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
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) {
59 let StmtDecl(ref d, _) = s.node,
60 let DeclLocal(ref l) = d.node,
61 let PatKind::Binding(BindByRef(_), i, None) = l.pat.node,
62 let Some(ref init) = l.init
64 let tyopt = if let Some(ref ty) = l.ty {
65 format!(": {}", snippet(cx, ty.span, "_"))
69 span_lint_and_then(cx,
72 "`ref` on an entire `let` pattern is discouraged, take a reference with & instead",
74 db.span_suggestion(s.span,
76 format!("let {}{} = &{};",
77 snippet(cx, i.span, "_"),
79 snippet(cx, init.span, "_")));
86 /// **What it does:** This lint checks for comparisons to NAN.
88 /// **Why is this bad?** NAN does not compare meaningfully to anything – not even itself – so those comparisons are simply wrong.
90 /// **Known problems:** None
92 /// **Example:** `x == NAN`
93 declare_lint!(pub CMP_NAN, Deny,
94 "comparisons to NAN (which will always return false, which is probably not intended)");
99 impl LintPass for CmpNan {
100 fn get_lints(&self) -> LintArray {
105 impl LateLintPass for CmpNan {
106 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
107 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
108 if cmp.node.is_comparison() {
109 if let ExprPath(_, ref path) = left.node {
110 check_nan(cx, path, expr.span);
112 if let ExprPath(_, ref path) = right.node {
113 check_nan(cx, path, expr.span);
120 fn check_nan(cx: &LateContext, path: &Path, span: Span) {
121 path.segments.last().map(|seg| {
122 if seg.name.as_str() == "NAN" {
126 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
131 /// **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).
133 /// **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).
135 /// **Known problems:** None
137 /// **Example:** `y == 1.23f64`
138 declare_lint!(pub FLOAT_CMP, Warn,
139 "using `==` or `!=` on float values (as floating-point operations \
140 usually involve rounding errors, it is always better to check for approximate \
141 equality within small bounds)");
143 #[derive(Copy,Clone)]
146 impl LintPass for FloatCmp {
147 fn get_lints(&self) -> LintArray {
148 lint_array!(FLOAT_CMP)
152 impl LateLintPass for FloatCmp {
153 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
154 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
156 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
157 if is_allowed(cx, left) || is_allowed(cx, right) {
160 if let Some(name) = get_item_name(cx, expr) {
161 let name = name.as_str();
162 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
163 name.ends_with("_eq") {
170 &format!("{}-comparison of f32 or f64 detected. Consider changing this to `({} - {}).abs() < \
171 epsilon` for some suitable value of epsilon. \
172 std::f32::EPSILON and std::f64::EPSILON are available.",
174 snippet(cx, left.span, ".."),
175 snippet(cx, right.span, "..")));
181 fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
182 let res = eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None);
183 if let Ok(ConstVal::Float(val)) = res {
184 use std::cmp::Ordering;
186 let zero = ConstFloat::FInfer {
191 let infinity = ConstFloat::FInfer {
192 f32: ::std::f32::INFINITY,
193 f64: ::std::f64::INFINITY,
196 let neg_infinity = ConstFloat::FInfer {
197 f32: ::std::f32::NEG_INFINITY,
198 f64: ::std::f64::NEG_INFINITY,
201 val.try_cmp(zero) == Ok(Ordering::Equal)
202 || val.try_cmp(infinity) == Ok(Ordering::Equal)
203 || val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
209 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
210 matches!(walk_ptrs_ty(cx.tcx.expr_ty(expr)).sty, ty::TyFloat(_))
213 /// **What it does:** This lint checks for conversions to owned values just for the sake of a comparison.
215 /// **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.
217 /// **Known problems:** None
219 /// **Example:** `x.to_owned() == y`
220 declare_lint!(pub CMP_OWNED, Warn,
221 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`");
223 #[derive(Copy,Clone)]
226 impl LintPass for CmpOwned {
227 fn get_lints(&self) -> LintArray {
228 lint_array!(CMP_OWNED)
232 impl LateLintPass for CmpOwned {
233 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
234 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
235 if cmp.node.is_comparison() {
236 check_to_owned(cx, left, right, true, cmp.span);
237 check_to_owned(cx, right, left, false, cmp.span)
243 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr, left: bool, op: Span) {
244 let (arg_ty, snip) = match expr.node {
245 ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
246 if name.as_str() == "to_string" || name.as_str() == "to_owned" && is_str_arg(cx, args) {
247 (cx.tcx.expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
252 ExprCall(ref path, ref v) if v.len() == 1 => {
253 if let ExprPath(None, ref path) = path.node {
254 if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
255 (cx.tcx.expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
266 let other_ty = cx.tcx.expr_ty(other);
267 let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
272 if !implements_trait(cx, arg_ty, partial_eq_trait_id, vec![other_ty]) {
280 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
281 compare without allocation",
283 snippet(cx, op, "=="),
284 snippet(cx, other.span, "..")));
289 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
290 compare without allocation",
291 snippet(cx, other.span, ".."),
292 snippet(cx, op, "=="),
298 fn is_str_arg(cx: &LateContext, args: &[P<Expr>]) -> bool {
300 matches!(walk_ptrs_ty(cx.tcx.expr_ty(&args[0])).sty, ty::TyStr)
303 /// **What it does:** This lint checks for getting the remainder of a division by one.
305 /// **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.
307 /// **Known problems:** None
309 /// **Example:** `x % 1`
310 declare_lint!(pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0");
312 #[derive(Copy,Clone)]
313 pub struct ModuloOne;
315 impl LintPass for ModuloOne {
316 fn get_lints(&self) -> LintArray {
317 lint_array!(MODULO_ONE)
321 impl LateLintPass for ModuloOne {
322 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
323 if let ExprBinary(ref cmp, _, ref right) = expr.node {
324 if let Spanned { node: BinOp_::BiRem, .. } = *cmp {
325 if is_integer_literal(right, 1) {
326 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
333 /// **What it does:** This lint checks for patterns in the form `name @ _`.
335 /// **Why is this bad?** It's almost always more readable to just use direct bindings.
337 /// **Known problems:** None
343 /// y @ _ => (), // easier written as `y`,
346 declare_lint!(pub REDUNDANT_PATTERN, Warn, "using `name @ _` in a pattern");
348 #[derive(Copy,Clone)]
349 pub struct PatternPass;
351 impl LintPass for PatternPass {
352 fn get_lints(&self) -> LintArray {
353 lint_array!(REDUNDANT_PATTERN)
357 impl LateLintPass for PatternPass {
358 fn check_pat(&mut self, cx: &LateContext, pat: &Pat) {
359 if let PatKind::Binding(_, ref ident, Some(ref right)) = pat.node {
360 if right.node == PatKind::Wild {
364 &format!("the `{} @ _` pattern can be written as just `{}`",
373 /// **What it does:** This lint checks for the use of bindings with a single leading underscore
375 /// **Why is this bad?** A single leading underscore is usually used to indicate that a binding
376 /// will not be used. Using such a binding breaks this expectation.
378 /// **Known problems:** The lint does not work properly with desugaring and macro, it has been
379 /// allowed in the mean time.
384 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
385 /// // We should rename `_x` to `x`
387 declare_lint!(pub USED_UNDERSCORE_BINDING, Allow,
388 "using a binding which is prefixed with an underscore");
390 #[derive(Copy, Clone)]
391 pub struct UsedUnderscoreBinding;
393 impl LintPass for UsedUnderscoreBinding {
394 fn get_lints(&self) -> LintArray {
395 lint_array!(USED_UNDERSCORE_BINDING)
399 impl LateLintPass for UsedUnderscoreBinding {
400 #[cfg_attr(rustfmt, rustfmt_skip)]
401 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
402 if in_attributes_expansion(cx, expr) {
403 // Don't lint things expanded by #[derive(...)], etc
406 let binding = match expr.node {
407 ExprPath(_, ref path) => {
408 let binding = path.segments
410 .expect("path should always have at least one segment")
413 if binding.starts_with('_') &&
414 !binding.starts_with("__") &&
415 binding != "_result" && // FIXME: #944
417 // don't lint if the declaration is in a macro
418 non_macro_local(cx, &cx.tcx.expect_def(expr.id)) {
424 ExprField(_, spanned) => {
425 let name = spanned.node.as_str();
426 if name.starts_with('_') && !name.starts_with("__") {
434 if let Some(binding) = binding {
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));
444 /// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
445 /// of what it means for an expression to be "used".
446 fn is_used(cx: &LateContext, expr: &Expr) -> bool {
447 if let Some(ref parent) = get_parent_expr(cx, expr) {
449 ExprAssign(_, ref rhs) |
450 ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
451 _ => is_used(cx, parent),
458 /// Test whether an expression is in a macro expansion (e.g. something generated by
459 /// `#[derive(...)`] or the like).
460 fn in_attributes_expansion(cx: &LateContext, expr: &Expr) -> bool {
461 cx.sess().codemap().with_expn_info(expr.span.expn_id, |info_opt| {
462 info_opt.map_or(false, |info| {
463 matches!(info.callee.format, ExpnFormat::MacroAttribute(_))
468 /// Test whether `def` is a variable defined outside a macro.
469 fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
471 def::Def::Local(_, id) | def::Def::Upvar(_, id, _, _) => {
472 if let Some(span) = cx.tcx.map.opt_span(id) {