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, in_macro, is_integer_literal, match_path,
14 snippet, span_lint, span_lint_and_then, walk_ptrs_ty
16 use utils::sugg::Sugg;
18 /// **What it does:** This lint checks for function arguments and let bindings denoted as `ref`.
20 /// **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.
22 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The type of `x` is more obvious with the former.
24 /// **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.
26 /// **Example:** `fn foo(ref x: u8) -> bool { .. }`
28 pub TOPLEVEL_REF_ARG, Warn,
29 "An entire binding was declared as `ref`, in a function argument (`fn foo(ref x: Bar)`), \
30 or a `let` statement (`let ref x = foo()`). In such cases, it is preferred to take \
34 #[allow(missing_copy_implementations)]
35 pub struct TopLevelRefPass;
37 impl LintPass for TopLevelRefPass {
38 fn get_lints(&self) -> LintArray {
39 lint_array!(TOPLEVEL_REF_ARG)
43 impl LateLintPass for TopLevelRefPass {
44 fn check_fn(&mut self, cx: &LateContext, k: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
45 if let FnKind::Closure(_) = k {
46 // Does not apply to closures
49 for ref arg in &decl.inputs {
50 if let PatKind::Binding(BindByRef(_), _, _) = arg.pat.node {
54 "`ref` directly on a function argument is ignored. Consider using a reference type instead.");
58 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, "_")));
87 /// **What it does:** This lint checks for comparisons to NAN.
89 /// **Why is this bad?** NAN does not compare meaningfully to anything – not even itself – so those comparisons are simply wrong.
91 /// **Known problems:** None
93 /// **Example:** `x == NAN`
94 declare_lint!(pub CMP_NAN, Deny,
95 "comparisons to NAN (which will always return false, which is probably not intended)");
100 impl LintPass for CmpNan {
101 fn get_lints(&self) -> LintArray {
106 impl LateLintPass for CmpNan {
107 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
108 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
109 if cmp.node.is_comparison() {
110 if let ExprPath(_, ref path) = left.node {
111 check_nan(cx, path, expr.span);
113 if let ExprPath(_, ref path) = right.node {
114 check_nan(cx, path, expr.span);
121 fn check_nan(cx: &LateContext, path: &Path, span: Span) {
122 path.segments.last().map(|seg| {
123 if seg.name.as_str() == "NAN" {
127 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
132 /// **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).
134 /// **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).
136 /// **Known problems:** None
138 /// **Example:** `y == 1.23f64`
139 declare_lint!(pub FLOAT_CMP, Warn,
140 "using `==` or `!=` on float values (as floating-point operations \
141 usually involve rounding errors, it is always better to check for approximate \
142 equality within small bounds)");
144 #[derive(Copy,Clone)]
147 impl LintPass for FloatCmp {
148 fn get_lints(&self) -> LintArray {
149 lint_array!(FLOAT_CMP)
153 impl LateLintPass for FloatCmp {
154 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
155 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
157 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
158 if is_allowed(cx, left) || is_allowed(cx, right) {
161 if let Some(name) = get_item_name(cx, expr) {
162 let name = name.as_str();
163 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
164 name.ends_with("_eq") {
168 span_lint_and_then(cx,
171 "strict comparison of f32 or f64",
173 let lhs = &Sugg::hir(cx, left, "..");
174 let rhs = &Sugg::hir(cx, right, "..");
176 db.span_suggestion(expr.span,
177 "consider comparing them within some error",
178 format!("({}).abs() < error", lhs - rhs));
179 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
186 fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
187 let res = eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None);
188 if let Ok(ConstVal::Float(val)) = res {
189 use std::cmp::Ordering;
191 let zero = ConstFloat::FInfer {
196 let infinity = ConstFloat::FInfer {
197 f32: ::std::f32::INFINITY,
198 f64: ::std::f64::INFINITY,
201 let neg_infinity = ConstFloat::FInfer {
202 f32: ::std::f32::NEG_INFINITY,
203 f64: ::std::f64::NEG_INFINITY,
206 val.try_cmp(zero) == Ok(Ordering::Equal)
207 || val.try_cmp(infinity) == Ok(Ordering::Equal)
208 || val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
214 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
215 matches!(walk_ptrs_ty(cx.tcx.expr_ty(expr)).sty, ty::TyFloat(_))
218 /// **What it does:** This lint checks for conversions to owned values just for the sake of a comparison.
220 /// **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.
222 /// **Known problems:** None
224 /// **Example:** `x.to_owned() == y`
225 declare_lint!(pub CMP_OWNED, Warn,
226 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`");
228 #[derive(Copy,Clone)]
231 impl LintPass for CmpOwned {
232 fn get_lints(&self) -> LintArray {
233 lint_array!(CMP_OWNED)
237 impl LateLintPass for CmpOwned {
238 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
239 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
240 if cmp.node.is_comparison() {
241 check_to_owned(cx, left, right, true, cmp.span);
242 check_to_owned(cx, right, left, false, cmp.span)
248 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr, left: bool, op: Span) {
249 let (arg_ty, snip) = match expr.node {
250 ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
251 if name.as_str() == "to_string" || name.as_str() == "to_owned" && is_str_arg(cx, args) {
252 (cx.tcx.expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
257 ExprCall(ref path, ref v) if v.len() == 1 => {
258 if let ExprPath(None, ref path) = path.node {
259 if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
260 (cx.tcx.expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
271 let other_ty = cx.tcx.expr_ty(other);
272 let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
277 if !implements_trait(cx, arg_ty, partial_eq_trait_id, vec![other_ty]) {
285 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
286 compare without allocation",
288 snippet(cx, op, "=="),
289 snippet(cx, other.span, "..")));
294 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
295 compare without allocation",
296 snippet(cx, other.span, ".."),
297 snippet(cx, op, "=="),
303 fn is_str_arg(cx: &LateContext, args: &[P<Expr>]) -> bool {
305 matches!(walk_ptrs_ty(cx.tcx.expr_ty(&args[0])).sty, ty::TyStr)
308 /// **What it does:** This lint checks for getting the remainder of a division by one.
310 /// **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.
312 /// **Known problems:** None
314 /// **Example:** `x % 1`
315 declare_lint!(pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0");
317 #[derive(Copy,Clone)]
318 pub struct ModuloOne;
320 impl LintPass for ModuloOne {
321 fn get_lints(&self) -> LintArray {
322 lint_array!(MODULO_ONE)
326 impl LateLintPass for ModuloOne {
327 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
328 if let ExprBinary(ref cmp, _, ref right) = expr.node {
329 if let Spanned { node: BinOp_::BiRem, .. } = *cmp {
330 if is_integer_literal(right, 1) {
331 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
338 /// **What it does:** This lint checks for patterns in the form `name @ _`.
340 /// **Why is this bad?** It's almost always more readable to just use direct bindings.
342 /// **Known problems:** None
348 /// y @ _ => (), // easier written as `y`,
351 declare_lint!(pub REDUNDANT_PATTERN, Warn, "using `name @ _` in a pattern");
353 #[derive(Copy,Clone)]
354 pub struct PatternPass;
356 impl LintPass for PatternPass {
357 fn get_lints(&self) -> LintArray {
358 lint_array!(REDUNDANT_PATTERN)
362 impl LateLintPass for PatternPass {
363 fn check_pat(&mut self, cx: &LateContext, pat: &Pat) {
364 if let PatKind::Binding(_, ref ident, Some(ref right)) = pat.node {
365 if right.node == PatKind::Wild {
369 &format!("the `{} @ _` pattern can be written as just `{}`",
378 /// **What it does:** This lint checks for the use of bindings with a single leading underscore
380 /// **Why is this bad?** A single leading underscore is usually used to indicate that a binding
381 /// will not be used. Using such a binding breaks this expectation.
383 /// **Known problems:** The lint does not work properly with desugaring and macro, it has been
384 /// allowed in the mean time.
389 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
390 /// // We should rename `_x` to `x`
392 declare_lint!(pub USED_UNDERSCORE_BINDING, Allow,
393 "using a binding which is prefixed with an underscore");
395 #[derive(Copy, Clone)]
396 pub struct UsedUnderscoreBinding;
398 impl LintPass for UsedUnderscoreBinding {
399 fn get_lints(&self) -> LintArray {
400 lint_array!(USED_UNDERSCORE_BINDING)
404 impl LateLintPass for UsedUnderscoreBinding {
405 #[cfg_attr(rustfmt, rustfmt_skip)]
406 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
407 if in_attributes_expansion(cx, expr) {
408 // Don't lint things expanded by #[derive(...)], etc
411 let binding = match expr.node {
412 ExprPath(_, ref path) => {
413 let binding = path.segments
415 .expect("path should always have at least one segment")
418 if binding.starts_with('_') &&
419 !binding.starts_with("__") &&
420 binding != "_result" && // FIXME: #944
422 // don't lint if the declaration is in a macro
423 non_macro_local(cx, &cx.tcx.expect_def(expr.id)) {
429 ExprField(_, spanned) => {
430 let name = spanned.node.as_str();
431 if name.starts_with('_') && !name.starts_with("__") {
439 if let Some(binding) = binding {
441 USED_UNDERSCORE_BINDING,
443 &format!("used binding `{}` which is prefixed with an underscore. A leading \
444 underscore signals that a binding will not be used.", binding));
449 /// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
450 /// of what it means for an expression to be "used".
451 fn is_used(cx: &LateContext, expr: &Expr) -> bool {
452 if let Some(ref parent) = get_parent_expr(cx, expr) {
454 ExprAssign(_, ref rhs) |
455 ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
456 _ => is_used(cx, parent),
463 /// Test whether an expression is in a macro expansion (e.g. something generated by
464 /// `#[derive(...)`] or the like).
465 fn in_attributes_expansion(cx: &LateContext, expr: &Expr) -> bool {
466 cx.sess().codemap().with_expn_info(expr.span.expn_id, |info_opt| {
467 info_opt.map_or(false, |info| {
468 matches!(info.callee.format, ExpnFormat::MacroAttribute(_))
473 /// Test whether `def` is a variable defined outside a macro.
474 fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
476 def::Def::Local(_, id) | def::Def::Upvar(_, id, _, _) => {
477 if let Some(span) = cx.tcx.map.opt_span(id) {