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:** Checks for function arguments and let bindings denoted as `ref`.
20 /// **Why is this bad?** The `ref` declaration makes the function take an owned
21 /// value, but turns the argument into a reference (which means that the value
22 /// is destroyed when exiting the function). This adds not much value: either
23 /// take a reference type, or take an owned value and create references in the
26 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
27 /// type of `x` is more obvious with the former.
29 /// **Known problems:** If the argument is dereferenced within the function,
30 /// removing the `ref` will lead to errors. This can be fixed by removing the
31 /// dereferences, e.g. changing `*x` to `x` within the function.
35 /// fn foo(ref x: u8) -> bool { .. }
38 pub TOPLEVEL_REF_ARG, Warn,
39 "An entire binding was declared as `ref`, in a function argument (`fn foo(ref x: Bar)`), \
40 or a `let` statement (`let ref x = foo()`). In such cases, it is preferred to take \
44 #[allow(missing_copy_implementations)]
45 pub struct TopLevelRefPass;
47 impl LintPass for TopLevelRefPass {
48 fn get_lints(&self) -> LintArray {
49 lint_array!(TOPLEVEL_REF_ARG)
53 impl LateLintPass for TopLevelRefPass {
54 fn check_fn(&mut self, cx: &LateContext, k: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
55 if let FnKind::Closure(_) = k {
56 // Does not apply to closures
59 for arg in &decl.inputs {
60 if let PatKind::Binding(BindByRef(_), _, _) = arg.pat.node {
64 "`ref` directly on a function argument is ignored. Consider using a reference type instead.");
68 fn check_stmt(&mut self, cx: &LateContext, s: &Stmt) {
70 let StmtDecl(ref d, _) = s.node,
71 let DeclLocal(ref l) = d.node,
72 let PatKind::Binding(BindByRef(mt), i, None) = l.pat.node,
73 let Some(ref init) = l.init
75 let init = Sugg::hir(cx, init, "..");
76 let (mutopt,initref) = if mt == Mutability::MutMutable {
77 ("mut ", init.mut_addr())
81 let tyopt = if let Some(ref ty) = l.ty {
82 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
86 span_lint_and_then(cx,
89 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
91 db.span_suggestion(s.span,
93 format!("let {name}{tyopt} = {initref};",
94 name=snippet(cx, i.span, "_"),
103 /// **What it does:** Checks for comparisons to NaN.
105 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
106 /// even itself – so those comparisons are simply wrong.
108 /// **Known problems:** None.
114 declare_lint!(pub CMP_NAN, Deny,
115 "comparisons to NAN (which will always return false, which is probably not intended)");
117 #[derive(Copy,Clone)]
120 impl LintPass for CmpNan {
121 fn get_lints(&self) -> LintArray {
126 impl LateLintPass for CmpNan {
127 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
128 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
129 if cmp.node.is_comparison() {
130 if let ExprPath(_, ref path) = left.node {
131 check_nan(cx, path, expr.span);
133 if let ExprPath(_, ref path) = right.node {
134 check_nan(cx, path, expr.span);
141 fn check_nan(cx: &LateContext, path: &Path, span: Span) {
142 path.segments.last().map(|seg| {
143 if seg.name.as_str() == "NAN" {
147 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
152 /// **What it does:** Checks for (in-)equality comparisons on floating-point
153 /// values (apart from zero), except in functions called `*eq*` (which probably
154 /// implement equality for a type involving floats).
156 /// **Why is this bad?** Floating point calculations are usually imprecise, so
157 /// asking if two values are *exactly* equal is asking for trouble. For a good
158 /// guide on what to do, see [the floating point
159 /// guide](http://www.floating-point-gui.de/errors/comparison).
161 /// **Known problems:** None.
166 /// y != x // where both are floats
168 declare_lint!(pub FLOAT_CMP, Warn,
169 "using `==` or `!=` on float values (as floating-point operations \
170 usually involve rounding errors, it is always better to check for approximate \
171 equality within small bounds)");
173 #[derive(Copy,Clone)]
176 impl LintPass for FloatCmp {
177 fn get_lints(&self) -> LintArray {
178 lint_array!(FLOAT_CMP)
182 impl LateLintPass for FloatCmp {
183 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
184 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
186 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
187 if is_allowed(cx, left) || is_allowed(cx, right) {
190 if let Some(name) = get_item_name(cx, expr) {
191 let name = name.as_str();
192 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
193 name.ends_with("_eq") {
197 span_lint_and_then(cx,
200 "strict comparison of f32 or f64",
202 let lhs = Sugg::hir(cx, left, "..");
203 let rhs = Sugg::hir(cx, right, "..");
205 db.span_suggestion(expr.span,
206 "consider comparing them within some error",
207 format!("({}).abs() < error", lhs - rhs));
208 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
215 fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
216 let res = eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None);
217 if let Ok(ConstVal::Float(val)) = res {
218 use std::cmp::Ordering;
220 let zero = ConstFloat::FInfer {
225 let infinity = ConstFloat::FInfer {
226 f32: ::std::f32::INFINITY,
227 f64: ::std::f64::INFINITY,
230 let neg_infinity = ConstFloat::FInfer {
231 f32: ::std::f32::NEG_INFINITY,
232 f64: ::std::f64::NEG_INFINITY,
235 val.try_cmp(zero) == Ok(Ordering::Equal)
236 || val.try_cmp(infinity) == Ok(Ordering::Equal)
237 || val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
243 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
244 matches!(walk_ptrs_ty(cx.tcx.expr_ty(expr)).sty, ty::TyFloat(_))
247 /// **What it does:** Checks for conversions to owned values just for the sake
250 /// **Why is this bad?** The comparison can operate on a reference, so creating
251 /// an owned value effectively throws it away directly afterwards, which is
252 /// needlessly consuming code and heap space.
254 /// **Known problems:** None.
258 /// x.to_owned() == y
260 declare_lint!(pub CMP_OWNED, Warn,
261 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`");
263 #[derive(Copy,Clone)]
266 impl LintPass for CmpOwned {
267 fn get_lints(&self) -> LintArray {
268 lint_array!(CMP_OWNED)
272 impl LateLintPass for CmpOwned {
273 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
274 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
275 if cmp.node.is_comparison() {
276 check_to_owned(cx, left, right, true, cmp.span);
277 check_to_owned(cx, right, left, false, cmp.span)
283 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr, left: bool, op: Span) {
284 let (arg_ty, snip) = match expr.node {
285 ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
286 if name.as_str() == "to_string" || name.as_str() == "to_owned" && is_str_arg(cx, args) {
287 (cx.tcx.expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
292 ExprCall(ref path, ref v) if v.len() == 1 => {
293 if let ExprPath(None, ref path) = path.node {
294 if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
295 (cx.tcx.expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
306 let other_ty = cx.tcx.expr_ty(other);
307 let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
312 if !implements_trait(cx, arg_ty, partial_eq_trait_id, vec![other_ty]) {
320 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
321 compare without allocation",
323 snippet(cx, op, "=="),
324 snippet(cx, other.span, "..")));
329 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
330 compare without allocation",
331 snippet(cx, other.span, ".."),
332 snippet(cx, op, "=="),
338 fn is_str_arg(cx: &LateContext, args: &[P<Expr>]) -> bool {
340 matches!(walk_ptrs_ty(cx.tcx.expr_ty(&args[0])).sty, ty::TyStr)
343 /// **What it does:** Checks for getting the remainder of a division by one.
345 /// **Why is this bad?** The result can only ever be zero. No one will write
346 /// such code deliberately, unless trying to win an Underhanded Rust
347 /// Contest. Even for that contest, it's probably a bad idea. Use something more
350 /// **Known problems:** None.
356 declare_lint!(pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0");
358 #[derive(Copy,Clone)]
359 pub struct ModuloOne;
361 impl LintPass for ModuloOne {
362 fn get_lints(&self) -> LintArray {
363 lint_array!(MODULO_ONE)
367 impl LateLintPass for ModuloOne {
368 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
369 if let ExprBinary(ref cmp, _, ref right) = expr.node {
370 if let Spanned { node: BinOp_::BiRem, .. } = *cmp {
371 if is_integer_literal(right, 1) {
372 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
379 /// **What it does:** Checks for patterns in the form `name @ _`.
381 /// **Why is this bad?** It's almost always more readable to just use direct bindings.
383 /// **Known problems:** None.
389 /// y @ _ => (), // easier written as `y`,
392 declare_lint!(pub REDUNDANT_PATTERN, Warn, "using `name @ _` in a pattern");
394 #[derive(Copy,Clone)]
395 pub struct PatternPass;
397 impl LintPass for PatternPass {
398 fn get_lints(&self) -> LintArray {
399 lint_array!(REDUNDANT_PATTERN)
403 impl LateLintPass for PatternPass {
404 fn check_pat(&mut self, cx: &LateContext, pat: &Pat) {
405 if let PatKind::Binding(_, ref ident, Some(ref right)) = pat.node {
406 if right.node == PatKind::Wild {
410 &format!("the `{} @ _` pattern can be written as just `{}`",
419 /// **What it does:** Checks for the use of bindings with a single leading underscore.
421 /// **Why is this bad?** A single leading underscore is usually used to indicate
422 /// that a binding will not be used. Using such a binding breaks this
425 /// **Known problems:** The lint does not work properly with desugaring and
426 /// macro, it has been allowed in the mean time.
431 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
432 /// // We should rename `_x` to `x`
434 declare_lint!(pub USED_UNDERSCORE_BINDING, Allow,
435 "using a binding which is prefixed with an underscore");
437 #[derive(Copy, Clone)]
438 pub struct UsedUnderscoreBinding;
440 impl LintPass for UsedUnderscoreBinding {
441 fn get_lints(&self) -> LintArray {
442 lint_array!(USED_UNDERSCORE_BINDING)
446 impl LateLintPass for UsedUnderscoreBinding {
447 #[cfg_attr(rustfmt, rustfmt_skip)]
448 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
449 if in_attributes_expansion(cx, expr) {
450 // Don't lint things expanded by #[derive(...)], etc
453 let binding = match expr.node {
454 ExprPath(_, ref path) => {
455 let binding = path.segments
457 .expect("path should always have at least one segment")
460 if binding.starts_with('_') &&
461 !binding.starts_with("__") &&
462 binding != "_result" && // FIXME: #944
464 // don't lint if the declaration is in a macro
465 non_macro_local(cx, &cx.tcx.expect_def(expr.id)) {
471 ExprField(_, spanned) => {
472 let name = spanned.node.as_str();
473 if name.starts_with('_') && !name.starts_with("__") {
481 if let Some(binding) = binding {
483 USED_UNDERSCORE_BINDING,
485 &format!("used binding `{}` which is prefixed with an underscore. A leading \
486 underscore signals that a binding will not be used.", binding));
491 /// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
492 /// of what it means for an expression to be "used".
493 fn is_used(cx: &LateContext, expr: &Expr) -> bool {
494 if let Some(parent) = get_parent_expr(cx, expr) {
496 ExprAssign(_, ref rhs) |
497 ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
498 _ => is_used(cx, parent),
505 /// Test whether an expression is in a macro expansion (e.g. something generated by
506 /// `#[derive(...)`] or the like).
507 fn in_attributes_expansion(cx: &LateContext, expr: &Expr) -> bool {
508 cx.sess().codemap().with_expn_info(expr.span.expn_id, |info_opt| {
509 info_opt.map_or(false, |info| {
510 matches!(info.callee.format, ExpnFormat::MacroAttribute(_))
515 /// Test whether `def` is a variable defined outside a macro.
516 fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
518 def::Def::Local(_, id) | def::Def::Upvar(_, id, _, _) => {
519 if let Some(span) = cx.tcx.map.opt_span(id) {