use reexport::*; use rustc::hir::*; use rustc::hir::intravisit::FnKind; use rustc::lint::*; use rustc::middle::const_val::ConstVal; use rustc::ty; use rustc_const_eval::ConstContext; use rustc_const_math::ConstFloat; use syntax::codemap::{Span, ExpnFormat}; use utils::{get_item_name, get_parent_expr, implements_trait, in_macro, is_integer_literal, match_path, snippet, span_lint, span_lint_and_then, walk_ptrs_ty, last_path_segment, iter_input_pats, in_constant, match_trait_method, paths}; use utils::sugg::Sugg; use syntax::ast::{LitKind, CRATE_NODE_ID}; /// **What it does:** Checks for function arguments and let bindings denoted as `ref`. /// /// **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. /// /// For let bindings, `let x = &foo;` is preferred over `let ref x = foo`. The /// type of `x` is more obvious with the former. /// /// **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. /// /// **Example:** /// ```rust /// fn foo(ref x: u8) -> bool { .. } /// ``` declare_lint! { pub TOPLEVEL_REF_ARG, Warn, "an entire binding declared as `ref`, in a function argument or a `let` statement" } /// **What it does:** Checks for comparisons to NaN. /// /// **Why is this bad?** NaN does not compare meaningfully to anything – not /// even itself – so those comparisons are simply wrong. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// x == NAN /// ``` declare_lint! { pub CMP_NAN, Deny, "comparisons to NAN, which will always return false, probably not intended" } /// **What it does:** 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). /// /// **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). /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// y == 1.23f64 /// y != x // where both are floats /// ``` declare_lint! { pub FLOAT_CMP, Warn, "using `==` or `!=` on float values instead of comparing difference with an epsilon" } /// **What it does:** Checks for conversions to owned values just for the sake /// of a comparison. /// /// **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. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// x.to_owned() == y /// ``` declare_lint! { pub CMP_OWNED, Warn, "creating owned instances for comparing with others, e.g. `x == \"foo\".to_string()`" } /// **What it does:** Checks for getting the remainder of a division by one. /// /// **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. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// x % 1 /// ``` declare_lint! { pub MODULO_ONE, Warn, "taking a number modulo 1, which always returns 0" } /// **What it does:** Checks for patterns in the form `name @ _`. /// /// **Why is this bad?** It's almost always more readable to just use direct bindings. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// match v { /// Some(x) => (), /// y @ _ => (), // easier written as `y`, /// } /// ``` declare_lint! { pub REDUNDANT_PATTERN, Warn, "using `name @ _` in a pattern" } /// **What it does:** Checks for the use of bindings with a single leading underscore. /// /// **Why is this bad?** A single leading underscore is usually used to indicate /// that a binding will not be used. Using such a binding breaks this /// expectation. /// /// **Known problems:** The lint does not work properly with desugaring and /// macro, it has been allowed in the mean time. /// /// **Example:** /// ```rust /// let _x = 0; /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore. /// // We should rename `_x` to `x` /// ``` declare_lint! { pub USED_UNDERSCORE_BINDING, Allow, "using a binding which is prefixed with an underscore" } /// **What it does:** Checks for the use of short circuit boolean conditions as a /// statement. /// /// **Why is this bad?** Using a short circuit boolean condition as a statement may /// hide the fact that the second part is executed or not depending on the outcome of /// the first part. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// f() && g(); // We should write `if f() { g(); }`. /// ``` declare_lint! { pub SHORT_CIRCUIT_STATEMENT, Warn, "using a short circuit boolean condition as a statement" } /// **What it does:** Catch casts from `0` to some pointer type /// /// **Why is this bad?** This generally means `null` and is better expressed as /// {`std`, `core`}`::ptr::`{`null`, `null_mut`}. /// /// **Known problems:** None. /// /// **Example:** /// /// ```rust /// 0 as *const u32 /// ``` declare_lint! { pub ZERO_PTR, Warn, "using 0 as *{const, mut} T" } #[derive(Copy, Clone)] pub struct Pass; impl LintPass for Pass { fn get_lints(&self) -> LintArray { lint_array!(TOPLEVEL_REF_ARG, CMP_NAN, FLOAT_CMP, CMP_OWNED, MODULO_ONE, REDUNDANT_PATTERN, USED_UNDERSCORE_BINDING, SHORT_CIRCUIT_STATEMENT, ZERO_PTR) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { fn check_fn( &mut self, cx: &LateContext<'a, 'tcx>, k: FnKind<'tcx>, decl: &'tcx FnDecl, body: &'tcx Body, _: Span, _: NodeId ) { if let FnKind::Closure(_) = k { // Does not apply to closures return; } for arg in iter_input_pats(decl, body) { if let PatKind::Binding(BindByRef(_), _, _, _) = arg.pat.node { span_lint(cx, TOPLEVEL_REF_ARG, arg.pat.span, "`ref` directly on a function argument is ignored. Consider using a reference type instead."); } } } fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, s: &'tcx Stmt) { if_let_chain! {[ let StmtDecl(ref d, _) = s.node, let DeclLocal(ref l) = d.node, let PatKind::Binding(BindByRef(mt), _, i, None) = l.pat.node, let Some(ref init) = l.init ], { let init = Sugg::hir(cx, init, ".."); let (mutopt,initref) = if mt == Mutability::MutMutable { ("mut ", init.mut_addr()) } else { ("", init.addr()) }; let tyopt = if let Some(ref ty) = l.ty { format!(": &{mutopt}{ty}", mutopt=mutopt, ty=snippet(cx, ty.span, "_")) } else { "".to_owned() }; span_lint_and_then(cx, TOPLEVEL_REF_ARG, l.pat.span, "`ref` on an entire `let` pattern is discouraged, take a reference with `&` instead", |db| { db.span_suggestion(s.span, "try", format!("let {name}{tyopt} = {initref};", name=snippet(cx, i.span, "_"), tyopt=tyopt, initref=initref)); } ); }}; if_let_chain! {[ let StmtSemi(ref expr, _) = s.node, let Expr_::ExprBinary(ref binop, ref a, ref b) = expr.node, binop.node == BiAnd || binop.node == BiOr, let Some(sugg) = Sugg::hir_opt(cx, a), ], { span_lint_and_then(cx, SHORT_CIRCUIT_STATEMENT, s.span, "boolean short circuit operator in statement may be clearer using an explicit test", |db| { let sugg = if binop.node == BiOr { !sugg } else { sugg }; db.span_suggestion(s.span, "replace it with", format!("if {} {{ {}; }}", sugg, &snippet(cx, b.span, ".."))); }); }}; } fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { match expr.node { ExprCast(ref e, ref ty) => { check_cast(cx, expr.span, e, ty); return; }, ExprBinary(ref cmp, ref left, ref right) => { let op = cmp.node; if op.is_comparison() { if let ExprPath(QPath::Resolved(_, ref path)) = left.node { check_nan(cx, path, expr); } if let ExprPath(QPath::Resolved(_, ref path)) = right.node { check_nan(cx, path, expr); } check_to_owned(cx, left, right); check_to_owned(cx, right, left); } if (op == BiEq || op == BiNe) && (is_float(cx, left) || is_float(cx, right)) { if is_allowed(cx, left) || is_allowed(cx, right) { return; } if let Some(name) = get_item_name(cx, expr) { let name = name.as_str(); if name == "eq" || name == "ne" || name == "is_nan" || name.starts_with("eq_") || name.ends_with("_eq") { return; } } span_lint_and_then(cx, FLOAT_CMP, expr.span, "strict comparison of f32 or f64", |db| { let lhs = Sugg::hir(cx, left, ".."); let rhs = Sugg::hir(cx, right, ".."); db.span_suggestion(expr.span, "consider comparing them within some error", format!("({}).abs() < error", lhs - rhs)); db.span_note(expr.span, "std::f32::EPSILON and std::f64::EPSILON are available."); }); } else if op == BiRem && is_integer_literal(right, 1) { span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0"); } }, _ => {}, } if in_attributes_expansion(expr) { // Don't lint things expanded by #[derive(...)], etc return; } let binding = match expr.node { ExprPath(ref qpath) => { let binding = last_path_segment(qpath).name.as_str(); if binding.starts_with('_') && !binding.starts_with("__") && binding != "_result" && // FIXME: #944 is_used(cx, expr) && // don't lint if the declaration is in a macro non_macro_local(cx, &cx.tables.qpath_def(qpath, expr.id)) { Some(binding) } else { None } }, ExprField(_, spanned) => { let name = spanned.node.as_str(); if name.starts_with('_') && !name.starts_with("__") { Some(name) } else { None } }, _ => None, }; if let Some(binding) = binding { span_lint(cx, USED_UNDERSCORE_BINDING, expr.span, &format!("used binding `{}` which is prefixed with an underscore. A leading \ underscore signals that a binding will not be used.", binding)); } } fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) { if let PatKind::Binding(_, _, ref ident, Some(ref right)) = pat.node { if right.node == PatKind::Wild { span_lint(cx, REDUNDANT_PATTERN, pat.span, &format!("the `{} @ _` pattern can be written as just `{}`", ident.node, ident.node)); } } } } fn check_nan(cx: &LateContext, path: &Path, expr: &Expr) { if !in_constant(cx, expr.id) { path.segments.last().map(|seg| if seg.name == "NAN" { span_lint(cx, CMP_NAN, expr.span, "doomed comparison with NAN, use `std::{f32,f64}::is_nan()` instead"); }); } } fn is_allowed(cx: &LateContext, expr: &Expr) -> bool { let res = ConstContext::with_tables(cx.tcx, cx.tables).eval(expr); if let Ok(ConstVal::Float(val)) = res { use std::cmp::Ordering; match val { val @ ConstFloat::F32(_) => { let zero = ConstFloat::F32(0.0); let infinity = ConstFloat::F32(::std::f32::INFINITY); let neg_infinity = ConstFloat::F32(::std::f32::NEG_INFINITY); val.try_cmp(zero) == Ok(Ordering::Equal) || val.try_cmp(infinity) == Ok(Ordering::Equal) || val.try_cmp(neg_infinity) == Ok(Ordering::Equal) }, val @ ConstFloat::F64(_) => { let zero = ConstFloat::F64(0.0); let infinity = ConstFloat::F64(::std::f64::INFINITY); let neg_infinity = ConstFloat::F64(::std::f64::NEG_INFINITY); val.try_cmp(zero) == Ok(Ordering::Equal) || val.try_cmp(infinity) == Ok(Ordering::Equal) || val.try_cmp(neg_infinity) == Ok(Ordering::Equal) }, } } else { false } } fn is_float(cx: &LateContext, expr: &Expr) -> bool { matches!(walk_ptrs_ty(cx.tables.expr_ty(expr)).sty, ty::TyFloat(_)) } fn check_to_owned(cx: &LateContext, expr: &Expr, other: &Expr) { let (arg_ty, snip) = match expr.node { ExprMethodCall(.., ref args) if args.len() == 1 => { if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) { (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, "..")) } else { return; } }, ExprCall(ref path, ref v) if v.len() == 1 => { if let ExprPath(ref path) = path.node { if match_path(path, &["String", "from_str"]) || match_path(path, &["String", "from"]) { (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, "..")) } else { return; } } else { return; } }, _ => return, }; let other_ty = cx.tables.expr_ty_adjusted(other); let partial_eq_trait_id = match cx.tcx.lang_items.eq_trait() { Some(id) => id, None => return, }; // *arg impls PartialEq if !arg_ty .builtin_deref(true, ty::LvaluePreference::NoPreference) .map_or(false, |tam| implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty], None)) // arg impls PartialEq<*other> && !other_ty .builtin_deref(true, ty::LvaluePreference::NoPreference) .map_or(false, |tam| implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty], None)) // arg impls PartialEq && !implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty], None) { return; } span_lint_and_then(cx, CMP_OWNED, expr.span, "this creates an owned instance just for comparison", |db| { // this is as good as our recursion check can get, we can't prove that the current function is // called by // PartialEq::eq, but we can at least ensure that this code is not part of it let parent_fn = cx.tcx.hir.get_parent(expr.id); let parent_impl = cx.tcx.hir.get_parent(parent_fn); if parent_impl != CRATE_NODE_ID { if let map::NodeItem(item) = cx.tcx.hir.get(parent_impl) { if let ItemImpl(.., Some(ref trait_ref), _, _) = item.node { if trait_ref.path.def.def_id() == partial_eq_trait_id { // we are implementing PartialEq, don't suggest not doing `to_owned`, otherwise we go into // recursion db.span_label(expr.span, "try calling implementing the comparison without allocating"); return; } } } } db.span_suggestion(expr.span, "try", snip.to_string()); }); } /// Heuristic to see if an expression is used. Should be compatible with `unused_variables`'s idea /// of what it means for an expression to be "used". fn is_used(cx: &LateContext, expr: &Expr) -> bool { if let Some(parent) = get_parent_expr(cx, expr) { match parent.node { ExprAssign(_, ref rhs) | ExprAssignOp(_, _, ref rhs) => **rhs == *expr, _ => is_used(cx, parent), } } else { true } } /// Test whether an expression is in a macro expansion (e.g. something generated by /// `#[derive(...)`] or the like). fn in_attributes_expansion(expr: &Expr) -> bool { expr.span.ctxt.outer().expn_info().map_or(false, |info| matches!(info.callee.format, ExpnFormat::MacroAttribute(_))) } /// Test whether `def` is a variable defined outside a macro. fn non_macro_local(cx: &LateContext, def: &def::Def) -> bool { match *def { def::Def::Local(id) | def::Def::Upvar(id, _, _) => { if let Some(span) = cx.tcx.hir.span_if_local(id) { !in_macro(span) } else { true } }, _ => false, } } fn check_cast(cx: &LateContext, span: Span, e: &Expr, ty: &Ty) { if_let_chain! {[ let TyPtr(MutTy { mutbl, .. }) = ty.node, let ExprLit(ref lit) = e.node, let LitKind::Int(value, ..) = lit.node, value == 0, !in_constant(cx, e.id) ], { let msg = match mutbl { Mutability::MutMutable => "`0 as *mut _` detected. Consider using `ptr::null_mut()`", Mutability::MutImmutable => "`0 as *const _` detected. Consider using `ptr::null()`", }; span_lint(cx, ZERO_PTR, span, msg); }} }