1 use crate::consts::{constant, Constant};
2 use crate::utils::sugg::Sugg;
4 get_item_name, get_parent_expr, implements_trait, in_constant, in_macro, is_integer_literal, iter_input_pats,
5 last_path_segment, match_qpath, match_trait_method, paths, snippet, span_lint, span_lint_and_then, walk_ptrs_ty,
8 use if_chain::if_chain;
10 use rustc::hir::intravisit::FnKind;
12 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
14 use rustc::{declare_tool_lint, lint_array};
15 use rustc_errors::Applicability;
16 use syntax::ast::LitKind;
17 use syntax::source_map::{ExpnFormat, Span};
19 /// **What it does:** Checks for function arguments and let bindings denoted as
22 /// **Why is this bad?** The `ref` declaration makes the function take an owned
23 /// value, but turns the argument into a reference (which means that the value
24 /// is destroyed when exiting the function). This adds not much value: either
25 /// take a reference type, or take an owned value and create references in the
28 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
29 /// type of `x` is more obvious with the former.
31 /// **Known problems:** If the argument is dereferenced within the function,
32 /// removing the `ref` will lead to errors. This can be fixed by removing the
33 /// dereferences, e.g. changing `*x` to `x` within the function.
37 /// fn foo(ref x: u8) -> bool {
41 declare_clippy_lint! {
44 "an entire binding declared as `ref`, in a function argument or a `let` statement"
47 /// **What it does:** Checks for comparisons to NaN.
49 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
50 /// even itself – so those comparisons are simply wrong.
52 /// **Known problems:** None.
58 declare_clippy_lint! {
61 "comparisons to NAN, which will always return false, probably not intended"
64 /// **What it does:** Checks for (in-)equality comparisons on floating-point
65 /// values (apart from zero), except in functions called `*eq*` (which probably
66 /// implement equality for a type involving floats).
68 /// **Why is this bad?** Floating point calculations are usually imprecise, so
69 /// asking if two values are *exactly* equal is asking for trouble. For a good
70 /// guide on what to do, see [the floating point
71 /// guide](http://www.floating-point-gui.de/errors/comparison).
73 /// **Known problems:** None.
78 /// y != x // where both are floats
80 declare_clippy_lint! {
83 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
86 /// **What it does:** Checks for conversions to owned values just for the sake
89 /// **Why is this bad?** The comparison can operate on a reference, so creating
90 /// an owned value effectively throws it away directly afterwards, which is
91 /// needlessly consuming code and heap space.
93 /// **Known problems:** None.
99 declare_clippy_lint! {
102 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
105 /// **What it does:** Checks for getting the remainder of a division by one.
107 /// **Why is this bad?** The result can only ever be zero. No one will write
108 /// such code deliberately, unless trying to win an Underhanded Rust
109 /// Contest. Even for that contest, it's probably a bad idea. Use something more
112 /// **Known problems:** None.
118 declare_clippy_lint! {
121 "taking a number modulo 1, which always returns 0"
124 /// **What it does:** Checks for patterns in the form `name @ _`.
126 /// **Why is this bad?** It's almost always more readable to just use direct
129 /// **Known problems:** None.
135 /// y @ _ => (), // easier written as `y`,
138 declare_clippy_lint! {
139 pub REDUNDANT_PATTERN,
141 "using `name @ _` in a pattern"
144 /// **What it does:** Checks for the use of bindings with a single leading
147 /// **Why is this bad?** A single leading underscore is usually used to indicate
148 /// that a binding will not be used. Using such a binding breaks this
151 /// **Known problems:** The lint does not work properly with desugaring and
152 /// macro, it has been allowed in the mean time.
157 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading
158 /// // underscore. We should rename `_x` to `x`
160 declare_clippy_lint! {
161 pub USED_UNDERSCORE_BINDING,
163 "using a binding which is prefixed with an underscore"
166 /// **What it does:** Checks for the use of short circuit boolean conditions as
170 /// **Why is this bad?** Using a short circuit boolean condition as a statement
171 /// may hide the fact that the second part is executed or not depending on the
172 /// outcome of the first part.
174 /// **Known problems:** None.
178 /// f() && g(); // We should write `if f() { g(); }`.
180 declare_clippy_lint! {
181 pub SHORT_CIRCUIT_STATEMENT,
183 "using a short circuit boolean condition as a statement"
186 /// **What it does:** Catch casts from `0` to some pointer type
188 /// **Why is this bad?** This generally means `null` and is better expressed as
189 /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}.
191 /// **Known problems:** None.
198 declare_clippy_lint! {
201 "using 0 as *{const, mut} T"
204 /// **What it does:** Checks for (in-)equality comparisons on floating-point
205 /// value and constant, except in functions called `*eq*` (which probably
206 /// implement equality for a type involving floats).
208 /// **Why is this bad?** Floating point calculations are usually imprecise, so
209 /// asking if two values are *exactly* equal is asking for trouble. For a good
210 /// guide on what to do, see [the floating point
211 /// guide](http://www.floating-point-gui.de/errors/comparison).
213 /// **Known problems:** None.
217 /// const ONE = 1.00f64;
218 /// x == ONE // where both are floats
220 declare_clippy_lint! {
223 "using `==` or `!=` on float constants instead of comparing difference with an epsilon"
226 #[derive(Copy, Clone)]
229 impl LintPass for Pass {
230 fn get_lints(&self) -> LintArray {
238 USED_UNDERSCORE_BINDING,
239 SHORT_CIRCUIT_STATEMENT,
245 fn name(&self) -> &'static str {
250 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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 init = Sugg::hir(cx, init, "..");
288 let (mutopt,initref) = if an == BindingAnnotation::RefMut {
289 ("mut ", init.mut_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_and_then(cx,
301 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
307 "let {name}{tyopt} = {initref};",
308 name=snippet(cx, i.span, "_"),
312 Applicability::MachineApplicable, // snippet
320 if let StmtKind::Semi(ref expr) = s.node;
321 if let ExprKind::Binary(ref binop, ref a, ref b) = expr.node;
322 if binop.node == BinOpKind::And || binop.node == BinOpKind::Or;
323 if let Some(sugg) = Sugg::hir_opt(cx, a);
325 span_lint_and_then(cx,
326 SHORT_CIRCUIT_STATEMENT,
328 "boolean short circuit operator in statement may be clearer using an explicit test",
330 let sugg = if binop.node == BinOpKind::Or { !sugg } else { sugg };
337 &snippet(cx, b.span, ".."),
339 Applicability::MachineApplicable, // snippet
346 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
348 ExprKind::Cast(ref e, ref ty) => {
349 check_cast(cx, expr.span, e, ty);
352 ExprKind::Binary(ref cmp, ref left, ref right) => {
354 if op.is_comparison() {
355 if let ExprKind::Path(QPath::Resolved(_, ref path)) = left.node {
356 check_nan(cx, path, expr);
358 if let ExprKind::Path(QPath::Resolved(_, ref path)) = right.node {
359 check_nan(cx, path, expr);
361 check_to_owned(cx, left, right);
362 check_to_owned(cx, right, left);
364 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
365 if is_allowed(cx, left) || is_allowed(cx, right) {
368 if let Some(name) = get_item_name(cx, expr) {
369 let name = name.as_str();
373 || name.starts_with("eq_")
374 || name.ends_with("_eq")
379 let (lint, msg) = if is_named_constant(cx, left) || is_named_constant(cx, right) {
380 (FLOAT_CMP_CONST, "strict comparison of f32 or f64 constant")
382 (FLOAT_CMP, "strict comparison of f32 or f64")
384 span_lint_and_then(cx, lint, expr.span, msg, |db| {
385 let lhs = Sugg::hir(cx, left, "..");
386 let rhs = Sugg::hir(cx, right, "..");
390 "consider comparing them within some error",
391 format!("({}).abs() < error", lhs - rhs),
392 Applicability::MachineApplicable, // snippet
394 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
396 } else if op == BinOpKind::Rem && is_integer_literal(right, 1) {
397 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
402 if in_attributes_expansion(expr) {
403 // Don't lint things expanded by #[derive(...)], etc
406 let binding = match expr.node {
407 ExprKind::Path(ref qpath) => {
408 let binding = last_path_segment(qpath).ident.as_str();
409 if binding.starts_with('_') &&
410 !binding.starts_with("__") &&
411 binding != "_result" && // FIXME: #944
413 // don't lint if the declaration is in a macro
414 non_macro_local(cx, &cx.tables.qpath_def(qpath, expr.hir_id))
421 ExprKind::Field(_, ident) => {
422 let name = ident.as_str();
423 if name.starts_with('_') && !name.starts_with("__") {
431 if let Some(binding) = binding {
434 USED_UNDERSCORE_BINDING,
437 "used binding `{}` which is prefixed with an underscore. A leading \
438 underscore signals that a binding will not be used.",
445 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
446 if let PatKind::Binding(.., ident, Some(ref right)) = pat.node {
447 if let PatKind::Wild = right.node {
453 "the `{} @ _` pattern can be written as just `{}`",
454 ident.name, ident.name
462 fn check_nan(cx: &LateContext<'_, '_>, path: &Path, expr: &Expr) {
463 if !in_constant(cx, expr.id) {
464 if let Some(seg) = path.segments.last() {
465 if seg.ident.name == "NAN" {
470 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead",
477 fn is_named_constant<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
478 if let Some((_, res)) = constant(cx, cx.tables, expr) {
485 fn is_allowed<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
486 match constant(cx, cx.tables, expr) {
487 Some((Constant::F32(f), _)) => f == 0.0 || f.is_infinite(),
488 Some((Constant::F64(f), _)) => f == 0.0 || f.is_infinite(),
493 fn is_float(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
494 matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::Float(_))
497 fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr, other: &Expr) {
498 let (arg_ty, snip) = match expr.node {
499 ExprKind::MethodCall(.., ref args) if args.len() == 1 => {
500 if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
501 (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
506 ExprKind::Call(ref path, ref v) if v.len() == 1 => {
507 if let ExprKind::Path(ref path) = path.node {
508 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
509 (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
520 let other_ty = cx.tables.expr_ty_adjusted(other);
521 let partial_eq_trait_id = match cx.tcx.lang_items().eq_trait() {
526 let deref_arg_impl_partial_eq_other = arg_ty.builtin_deref(true).map_or(false, |tam| {
527 implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty.into()])
529 let arg_impl_partial_eq_deref_other = other_ty.builtin_deref(true).map_or(false, |tam| {
530 implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty.into()])
532 let arg_impl_partial_eq_other = implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty.into()]);
534 if !deref_arg_impl_partial_eq_other && !arg_impl_partial_eq_deref_other && !arg_impl_partial_eq_other {
538 let other_gets_derefed = match other.node {
539 ExprKind::Unary(UnDeref, _) => true,
543 let lint_span = if other_gets_derefed {
544 expr.span.to(other.span)
553 "this creates an owned instance just for comparison",
555 // this also catches PartialEq implementations that call to_owned
556 if other_gets_derefed {
557 db.span_label(lint_span, "try implementing the comparison without allocating");
561 let try_hint = if deref_arg_impl_partial_eq_other {
562 // suggest deref on the left
565 // suggest dropping the to_owned on the left
573 Applicability::MachineApplicable, // snippet
579 /// Heuristic to see if an expression is used. Should be compatible with
580 /// `unused_variables`'s idea
581 /// of what it means for an expression to be "used".
582 fn is_used(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
583 if let Some(parent) = get_parent_expr(cx, expr) {
585 ExprKind::Assign(_, ref rhs) | ExprKind::AssignOp(_, _, ref rhs) => SpanlessEq::new(cx).eq_expr(rhs, expr),
586 _ => is_used(cx, parent),
593 /// Test whether an expression is in a macro expansion (e.g. something
595 /// `#[derive(...)`] or the like).
596 fn in_attributes_expansion(expr: &Expr) -> bool {
601 .map_or(false, |info| matches!(info.format, ExpnFormat::MacroAttribute(_)))
604 /// Test whether `def` is a variable defined outside a macro.
605 fn non_macro_local(cx: &LateContext<'_, '_>, def: &def::Def) -> bool {
607 def::Def::Local(id) | def::Def::Upvar(id, _, _) => !in_macro(cx.tcx.hir().span(id)),
612 fn check_cast(cx: &LateContext<'_, '_>, span: Span, e: &Expr, ty: &Ty) {
614 if let TyKind::Ptr(MutTy { mutbl, .. }) = ty.node;
615 if let ExprKind::Lit(ref lit) = e.node;
616 if let LitKind::Int(value, ..) = lit.node;
618 if !in_constant(cx, e.id);
620 let msg = match mutbl {
621 Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`",
622 Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`",
624 span_lint(cx, ZERO_PTR, span, msg);