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 { .. }
40 "an entire binding declared as `ref`, in a function argument or a `let` statement"
43 /// **What it does:** Checks for comparisons to NaN.
45 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
46 /// even itself – so those comparisons are simply wrong.
48 /// **Known problems:** None.
57 "comparisons to NAN, which will always return false, probably not intended"
60 /// **What it does:** Checks for (in-)equality comparisons on floating-point
61 /// values (apart from zero), except in functions called `*eq*` (which probably
62 /// implement equality for a type involving floats).
64 /// **Why is this bad?** Floating point calculations are usually imprecise, so
65 /// asking if two values are *exactly* equal is asking for trouble. For a good
66 /// guide on what to do, see [the floating point
67 /// guide](http://www.floating-point-gui.de/errors/comparison).
69 /// **Known problems:** None.
74 /// y != x // where both are floats
79 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
82 /// **What it does:** Checks for conversions to owned values just for the sake
85 /// **Why is this bad?** The comparison can operate on a reference, so creating
86 /// an owned value effectively throws it away directly afterwards, which is
87 /// needlessly consuming code and heap space.
89 /// **Known problems:** None.
98 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
101 /// **What it does:** Checks for getting the remainder of a division by one.
103 /// **Why is this bad?** The result can only ever be zero. No one will write
104 /// such code deliberately, unless trying to win an Underhanded Rust
105 /// Contest. Even for that contest, it's probably a bad idea. Use something more
108 /// **Known problems:** None.
117 "taking a number modulo 1, which always returns 0"
120 /// **What it does:** Checks for patterns in the form `name @ _`.
122 /// **Why is this bad?** It's almost always more readable to just use direct bindings.
124 /// **Known problems:** None.
130 /// y @ _ => (), // easier written as `y`,
134 pub REDUNDANT_PATTERN,
136 "using `name @ _` in a pattern"
139 /// **What it does:** Checks for the use of bindings with a single leading underscore.
141 /// **Why is this bad?** A single leading underscore is usually used to indicate
142 /// that a binding will not be used. Using such a binding breaks this
145 /// **Known problems:** The lint does not work properly with desugaring and
146 /// macro, it has been allowed in the mean time.
151 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
152 /// // We should rename `_x` to `x`
155 pub USED_UNDERSCORE_BINDING,
157 "using a binding which is prefixed with an underscore"
160 #[derive(Copy, Clone)]
163 impl LintPass for Pass {
164 fn get_lints(&self) -> LintArray {
165 lint_array!(TOPLEVEL_REF_ARG, CMP_NAN, FLOAT_CMP, CMP_OWNED, MODULO_ONE, REDUNDANT_PATTERN,
166 USED_UNDERSCORE_BINDING)
170 impl LateLintPass for Pass {
171 fn check_fn(&mut self, cx: &LateContext, k: FnKind, decl: &FnDecl, _: &Expr, _: Span, _: NodeId) {
172 if let FnKind::Closure(_) = k {
173 // Does not apply to closures
176 for arg in &decl.inputs {
177 if let PatKind::Binding(BindByRef(_), _, _) = arg.pat.node {
181 "`ref` directly on a function argument is ignored. Consider using a reference type instead.");
186 fn check_stmt(&mut self, cx: &LateContext, s: &Stmt) {
188 let StmtDecl(ref d, _) = s.node,
189 let DeclLocal(ref l) = d.node,
190 let PatKind::Binding(BindByRef(mt), i, None) = l.pat.node,
191 let Some(ref init) = l.init
193 let init = Sugg::hir(cx, init, "..");
194 let (mutopt,initref) = if mt == Mutability::MutMutable {
195 ("mut ", init.mut_addr())
199 let tyopt = if let Some(ref ty) = l.ty {
200 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
204 span_lint_and_then(cx,
207 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
209 db.span_suggestion(s.span,
211 format!("let {name}{tyopt} = {initref};",
212 name=snippet(cx, i.span, "_"),
220 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
221 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
223 if op.is_comparison() {
224 if let ExprPath(_, ref path) = left.node {
225 check_nan(cx, path, expr.span);
227 if let ExprPath(_, ref path) = right.node {
228 check_nan(cx, path, expr.span);
230 check_to_owned(cx, left, right, true, cmp.span);
231 check_to_owned(cx, right, left, false, cmp.span)
233 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
234 if is_allowed(cx, left) || is_allowed(cx, right) {
237 if let Some(name) = get_item_name(cx, expr) {
238 let name = &*name.as_str();
239 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
240 name.ends_with("_eq") {
244 span_lint_and_then(cx,
247 "strict comparison of f32 or f64",
249 let lhs = Sugg::hir(cx, left, "..");
250 let rhs = Sugg::hir(cx, right, "..");
252 db.span_suggestion(expr.span,
253 "consider comparing them within some error",
254 format!("({}).abs() < error", lhs - rhs));
255 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
257 } else if op == BiRem && is_integer_literal(right, 1) {
258 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
261 if in_attributes_expansion(cx, expr) {
262 // Don't lint things expanded by #[derive(...)], etc
265 let binding = match expr.node {
266 ExprPath(_, ref path) => {
267 let binding = path.segments
269 .expect("path should always have at least one segment")
272 if binding.starts_with('_') &&
273 !binding.starts_with("__") &&
274 &*binding != "_result" && // FIXME: #944
276 // don't lint if the declaration is in a macro
277 non_macro_local(cx, &cx.tcx.expect_def(expr.id)) {
283 ExprField(_, spanned) => {
284 let name = spanned.node.as_str();
285 if name.starts_with('_') && !name.starts_with("__") {
293 if let Some(binding) = binding {
295 USED_UNDERSCORE_BINDING,
297 &format!("used binding `{}` which is prefixed with an underscore. A leading \
298 underscore signals that a binding will not be used.", binding));
302 fn check_pat(&mut self, cx: &LateContext, pat: &Pat) {
303 if let PatKind::Binding(_, ref ident, Some(ref right)) = pat.node {
304 if right.node == PatKind::Wild {
308 &format!("the `{} @ _` pattern can be written as just `{}`",
316 fn check_nan(cx: &LateContext, path: &Path, span: Span) {
317 path.segments.last().map(|seg| {
318 if &*seg.name.as_str() == "NAN" {
322 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
327 fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
328 let res = eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None);
329 if let Ok(ConstVal::Float(val)) = res {
330 use std::cmp::Ordering;
332 let zero = ConstFloat::FInfer {
337 let infinity = ConstFloat::FInfer {
338 f32: ::std::f32::INFINITY,
339 f64: ::std::f64::INFINITY,
342 let neg_infinity = ConstFloat::FInfer {
343 f32: ::std::f32::NEG_INFINITY,
344 f64: ::std::f64::NEG_INFINITY,
347 val.try_cmp(zero) == Ok(Ordering::Equal)
348 || val.try_cmp(infinity) == Ok(Ordering::Equal)
349 || val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
355 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
356 matches!(walk_ptrs_ty(cx.tcx.tables().expr_ty(expr)).sty, ty::TyFloat(_))
359 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr, left: bool, op: Span) {
360 let (arg_ty, snip) = match expr.node {
361 ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
362 let name = &*name.as_str();
363 if name == "to_string" || name == "to_owned" && is_str_arg(cx, args) {
364 (cx.tcx.tables().expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
369 ExprCall(ref path, ref v) if v.len() == 1 => {
370 if let ExprPath(None, ref path) = path.node {
371 if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
372 (cx.tcx.tables().expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
383 let other_ty = cx.tcx.tables().expr_ty(other);
384 let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
389 if !implements_trait(cx, arg_ty, partial_eq_trait_id, vec![other_ty]) {
397 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
398 compare without allocation",
400 snippet(cx, op, "=="),
401 snippet(cx, other.span, "..")));
406 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
407 compare without allocation",
408 snippet(cx, other.span, ".."),
409 snippet(cx, op, "=="),
415 fn is_str_arg(cx: &LateContext, args: &[P<Expr>]) -> bool {
417 matches!(walk_ptrs_ty(cx.tcx.tables().expr_ty(&args[0])).sty, ty::TyStr)
420 /// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
421 /// of what it means for an expression to be "used".
422 fn is_used(cx: &LateContext, expr: &Expr) -> bool {
423 if let Some(parent) = get_parent_expr(cx, expr) {
425 ExprAssign(_, ref rhs) |
426 ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
427 _ => is_used(cx, parent),
434 /// Test whether an expression is in a macro expansion (e.g. something generated by
435 /// `#[derive(...)`] or the like).
436 fn in_attributes_expansion(cx: &LateContext, expr: &Expr) -> bool {
437 cx.sess().codemap().with_expn_info(expr.span.expn_id, |info_opt| {
438 info_opt.map_or(false, |info| {
439 matches!(info.callee.format, ExpnFormat::MacroAttribute(_))
444 /// Test whether `def` is a variable defined outside a macro.
445 fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
447 def::Def::Local(id) | def::Def::Upvar(id, _, _) => {
448 let id = cx.tcx.map.as_local_node_id(id).expect("That DefId should be valid");
450 if let Some(span) = cx.tcx.map.opt_span(id) {