &Ty) {
647 if let TyKind::Ptr(MutTy { mutbl, .. }) = ty.node;
648 if let ExprKind::Lit(ref lit) = e.node;
649 if let LitKind::Int(value, ..) = lit.node;
651 if !in_constant(cx, e.hir_id);
653 let msg = match mutbl {
654 Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`",
655 Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`",
657 span_lint(cx, ZERO_PTR, span, msg);