250 lines
8.4 KiB
Rust
250 lines
8.4 KiB
Rust
use rustc::lint::*;
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use rustc::hir::def_id::DefId;
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use rustc::ty;
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use rustc::hir::*;
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use std::collections::HashSet;
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use syntax::ast::{Lit, LitKind, Name};
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use syntax::codemap::{Span, Spanned};
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use utils::{get_item_name, in_macro, snippet, span_lint, span_lint_and_sugg, walk_ptrs_ty};
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/// **What it does:** 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?** Some structures can answer `.is_empty()` much faster
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/// than calculating their length. Notably, for slices, getting the length
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/// requires a subtraction whereas `.is_empty()` is just a comparison. So it is
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/// good to get into the habit of using `.is_empty()`, and having it is cheap.
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/// Besides, it makes the intent clearer than a manual comparison.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// if x.len() == 0 { .. }
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/// ```
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declare_lint! {
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pub LEN_ZERO,
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Warn,
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"checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` \
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could be used instead"
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}
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/// **What it does:** 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?** 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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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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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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declare_lint! {
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pub LEN_WITHOUT_IS_EMPTY,
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Warn,
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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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#[derive(Copy, Clone)]
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pub struct LenZero;
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impl LintPass for LenZero {
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fn get_lints(&self) -> LintArray {
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lint_array!(LEN_ZERO, LEN_WITHOUT_IS_EMPTY)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LenZero {
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fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
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if in_macro(item.span) {
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return;
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}
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match item.node {
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ItemTrait(_, _, _, _, ref trait_items) => check_trait_items(cx, item, trait_items),
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ItemImpl(_, _, _, _, None, _, ref impl_items) => check_impl_items(cx, item, impl_items),
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_ => (),
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}
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}
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if in_macro(expr.span) {
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return;
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}
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if let ExprBinary(Spanned { node: cmp, .. }, ref left, ref right) = expr.node {
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match cmp {
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BiEq => check_cmp(cx, expr.span, left, right, ""),
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BiGt | BiNe => check_cmp(cx, expr.span, left, right, "!"),
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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 check_trait_items(cx: &LateContext, visited_trait: &Item, trait_items: &[TraitItemRef]) {
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fn is_named_self(cx: &LateContext, item: &TraitItemRef, name: &str) -> bool {
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item.name == name && if let AssociatedItemKind::Method { has_self } = item.kind {
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has_self && {
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let did = cx.tcx.hir.local_def_id(item.id.node_id);
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cx.tcx.fn_sig(did).inputs().skip_binder().len() == 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 HashSet<DefId>, cx: &LateContext) {
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if set.insert(traitt) {
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for supertrait in ::rustc::traits::supertrait_def_ids(cx.tcx, 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.access_levels.is_exported(visited_trait.id) && trait_items.iter().any(|i| is_named_self(cx, i, "len")) {
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let mut current_and_super_traits = HashSet::new();
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let visited_trait_def_id = cx.tcx.hir.local_def_id(visited_trait.id);
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fill_trait_set(visited_trait_def_id, &mut current_and_super_traits, cx);
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let is_empty_method_found = current_and_super_traits
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.iter()
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.flat_map(|&i| cx.tcx.associated_items(i))
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.any(|i| {
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i.kind == ty::AssociatedKind::Method && i.method_has_self_argument && i.name == "is_empty"
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&& cx.tcx.fn_sig(i.def_id).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.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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fn check_impl_items(cx: &LateContext, item: &Item, impl_items: &[ImplItemRef]) {
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fn is_named_self(cx: &LateContext, item: &ImplItemRef, name: &str) -> bool {
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item.name == name && if let AssociatedItemKind::Method { has_self } = item.kind {
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has_self && {
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let did = cx.tcx.hir.local_def_id(item.id.node_id);
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cx.tcx.fn_sig(did).inputs().skip_binder().len() == 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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let is_empty = if let Some(is_empty) = impl_items.iter().find(|i| is_named_self(cx, i, "is_empty")) {
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if cx.access_levels.is_exported(is_empty.id.node_id) {
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return;
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} else {
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"a private"
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}
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} else {
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"no corresponding"
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};
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if let Some(i) = impl_items.iter().find(|i| is_named_self(cx, i, "len")) {
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if cx.access_levels.is_exported(i.id.node_id) {
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let def_id = cx.tcx.hir.local_def_id(item.id);
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let ty = cx.tcx.type_of(def_id);
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span_lint(
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cx,
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LEN_WITHOUT_IS_EMPTY,
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item.span,
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&format!("item `{}` has a public `len` method but {} `is_empty` method", ty, is_empty),
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);
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}
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}
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}
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fn check_cmp(cx: &LateContext, span: Span, left: &Expr, right: &Expr, op: &str) {
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// check if we are in an is_empty() method
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if let Some(name) = get_item_name(cx, left) {
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if name == "is_empty" {
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return;
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}
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}
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match (&left.node, &right.node) {
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(&ExprLit(ref lit), &ExprMethodCall(ref method_path, _, ref args)) |
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(&ExprMethodCall(ref method_path, _, ref args), &ExprLit(ref lit)) => {
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check_len_zero(cx, span, method_path.name, args, lit, op)
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},
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_ => (),
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}
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}
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fn check_len_zero(cx: &LateContext, span: Span, name: Name, args: &[Expr], lit: &Lit, op: &str) {
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if let Spanned {
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node: LitKind::Int(0, _),
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..
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} = *lit
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{
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if name == "len" && args.len() == 1 && has_is_empty(cx, &args[0]) {
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span_lint_and_sugg(
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cx,
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LEN_ZERO,
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span,
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"length comparison to zero",
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"using `is_empty` is more concise",
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format!("{}{}.is_empty()", op, snippet(cx, args[0].span, "_")),
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);
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}
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}
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}
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/// Check if this type has an `is_empty` method.
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fn has_is_empty(cx: &LateContext, expr: &Expr) -> bool {
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/// Get an `AssociatedItem` and return true if it matches `is_empty(self)`.
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fn is_is_empty(cx: &LateContext, item: &ty::AssociatedItem) -> bool {
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if let ty::AssociatedKind::Method = item.kind {
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if item.name == "is_empty" {
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let sig = cx.tcx.fn_sig(item.def_id);
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let ty = sig.skip_binder();
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ty.inputs().len() == 1
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} else {
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false
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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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/// Check the inherent impl's items for an `is_empty(self)` method.
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fn has_is_empty_impl(cx: &LateContext, id: DefId) -> bool {
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cx.tcx.inherent_impls(id).iter().any(|imp| {
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cx.tcx
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.associated_items(*imp)
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.any(|item| is_is_empty(cx, &item))
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})
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}
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let ty = &walk_ptrs_ty(cx.tables.expr_ty(expr));
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match ty.sty {
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ty::TyDynamic(..) => cx.tcx
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.associated_items(ty.ty_to_def_id().expect("trait impl not found"))
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.any(|item| is_is_empty(cx, &item)),
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ty::TyProjection(_) => ty.ty_to_def_id()
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.map_or(false, |id| has_is_empty_impl(cx, id)),
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ty::TyAdt(id, _) => has_is_empty_impl(cx, id.did),
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ty::TyArray(..) | ty::TySlice(..) | ty::TyStr => true,
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_ => false,
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}
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}
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