use rustc::hir::def_id::DefId; use rustc::hir::*; use rustc::lint::*; use rustc::ty; use std::collections::HashSet; use syntax::ast::{Lit, LitKind, Name}; use syntax::codemap::{Span, Spanned}; use crate::utils::{get_item_name, in_macro, snippet, span_lint, span_lint_and_sugg, walk_ptrs_ty}; /// **What it does:** Checks for getting the length of something via `.len()` /// just to compare to zero, and suggests using `.is_empty()` where applicable. /// /// **Why is this bad?** Some structures can answer `.is_empty()` much faster /// than calculating their length. Notably, for slices, getting the length /// requires a subtraction whereas `.is_empty()` is just a comparison. So it is /// good to get into the habit of using `.is_empty()`, and having it is cheap. /// Besides, it makes the intent clearer than a manual comparison. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// if x.len() == 0 { .. } /// ``` declare_clippy_lint! { pub LEN_ZERO, style, "checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` \ could be used instead" } /// **What it does:** Checks for items that implement `.len()` but not /// `.is_empty()`. /// /// **Why is this bad?** It is good custom to have both methods, because for /// some data structures, asking about the length will be a costly operation, /// whereas `.is_empty()` can usually answer in constant time. Also it used to /// lead to false positives on the [`len_zero`](#len_zero) lint – currently that /// lint will ignore such entities. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// impl X { /// pub fn len(&self) -> usize { .. } /// } /// ``` declare_clippy_lint! { pub LEN_WITHOUT_IS_EMPTY, style, "traits or impls with a public `len` method but no corresponding `is_empty` method" } #[derive(Copy, Clone)] pub struct LenZero; impl LintPass for LenZero { fn get_lints(&self) -> LintArray { lint_array!(LEN_ZERO, LEN_WITHOUT_IS_EMPTY) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LenZero { fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) { if in_macro(item.span) { return; } match item.node { ItemTrait(_, _, _, _, ref trait_items) => check_trait_items(cx, item, trait_items), ItemImpl(_, _, _, _, None, _, ref impl_items) => check_impl_items(cx, item, impl_items), _ => (), } } fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { if in_macro(expr.span) { return; } if let ExprBinary(Spanned { node: cmp, .. }, ref left, ref right) = expr.node { match cmp { BiEq => { check_cmp(cx, expr.span, left, right, "", 0); // len == 0 check_cmp(cx, expr.span, right, left, "", 0); // 0 == len }, BiNe => { check_cmp(cx, expr.span, left, right, "!", 0); // len != 0 check_cmp(cx, expr.span, right, left, "!", 0); // 0 != len }, BiGt => { check_cmp(cx, expr.span, left, right, "!", 0); // len > 0 check_cmp(cx, expr.span, right, left, "", 1); // 1 > len }, BiLt => { check_cmp(cx, expr.span, left, right, "", 1); // len < 1 check_cmp(cx, expr.span, right, left, "!", 0); // 0 < len }, BiGe => check_cmp(cx, expr.span, left, right, "!", 1), // len <= 1 BiLe => check_cmp(cx, expr.span, right, left, "!", 1), // 1 >= len _ => (), } } } } fn check_trait_items(cx: &LateContext, visited_trait: &Item, trait_items: &[TraitItemRef]) { fn is_named_self(cx: &LateContext, item: &TraitItemRef, name: &str) -> bool { item.name == name && if let AssociatedItemKind::Method { has_self } = item.kind { has_self && { let did = cx.tcx.hir.local_def_id(item.id.node_id); cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1 } } else { false } } // fill the set with current and super traits fn fill_trait_set(traitt: DefId, set: &mut HashSet, cx: &LateContext) { if set.insert(traitt) { for supertrait in ::rustc::traits::supertrait_def_ids(cx.tcx, traitt) { fill_trait_set(supertrait, set, cx); } } } if cx.access_levels.is_exported(visited_trait.id) && trait_items.iter().any(|i| is_named_self(cx, i, "len")) { let mut current_and_super_traits = HashSet::new(); let visited_trait_def_id = cx.tcx.hir.local_def_id(visited_trait.id); fill_trait_set(visited_trait_def_id, &mut current_and_super_traits, cx); let is_empty_method_found = current_and_super_traits .iter() .flat_map(|&i| cx.tcx.associated_items(i)) .any(|i| { i.kind == ty::AssociatedKind::Method && i.method_has_self_argument && i.name == "is_empty" && cx.tcx.fn_sig(i.def_id).inputs().skip_binder().len() == 1 }); if !is_empty_method_found { span_lint( cx, LEN_WITHOUT_IS_EMPTY, visited_trait.span, &format!( "trait `{}` has a `len` method but no (possibly inherited) `is_empty` method", visited_trait.name ), ); } } } fn check_impl_items(cx: &LateContext, item: &Item, impl_items: &[ImplItemRef]) { fn is_named_self(cx: &LateContext, item: &ImplItemRef, name: &str) -> bool { item.name == name && if let AssociatedItemKind::Method { has_self } = item.kind { has_self && { let did = cx.tcx.hir.local_def_id(item.id.node_id); cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1 } } else { false } } let is_empty = if let Some(is_empty) = impl_items.iter().find(|i| is_named_self(cx, i, "is_empty")) { if cx.access_levels.is_exported(is_empty.id.node_id) { return; } else { "a private" } } else { "no corresponding" }; if let Some(i) = impl_items.iter().find(|i| is_named_self(cx, i, "len")) { if cx.access_levels.is_exported(i.id.node_id) { let def_id = cx.tcx.hir.local_def_id(item.id); let ty = cx.tcx.type_of(def_id); span_lint( cx, LEN_WITHOUT_IS_EMPTY, item.span, &format!( "item `{}` has a public `len` method but {} `is_empty` method", ty, is_empty ), ); } } } fn check_cmp(cx: &LateContext, span: Span, method: &Expr, lit: &Expr, op: &str, compare_to: u32) { if let (&ExprMethodCall(ref method_path, _, ref args), &ExprLit(ref lit)) = (&method.node, &lit.node) { // check if we are in an is_empty() method if let Some(name) = get_item_name(cx, method) { if name == "is_empty" { return; } } check_len(cx, span, method_path.name, args, lit, op, compare_to) } } fn check_len(cx: &LateContext, span: Span, method_name: Name, args: &[Expr], lit: &Lit, op: &str, compare_to: u32) { if let Spanned { node: LitKind::Int(lit, _), .. } = *lit { // check if length is compared to the specified number if lit != u128::from(compare_to) { return; } if method_name == "len" && args.len() == 1 && has_is_empty(cx, &args[0]) { span_lint_and_sugg( cx, LEN_ZERO, span, &format!("length comparison to {}", if compare_to == 0 { "zero" } else { "one" }), "using `is_empty` is more concise", format!("{}{}.is_empty()", op, snippet(cx, args[0].span, "_")), ); } } } /// Check if this type has an `is_empty` method. fn has_is_empty(cx: &LateContext, expr: &Expr) -> bool { /// Get an `AssociatedItem` and return true if it matches `is_empty(self)`. fn is_is_empty(cx: &LateContext, item: &ty::AssociatedItem) -> bool { if let ty::AssociatedKind::Method = item.kind { if item.name == "is_empty" { let sig = cx.tcx.fn_sig(item.def_id); let ty = sig.skip_binder(); ty.inputs().len() == 1 } else { false } } else { false } } /// Check the inherent impl's items for an `is_empty(self)` method. fn has_is_empty_impl(cx: &LateContext, id: DefId) -> bool { cx.tcx.inherent_impls(id).iter().any(|imp| { cx.tcx .associated_items(*imp) .any(|item| is_is_empty(cx, &item)) }) } let ty = &walk_ptrs_ty(cx.tables.expr_ty(expr)); match ty.sty { ty::TyDynamic(..) => cx.tcx .associated_items(ty.ty_to_def_id().expect("trait impl not found")) .any(|item| is_is_empty(cx, &item)), ty::TyProjection(_) => ty.ty_to_def_id() .map_or(false, |id| has_is_empty_impl(cx, id)), ty::TyAdt(id, _) => has_is_empty_impl(cx, id.did), ty::TyArray(..) | ty::TySlice(..) | ty::TyStr => true, _ => false, } }