642 lines
22 KiB
Rust
642 lines
22 KiB
Rust
use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then};
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use clippy_utils::source::{snippet_opt, snippet_with_context};
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use clippy_utils::sugg::{has_enclosing_paren, Sugg};
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use clippy_utils::{get_item_name, get_parent_as_impl, is_lint_allowed, peel_ref_operators};
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use rustc_ast::ast::LitKind;
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use rustc_errors::Applicability;
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use rustc_hir::def::Res;
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use rustc_hir::def_id::{DefId, DefIdSet};
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use rustc_hir::{
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AssocItemKind, BinOpKind, Expr, ExprKind, FnRetTy, GenericArg, GenericBound, ImplItem, ImplItemKind,
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ImplicitSelfKind, Item, ItemKind, Mutability, Node, OpaqueTyOrigin, PatKind, PathSegment, PrimTy, QPath,
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TraitItemRef, TyKind,
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};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, AssocKind, FnSig, Ty};
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use rustc_session::declare_lint_pass;
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use rustc_span::source_map::Spanned;
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use rustc_span::symbol::sym;
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use rustc_span::{Span, Symbol};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for getting the length of something via `.len()`
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/// just to compare to zero, and suggests using `.is_empty()` where applicable.
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///
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/// ### Why is this bad?
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/// Some structures can answer `.is_empty()` much faster
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/// than calculating their length. So it is good to get into the habit of using
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/// `.is_empty()`, and having it is cheap.
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/// Besides, it makes the intent clearer than a manual comparison in some contexts.
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///
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/// ### Example
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/// ```ignore
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/// if x.len() == 0 {
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/// ..
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/// }
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/// if y.len() != 0 {
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/// ..
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/// }
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/// ```
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/// instead use
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/// ```ignore
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/// if x.is_empty() {
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/// ..
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/// }
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/// if !y.is_empty() {
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/// ..
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/// }
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub LEN_ZERO,
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style,
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"checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for items that implement `.len()` but not
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/// `.is_empty()`.
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///
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/// ### Why is this bad?
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/// It is good custom to have both methods, because for
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/// some data structures, asking about the length will be a costly operation,
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/// whereas `.is_empty()` can usually answer in constant time. Also it used to
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/// lead to false positives on the [`len_zero`](#len_zero) lint – currently that
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/// lint will ignore such entities.
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///
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/// ### Example
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/// ```ignore
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/// impl X {
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/// pub fn len(&self) -> usize {
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/// ..
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/// }
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/// }
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub LEN_WITHOUT_IS_EMPTY,
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style,
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"traits or impls with a public `len` method but no corresponding `is_empty` method"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for comparing to an empty slice such as `""` or `[]`,
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/// and suggests using `.is_empty()` where applicable.
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///
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/// ### Why is this bad?
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/// Some structures can answer `.is_empty()` much faster
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/// than checking for equality. So it is good to get into the habit of using
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/// `.is_empty()`, and having it is cheap.
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/// Besides, it makes the intent clearer than a manual comparison in some contexts.
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///
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/// ### Example
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///
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/// ```ignore
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/// if s == "" {
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/// ..
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/// }
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///
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/// if arr == [] {
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/// ..
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/// }
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/// ```
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/// Use instead:
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/// ```ignore
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/// if s.is_empty() {
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/// ..
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/// }
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///
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/// if arr.is_empty() {
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/// ..
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/// }
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/// ```
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#[clippy::version = "1.49.0"]
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pub COMPARISON_TO_EMPTY,
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style,
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"checking `x == \"\"` or `x == []` (or similar) when `.is_empty()` could be used instead"
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}
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declare_lint_pass!(LenZero => [LEN_ZERO, LEN_WITHOUT_IS_EMPTY, COMPARISON_TO_EMPTY]);
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impl<'tcx> LateLintPass<'tcx> for LenZero {
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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if let ItemKind::Trait(_, _, _, _, trait_items) = item.kind
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&& !item.span.from_expansion()
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{
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check_trait_items(cx, item, trait_items);
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
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if item.ident.name == sym::len
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&& let ImplItemKind::Fn(sig, _) = &item.kind
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&& sig.decl.implicit_self.has_implicit_self()
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&& sig.decl.inputs.len() == 1
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&& cx.effective_visibilities.is_exported(item.owner_id.def_id)
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&& matches!(sig.decl.output, FnRetTy::Return(_))
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&& let Some(imp) = get_parent_as_impl(cx.tcx, item.hir_id())
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&& imp.of_trait.is_none()
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&& let TyKind::Path(ty_path) = &imp.self_ty.kind
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&& let Some(ty_id) = cx.qpath_res(ty_path, imp.self_ty.hir_id).opt_def_id()
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&& let Some(local_id) = ty_id.as_local()
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&& let ty_hir_id = cx.tcx.local_def_id_to_hir_id(local_id)
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&& !is_lint_allowed(cx, LEN_WITHOUT_IS_EMPTY, ty_hir_id)
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&& let Some(output) =
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parse_len_output(cx, cx.tcx.fn_sig(item.owner_id).instantiate_identity().skip_binder())
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{
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let (name, kind) = match cx.tcx.hir_node(ty_hir_id) {
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Node::ForeignItem(x) => (x.ident.name, "extern type"),
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Node::Item(x) => match x.kind {
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ItemKind::Struct(..) => (x.ident.name, "struct"),
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ItemKind::Enum(..) => (x.ident.name, "enum"),
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ItemKind::Union(..) => (x.ident.name, "union"),
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_ => (x.ident.name, "type"),
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},
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_ => return,
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};
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check_for_is_empty(cx, sig.span, sig.decl.implicit_self, output, ty_id, name, kind);
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}
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}
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let ExprKind::Let(lt) = expr.kind
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&& match lt.pat.kind {
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PatKind::Slice([], None, []) => true,
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PatKind::Lit(lit) if is_empty_string(lit) => true,
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_ => false,
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}
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&& !expr.span.from_expansion()
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&& has_is_empty(cx, lt.init)
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{
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let mut applicability = Applicability::MachineApplicable;
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let lit1 = peel_ref_operators(cx, lt.init);
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let lit_str = Sugg::hir_with_context(cx, lit1, lt.span.ctxt(), "_", &mut applicability).maybe_par();
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span_lint_and_sugg(
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cx,
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COMPARISON_TO_EMPTY,
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lt.span,
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"comparison to empty slice using `if let`",
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"using `is_empty` is clearer and more explicit",
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format!("{lit_str}.is_empty()"),
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applicability,
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);
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}
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if let ExprKind::Binary(Spanned { node: cmp, .. }, left, right) = expr.kind
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&& !expr.span.from_expansion()
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{
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// expr.span might contains parenthesis, see issue #10529
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let actual_span = span_without_enclosing_paren(cx, expr.span);
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match cmp {
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BinOpKind::Eq => {
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check_cmp(cx, actual_span, left, right, "", 0); // len == 0
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check_cmp(cx, actual_span, right, left, "", 0); // 0 == len
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},
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BinOpKind::Ne => {
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check_cmp(cx, actual_span, left, right, "!", 0); // len != 0
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check_cmp(cx, actual_span, right, left, "!", 0); // 0 != len
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},
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BinOpKind::Gt => {
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check_cmp(cx, actual_span, left, right, "!", 0); // len > 0
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check_cmp(cx, actual_span, right, left, "", 1); // 1 > len
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},
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BinOpKind::Lt => {
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check_cmp(cx, actual_span, left, right, "", 1); // len < 1
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check_cmp(cx, actual_span, right, left, "!", 0); // 0 < len
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},
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BinOpKind::Ge => check_cmp(cx, actual_span, left, right, "!", 1), // len >= 1
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BinOpKind::Le => check_cmp(cx, actual_span, right, left, "!", 1), // 1 <= len
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_ => (),
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}
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}
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}
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}
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fn span_without_enclosing_paren(cx: &LateContext<'_>, span: Span) -> Span {
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let Some(snippet) = snippet_opt(cx, span) else {
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return span;
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};
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if has_enclosing_paren(snippet) {
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let source_map = cx.tcx.sess.source_map();
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let left_paren = source_map.start_point(span);
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let right_parent = source_map.end_point(span);
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left_paren.between(right_parent)
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} else {
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span
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}
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}
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fn check_trait_items(cx: &LateContext<'_>, visited_trait: &Item<'_>, trait_items: &[TraitItemRef]) {
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fn is_named_self(cx: &LateContext<'_>, item: &TraitItemRef, name: Symbol) -> bool {
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item.ident.name == name
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&& if let AssocItemKind::Fn { has_self } = item.kind {
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has_self && {
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cx.tcx
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.fn_sig(item.id.owner_id)
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.skip_binder()
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.inputs()
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.skip_binder()
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.len()
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== 1
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}
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} else {
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false
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}
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}
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// fill the set with current and super traits
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fn fill_trait_set(traitt: DefId, set: &mut DefIdSet, cx: &LateContext<'_>) {
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if set.insert(traitt) {
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for supertrait in cx.tcx.supertrait_def_ids(traitt) {
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fill_trait_set(supertrait, set, cx);
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}
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}
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}
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if cx.effective_visibilities.is_exported(visited_trait.owner_id.def_id)
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&& trait_items.iter().any(|i| is_named_self(cx, i, sym::len))
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{
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let mut current_and_super_traits = DefIdSet::default();
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fill_trait_set(visited_trait.owner_id.to_def_id(), &mut current_and_super_traits, cx);
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let is_empty = sym!(is_empty);
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let is_empty_method_found = current_and_super_traits
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.items()
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.flat_map(|&i| cx.tcx.associated_items(i).filter_by_name_unhygienic(is_empty))
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.any(|i| {
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i.kind == AssocKind::Fn
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&& i.fn_has_self_parameter
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&& cx.tcx.fn_sig(i.def_id).skip_binder().inputs().skip_binder().len() == 1
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});
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if !is_empty_method_found {
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span_lint(
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cx,
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LEN_WITHOUT_IS_EMPTY,
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visited_trait.span,
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format!(
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"trait `{}` has a `len` method but no (possibly inherited) `is_empty` method",
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visited_trait.ident.name
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),
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);
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}
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}
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}
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#[derive(Debug, Clone, Copy)]
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enum LenOutput {
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Integral,
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Option(DefId),
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Result(DefId),
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}
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fn extract_future_output<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<&'tcx PathSegment<'tcx>> {
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if let ty::Alias(_, alias_ty) = ty.kind()
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&& let Some(Node::Item(item)) = cx.tcx.hir().get_if_local(alias_ty.def_id)
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&& let Item {
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kind: ItemKind::OpaqueTy(opaque),
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..
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} = item
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&& let OpaqueTyOrigin::AsyncFn(_) = opaque.origin
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&& let [GenericBound::Trait(trait_ref, _)] = &opaque.bounds
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&& let Some(segment) = trait_ref.trait_ref.path.segments.last()
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&& let Some(generic_args) = segment.args
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&& let [constraint] = generic_args.constraints
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&& let Some(ty) = constraint.ty()
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&& let TyKind::Path(QPath::Resolved(_, path)) = ty.kind
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&& let [segment] = path.segments
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{
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return Some(segment);
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}
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None
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}
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fn is_first_generic_integral<'tcx>(segment: &'tcx PathSegment<'tcx>) -> bool {
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if let Some(generic_args) = segment.args {
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if generic_args.args.is_empty() {
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return false;
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}
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let arg = &generic_args.args[0];
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if let GenericArg::Type(rustc_hir::Ty {
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kind: TyKind::Path(QPath::Resolved(_, path)),
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..
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}) = arg
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{
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let segments = &path.segments;
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let segment = &segments[0];
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let res = &segment.res;
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if matches!(res, Res::PrimTy(PrimTy::Uint(_))) || matches!(res, Res::PrimTy(PrimTy::Int(_))) {
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return true;
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}
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}
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}
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false
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}
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fn parse_len_output<'tcx>(cx: &LateContext<'tcx>, sig: FnSig<'tcx>) -> Option<LenOutput> {
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if let Some(segment) = extract_future_output(cx, sig.output()) {
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let res = segment.res;
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if matches!(res, Res::PrimTy(PrimTy::Uint(_))) || matches!(res, Res::PrimTy(PrimTy::Int(_))) {
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return Some(LenOutput::Integral);
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}
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if let Res::Def(_, def_id) = res {
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if cx.tcx.is_diagnostic_item(sym::Option, def_id) && is_first_generic_integral(segment) {
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return Some(LenOutput::Option(def_id));
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} else if cx.tcx.is_diagnostic_item(sym::Result, def_id) && is_first_generic_integral(segment) {
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return Some(LenOutput::Result(def_id));
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}
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}
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return None;
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}
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match *sig.output().kind() {
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ty::Int(_) | ty::Uint(_) => Some(LenOutput::Integral),
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ty::Adt(adt, subs) if cx.tcx.is_diagnostic_item(sym::Option, adt.did()) => {
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subs.type_at(0).is_integral().then(|| LenOutput::Option(adt.did()))
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},
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ty::Adt(adt, subs) if cx.tcx.is_diagnostic_item(sym::Result, adt.did()) => {
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subs.type_at(0).is_integral().then(|| LenOutput::Result(adt.did()))
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},
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_ => None,
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}
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}
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impl LenOutput {
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fn matches_is_empty_output<'tcx>(self, cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
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if let Some(segment) = extract_future_output(cx, ty) {
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return match (self, segment.res) {
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(_, Res::PrimTy(PrimTy::Bool)) => true,
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(Self::Option(_), Res::Def(_, def_id)) if cx.tcx.is_diagnostic_item(sym::Option, def_id) => true,
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(Self::Result(_), Res::Def(_, def_id)) if cx.tcx.is_diagnostic_item(sym::Result, def_id) => true,
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_ => false,
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};
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}
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match (self, ty.kind()) {
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(_, &ty::Bool) => true,
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(Self::Option(id), &ty::Adt(adt, subs)) if id == adt.did() => subs.type_at(0).is_bool(),
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(Self::Result(id), &ty::Adt(adt, subs)) if id == adt.did() => subs.type_at(0).is_bool(),
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_ => false,
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}
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}
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fn expected_sig(self, self_kind: ImplicitSelfKind) -> String {
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let self_ref = match self_kind {
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ImplicitSelfKind::RefImm => "&",
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ImplicitSelfKind::RefMut => "&mut ",
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_ => "",
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};
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match self {
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Self::Integral => format!("expected signature: `({self_ref}self) -> bool`"),
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Self::Option(_) => {
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format!("expected signature: `({self_ref}self) -> bool` or `({self_ref}self) -> Option<bool>")
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},
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Self::Result(..) => {
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format!("expected signature: `({self_ref}self) -> bool` or `({self_ref}self) -> Result<bool>")
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},
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}
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}
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}
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/// Checks if the given signature matches the expectations for `is_empty`
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fn check_is_empty_sig<'tcx>(
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cx: &LateContext<'tcx>,
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sig: FnSig<'tcx>,
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self_kind: ImplicitSelfKind,
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len_output: LenOutput,
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) -> bool {
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match &**sig.inputs_and_output {
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[arg, res] if len_output.matches_is_empty_output(cx, *res) => {
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matches!(
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(arg.kind(), self_kind),
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(ty::Ref(_, _, Mutability::Not), ImplicitSelfKind::RefImm)
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| (ty::Ref(_, _, Mutability::Mut), ImplicitSelfKind::RefMut)
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) || (!arg.is_ref() && matches!(self_kind, ImplicitSelfKind::Imm | ImplicitSelfKind::Mut))
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},
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_ => false,
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}
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}
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/// Checks if the given type has an `is_empty` method with the appropriate signature.
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fn check_for_is_empty(
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cx: &LateContext<'_>,
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span: Span,
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self_kind: ImplicitSelfKind,
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output: LenOutput,
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impl_ty: DefId,
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item_name: Symbol,
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item_kind: &str,
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) {
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// Implementor may be a type alias, in which case we need to get the `DefId` of the aliased type to
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// find the correct inherent impls.
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let impl_ty = if let Some(adt) = cx.tcx.type_of(impl_ty).skip_binder().ty_adt_def() {
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adt.did()
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} else {
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return;
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};
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let is_empty = Symbol::intern("is_empty");
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let is_empty = cx
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.tcx
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.inherent_impls(impl_ty)
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.into_iter()
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.flatten()
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.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 method.span.from_expansion() {
|
||
return;
|
||
}
|
||
|
||
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 == 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).into_iter().flatten().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,
|
||
}
|
||
}
|