3 use rustc::hir::intravisit::FnKind;
5 use rustc::middle::const_val::ConstVal;
7 use rustc_const_eval::EvalHint::ExprTypeChecked;
8 use rustc_const_eval::eval_const_expr_partial;
9 use rustc_const_math::ConstFloat;
10 use syntax::codemap::{Span, Spanned, ExpnFormat};
13 get_item_name, get_parent_expr, implements_trait, is_integer_literal, match_path, snippet,
14 span_lint, span_lint_and_then, walk_ptrs_ty
17 /// **What it does:** This lint checks for function arguments and let bindings denoted as `ref`.
19 /// **Why is this bad?** The `ref` declaration makes the function take an owned value, but turns the argument into a reference (which means that the value is destroyed when exiting the function). This adds not much value: either take a reference type, or take an owned value and create references in the body.
21 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The type of `x` is more obvious with the former.
23 /// **Known problems:** If the argument is dereferenced within the function, removing the `ref` will lead to errors. This can be fixed by removing the dereferences, e.g. changing `*x` to `x` within the function.
25 /// **Example:** `fn foo(ref x: u8) -> bool { .. }`
27 pub TOPLEVEL_REF_ARG, Warn,
28 "An entire binding was declared as `ref`, in a function argument (`fn foo(ref x: Bar)`), \
29 or a `let` statement (`let ref x = foo()`). In such cases, it is preferred to take \
33 #[allow(missing_copy_implementations)]
34 pub struct TopLevelRefPass;
36 impl LintPass for TopLevelRefPass {
37 fn get_lints(&self) -> LintArray {
38 lint_array!(TOPLEVEL_REF_ARG)
42 impl LateLintPass for TopLevelRefPass {
43 fn check_fn(&mut self, cx: &LateContext, k: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
44 if let FnKind::Closure(_) = k {
45 // Does not apply to closures
48 for ref arg in &decl.inputs {
49 if let PatKind::Binding(BindByRef(_), _, _) = arg.pat.node {
53 "`ref` directly on a function argument is ignored. Consider using a reference type instead.");
57 fn check_stmt(&mut self, cx: &LateContext, s: &Stmt) {
60 let StmtDecl(ref d, _) = s.node,
61 let DeclLocal(ref l) = d.node,
62 let PatKind::Binding(BindByRef(_), i, None) = l.pat.node,
63 let Some(ref init) = l.init
65 let tyopt = if let Some(ref ty) = l.ty {
66 format!(": {}", snippet(cx, ty.span, "_"))
70 span_lint_and_then(cx,
73 "`ref` on an entire `let` pattern is discouraged, take a reference with & instead",
75 db.span_suggestion(s.span,
77 format!("let {}{} = &{};",
78 snippet(cx, i.span, "_"),
80 snippet(cx, init.span, "_")));
88 /// **What it does:** This lint checks for comparisons to NAN.
90 /// **Why is this bad?** NAN does not compare meaningfully to anything – not even itself – so those comparisons are simply wrong.
92 /// **Known problems:** None
94 /// **Example:** `x == NAN`
95 declare_lint!(pub CMP_NAN, Deny,
96 "comparisons to NAN (which will always return false, which is probably not intended)");
101 impl LintPass for CmpNan {
102 fn get_lints(&self) -> LintArray {
107 impl LateLintPass for CmpNan {
108 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
109 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
110 if cmp.node.is_comparison() {
111 if let ExprPath(_, ref path) = left.node {
112 check_nan(cx, path, expr.span);
114 if let ExprPath(_, ref path) = right.node {
115 check_nan(cx, path, expr.span);
122 fn check_nan(cx: &LateContext, path: &Path, span: Span) {
123 path.segments.last().map(|seg| {
124 if seg.name.as_str() == "NAN" {
128 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
133 /// **What it does:** This lint checks for (in-)equality comparisons on floating-point values (apart from zero), except in functions called `*eq*` (which probably implement equality for a type involving floats).
135 /// **Why is this bad?** Floating point calculations are usually imprecise, so asking if two values are *exactly* equal is asking for trouble. For a good guide on what to do, see [the floating point guide](http://www.floating-point-gui.de/errors/comparison).
137 /// **Known problems:** None
139 /// **Example:** `y == 1.23f64`
140 declare_lint!(pub FLOAT_CMP, Warn,
141 "using `==` or `!=` on float values (as floating-point operations \
142 usually involve rounding errors, it is always better to check for approximate \
143 equality within small bounds)");
145 #[derive(Copy,Clone)]
148 impl LintPass for FloatCmp {
149 fn get_lints(&self) -> LintArray {
150 lint_array!(FLOAT_CMP)
154 impl LateLintPass for FloatCmp {
155 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
156 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
158 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
159 if is_allowed(cx, left) || is_allowed(cx, right) {
162 if let Some(name) = get_item_name(cx, expr) {
163 let name = name.as_str();
164 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
165 name.ends_with("_eq") {
172 &format!("{}-comparison of f32 or f64 detected. Consider changing this to `({} - {}).abs() < \
173 epsilon` for some suitable value of epsilon. \
174 std::f32::EPSILON and std::f64::EPSILON are available.",
176 snippet(cx, left.span, ".."),
177 snippet(cx, right.span, "..")));
183 fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
184 let res = eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None);
185 if let Ok(ConstVal::Float(val)) = res {
186 use std::cmp::Ordering;
188 let zero = ConstFloat::FInfer {
193 let infinity = ConstFloat::FInfer {
194 f32: ::std::f32::INFINITY,
195 f64: ::std::f64::INFINITY,
198 let neg_infinity = ConstFloat::FInfer {
199 f32: ::std::f32::NEG_INFINITY,
200 f64: ::std::f64::NEG_INFINITY,
203 val.try_cmp(zero) == Ok(Ordering::Equal)
204 || val.try_cmp(infinity) == Ok(Ordering::Equal)
205 || val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
211 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
212 matches!(walk_ptrs_ty(cx.tcx.expr_ty(expr)).sty, ty::TyFloat(_))
215 /// **What it does:** This lint checks for conversions to owned values just for the sake of a comparison.
217 /// **Why is this bad?** The comparison can operate on a reference, so creating an owned value effectively throws it away directly afterwards, which is needlessly consuming code and heap space.
219 /// **Known problems:** None
221 /// **Example:** `x.to_owned() == y`
222 declare_lint!(pub CMP_OWNED, Warn,
223 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`");
225 #[derive(Copy,Clone)]
228 impl LintPass for CmpOwned {
229 fn get_lints(&self) -> LintArray {
230 lint_array!(CMP_OWNED)
234 impl LateLintPass for CmpOwned {
235 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
236 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
237 if cmp.node.is_comparison() {
238 check_to_owned(cx, left, right, true, cmp.span);
239 check_to_owned(cx, right, left, false, cmp.span)
245 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr, left: bool, op: Span) {
246 let (arg_ty, snip) = match expr.node {
247 ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
248 if name.as_str() == "to_string" || name.as_str() == "to_owned" && is_str_arg(cx, args) {
249 (cx.tcx.expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
254 ExprCall(ref path, ref v) if v.len() == 1 => {
255 if let ExprPath(None, ref path) = path.node {
256 if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
257 (cx.tcx.expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
268 let other_ty = cx.tcx.expr_ty(other);
269 let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
274 if !implements_trait(cx, arg_ty, partial_eq_trait_id, vec![other_ty]) {
282 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
283 compare without allocation",
285 snippet(cx, op, "=="),
286 snippet(cx, other.span, "..")));
291 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
292 compare without allocation",
293 snippet(cx, other.span, ".."),
294 snippet(cx, op, "=="),
300 fn is_str_arg(cx: &LateContext, args: &[P<Expr>]) -> bool {
302 matches!(walk_ptrs_ty(cx.tcx.expr_ty(&args[0])).sty, ty::TyStr)
305 /// **What it does:** This lint checks for getting the remainder of a division by one.
307 /// **Why is this bad?** The result can only ever be zero. No one will write such code deliberately, unless trying to win an Underhanded Rust Contest. Even for that contest, it's probably a bad idea. Use something more underhanded.
309 /// **Known problems:** None
311 /// **Example:** `x % 1`
312 declare_lint!(pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0");
314 #[derive(Copy,Clone)]
315 pub struct ModuloOne;
317 impl LintPass for ModuloOne {
318 fn get_lints(&self) -> LintArray {
319 lint_array!(MODULO_ONE)
323 impl LateLintPass for ModuloOne {
324 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
325 if let ExprBinary(ref cmp, _, ref right) = expr.node {
326 if let Spanned { node: BinOp_::BiRem, .. } = *cmp {
327 if is_integer_literal(right, 1) {
328 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
335 /// **What it does:** This lint checks for patterns in the form `name @ _`.
337 /// **Why is this bad?** It's almost always more readable to just use direct bindings.
339 /// **Known problems:** None
345 /// y @ _ => (), // easier written as `y`,
348 declare_lint!(pub REDUNDANT_PATTERN, Warn, "using `name @ _` in a pattern");
350 #[derive(Copy,Clone)]
351 pub struct PatternPass;
353 impl LintPass for PatternPass {
354 fn get_lints(&self) -> LintArray {
355 lint_array!(REDUNDANT_PATTERN)
359 impl LateLintPass for PatternPass {
360 fn check_pat(&mut self, cx: &LateContext, pat: &Pat) {
361 if let PatKind::Binding(_, ref ident, Some(ref right)) = pat.node {
362 if right.node == PatKind::Wild {
366 &format!("the `{} @ _` pattern can be written as just `{}`",
375 /// **What it does:** This lint checks for the use of bindings with a single leading underscore
377 /// **Why is this bad?** A single leading underscore is usually used to indicate that a binding
378 /// will not be used. Using such a binding breaks this expectation.
380 /// **Known problems:** The lint does not work properly with desugaring and macro, it has been
381 /// allowed in the mean time.
386 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
387 /// // We should rename `_x` to `x`
389 declare_lint!(pub USED_UNDERSCORE_BINDING, Allow,
390 "using a binding which is prefixed with an underscore");
392 #[derive(Copy, Clone)]
393 pub struct UsedUnderscoreBinding;
395 impl LintPass for UsedUnderscoreBinding {
396 fn get_lints(&self) -> LintArray {
397 lint_array!(USED_UNDERSCORE_BINDING)
401 impl LateLintPass for UsedUnderscoreBinding {
402 #[cfg_attr(rustfmt, rustfmt_skip)]
403 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
404 if in_attributes_expansion(cx, expr) {
405 // Don't lint things expanded by #[derive(...)], etc
408 let binding = match expr.node {
409 ExprPath(_, ref path) => {
410 let segment = path.segments
412 .expect("path should always have at least one segment")
414 if segment.as_str().starts_with('_') &&
415 !segment.as_str().starts_with("__") &&
416 segment != segment.unhygienize() && // not in bang macro
418 Some(segment.as_str())
423 ExprField(_, spanned) => {
424 let name = spanned.node.as_str();
425 if name.starts_with('_') && !name.starts_with("__") {
433 if let Some(binding) = binding {
434 if binding != "_result" { // FIXME: #944
436 USED_UNDERSCORE_BINDING,
438 &format!("used binding `{}` which is prefixed with an underscore. A leading \
439 underscore signals that a binding will not be used.", binding));
445 /// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
446 /// of what it means for an expression to be "used".
447 fn is_used(cx: &LateContext, expr: &Expr) -> bool {
448 if let Some(ref parent) = get_parent_expr(cx, expr) {
450 ExprAssign(_, ref rhs) |
451 ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
452 _ => is_used(cx, parent),
459 /// Test whether an expression is in a macro expansion (e.g. something generated by
460 /// `#[derive(...)`] or the like).
461 fn in_attributes_expansion(cx: &LateContext, expr: &Expr) -> bool {
462 cx.sess().codemap().with_expn_info(expr.span.expn_id, |info_opt| {
463 info_opt.map_or(false, |info| {
464 matches!(info.callee.format, ExpnFormat::MacroAttribute(_))