3 use rustc::hir::intravisit::FnKind;
5 use rustc::middle::const_val::ConstVal;
7 use rustc_const_eval::ConstContext;
8 use rustc_const_math::ConstFloat;
9 use syntax::codemap::{Span, Spanned, ExpnFormat};
10 use utils::{get_item_name, get_parent_expr, implements_trait, in_macro, is_integer_literal, match_path, snippet,
11 span_lint, span_lint_and_then, walk_ptrs_ty, last_path_segment, iter_input_pats};
12 use utils::sugg::Sugg;
14 /// **What it does:** Checks for function arguments and let bindings denoted as `ref`.
16 /// **Why is this bad?** The `ref` declaration makes the function take an owned
17 /// value, but turns the argument into a reference (which means that the value
18 /// is destroyed when exiting the function). This adds not much value: either
19 /// take a reference type, or take an owned value and create references in the
22 /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The
23 /// type of `x` is more obvious with the former.
25 /// **Known problems:** If the argument is dereferenced within the function,
26 /// removing the `ref` will lead to errors. This can be fixed by removing the
27 /// dereferences, e.g. changing `*x` to `x` within the function.
31 /// fn foo(ref x: u8) -> bool { .. }
36 "an entire binding declared as `ref`, in a function argument or a `let` statement"
39 /// **What it does:** Checks for comparisons to NaN.
41 /// **Why is this bad?** NaN does not compare meaningfully to anything – not
42 /// even itself – so those comparisons are simply wrong.
44 /// **Known problems:** None.
53 "comparisons to NAN, which will always return false, probably not intended"
56 /// **What it does:** Checks for (in-)equality comparisons on floating-point
57 /// values (apart from zero), except in functions called `*eq*` (which probably
58 /// implement equality for a type involving floats).
60 /// **Why is this bad?** Floating point calculations are usually imprecise, so
61 /// asking if two values are *exactly* equal is asking for trouble. For a good
62 /// guide on what to do, see [the floating point
63 /// guide](http://www.floating-point-gui.de/errors/comparison).
65 /// **Known problems:** None.
70 /// y != x // where both are floats
75 "using `==` or `!=` on float values instead of comparing difference with an epsilon"
78 /// **What it does:** Checks for conversions to owned values just for the sake
81 /// **Why is this bad?** The comparison can operate on a reference, so creating
82 /// an owned value effectively throws it away directly afterwards, which is
83 /// needlessly consuming code and heap space.
85 /// **Known problems:** None.
94 "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`"
97 /// **What it does:** Checks for getting the remainder of a division by one.
99 /// **Why is this bad?** The result can only ever be zero. No one will write
100 /// such code deliberately, unless trying to win an Underhanded Rust
101 /// Contest. Even for that contest, it's probably a bad idea. Use something more
104 /// **Known problems:** None.
113 "taking a number modulo 1, which always returns 0"
116 /// **What it does:** Checks for patterns in the form `name @ _`.
118 /// **Why is this bad?** It's almost always more readable to just use direct bindings.
120 /// **Known problems:** None.
126 /// y @ _ => (), // easier written as `y`,
130 pub REDUNDANT_PATTERN,
132 "using `name @ _` in a pattern"
135 /// **What it does:** Checks for the use of bindings with a single leading underscore.
137 /// **Why is this bad?** A single leading underscore is usually used to indicate
138 /// that a binding will not be used. Using such a binding breaks this
141 /// **Known problems:** The lint does not work properly with desugaring and
142 /// macro, it has been allowed in the mean time.
147 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
148 /// // We should rename `_x` to `x`
151 pub USED_UNDERSCORE_BINDING,
153 "using a binding which is prefixed with an underscore"
156 /// **What it does:** Checks for the use of short circuit boolean conditions as a
159 /// **Why is this bad?** Using a short circuit boolean condition as a statement may
160 /// hide the fact that the second part is executed or not depending on the outcome of
163 /// **Known problems:** None.
167 /// f() && g(); // We should write `if f() { g(); }`.
170 pub SHORT_CIRCUIT_STATEMENT,
172 "using a short circuit boolean condition as a statement"
175 #[derive(Copy, Clone)]
178 impl LintPass for Pass {
179 fn get_lints(&self) -> LintArray {
180 lint_array!(TOPLEVEL_REF_ARG,
186 USED_UNDERSCORE_BINDING,
187 SHORT_CIRCUIT_STATEMENT)
191 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
194 cx: &LateContext<'a, 'tcx>,
201 if let FnKind::Closure(_) = k {
202 // Does not apply to closures
205 for arg in iter_input_pats(decl, body) {
206 if let PatKind::Binding(BindByRef(_), _, _, _) = arg.pat.node {
210 "`ref` directly on a function argument is ignored. Consider using a reference type instead.");
215 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) {
217 let StmtDecl(ref d, _) = s.node,
218 let DeclLocal(ref l) = d.node,
219 let PatKind::Binding(BindByRef(mt), _, i, None) = l.pat.node,
220 let Some(ref init) = l.init
222 let init = Sugg::hir(cx, init, "..");
223 let (mutopt,initref) = if mt == Mutability::MutMutable {
224 ("mut ", init.mut_addr())
228 let tyopt = if let Some(ref ty) = l.ty {
229 format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_"))
233 span_lint_and_then(cx,
236 "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead",
238 db.span_suggestion(s.span,
240 format!("let {name}{tyopt} = {initref};",
241 name=snippet(cx, i.span, "_"),
248 let StmtSemi(ref expr, _) = s.node,
249 let Expr_::ExprBinary(ref binop, ref a, ref b) = expr.node,
250 binop.node == BiAnd || binop.node == BiOr,
251 let Some(sugg) = Sugg::hir_opt(cx, a),
253 span_lint_and_then(cx,
254 SHORT_CIRCUIT_STATEMENT,
256 "boolean short circuit operator in statement may be clearer using an explicit test",
258 let sugg = if binop.node == BiOr { !sugg } else { sugg };
259 db.span_suggestion(s.span, "replace it with",
260 format!("if {} {{ {}; }}", sugg, &snippet(cx, b.span, "..")));
265 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
266 if let ExprBinary(ref cmp, ref left, ref right) = expr.node {
268 if op.is_comparison() {
269 if let ExprPath(QPath::Resolved(_, ref path)) = left.node {
270 check_nan(cx, path, expr.span);
272 if let ExprPath(QPath::Resolved(_, ref path)) = right.node {
273 check_nan(cx, path, expr.span);
275 check_to_owned(cx, left, right, true, cmp.span);
276 check_to_owned(cx, right, left, false, cmp.span)
278 if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) {
279 if is_allowed(cx, left) || is_allowed(cx, right) {
282 if let Some(name) = get_item_name(cx, expr) {
283 let name = &*name.as_str();
284 if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") ||
285 name.ends_with("_eq") {
289 span_lint_and_then(cx, FLOAT_CMP, expr.span, "strict comparison of f32 or f64", |db| {
290 let lhs = Sugg::hir(cx, left, "..");
291 let rhs = Sugg::hir(cx, right, "..");
293 db.span_suggestion(expr.span,
294 "consider comparing them within some error",
295 format!("({}).abs() < error", lhs - rhs));
296 db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available.");
298 } else if op == BiRem && is_integer_literal(right, 1) {
299 span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
302 if in_attributes_expansion(cx, expr) {
303 // Don't lint things expanded by #[derive(...)], etc
306 let binding = match expr.node {
307 ExprPath(ref qpath) => {
308 let binding = last_path_segment(qpath).name.as_str();
309 if binding.starts_with('_') &&
310 !binding.starts_with("__") &&
311 &*binding != "_result" && // FIXME: #944
313 // don't lint if the declaration is in a macro
314 non_macro_local(cx, &cx.tables.qpath_def(qpath, expr.id)) {
320 ExprField(_, spanned) => {
321 let name = spanned.node.as_str();
322 if name.starts_with('_') && !name.starts_with("__") {
330 if let Some(binding) = binding {
332 USED_UNDERSCORE_BINDING,
334 &format!("used binding `{}` which is prefixed with an underscore. A leading \
335 underscore signals that a binding will not be used.",
340 fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
341 if let PatKind::Binding(_, _, ref ident, Some(ref right)) = pat.node {
342 if right.node == PatKind::Wild {
346 &format!("the `{} @ _` pattern can be written as just `{}`", ident.node, ident.node));
352 fn check_nan(cx: &LateContext, path: &Path, span: Span) {
353 path.segments.last().map(|seg| if &*seg.name.as_str() == "NAN" {
357 "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead");
361 fn is_allowed(cx: &LateContext, expr: &Expr) -> bool {
362 let res = ConstContext::with_tables(cx.tcx, cx.tables).eval(expr);
363 if let Ok(ConstVal::Float(val)) = res {
364 use std::cmp::Ordering;
366 let zero = ConstFloat::F64(0.0);
368 let infinity = ConstFloat::F64(::std::f64::INFINITY);
371 let neg_infinity = ConstFloat::F64(::std::f64::NEG_INFINITY);
373 val.try_cmp(zero) == Ok(Ordering::Equal) || val.try_cmp(infinity) == Ok(Ordering::Equal) ||
374 val.try_cmp(neg_infinity) == Ok(Ordering::Equal)
380 fn is_float(cx: &LateContext, expr: &Expr) -> bool {
381 matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::TyFloat(_))
384 fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr, left: bool, op: Span) {
385 let (arg_ty, snip) = match expr.node {
386 ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) if args.len() == 1 => {
387 let name = &*name.as_str();
388 if name == "to_string" || name == "to_owned" && is_str_arg(cx, args) {
389 (cx.tables.expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
394 ExprCall(ref path, ref v) if v.len() == 1 => {
395 if let ExprPath(ref path) = path.node {
396 if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) {
397 (cx.tables.expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
408 let other_ty = cx.tables.expr_ty(other);
409 let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() {
414 if !implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty], None) {
422 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
423 compare without allocation",
425 snippet(cx, op, "=="),
426 snippet(cx, other.span, "..")));
431 &format!("this creates an owned instance just for comparison. Consider using `{} {} {}` to \
432 compare without allocation",
433 snippet(cx, other.span, ".."),
434 snippet(cx, op, "=="),
440 fn is_str_arg(cx: &LateContext, args: &[Expr]) -> bool {
441 args.len() == 1 && matches!(walk_ptrs_ty(cx.tables.expr_ty(&args[0])).sty, ty::TyStr)
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(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| matches!(info.callee.format, ExpnFormat::MacroAttribute(_)))
466 /// Test whether `def` is a variable defined outside a macro.
467 fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool {
469 def::Def::Local(id) |
470 def::Def::Upvar(id, _, _) => {
471 if let Some(span) = cx.tcx.hir.span_if_local(id) {