| use crate::utils::{get_item_name, snippet_with_applicability, span_lint, span_lint_and_sugg, walk_ptrs_ty}; |
| use rustc::hir::def_id::DefId; |
| use rustc::hir::*; |
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| use rustc::ty; |
| use rustc::{declare_lint_pass, declare_tool_lint}; |
| use rustc_data_structures::fx::FxHashSet; |
| use rustc_errors::Applicability; |
| use syntax::ast::{LitKind, Name}; |
| use syntax::source_map::{Span, Spanned}; |
| |
| declare_clippy_lint! { |
| /// **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:** |
| /// ```ignore |
| /// if x.len() == 0 { |
| /// .. |
| /// } |
| /// if y.len() != 0 { |
| /// .. |
| /// } |
| /// ``` |
| /// instead use |
| /// ```ignore |
| /// if x.is_empty() { |
| /// .. |
| /// } |
| /// if !y.is_empty() { |
| /// .. |
| /// } |
| /// ``` |
| pub LEN_ZERO, |
| style, |
| "checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead" |
| } |
| |
| declare_clippy_lint! { |
| /// **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:** |
| /// ```ignore |
| /// impl X { |
| /// pub fn len(&self) -> usize { |
| /// .. |
| /// } |
| /// } |
| /// ``` |
| pub LEN_WITHOUT_IS_EMPTY, |
| style, |
| "traits or impls with a public `len` method but no corresponding `is_empty` method" |
| } |
| |
| declare_lint_pass!(LenZero => [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 item.span.from_expansion() { |
| return; |
| } |
| |
| match item.kind { |
| ItemKind::Trait(_, _, _, _, ref trait_items) => check_trait_items(cx, item, trait_items), |
| ItemKind::Impl(_, _, _, _, None, _, ref impl_items) => check_impl_items(cx, item, impl_items), |
| _ => (), |
| } |
| } |
| |
| fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { |
| if expr.span.from_expansion() { |
| return; |
| } |
| |
| if let ExprKind::Binary(Spanned { node: cmp, .. }, ref left, ref right) = expr.kind { |
| match cmp { |
| BinOpKind::Eq => { |
| check_cmp(cx, expr.span, left, right, "", 0); // len == 0 |
| check_cmp(cx, expr.span, right, left, "", 0); // 0 == len |
| }, |
| BinOpKind::Ne => { |
| check_cmp(cx, expr.span, left, right, "!", 0); // len != 0 |
| check_cmp(cx, expr.span, right, left, "!", 0); // 0 != len |
| }, |
| BinOpKind::Gt => { |
| check_cmp(cx, expr.span, left, right, "!", 0); // len > 0 |
| check_cmp(cx, expr.span, right, left, "", 1); // 1 > len |
| }, |
| BinOpKind::Lt => { |
| check_cmp(cx, expr.span, left, right, "", 1); // len < 1 |
| check_cmp(cx, expr.span, right, left, "!", 0); // 0 < len |
| }, |
| BinOpKind::Ge => check_cmp(cx, expr.span, left, right, "!", 1), // len >= 1 |
| BinOpKind::Le => 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.ident.name.as_str() == name |
| && if let AssocItemKind::Method { has_self } = item.kind { |
| has_self && { |
| let did = cx.tcx.hir().local_def_id(item.id.hir_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 FxHashSet<DefId>, 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.hir_id) && trait_items.iter().any(|i| is_named_self(cx, i, "len")) { |
| let mut current_and_super_traits = FxHashSet::default(); |
| let visited_trait_def_id = cx.tcx.hir().local_def_id(visited_trait.hir_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::AssocKind::Method |
| && i.method_has_self_argument |
| && i.ident.name == sym!(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.ident.name |
| ), |
| ); |
| } |
| } |
| } |
| |
| fn check_impl_items(cx: &LateContext<'_, '_>, item: &Item, impl_items: &[ImplItemRef]) { |
| fn is_named_self(cx: &LateContext<'_, '_>, item: &ImplItemRef, name: &str) -> bool { |
| item.ident.name.as_str() == name |
| && if let AssocItemKind::Method { has_self } = item.kind { |
| has_self && { |
| let did = cx.tcx.hir().local_def_id(item.id.hir_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.hir_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.hir_id) { |
| let def_id = cx.tcx.hir().local_def_id(item.hir_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 (&ExprKind::MethodCall(ref method_path, _, ref args), &ExprKind::Lit(ref lit)) = (&method.kind, &lit.kind) { |
| // check if we are in an is_empty() method |
| if let Some(name) = get_item_name(cx, method) { |
| if name.as_str() == "is_empty" { |
| return; |
| } |
| } |
| |
| check_len(cx, span, method_path.ident.name, args, &lit.node, op, compare_to) |
| } |
| } |
| |
| fn check_len( |
| cx: &LateContext<'_, '_>, |
| span: Span, |
| method_name: Name, |
| args: &[Expr], |
| lit: &LitKind, |
| op: &str, |
| compare_to: u32, |
| ) { |
| if let LitKind::Int(lit, _) = *lit { |
| // check if length is compared to the specified number |
| if lit != u128::from(compare_to) { |
| return; |
| } |
| |
| if method_name.as_str() == "len" && args.len() == 1 && has_is_empty(cx, &args[0]) { |
| let mut applicability = Applicability::MachineApplicable; |
| span_lint_and_sugg( |
| cx, |
| LEN_ZERO, |
| span, |
| &format!("length comparison to {}", if compare_to == 0 { "zero" } else { "one" }), |
| &format!("using `{}is_empty` is clearer and more explicit", op), |
| format!( |
| "{}{}.is_empty()", |
| op, |
| snippet_with_applicability(cx, args[0].span, "_", &mut applicability) |
| ), |
| applicability, |
| ); |
| } |
| } |
| } |
| |
| /// Checks if this type has an `is_empty` method. |
| fn has_is_empty(cx: &LateContext<'_, '_>, expr: &Expr) -> bool { |
| /// Gets an `AssocItem` and return true if it matches `is_empty(self)`. |
| fn is_is_empty(cx: &LateContext<'_, '_>, item: &ty::AssocItem) -> bool { |
| if let ty::AssocKind::Method = item.kind { |
| if item.ident.name.as_str() == "is_empty" { |
| let sig = cx.tcx.fn_sig(item.def_id); |
| let ty = sig.skip_binder(); |
| ty.inputs().len() == 1 |
| } else { |
| false |
| } |
| } else { |
| false |
| } |
| } |
| |
| /// Checks 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.kind { |
| ty::Dynamic(ref tt, ..) => { |
| if let Some(principal) = tt.principal() { |
| cx.tcx |
| .associated_items(principal.def_id()) |
| .any(|item| is_is_empty(cx, &item)) |
| } else { |
| false |
| } |
| }, |
| ty::Projection(ref proj) => has_is_empty_impl(cx, proj.item_def_id), |
| ty::Adt(id, _) => has_is_empty_impl(cx, id.did), |
| ty::Array(..) | ty::Slice(..) | ty::Str => true, |
| _ => false, |
| } |
| } |