| use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then}; |
| use clippy_utils::source::snippet_with_context; |
| use clippy_utils::sugg::Sugg; |
| use clippy_utils::{get_item_name, get_parent_as_impl, is_lint_allowed, peel_ref_operators}; |
| use if_chain::if_chain; |
| use rustc_ast::ast::LitKind; |
| use rustc_errors::Applicability; |
| use rustc_hir::def::Res; |
| use rustc_hir::def_id::{DefId, DefIdSet}; |
| use rustc_hir::{ |
| AssocItemKind, BinOpKind, Expr, ExprKind, FnRetTy, GenericArg, GenericBound, ImplItem, ImplItemKind, |
| ImplicitSelfKind, Item, ItemKind, LangItem, Mutability, Node, PatKind, PathSegment, PrimTy, QPath, TraitItemRef, |
| TyKind, TypeBindingKind, |
| }; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::ty::{self, AssocKind, FnSig, Ty}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::source_map::{Span, Spanned, Symbol}; |
| use rustc_span::symbol::sym; |
| |
| 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. 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 in some contexts. |
| /// |
| /// ### Example |
| /// ```ignore |
| /// if x.len() == 0 { |
| /// .. |
| /// } |
| /// if y.len() != 0 { |
| /// .. |
| /// } |
| /// ``` |
| /// instead use |
| /// ```ignore |
| /// if x.is_empty() { |
| /// .. |
| /// } |
| /// if !y.is_empty() { |
| /// .. |
| /// } |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| 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. |
| /// |
| /// ### Example |
| /// ```ignore |
| /// impl X { |
| /// pub fn len(&self) -> usize { |
| /// .. |
| /// } |
| /// } |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| pub LEN_WITHOUT_IS_EMPTY, |
| style, |
| "traits or impls with a public `len` method but no corresponding `is_empty` method" |
| } |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks for comparing to an empty slice such as `""` or `[]`, |
| /// and suggests using `.is_empty()` where applicable. |
| /// |
| /// ### Why is this bad? |
| /// Some structures can answer `.is_empty()` much faster |
| /// than checking for equality. 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 in some contexts. |
| /// |
| /// ### Example |
| /// |
| /// ```ignore |
| /// if s == "" { |
| /// .. |
| /// } |
| /// |
| /// if arr == [] { |
| /// .. |
| /// } |
| /// ``` |
| /// Use instead: |
| /// ```ignore |
| /// if s.is_empty() { |
| /// .. |
| /// } |
| /// |
| /// if arr.is_empty() { |
| /// .. |
| /// } |
| /// ``` |
| #[clippy::version = "1.49.0"] |
| pub COMPARISON_TO_EMPTY, |
| style, |
| "checking `x == \"\"` or `x == []` (or similar) when `.is_empty()` could be used instead" |
| } |
| |
| declare_lint_pass!(LenZero => [LEN_ZERO, LEN_WITHOUT_IS_EMPTY, COMPARISON_TO_EMPTY]); |
| |
| impl<'tcx> LateLintPass<'tcx> for LenZero { |
| fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) { |
| if item.span.from_expansion() { |
| return; |
| } |
| |
| if let ItemKind::Trait(_, _, _, _, trait_items) = item.kind { |
| check_trait_items(cx, item, trait_items); |
| } |
| } |
| |
| fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) { |
| if_chain! { |
| if item.ident.name == sym::len; |
| if let ImplItemKind::Fn(sig, _) = &item.kind; |
| if sig.decl.implicit_self.has_implicit_self(); |
| if sig.decl.inputs.len() == 1; |
| if cx.effective_visibilities.is_exported(item.owner_id.def_id); |
| if matches!(sig.decl.output, FnRetTy::Return(_)); |
| if let Some(imp) = get_parent_as_impl(cx.tcx, item.hir_id()); |
| if imp.of_trait.is_none(); |
| if let TyKind::Path(ty_path) = &imp.self_ty.kind; |
| if let Some(ty_id) = cx.qpath_res(ty_path, imp.self_ty.hir_id).opt_def_id(); |
| if let Some(local_id) = ty_id.as_local(); |
| let ty_hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_id); |
| if !is_lint_allowed(cx, LEN_WITHOUT_IS_EMPTY, ty_hir_id); |
| if let Some(output) = parse_len_output( |
| cx, |
| cx.tcx.fn_sig(item.owner_id).instantiate_identity().skip_binder() |
| ); |
| then { |
| let (name, kind) = match cx.tcx.hir().find(ty_hir_id) { |
| Some(Node::ForeignItem(x)) => (x.ident.name, "extern type"), |
| Some(Node::Item(x)) => match x.kind { |
| ItemKind::Struct(..) => (x.ident.name, "struct"), |
| ItemKind::Enum(..) => (x.ident.name, "enum"), |
| ItemKind::Union(..) => (x.ident.name, "union"), |
| _ => (x.ident.name, "type"), |
| } |
| _ => return, |
| }; |
| check_for_is_empty(cx, sig.span, sig.decl.implicit_self, output, ty_id, name, kind) |
| } |
| } |
| } |
| |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| if expr.span.from_expansion() { |
| return; |
| } |
| |
| if let ExprKind::Let(lt) = expr.kind |
| && has_is_empty(cx, lt.init) |
| && match lt.pat.kind { |
| PatKind::Slice([], None, []) => true, |
| PatKind::Lit(lit) if is_empty_string(lit) => true, |
| _ => false, |
| } |
| { |
| let mut applicability = Applicability::MachineApplicable; |
| |
| let lit1 = peel_ref_operators(cx, lt.init); |
| let lit_str = |
| Sugg::hir_with_context(cx, lit1, lt.span.ctxt(), "_", &mut applicability).maybe_par(); |
| |
| span_lint_and_sugg( |
| cx, |
| COMPARISON_TO_EMPTY, |
| lt.span, |
| "comparison to empty slice using `if let`", |
| "using `is_empty` is clearer and more explicit", |
| format!("{lit_str}.is_empty()"), |
| applicability, |
| ); |
| } |
| |
| if let ExprKind::Binary(Spanned { node: cmp, .. }, left, right) = expr.kind { |
| // expr.span might contains parenthesis, see issue #10529 |
| let actual_span = left.span.with_hi(right.span.hi()); |
| match cmp { |
| BinOpKind::Eq => { |
| check_cmp(cx, actual_span, left, right, "", 0); // len == 0 |
| check_cmp(cx, actual_span, right, left, "", 0); // 0 == len |
| }, |
| BinOpKind::Ne => { |
| check_cmp(cx, actual_span, left, right, "!", 0); // len != 0 |
| check_cmp(cx, actual_span, right, left, "!", 0); // 0 != len |
| }, |
| BinOpKind::Gt => { |
| check_cmp(cx, actual_span, left, right, "!", 0); // len > 0 |
| check_cmp(cx, actual_span, right, left, "", 1); // 1 > len |
| }, |
| BinOpKind::Lt => { |
| check_cmp(cx, actual_span, left, right, "", 1); // len < 1 |
| check_cmp(cx, actual_span, right, left, "!", 0); // 0 < len |
| }, |
| BinOpKind::Ge => check_cmp(cx, actual_span, left, right, "!", 1), // len >= 1 |
| BinOpKind::Le => check_cmp(cx, actual_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: Symbol) -> bool { |
| item.ident.name == name |
| && if let AssocItemKind::Fn { has_self } = item.kind { |
| has_self && { |
| cx.tcx |
| .fn_sig(item.id.owner_id) |
| .skip_binder() |
| .inputs() |
| .skip_binder() |
| .len() |
| == 1 |
| } |
| } else { |
| false |
| } |
| } |
| |
| // fill the set with current and super traits |
| fn fill_trait_set(traitt: DefId, set: &mut DefIdSet, cx: &LateContext<'_>) { |
| if set.insert(traitt) { |
| for supertrait in rustc_trait_selection::traits::supertrait_def_ids(cx.tcx, traitt) { |
| fill_trait_set(supertrait, set, cx); |
| } |
| } |
| } |
| |
| if cx.effective_visibilities.is_exported(visited_trait.owner_id.def_id) |
| && trait_items.iter().any(|i| is_named_self(cx, i, sym::len)) |
| { |
| let mut current_and_super_traits = DefIdSet::default(); |
| fill_trait_set(visited_trait.owner_id.to_def_id(), &mut current_and_super_traits, cx); |
| let is_empty = sym!(is_empty); |
| |
| let is_empty_method_found = current_and_super_traits |
| .items() |
| .flat_map(|&i| cx.tcx.associated_items(i).filter_by_name_unhygienic(is_empty)) |
| .any(|i| { |
| i.kind == ty::AssocKind::Fn |
| && i.fn_has_self_parameter |
| && cx.tcx.fn_sig(i.def_id).skip_binder().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 |
| ), |
| ); |
| } |
| } |
| } |
| |
| #[derive(Debug, Clone, Copy)] |
| enum LenOutput { |
| Integral, |
| Option(DefId), |
| Result(DefId), |
| } |
| |
| fn extract_future_output<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<&'tcx PathSegment<'tcx>> { |
| if let ty::Alias(_, alias_ty) = ty.kind() && |
| let Some(Node::Item(item)) = cx.tcx.hir().get_if_local(alias_ty.def_id) && |
| let Item { kind: ItemKind::OpaqueTy(opaque), .. } = item && |
| opaque.bounds.len() == 1 && |
| let GenericBound::LangItemTrait(LangItem::Future, _, _, generic_args) = &opaque.bounds[0] && |
| generic_args.bindings.len() == 1 && |
| let TypeBindingKind::Equality { |
| term: rustc_hir::Term::Ty(rustc_hir::Ty {kind: TyKind::Path(QPath::Resolved(_, path)), .. }), |
| } = &generic_args.bindings[0].kind && |
| path.segments.len() == 1 { |
| return Some(&path.segments[0]); |
| } |
| |
| None |
| } |
| |
| fn is_first_generic_integral<'tcx>(segment: &'tcx PathSegment<'tcx>) -> bool { |
| if let Some(generic_args) = segment.args { |
| if generic_args.args.is_empty() { |
| return false; |
| } |
| let arg = &generic_args.args[0]; |
| if let GenericArg::Type(rustc_hir::Ty { |
| kind: TyKind::Path(QPath::Resolved(_, path)), |
| .. |
| }) = arg |
| { |
| let segments = &path.segments; |
| let segment = &segments[0]; |
| let res = &segment.res; |
| if matches!(res, Res::PrimTy(PrimTy::Uint(_))) || matches!(res, Res::PrimTy(PrimTy::Int(_))) { |
| return true; |
| } |
| } |
| } |
| |
| false |
| } |
| |
| fn parse_len_output<'tcx>(cx: &LateContext<'tcx>, sig: FnSig<'tcx>) -> Option<LenOutput> { |
| if let Some(segment) = extract_future_output(cx, sig.output()) { |
| let res = segment.res; |
| |
| if matches!(res, Res::PrimTy(PrimTy::Uint(_))) || matches!(res, Res::PrimTy(PrimTy::Int(_))) { |
| return Some(LenOutput::Integral); |
| } |
| |
| if let Res::Def(_, def_id) = res { |
| if cx.tcx.is_diagnostic_item(sym::Option, def_id) && is_first_generic_integral(segment) { |
| return Some(LenOutput::Option(def_id)); |
| } else if cx.tcx.is_diagnostic_item(sym::Result, def_id) && is_first_generic_integral(segment) { |
| return Some(LenOutput::Result(def_id)); |
| } |
| } |
| |
| return None; |
| } |
| |
| match *sig.output().kind() { |
| ty::Int(_) | ty::Uint(_) => Some(LenOutput::Integral), |
| ty::Adt(adt, subs) if cx.tcx.is_diagnostic_item(sym::Option, adt.did()) => { |
| subs.type_at(0).is_integral().then(|| LenOutput::Option(adt.did())) |
| }, |
| ty::Adt(adt, subs) if cx.tcx.is_diagnostic_item(sym::Result, adt.did()) => { |
| subs.type_at(0).is_integral().then(|| LenOutput::Result(adt.did())) |
| }, |
| _ => None, |
| } |
| } |
| |
| impl LenOutput { |
| fn matches_is_empty_output<'tcx>(self, cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool { |
| if let Some(segment) = extract_future_output(cx, ty) { |
| return match (self, segment.res) { |
| (_, Res::PrimTy(PrimTy::Bool)) => true, |
| (Self::Option(_), Res::Def(_, def_id)) if cx.tcx.is_diagnostic_item(sym::Option, def_id) => true, |
| (Self::Result(_), Res::Def(_, def_id)) if cx.tcx.is_diagnostic_item(sym::Result, def_id) => true, |
| _ => false, |
| }; |
| } |
| |
| match (self, ty.kind()) { |
| (_, &ty::Bool) => true, |
| (Self::Option(id), &ty::Adt(adt, subs)) if id == adt.did() => subs.type_at(0).is_bool(), |
| (Self::Result(id), &ty::Adt(adt, subs)) if id == adt.did() => subs.type_at(0).is_bool(), |
| _ => false, |
| } |
| } |
| |
| fn expected_sig(self, self_kind: ImplicitSelfKind) -> String { |
| let self_ref = match self_kind { |
| ImplicitSelfKind::ImmRef => "&", |
| ImplicitSelfKind::MutRef => "&mut ", |
| _ => "", |
| }; |
| match self { |
| Self::Integral => format!("expected signature: `({self_ref}self) -> bool`"), |
| Self::Option(_) => { |
| format!("expected signature: `({self_ref}self) -> bool` or `({self_ref}self) -> Option<bool>") |
| }, |
| Self::Result(..) => { |
| format!("expected signature: `({self_ref}self) -> bool` or `({self_ref}self) -> Result<bool>") |
| }, |
| } |
| } |
| } |
| |
| /// Checks if the given signature matches the expectations for `is_empty` |
| fn check_is_empty_sig<'tcx>( |
| cx: &LateContext<'tcx>, |
| sig: FnSig<'tcx>, |
| self_kind: ImplicitSelfKind, |
| len_output: LenOutput, |
| ) -> bool { |
| match &**sig.inputs_and_output { |
| [arg, res] if len_output.matches_is_empty_output(cx, *res) => { |
| matches!( |
| (arg.kind(), self_kind), |
| (ty::Ref(_, _, Mutability::Not), ImplicitSelfKind::ImmRef) |
| | (ty::Ref(_, _, Mutability::Mut), ImplicitSelfKind::MutRef) |
| ) || (!arg.is_ref() && matches!(self_kind, ImplicitSelfKind::Imm | ImplicitSelfKind::Mut)) |
| }, |
| _ => false, |
| } |
| } |
| |
| /// Checks if the given type has an `is_empty` method with the appropriate signature. |
| fn check_for_is_empty( |
| cx: &LateContext<'_>, |
| span: Span, |
| self_kind: ImplicitSelfKind, |
| output: LenOutput, |
| impl_ty: DefId, |
| item_name: Symbol, |
| item_kind: &str, |
| ) { |
| let is_empty = Symbol::intern("is_empty"); |
| let is_empty = cx |
| .tcx |
| .inherent_impls(impl_ty) |
| .iter() |
| .flat_map(|&id| cx.tcx.associated_items(id).filter_by_name_unhygienic(is_empty)) |
| .find(|item| item.kind == AssocKind::Fn); |
| |
| let (msg, is_empty_span, self_kind) = match is_empty { |
| None => ( |
| format!( |
| "{item_kind} `{}` has a public `len` method, but no `is_empty` method", |
| item_name.as_str(), |
| ), |
| None, |
| None, |
| ), |
| Some(is_empty) if !cx.effective_visibilities.is_exported(is_empty.def_id.expect_local()) => ( |
| format!( |
| "{item_kind} `{}` has a public `len` method, but a private `is_empty` method", |
| item_name.as_str(), |
| ), |
| Some(cx.tcx.def_span(is_empty.def_id)), |
| None, |
| ), |
| Some(is_empty) |
| if !(is_empty.fn_has_self_parameter |
| && check_is_empty_sig( |
| cx, |
| cx.tcx.fn_sig(is_empty.def_id).instantiate_identity().skip_binder(), |
| self_kind, |
| output, |
| )) => |
| { |
| ( |
| format!( |
| "{item_kind} `{}` has a public `len` method, but the `is_empty` method has an unexpected signature", |
| item_name.as_str(), |
| ), |
| Some(cx.tcx.def_span(is_empty.def_id)), |
| Some(self_kind), |
| ) |
| }, |
| Some(_) => return, |
| }; |
| |
| span_lint_and_then(cx, LEN_WITHOUT_IS_EMPTY, span, &msg, |db| { |
| if let Some(span) = is_empty_span { |
| db.span_note(span, "`is_empty` defined here"); |
| } |
| if let Some(self_kind) = self_kind { |
| db.note(output.expected_sig(self_kind)); |
| } |
| }); |
| } |
| |
| fn check_cmp(cx: &LateContext<'_>, span: Span, method: &Expr<'_>, lit: &Expr<'_>, op: &str, compare_to: u32) { |
| if let (&ExprKind::MethodCall(method_path, receiver, args, _), ExprKind::Lit(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, |
| receiver, |
| args, |
| &lit.node, |
| op, |
| compare_to, |
| ); |
| } else { |
| check_empty_expr(cx, span, method, lit, op); |
| } |
| } |
| |
| // FIXME(flip1995): Figure out how to reduce the number of arguments |
| #[allow(clippy::too_many_arguments)] |
| fn check_len( |
| cx: &LateContext<'_>, |
| span: Span, |
| method_name: Symbol, |
| receiver: &Expr<'_>, |
| 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 == sym::len && args.is_empty() && has_is_empty(cx, receiver) { |
| 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 `{op}is_empty` is clearer and more explicit"), |
| format!( |
| "{op}{}.is_empty()", |
| snippet_with_context(cx, receiver.span, span.ctxt(), "_", &mut applicability).0, |
| ), |
| applicability, |
| ); |
| } |
| } |
| } |
| |
| fn check_empty_expr(cx: &LateContext<'_>, span: Span, lit1: &Expr<'_>, lit2: &Expr<'_>, op: &str) { |
| if (is_empty_array(lit2) || is_empty_string(lit2)) && has_is_empty(cx, lit1) { |
| let mut applicability = Applicability::MachineApplicable; |
| |
| let lit1 = peel_ref_operators(cx, lit1); |
| let lit_str = Sugg::hir_with_context(cx, lit1, span.ctxt(), "_", &mut applicability).maybe_par(); |
| |
| span_lint_and_sugg( |
| cx, |
| COMPARISON_TO_EMPTY, |
| span, |
| "comparison to empty slice", |
| &format!("using `{op}is_empty` is clearer and more explicit"), |
| format!("{op}{lit_str}.is_empty()"), |
| applicability, |
| ); |
| } |
| } |
| |
| fn is_empty_string(expr: &Expr<'_>) -> bool { |
| if let ExprKind::Lit(lit) = expr.kind { |
| if let LitKind::Str(lit, _) = lit.node { |
| let lit = lit.as_str(); |
| return lit.is_empty(); |
| } |
| } |
| false |
| } |
| |
| fn is_empty_array(expr: &Expr<'_>) -> bool { |
| if let ExprKind::Array(arr) = expr.kind { |
| return arr.is_empty(); |
| } |
| false |
| } |
| |
| /// 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 item.kind == ty::AssocKind::Fn { |
| let sig = cx.tcx.fn_sig(item.def_id).skip_binder(); |
| let ty = sig.skip_binder(); |
| ty.inputs().len() == 1 |
| } else { |
| false |
| } |
| } |
| |
| /// Checks the inherent impl's items for an `is_empty(self)` method. |
| fn has_is_empty_impl(cx: &LateContext<'_>, id: DefId) -> bool { |
| let is_empty = sym!(is_empty); |
| cx.tcx.inherent_impls(id).iter().any(|imp| { |
| cx.tcx |
| .associated_items(*imp) |
| .filter_by_name_unhygienic(is_empty) |
| .any(|item| is_is_empty(cx, item)) |
| }) |
| } |
| |
| let ty = &cx.typeck_results().expr_ty(expr).peel_refs(); |
| match ty.kind() { |
| ty::Dynamic(tt, ..) => tt.principal().map_or(false, |principal| { |
| let is_empty = sym!(is_empty); |
| cx.tcx |
| .associated_items(principal.def_id()) |
| .filter_by_name_unhygienic(is_empty) |
| .any(|item| is_is_empty(cx, item)) |
| }), |
| ty::Alias(ty::Projection, ref proj) => has_is_empty_impl(cx, proj.def_id), |
| ty::Adt(id, _) => has_is_empty_impl(cx, id.did()), |
| ty::Array(..) | ty::Slice(..) | ty::Str => true, |
| _ => false, |
| } |
| } |
