457 lines
16 KiB
Rust
457 lines
16 KiB
Rust
use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
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use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
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use clippy_utils::{SpanlessEq, SpanlessHash};
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use core::hash::{Hash, Hasher};
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use if_chain::if_chain;
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use itertools::Itertools;
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use rustc_data_structures::fx::{FxHashMap, FxHashSet};
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use rustc_data_structures::unhash::UnhashMap;
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use rustc_errors::Applicability;
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use rustc_hir::def::Res;
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use rustc_hir::{
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GenericArg, GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath,
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TraitBoundModifier, TraitItem, TraitRef, Ty, TyKind, WherePredicate,
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};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::{BytePos, Span};
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use std::collections::hash_map::Entry;
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declare_clippy_lint! {
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/// ### What it does
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/// This lint warns about unnecessary type repetitions in trait bounds
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///
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/// ### Why is this bad?
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/// Repeating the type for every bound makes the code
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/// less readable than combining the bounds
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///
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/// ### Example
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/// ```rust
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/// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
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/// ```
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///
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/// Use instead:
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/// ```rust
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/// pub fn foo<T>(t: T) where T: Copy + Clone {}
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/// ```
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#[clippy::version = "1.38.0"]
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pub TYPE_REPETITION_IN_BOUNDS,
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nursery,
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"types are repeated unnecessarily in trait bounds, use `+` instead of using `T: _, T: _`"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for cases where generics or trait objects are being used and multiple
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/// syntax specifications for trait bounds are used simultaneously.
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///
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/// ### Why is this bad?
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/// Duplicate bounds makes the code
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/// less readable than specifying them only once.
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///
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/// ### Example
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/// ```rust
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/// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
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/// ```
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///
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/// Use instead:
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/// ```rust
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/// # mod hidden {
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/// fn func<T: Clone + Default>(arg: T) {}
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/// # }
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///
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/// // or
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///
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/// fn func<T>(arg: T) where T: Clone + Default {}
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/// ```
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///
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/// ```rust
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/// fn foo<T: Default + Default>(bar: T) {}
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/// ```
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/// Use instead:
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/// ```rust
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/// fn foo<T: Default>(bar: T) {}
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/// ```
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///
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/// ```rust
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/// fn foo<T>(bar: T) where T: Default + Default {}
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/// ```
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/// Use instead:
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/// ```rust
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/// fn foo<T>(bar: T) where T: Default {}
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/// ```
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#[clippy::version = "1.47.0"]
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pub TRAIT_DUPLICATION_IN_BOUNDS,
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nursery,
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"check if the same trait bounds are specified more than once during a generic declaration"
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}
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#[derive(Copy, Clone)]
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pub struct TraitBounds {
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max_trait_bounds: u64,
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}
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impl TraitBounds {
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#[must_use]
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pub fn new(max_trait_bounds: u64) -> Self {
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Self { max_trait_bounds }
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}
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}
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impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
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impl<'tcx> LateLintPass<'tcx> for TraitBounds {
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fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
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self.check_type_repetition(cx, gen);
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check_trait_bound_duplication(cx, gen);
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}
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
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// special handling for self trait bounds as these are not considered generics
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// ie. trait Foo: Display {}
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if let Item {
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kind: ItemKind::Trait(_, _, _, bounds, ..),
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..
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} = item
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{
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rollup_traits(cx, bounds, "these bounds contain repeated elements");
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}
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}
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fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
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let mut self_bounds_map = FxHashMap::default();
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for predicate in item.generics.predicates {
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if_chain! {
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if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
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if bound_predicate.origin != PredicateOrigin::ImplTrait;
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if !bound_predicate.span.from_expansion();
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if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
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if let Some(PathSegment {
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res: Res::SelfTyParam { trait_: def_id }, ..
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}) = segments.first();
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if let Some(
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Node::Item(
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Item {
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kind: ItemKind::Trait(_, _, _, self_bounds, _),
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.. }
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)
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) = cx.tcx.hir().get_if_local(*def_id);
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then {
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if self_bounds_map.is_empty() {
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for bound in self_bounds.iter() {
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let Some((self_res, self_segments, _)) = get_trait_info_from_bound(bound) else { continue };
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self_bounds_map.insert(self_res, self_segments);
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}
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}
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bound_predicate
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.bounds
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.iter()
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.filter_map(get_trait_info_from_bound)
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.for_each(|(trait_item_res, trait_item_segments, span)| {
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if let Some(self_segments) = self_bounds_map.get(&trait_item_res) {
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if SpanlessEq::new(cx).eq_path_segments(self_segments, trait_item_segments) {
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span_lint_and_help(
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cx,
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TRAIT_DUPLICATION_IN_BOUNDS,
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span,
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"this trait bound is already specified in trait declaration",
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None,
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"consider removing this trait bound",
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);
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}
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}
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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_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) {
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if_chain! {
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if let TyKind::Ref(.., mut_ty) = &ty.kind;
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if let TyKind::TraitObject(bounds, ..) = mut_ty.ty.kind;
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if bounds.len() > 2;
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then {
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// Build up a hash of every trait we've seen
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// When we see a trait for the first time, add it to unique_traits
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// so we can later use it to build a string of all traits exactly once, without duplicates
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let mut seen_def_ids = FxHashSet::default();
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let mut unique_traits = Vec::new();
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// Iterate the bounds and add them to our seen hash
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// If we haven't yet seen it, add it to the fixed traits
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for bound in bounds.iter() {
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let Some(def_id) = bound.trait_ref.trait_def_id() else { continue; };
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let new_trait = seen_def_ids.insert(def_id);
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if new_trait {
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unique_traits.push(bound);
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}
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}
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// If the number of unique traits isn't the same as the number of traits in the bounds,
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// there must be 1 or more duplicates
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if bounds.len() != unique_traits.len() {
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let mut bounds_span = bounds[0].span;
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for bound in bounds.iter().skip(1) {
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bounds_span = bounds_span.to(bound.span);
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}
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let fixed_trait_snippet = unique_traits
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.iter()
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.filter_map(|b| snippet_opt(cx, b.span))
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.collect::<Vec<_>>()
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.join(" + ");
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span_lint_and_sugg(
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cx,
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TRAIT_DUPLICATION_IN_BOUNDS,
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bounds_span,
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"this trait bound is already specified in trait declaration",
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"try",
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fixed_trait_snippet,
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Applicability::MaybeIncorrect,
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);
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}
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}
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}
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}
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}
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impl TraitBounds {
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fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
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struct SpanlessTy<'cx, 'tcx> {
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ty: &'tcx Ty<'tcx>,
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cx: &'cx LateContext<'tcx>,
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}
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impl PartialEq for SpanlessTy<'_, '_> {
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fn eq(&self, other: &Self) -> bool {
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let mut eq = SpanlessEq::new(self.cx);
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eq.inter_expr().eq_ty(self.ty, other.ty)
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}
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}
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impl Hash for SpanlessTy<'_, '_> {
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fn hash<H: Hasher>(&self, h: &mut H) {
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let mut t = SpanlessHash::new(self.cx);
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t.hash_ty(self.ty);
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h.write_u64(t.finish());
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}
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}
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impl Eq for SpanlessTy<'_, '_> {}
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if gen.span.from_expansion() {
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return;
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}
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let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
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let mut applicability = Applicability::MaybeIncorrect;
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for bound in gen.predicates {
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if_chain! {
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if let WherePredicate::BoundPredicate(ref p) = bound;
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if p.origin != PredicateOrigin::ImplTrait;
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if p.bounds.len() as u64 <= self.max_trait_bounds;
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if !p.span.from_expansion();
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if let Some(ref v) = map.insert(
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SpanlessTy { ty: p.bounded_ty, cx },
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p.bounds.iter().collect::<Vec<_>>()
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);
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then {
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let trait_bounds = v
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.iter()
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.copied()
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.chain(p.bounds.iter())
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.filter_map(get_trait_info_from_bound)
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.map(|(_, _, span)| snippet_with_applicability(cx, span, "..", &mut applicability))
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.join(" + ");
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let hint_string = format!(
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"consider combining the bounds: `{}: {trait_bounds}`",
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snippet(cx, p.bounded_ty.span, "_"),
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);
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span_lint_and_help(
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cx,
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TYPE_REPETITION_IN_BOUNDS,
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p.span,
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"this type has already been used as a bound predicate",
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None,
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&hint_string,
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);
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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_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
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if gen.span.from_expansion() {
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return;
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}
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// Explanation:
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// fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
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// where T: Clone + Default, { unimplemented!(); }
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// ^^^^^^^^^^^^^^^^^^
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// |
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// collects each of these where clauses into a set keyed by generic name and comparable trait
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// eg. (T, Clone)
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let where_predicates = gen
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.predicates
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.iter()
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.filter_map(|pred| {
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if_chain! {
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if pred.in_where_clause();
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if let WherePredicate::BoundPredicate(bound_predicate) = pred;
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if let TyKind::Path(QPath::Resolved(_, path)) = bound_predicate.bounded_ty.kind;
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then {
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return Some(
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rollup_traits(cx, bound_predicate.bounds, "these where clauses contain repeated elements")
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.into_iter().map(|(trait_ref, _)| (path.res, trait_ref)))
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}
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}
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None
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})
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.flatten()
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.collect::<FxHashSet<_>>();
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// Explanation:
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// fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z) ...
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// ^^^^^^^^^^^^^^^^^^ ^^^^^^^
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// |
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// compare trait bounds keyed by generic name and comparable trait to collected where
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// predicates eg. (T, Clone)
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for predicate in gen.predicates.iter().filter(|pred| !pred.in_where_clause()) {
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if_chain! {
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if let WherePredicate::BoundPredicate(bound_predicate) = predicate;
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if bound_predicate.origin != PredicateOrigin::ImplTrait;
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if !bound_predicate.span.from_expansion();
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if let TyKind::Path(QPath::Resolved(_, path)) = bound_predicate.bounded_ty.kind;
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then {
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let traits = rollup_traits(cx, bound_predicate.bounds, "these bounds contain repeated elements");
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for (trait_ref, span) in traits {
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let key = (path.res, trait_ref);
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if where_predicates.contains(&key) {
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span_lint_and_help(
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cx,
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TRAIT_DUPLICATION_IN_BOUNDS,
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span,
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"this trait bound is already specified in the where clause",
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None,
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"consider removing this trait bound",
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);
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}
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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(Clone, PartialEq, Eq, Hash, Debug)]
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struct ComparableTraitRef(Res, Vec<Res>);
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impl Default for ComparableTraitRef {
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fn default() -> Self {
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Self(Res::Err, Vec::new())
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}
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}
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fn get_trait_info_from_bound<'a>(bound: &'a GenericBound<'_>) -> Option<(Res, &'a [PathSegment<'a>], Span)> {
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if let GenericBound::Trait(t, tbm) = bound {
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let trait_path = t.trait_ref.path;
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let trait_span = {
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let path_span = trait_path.span;
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if let TraitBoundModifier::Maybe = tbm {
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path_span.with_lo(path_span.lo() - BytePos(1)) // include the `?`
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} else {
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path_span
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}
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};
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Some((trait_path.res, trait_path.segments, trait_span))
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} else {
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None
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}
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}
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// FIXME: ComparableTraitRef does not support nested bounds needed for associated_type_bounds
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fn into_comparable_trait_ref(trait_ref: &TraitRef<'_>) -> ComparableTraitRef {
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ComparableTraitRef(
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trait_ref.path.res,
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trait_ref
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.path
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.segments
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.iter()
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.filter_map(|segment| {
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// get trait bound type arguments
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Some(segment.args?.args.iter().filter_map(|arg| {
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if_chain! {
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if let GenericArg::Type(ty) = arg;
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if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
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then { return Some(path.res) }
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}
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None
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}))
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})
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.flatten()
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.collect(),
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)
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}
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fn rollup_traits(cx: &LateContext<'_>, bounds: &[GenericBound<'_>], msg: &str) -> Vec<(ComparableTraitRef, Span)> {
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let mut map = FxHashMap::default();
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let mut repeated_res = false;
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let only_comparable_trait_refs = |bound: &GenericBound<'_>| {
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if let GenericBound::Trait(t, _) = bound {
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Some((into_comparable_trait_ref(&t.trait_ref), t.span))
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} else {
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None
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}
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};
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let mut i = 0usize;
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for bound in bounds.iter().filter_map(only_comparable_trait_refs) {
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let (comparable_bound, span_direct) = bound;
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match map.entry(comparable_bound) {
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Entry::Occupied(_) => repeated_res = true,
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Entry::Vacant(e) => {
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e.insert((span_direct, i));
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i += 1;
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},
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}
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}
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// Put bounds in source order
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let mut comparable_bounds = vec![Default::default(); map.len()];
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for (k, (v, i)) in map {
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comparable_bounds[i] = (k, v);
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}
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if_chain! {
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if repeated_res;
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if let [first_trait, .., last_trait] = bounds;
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then {
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let all_trait_span = first_trait.span().to(last_trait.span());
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let traits = comparable_bounds.iter()
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.filter_map(|&(_, span)| snippet_opt(cx, span))
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.collect::<Vec<_>>();
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let traits = traits.join(" + ");
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span_lint_and_sugg(
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cx,
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TRAIT_DUPLICATION_IN_BOUNDS,
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all_trait_span,
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msg,
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"try",
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traits,
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Applicability::MachineApplicable
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);
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}
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}
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comparable_bounds
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}
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