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};
11 use utils::{get_item_name, get_parent_expr, implements_trait, in_macro, is_integer_literal, match_path, snippet,
12 span_lint, span_lint_and_then, walk_ptrs_ty, last_path_segment};
13 use utils::sugg::Sugg;
15 /// **What it does:** Checks for function arguments and let bindings denoted as `ref`.
17 /// **Why is this bad?** The `ref` declaration makes the function take an owned
18 /// value, but turns the argument into a reference (which means that the value
19 /// is destroyed when exiting the function). This adds not much value: either
20 /// take a reference type, or take an owned value and create references in the
23 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
24 /// type of `x` is more obvious with the former.
26 /// **Known problems:** If the argument is dereferenced within the function,
27 /// removing the `ref` will lead to errors. This can be fixed by removing the
28 /// dereferences, e.g. changing `*x` to `x` within the function.
32 /// fn foo(ref x: u8) -> bool { .. }
37 "an entire binding declared as `ref`, in a function argument or a `let` statement"
40 /// **What it does:** Checks for comparisons to NaN.
42 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
43 /// even itself – so those comparisons are simply wrong.
45 /// **Known problems:** None.
54 "comparisons to NAN, which will always return false, probably not intended"
57 /// **What it does:** Checks for (in-)equality comparisons on floating-point
58 /// values (apart from zero), except in functions called `*eq*` (which probably
59 /// implement equality for a type involving floats).
61 /// **Why is this bad?** Floating point calculations are usually imprecise, so
62 /// asking if two values are *exactly* equal is asking for trouble. For a good
63 /// guide on what to do, see [the floating point
64 /// guide](http://www.floating-point-gui.de/errors/comparison).
66 /// **Known problems:** None.
71 /// y != x // where both are floats
76 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
79 /// **What it does:** Checks for conversions to owned values just for the sake
82 /// **Why is this bad?** The comparison can operate on a reference, so creating
83 /// an owned value effectively throws it away directly afterwards, which is
84 /// needlessly consuming code and heap space.
86 /// **Known problems:** None.
95 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
98 /// **What it does:** Checks for getting the remainder of a division by one.
100 /// **Why is this bad?** The result can only ever be zero. No one will write
101 /// such code deliberately, unless trying to win an Underhanded Rust
102 /// Contest. Even for that contest, it's probably a bad idea. Use something more
105 /// **Known problems:** None.
114 "taking a number modulo 1, which always returns 0"
117 /// **What it does:** Checks for patterns in the form `name @ _`.
119 /// **Why is this bad?** It's almost always more readable to just use direct bindings.
121 /// **Known problems:** None.
127 /// y @ _ => (), // easier written as `y`,
131 pub REDUNDANT_PATTERN,
133 "using `name @ _` in a pattern"
136 /// **What it does:** Checks for the use of bindings with a single leading underscore.
138 /// **Why is this bad?** A single leading underscore is usually used to indicate
139 /// that a binding will not be used. Using such a binding breaks this
142 /// **Known problems:** The lint does not work properly with desugaring and
143 /// macro, it has been allowed in the mean time.
148 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
149 /// // We should rename `_x` to `x`
152 pub USED_UNDERSCORE_BINDING,
154 "using a binding which is prefixed with an underscore"
157 #[derive(Copy, Clone)]
160 impl LintPass for Pass {
161 fn get_lints(&self) -> LintArray {
162 lint_array!(TOPLEVEL_REF_ARG, CMP_NAN, FLOAT_CMP, CMP_OWNED, MODULO_ONE, REDUNDANT_PATTERN,
163 USED_UNDERSCORE_BINDING)
167 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
168 fn check_fn(&mut self, cx: &LateContext<'a, 'tcx>, k: FnKind<'tcx>, decl: &'tcx FnDecl, _: &'tcx Expr, _: Span,
170 if let FnKind::Closure(_) = k {
171 // Does not apply to closures
174 for arg in &decl.inputs {
175 if let PatKind::Binding(BindByRef(_), _, _, _) = arg.pat.node {
179 "`ref` directly on a function argument is ignored. Consider using a reference type instead.");
184 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) {
186 let StmtDecl(ref d, _) = s.node,
187 let DeclLocal(ref l) = d.node,
188 let PatKind::Binding(BindByRef(mt), _, i, None) = l.pat.node,
189 let Some(ref init) = l.init
191 let init = Sugg::hir(cx, init, "..");
192 let (mutopt,initref) = if mt == Mutability::MutMutable {
193 ("mut ", init.mut_addr())
197 let tyopt = if let Some(ref ty) = l.ty {
198 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
202 span_lint_and_then(cx,
205 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
207 db.span_suggestion(s.span,
209 format!("let {name}{tyopt} = {initref};",
210 name=snippet(cx, i.span, "_"),
218 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
219 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
221 if op.is_comparison() {
222 if let ExprPath(QPath::Resolved(_, ref path)) = left.node {
223 check_nan(cx, path, expr.span);
225 if let ExprPath(QPath::Resolved(_, ref path)) = right.node {
226 check_nan(cx, path, expr.span);
228 check_to_owned(cx, left, right, true, cmp.span);
229 check_to_owned(cx, right, left, false, cmp.span)
231 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
232 if is_allowed(cx, left) || is_allowed(cx, right) {
235 if let Some(name) = get_item_name(cx, expr) {
236 let name = &*name.as_str();
237 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
238 name.ends_with("_eq") {
242 span_lint_and_then(cx, FLOAT_CMP, expr.span, "strict comparison of f32 or f64", |db| {
243 let lhs = Sugg::hir(cx, left, "..");
244 let rhs = Sugg::hir(cx, right, "..");
246 db.span_suggestion(expr.span,
247 "consider comparing them within some error",
248 format!("({}).abs() < error", lhs - rhs));
249 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
251 } else if op == BiRem && is_integer_literal(right, 1) {
252 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
255 if in_attributes_expansion(cx, expr) {
256 // Don't lint things expanded by #[derive(...)], etc
259 let binding = match expr.node {
260 ExprPath(ref qpath) => {
261 let binding = last_path_segment(qpath).name.as_str();
262 if binding.starts_with('_') &&
263 !binding.starts_with("__") &&
264 &*binding != "_result" && // FIXME: #944
266 // don't lint if the declaration is in a macro
267 non_macro_local(cx, &cx.tcx.tables().qpath_def(qpath, expr.id)) {
273 ExprField(_, spanned) => {
274 let name = spanned.node.as_str();
275 if name.starts_with('_') && !name.starts_with("__") {
283 if let Some(binding) = binding {
285 USED_UNDERSCORE_BINDING,
287 &format!("used binding `{}` which is prefixed with an underscore. A leading \
288 underscore signals that a binding will not be used.", binding));
292 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
293 if let PatKind::Binding(_, _, ref ident, Some(ref right)) = pat.node {
294 if right.node == PatKind::Wild {
298 &format!("the `{} @ _` pattern can be written as just `{}`",
306 fn check_nan(cx: &LateContext, path: &Path, span: Span) {
307 path.segments.last().map(|seg| {
308 if &*seg.name.as_str() == "NAN" {
312 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
317 fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
318 let res = eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None);
319 if let Ok(ConstVal::Float(val)) = res {
320 use std::cmp::Ordering;
322 let zero = ConstFloat::FInfer {
327 let infinity = ConstFloat::FInfer {
328 f32: ::std::f32::INFINITY,
329 f64: ::std::f64::INFINITY,
332 let neg_infinity = ConstFloat::FInfer {
333 f32: ::std::f32::NEG_INFINITY,
334 f64: ::std::f64::NEG_INFINITY,
337 val.try_cmp(zero) == Ok(Ordering::Equal) || val.try_cmp(infinity) == Ok(Ordering::Equal) ||
338 val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
344 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
345 matches!(walk_ptrs_ty(cx.tcx.tables().expr_ty(expr)).sty, ty::TyFloat(_))
348 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr, left: bool, op: Span) {
349 let (arg_ty, snip) = match expr.node {
350 ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
351 let name = &*name.as_str();
352 if name == "to_string" || name == "to_owned" && is_str_arg(cx, args) {
353 (cx.tcx.tables().expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
358 ExprCall(ref path, ref v) if v.len() == 1 => {
359 if let ExprPath(ref path) = path.node {
360 if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
361 (cx.tcx.tables().expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
372 let other_ty = cx.tcx.tables().expr_ty(other);
373 let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
378 if !implements_trait(cx, arg_ty, partial_eq_trait_id, vec![other_ty]) {
386 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
387 compare without allocation",
389 snippet(cx, op, "=="),
390 snippet(cx, other.span, "..")));
395 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
396 compare without allocation",
397 snippet(cx, other.span, ".."),
398 snippet(cx, op, "=="),
404 fn is_str_arg(cx: &LateContext, args: &[Expr]) -> bool {
405 args.len() == 1 && matches!(walk_ptrs_ty(cx.tcx.tables().expr_ty(&args[0])).sty, ty::TyStr)
408 /// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea
409 /// of what it means for an expression to be "used".
410 fn is_used(cx: &LateContext, expr: &Expr) -> bool {
411 if let Some(parent) = get_parent_expr(cx, expr) {
413 ExprAssign(_, ref rhs) |
414 ExprAssignOp(_, _, ref rhs) => **rhs == *expr,
415 _ => is_used(cx, parent),
422 /// Test whether an expression is in a macro expansion (e.g. something generated by
423 /// `#[derive(...)`] or the like).
424 fn in_attributes_expansion(cx: &LateContext, expr: &Expr) -> bool {
425 cx.sess().codemap().with_expn_info(expr.span.expn_id, |info_opt| {
426 info_opt.map_or(false, |info| matches!(info.callee.format, ExpnFormat::MacroAttribute(_)))
430 /// Test whether `def` is a variable defined outside a macro.
431 fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
433 def::Def::Local(id) |
434 def::Def::Upvar(id, _, _) => {
435 if let Some(span) = cx.tcx.map.span_if_local(id) {