[rustc.git] / src / tools / clippy / clippy_lints / src / trait_bounds.rs

use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
use clippy_utils::{SpanlessEq, SpanlessHash};
use core::hash::{Hash, Hasher};
use if_chain::if_chain;
use itertools::Itertools;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::unhash::UnhashMap;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::{
    GenericArg, GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath,
    TraitBoundModifier, TraitItem, TraitRef, Ty, TyKind, WherePredicate,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{BytePos, Span};
use std::collections::hash_map::Entry;

declare_clippy_lint! {
    /// ### What it does
    /// This lint warns about unnecessary type repetitions in trait bounds
    ///
    /// ### Why is this bad?
    /// Repeating the type for every bound makes the code
    /// less readable than combining the bounds
    ///
    /// ### Example
    /// ```rust
    /// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
    /// ```
    ///
    /// Use instead:
    /// ```rust
    /// pub fn foo<T>(t: T) where T: Copy + Clone {}
    /// ```
    #[clippy::version = "1.38.0"]
    pub TYPE_REPETITION_IN_BOUNDS,
    nursery,
    "types are repeated unnecessarily in trait bounds, use `+` instead of using `T: _, T: _`"
}

declare_clippy_lint! {
    /// ### What it does
    /// Checks for cases where generics or trait objects are being used and multiple
    /// syntax specifications for trait bounds are used simultaneously.
    ///
    /// ### Why is this bad?
    /// Duplicate bounds makes the code
    /// less readable than specifying them only once.
    ///
    /// ### Example
    /// ```rust
    /// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
    /// ```
    ///
    /// Use instead:
    /// ```rust
    /// # mod hidden {
    /// fn func<T: Clone + Default>(arg: T) {}
    /// # }
    ///
    /// // or
    ///
    /// fn func<T>(arg: T) where T: Clone + Default {}
    /// ```
    ///
    /// ```rust
    /// fn foo<T: Default + Default>(bar: T) {}
    /// ```
    /// Use instead:
    /// ```rust
    /// fn foo<T: Default>(bar: T) {}
    /// ```
    ///
    /// ```rust
    /// fn foo<T>(bar: T) where T: Default + Default {}
    /// ```
    /// Use instead:
    /// ```rust
    /// fn foo<T>(bar: T) where T: Default {}
    /// ```
    #[clippy::version = "1.47.0"]
    pub TRAIT_DUPLICATION_IN_BOUNDS,
    nursery,
    "check if the same trait bounds are specified more than once during a generic declaration"
}

#[derive(Copy, Clone)]
pub struct TraitBounds {
    max_trait_bounds: u64,
}

impl TraitBounds {
    #[must_use]
    pub fn new(max_trait_bounds: u64) -> Self {
        Self { max_trait_bounds }
    }
}

impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);

impl<'tcx> LateLintPass<'tcx> for TraitBounds {
    fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
        self.check_type_repetition(cx, gen);
        check_trait_bound_duplication(cx, gen);
    }

    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
        // special handling for self trait bounds as these are not considered generics
        // ie. trait Foo: Display {}
        if let Item {
            kind: ItemKind::Trait(_, _, _, bounds, ..),
            ..
        } = item
        {
            rollup_traits(cx, bounds, "these bounds contain repeated elements");
        }
    }

    fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
        let mut self_bounds_map = FxHashMap::default();

        for predicate in item.generics.predicates {
            if_chain! {
                if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
                if bound_predicate.origin != PredicateOrigin::ImplTrait;
                if !bound_predicate.span.from_expansion();
                if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
                if let Some(PathSegment {
                    res: Res::SelfTyParam { trait_: def_id }, ..
                }) = segments.first();
                if let Some(
                    Node::Item(
                        Item {
                            kind: ItemKind::Trait(_, _, _, self_bounds, _),
                            .. }
                        )
                    ) = cx.tcx.hir().get_if_local(*def_id);
                then {
                    if self_bounds_map.is_empty() {
                        for bound in self_bounds.iter() {
                            let Some((self_res, self_segments, _)) = get_trait_info_from_bound(bound) else { continue };
                            self_bounds_map.insert(self_res, self_segments);
                        }
                    }

                    bound_predicate
                        .bounds
                        .iter()
                        .filter_map(get_trait_info_from_bound)
                        .for_each(|(trait_item_res, trait_item_segments, span)| {
                            if let Some(self_segments) = self_bounds_map.get(&trait_item_res) {
                                if SpanlessEq::new(cx).eq_path_segments(self_segments, trait_item_segments) {
                                    span_lint_and_help(
                                        cx,
                                        TRAIT_DUPLICATION_IN_BOUNDS,
                                        span,
                                        "this trait bound is already specified in trait declaration",
                                        None,
                                        "consider removing this trait bound",
                                    );
                                }
                            }
                        });
                }
            }
        }
    }

    fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) {
        if_chain! {
            if let TyKind::Ref(.., mut_ty) = &ty.kind;
            if let TyKind::TraitObject(bounds, ..) = mut_ty.ty.kind;
            if bounds.len() > 2;
            then {

                // Build up a hash of every trait we've seen
                // When we see a trait for the first time, add it to unique_traits
                // so we can later use it to build a string of all traits exactly once, without duplicates

                let mut seen_def_ids = FxHashSet::default();
                let mut unique_traits = Vec::new();

                // Iterate the bounds and add them to our seen hash
                // If we haven't yet seen it, add it to the fixed traits
                for bound in bounds.iter() {
                    let Some(def_id) = bound.trait_ref.trait_def_id() else { continue; };

                    let new_trait = seen_def_ids.insert(def_id);

                    if new_trait {
                        unique_traits.push(bound);
                    }
                }

                // If the number of unique traits isn't the same as the number of traits in the bounds,
                // there must be 1 or more duplicates
                if bounds.len() != unique_traits.len() {
                    let mut bounds_span = bounds[0].span;

                    for bound in bounds.iter().skip(1) {
                        bounds_span = bounds_span.to(bound.span);
                    }

                    let fixed_trait_snippet = unique_traits
                        .iter()
                        .filter_map(|b| snippet_opt(cx, b.span))
                        .collect::<Vec<_>>()
                        .join(" + ");

                    span_lint_and_sugg(
                        cx,
                        TRAIT_DUPLICATION_IN_BOUNDS,
                        bounds_span,
                        "this trait bound is already specified in trait declaration",
                        "try",
                        fixed_trait_snippet,
                        Applicability::MaybeIncorrect,
                    );
                }
            }
        }
    }
}

impl TraitBounds {
    fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
        struct SpanlessTy<'cx, 'tcx> {
            ty: &'tcx Ty<'tcx>,
            cx: &'cx LateContext<'tcx>,
        }
        impl PartialEq for SpanlessTy<'_, '_> {
            fn eq(&self, other: &Self) -> bool {
                let mut eq = SpanlessEq::new(self.cx);
                eq.inter_expr().eq_ty(self.ty, other.ty)
            }
        }
        impl Hash for SpanlessTy<'_, '_> {
            fn hash<H: Hasher>(&self, h: &mut H) {
                let mut t = SpanlessHash::new(self.cx);
                t.hash_ty(self.ty);
                h.write_u64(t.finish());
            }
        }
        impl Eq for SpanlessTy<'_, '_> {}

        if gen.span.from_expansion() {
            return;
        }
        let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
        let mut applicability = Applicability::MaybeIncorrect;
        for bound in gen.predicates {
            if_chain! {
                if let WherePredicate::BoundPredicate(ref p) = bound;
                if p.origin != PredicateOrigin::ImplTrait;
                if p.bounds.len() as u64 <= self.max_trait_bounds;
                if !p.span.from_expansion();
                if let Some(ref v) = map.insert(
                    SpanlessTy { ty: p.bounded_ty, cx },
                    p.bounds.iter().collect::<Vec<_>>()
                );

                then {
                    let trait_bounds = v
                        .iter()
                        .copied()
                        .chain(p.bounds.iter())
                        .filter_map(get_trait_info_from_bound)
                        .map(|(_, _, span)| snippet_with_applicability(cx, span, "..", &mut applicability))
                        .join(" + ");
                    let hint_string = format!(
                        "consider combining the bounds: `{}: {trait_bounds}`",
                        snippet(cx, p.bounded_ty.span, "_"),
                    );
                    span_lint_and_help(
                        cx,
                        TYPE_REPETITION_IN_BOUNDS,
                        p.span,
                        "this type has already been used as a bound predicate",
                        None,
                        &hint_string,
                    );
                }
            }
        }
    }
}

fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
    if gen.span.from_expansion() {
        return;
    }

    // Explanation:
    // fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
    // where T: Clone + Default, { unimplemented!(); }
    //       ^^^^^^^^^^^^^^^^^^
    //       |
    // collects each of these where clauses into a set keyed by generic name and comparable trait
    // eg. (T, Clone)
    let where_predicates = gen
        .predicates
        .iter()
        .filter_map(|pred| {
            if_chain! {
                if pred.in_where_clause();
                if let WherePredicate::BoundPredicate(bound_predicate) = pred;
                if let TyKind::Path(QPath::Resolved(_, path)) =  bound_predicate.bounded_ty.kind;
                then {
                    return Some(
                        rollup_traits(cx, bound_predicate.bounds, "these where clauses contain repeated elements")
                        .into_iter().map(|(trait_ref, _)| (path.res, trait_ref)))
                }
            }
            None
        })
        .flatten()
        .collect::<FxHashSet<_>>();

    // Explanation:
    // fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z) ...
    //            ^^^^^^^^^^^^^^^^^^  ^^^^^^^
    //            |
    // compare trait bounds keyed by generic name and comparable trait to collected where
    // predicates eg. (T, Clone)
    for predicate in gen.predicates.iter().filter(|pred| !pred.in_where_clause()) {
        if_chain! {
            if let WherePredicate::BoundPredicate(bound_predicate) = predicate;
            if bound_predicate.origin != PredicateOrigin::ImplTrait;
            if !bound_predicate.span.from_expansion();
            if let TyKind::Path(QPath::Resolved(_, path)) =  bound_predicate.bounded_ty.kind;
            then {
                let traits = rollup_traits(cx, bound_predicate.bounds, "these bounds contain repeated elements");
                for (trait_ref, span) in traits {
                    let key = (path.res, trait_ref);
                    if where_predicates.contains(&key) {
                        span_lint_and_help(
                            cx,
                            TRAIT_DUPLICATION_IN_BOUNDS,
                            span,
                            "this trait bound is already specified in the where clause",
                            None,
                            "consider removing this trait bound",
                            );
                    }
                }
            }
        }
    }
}

#[derive(Clone, PartialEq, Eq, Hash, Debug)]
struct ComparableTraitRef(Res, Vec<Res>);
impl Default for ComparableTraitRef {
    fn default() -> Self {
        Self(Res::Err, Vec::new())
    }
}

fn get_trait_info_from_bound<'a>(bound: &'a GenericBound<'_>) -> Option<(Res, &'a [PathSegment<'a>], Span)> {
    if let GenericBound::Trait(t, tbm) = bound {
        let trait_path = t.trait_ref.path;
        let trait_span = {
            let path_span = trait_path.span;
            if let TraitBoundModifier::Maybe = tbm {
                path_span.with_lo(path_span.lo() - BytePos(1)) // include the `?`
            } else {
                path_span
            }
        };
        Some((trait_path.res, trait_path.segments, trait_span))
    } else {
        None
    }
}

// FIXME: ComparableTraitRef does not support nested bounds needed for associated_type_bounds
fn into_comparable_trait_ref(trait_ref: &TraitRef<'_>) -> ComparableTraitRef {
    ComparableTraitRef(
        trait_ref.path.res,
        trait_ref
            .path
            .segments
            .iter()
            .filter_map(|segment| {
                // get trait bound type arguments
                Some(segment.args?.args.iter().filter_map(|arg| {
                    if_chain! {
                        if let GenericArg::Type(ty) = arg;
                        if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
                        then { return Some(path.res) }
                    }
                    None
                }))
            })
            .flatten()
            .collect(),
    )
}

fn rollup_traits(cx: &LateContext<'_>, bounds: &[GenericBound<'_>], msg: &str) -> Vec<(ComparableTraitRef, Span)> {
    let mut map = FxHashMap::default();
    let mut repeated_res = false;

    let only_comparable_trait_refs = |bound: &GenericBound<'_>| {
        if let GenericBound::Trait(t, _) = bound {
            Some((into_comparable_trait_ref(&t.trait_ref), t.span))
        } else {
            None
        }
    };

    let mut i = 0usize;
    for bound in bounds.iter().filter_map(only_comparable_trait_refs) {
        let (comparable_bound, span_direct) = bound;
        match map.entry(comparable_bound) {
            Entry::Occupied(_) => repeated_res = true,
            Entry::Vacant(e) => {
                e.insert((span_direct, i));
                i += 1;
            },
        }
    }

    // Put bounds in source order
    let mut comparable_bounds = vec![Default::default(); map.len()];
    for (k, (v, i)) in map {
        comparable_bounds[i] = (k, v);
    }

    if_chain! {
        if repeated_res;
        if let [first_trait, .., last_trait] = bounds;
        then {
            let all_trait_span = first_trait.span().to(last_trait.span());

            let traits = comparable_bounds.iter()
                .filter_map(|&(_, span)| snippet_opt(cx, span))
                .collect::<Vec<_>>();
            let traits = traits.join(" + ");

            span_lint_and_sugg(
                cx,
                TRAIT_DUPLICATION_IN_BOUNDS,
                all_trait_span,
                msg,
                "try",
                traits,
                Applicability::MachineApplicable
            );
        }
    }

    comparable_bounds
}
Commit	Line	Data
064997fb FG	1	use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
064997fb FG	2	use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
5099ac24 FG	3	use clippy_utils::{SpanlessEq, SpanlessHash};
5099ac24 FG	4	use core::hash::{Hash, Hasher};
f20569fa	5	use if_chain::if_chain;
064997fb	6	use itertools::Itertools;
f2b60f7d	7	use rustc_data_structures::fx::{FxHashMap, FxHashSet};
17df50a5	8	use rustc_data_structures::unhash::UnhashMap;
f20569fa	9	use rustc_errors::Applicability;
5099ac24 FG	10	use rustc_hir::def::Res;
5099ac24 FG	11	use rustc_hir::{
064997fb FG	12	GenericArg, GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath,
064997fb FG	13	TraitBoundModifier, TraitItem, TraitRef, Ty, TyKind, WherePredicate,
5099ac24	14	};
f20569fa XL	15	use rustc_lint::{LateContext, LateLintPass};
f20569fa XL	16	use rustc_session::{declare_tool_lint, impl_lint_pass};
064997fb	17	use rustc_span::{BytePos, Span};
f2b60f7d	18	use std::collections::hash_map::Entry;
f20569fa XL	19
f20569fa XL	20	declare_clippy_lint! {
94222f64 XL	21	/// ### What it does
94222f64 XL	22	/// This lint warns about unnecessary type repetitions in trait bounds
f20569fa	23	///
94222f64 XL	24	/// ### Why is this bad?
94222f64 XL	25	/// Repeating the type for every bound makes the code
f20569fa XL	26	/// less readable than combining the bounds
f20569fa XL	27	///
94222f64	28	/// ### Example
f20569fa XL	29	/// ```rust
	30	/// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
	31	/// ```
	32	///
923072b8	33	/// Use instead:
f20569fa XL	34	/// ```rust
	35	/// pub fn foo<T>(t: T) where T: Copy + Clone {}
	36	/// ```
a2a8927a	37	#[clippy::version = "1.38.0"]
f20569fa	38	pub TYPE_REPETITION_IN_BOUNDS,
064997fb	39	nursery,
49aad941	40	"types are repeated unnecessarily in trait bounds, use `+` instead of using `T: _, T: _`"
f20569fa XL	41	}
	42
	43	declare_clippy_lint! {
94222f64	44	/// ### What it does
49aad941	45	/// Checks for cases where generics or trait objects are being used and multiple
f20569fa XL	46	/// syntax specifications for trait bounds are used simultaneously.
f20569fa XL	47	///
94222f64 XL	48	/// ### Why is this bad?
94222f64 XL	49	/// Duplicate bounds makes the code
5e7ed085	50	/// less readable than specifying them only once.
f20569fa	51	///
94222f64	52	/// ### Example
f20569fa XL	53	/// ```rust
	54	/// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
	55	/// ```
	56	///
923072b8	57	/// Use instead:
f20569fa	58	/// ```rust
923072b8	59	/// # mod hidden {
f20569fa	60	/// fn func<T: Clone + Default>(arg: T) {}
923072b8 FG	61	/// # }
	62	///
	63	/// // or
f20569fa	64	///
f20569fa XL	65	/// fn func<T>(arg: T) where T: Clone + Default {}
f20569fa XL	66	/// ```
064997fb FG	67	///
	68	/// ```rust
	69	/// fn foo<T: Default + Default>(bar: T) {}
	70	/// ```
	71	/// Use instead:
	72	/// ```rust
	73	/// fn foo<T: Default>(bar: T) {}
	74	/// ```
	75	///
	76	/// ```rust
	77	/// fn foo<T>(bar: T) where T: Default + Default {}
	78	/// ```
	79	/// Use instead:
	80	/// ```rust
	81	/// fn foo<T>(bar: T) where T: Default {}
	82	/// ```
a2a8927a	83	#[clippy::version = "1.47.0"]
f20569fa	84	pub TRAIT_DUPLICATION_IN_BOUNDS,
064997fb FG	85	nursery,
064997fb FG	86	"check if the same trait bounds are specified more than once during a generic declaration"
f20569fa XL	87	}
	88
	89	#[derive(Copy, Clone)]
	90	pub struct TraitBounds {
	91	max_trait_bounds: u64,
	92	}
	93
	94	impl TraitBounds {
	95	#[must_use]
	96	pub fn new(max_trait_bounds: u64) -> Self {
	97	Self { max_trait_bounds }
	98	}
	99	}
	100
	101	impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
	102
	103	impl<'tcx> LateLintPass<'tcx> for TraitBounds {
	104	fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
	105	self.check_type_repetition(cx, gen);
	106	check_trait_bound_duplication(cx, gen);
064997fb FG	107	}
	108
	109	fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
	110	// special handling for self trait bounds as these are not considered generics
	111	// ie. trait Foo: Display {}
	112	if let Item {
	113	kind: ItemKind::Trait(_, _, _, bounds, ..),
	114	..
	115	} = item
	116	{
	117	rollup_traits(cx, bounds, "these bounds contain repeated elements");
	118	}
f20569fa	119	}
f20569fa	120
5099ac24	121	fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
5099ac24 FG	122	let mut self_bounds_map = FxHashMap::default();
5099ac24 FG	123
04454e1e	124	for predicate in item.generics.predicates {
5099ac24 FG	125	if_chain! {
5099ac24 FG	126	if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
04454e1e	127	if bound_predicate.origin != PredicateOrigin::ImplTrait;
5099ac24 FG	128	if !bound_predicate.span.from_expansion();
5099ac24 FG	129	if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
5e7ed085	130	if let Some(PathSegment {
2b03887a	131	res: Res::SelfTyParam { trait_: def_id }, ..
5e7ed085	132	}) = segments.first();
5099ac24 FG	133	if let Some(
	134	Node::Item(
	135	Item {
	136	kind: ItemKind::Trait(_, _, _, self_bounds, _),
	137	.. }
	138	)
	139	) = cx.tcx.hir().get_if_local(*def_id);
	140	then {
	141	if self_bounds_map.is_empty() {
	142	for bound in self_bounds.iter() {
	143	let Some((self_res, self_segments, _)) = get_trait_info_from_bound(bound) else { continue };
	144	self_bounds_map.insert(self_res, self_segments);
	145	}
	146	}
	147
	148	bound_predicate
	149	.bounds
	150	.iter()
	151	.filter_map(get_trait_info_from_bound)
	152	.for_each(\|(trait_item_res, trait_item_segments, span)\| {
	153	if let Some(self_segments) = self_bounds_map.get(&trait_item_res) {
	154	if SpanlessEq::new(cx).eq_path_segments(self_segments, trait_item_segments) {
	155	span_lint_and_help(
	156	cx,
	157	TRAIT_DUPLICATION_IN_BOUNDS,
	158	span,
	159	"this trait bound is already specified in trait declaration",
	160	None,
	161	"consider removing this trait bound",
	162	);
	163	}
	164	}
	165	});
	166	}
	167	}
	168	}
f20569fa	169	}
49aad941 FG	170
	171	fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) {
	172	if_chain! {
	173	if let TyKind::Ref(.., mut_ty) = &ty.kind;
	174	if let TyKind::TraitObject(bounds, ..) = mut_ty.ty.kind;
	175	if bounds.len() > 2;
	176	then {
	177
	178	// Build up a hash of every trait we've seen
	179	// When we see a trait for the first time, add it to unique_traits
	180	// so we can later use it to build a string of all traits exactly once, without duplicates
	181
	182	let mut seen_def_ids = FxHashSet::default();
	183	let mut unique_traits = Vec::new();
	184
	185	// Iterate the bounds and add them to our seen hash
	186	// If we haven't yet seen it, add it to the fixed traits
	187	for bound in bounds.iter() {
	188	let Some(def_id) = bound.trait_ref.trait_def_id() else { continue; };
	189
	190	let new_trait = seen_def_ids.insert(def_id);
	191
	192	if new_trait {
	193	unique_traits.push(bound);
	194	}
	195	}
	196
	197	// If the number of unique traits isn't the same as the number of traits in the bounds,
	198	// there must be 1 or more duplicates
	199	if bounds.len() != unique_traits.len() {
	200	let mut bounds_span = bounds[0].span;
	201
	202	for bound in bounds.iter().skip(1) {
	203	bounds_span = bounds_span.to(bound.span);
	204	}
	205
	206	let fixed_trait_snippet = unique_traits
	207	.iter()
	208	.filter_map(\|b\| snippet_opt(cx, b.span))
	209	.collect::<Vec<_>>()
	210	.join(" + ");
	211
	212	span_lint_and_sugg(
	213	cx,
	214	TRAIT_DUPLICATION_IN_BOUNDS,
	215	bounds_span,
	216	"this trait bound is already specified in trait declaration",
	217	"try",
	218	fixed_trait_snippet,
	219	Applicability::MaybeIncorrect,
	220	);
	221	}
	222	}
	223	}
	224	}
f20569fa XL	225	}
	226
	227	impl TraitBounds {
5099ac24 FG	228	fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
	229	struct SpanlessTy<'cx, 'tcx> {
	230	ty: &'tcx Ty<'tcx>,
	231	cx: &'cx LateContext<'tcx>,
	232	}
	233	impl PartialEq for SpanlessTy<'_, '_> {
	234	fn eq(&self, other: &Self) -> bool {
	235	let mut eq = SpanlessEq::new(self.cx);
	236	eq.inter_expr().eq_ty(self.ty, other.ty)
	237	}
	238	}
	239	impl Hash for SpanlessTy<'_, '_> {
	240	fn hash<H: Hasher>(&self, h: &mut H) {
	241	let mut t = SpanlessHash::new(self.cx);
	242	t.hash_ty(self.ty);
	243	h.write_u64(t.finish());
	244	}
	245	}
	246	impl Eq for SpanlessTy<'_, '_> {}
	247
a2a8927a	248	if gen.span.from_expansion() {
f20569fa XL	249	return;
f20569fa XL	250	}
5099ac24	251	let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
f20569fa	252	let mut applicability = Applicability::MaybeIncorrect;
04454e1e	253	for bound in gen.predicates {
f20569fa XL	254	if_chain! {
f20569fa XL	255	if let WherePredicate::BoundPredicate(ref p) = bound;
04454e1e	256	if p.origin != PredicateOrigin::ImplTrait;
f20569fa	257	if p.bounds.len() as u64 <= self.max_trait_bounds;
a2a8927a	258	if !p.span.from_expansion();
5099ac24 FG	259	if let Some(ref v) = map.insert(
	260	SpanlessTy { ty: p.bounded_ty, cx },
	261	p.bounds.iter().collect::<Vec<_>>()
	262	);
f20569fa XL	263
f20569fa XL	264	then {
064997fb FG	265	let trait_bounds = v
	266	.iter()
	267	.copied()
	268	.chain(p.bounds.iter())
	269	.filter_map(get_trait_info_from_bound)
	270	.map(\|(_, _, span)\| snippet_with_applicability(cx, span, "..", &mut applicability))
	271	.join(" + ");
	272	let hint_string = format!(
2b03887a	273	"consider combining the bounds: `{}: {trait_bounds}`",
064997fb	274	snippet(cx, p.bounded_ty.span, "_"),
f20569fa	275	);
f20569fa XL	276	span_lint_and_help(
	277	cx,
	278	TYPE_REPETITION_IN_BOUNDS,
	279	p.span,
	280	"this type has already been used as a bound predicate",
	281	None,
	282	&hint_string,
	283	);
	284	}
	285	}
	286	}
	287	}
	288	}
	289
	290	fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
f2b60f7d	291	if gen.span.from_expansion() {
f20569fa XL	292	return;
	293	}
	294
f2b60f7d FG	295	// Explanation:
	296	// fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
	297	// where T: Clone + Default, { unimplemented!(); }
	298	// ^^^^^^^^^^^^^^^^^^
	299	// \|
	300	// collects each of these where clauses into a set keyed by generic name and comparable trait
	301	// eg. (T, Clone)
	302	let where_predicates = gen
	303	.predicates
	304	.iter()
	305	.filter_map(\|pred\| {
	306	if_chain! {
	307	if pred.in_where_clause();
	308	if let WherePredicate::BoundPredicate(bound_predicate) = pred;
	309	if let TyKind::Path(QPath::Resolved(_, path)) = bound_predicate.bounded_ty.kind;
	310	then {
	311	return Some(
	312	rollup_traits(cx, bound_predicate.bounds, "these where clauses contain repeated elements")
	313	.into_iter().map(\|(trait_ref, _)\| (path.res, trait_ref)))
	314	}
	315	}
	316	None
	317	})
	318	.flatten()
	319	.collect::<FxHashSet<_>>();
	320
	321	// Explanation:
	322	// fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z) ...
	323	// ^^^^^^^^^^^^^^^^^^ ^^^^^^^
	324	// \|
	325	// compare trait bounds keyed by generic name and comparable trait to collected where
	326	// predicates eg. (T, Clone)
	327	for predicate in gen.predicates.iter().filter(\|pred\| !pred.in_where_clause()) {
f20569fa	328	if_chain! {
f2b60f7d	329	if let WherePredicate::BoundPredicate(bound_predicate) = predicate;
04454e1e	330	if bound_predicate.origin != PredicateOrigin::ImplTrait;
a2a8927a	331	if !bound_predicate.span.from_expansion();
f2b60f7d	332	if let TyKind::Path(QPath::Resolved(_, path)) = bound_predicate.bounded_ty.kind;
f20569fa	333	then {
f2b60f7d FG	334	let traits = rollup_traits(cx, bound_predicate.bounds, "these bounds contain repeated elements");
	335	for (trait_ref, span) in traits {
	336	let key = (path.res, trait_ref);
	337	if where_predicates.contains(&key) {
f20569fa XL	338	span_lint_and_help(
	339	cx,
	340	TRAIT_DUPLICATION_IN_BOUNDS,
f2b60f7d	341	span,
f20569fa XL	342	"this trait bound is already specified in the where clause",
	343	None,
	344	"consider removing this trait bound",
f2b60f7d	345	);
04454e1e	346	}
f20569fa XL	347	}
	348	}
	349	}
	350	}
	351	}
5099ac24	352
f2b60f7d	353	#[derive(Clone, PartialEq, Eq, Hash, Debug)]
064997fb	354	struct ComparableTraitRef(Res, Vec<Res>);
f2b60f7d FG	355	impl Default for ComparableTraitRef {
	356	fn default() -> Self {
	357	Self(Res::Err, Vec::new())
064997fb FG	358	}
	359	}
	360
5099ac24	361	fn get_trait_info_from_bound<'a>(bound: &'a GenericBound<'_>) -> Option<(Res, &'a [PathSegment<'a>], Span)> {
064997fb FG	362	if let GenericBound::Trait(t, tbm) = bound {
	363	let trait_path = t.trait_ref.path;
	364	let trait_span = {
	365	let path_span = trait_path.span;
	366	if let TraitBoundModifier::Maybe = tbm {
	367	path_span.with_lo(path_span.lo() - BytePos(1)) // include the `?`
	368	} else {
	369	path_span
	370	}
	371	};
	372	Some((trait_path.res, trait_path.segments, trait_span))
5099ac24 FG	373	} else {
	374	None
	375	}
	376	}
064997fb FG	377
	378	// FIXME: ComparableTraitRef does not support nested bounds needed for associated_type_bounds
	379	fn into_comparable_trait_ref(trait_ref: &TraitRef<'_>) -> ComparableTraitRef {
	380	ComparableTraitRef(
	381	trait_ref.path.res,
	382	trait_ref
	383	.path
	384	.segments
	385	.iter()
	386	.filter_map(\|segment\| {
	387	// get trait bound type arguments
	388	Some(segment.args?.args.iter().filter_map(\|arg\| {
	389	if_chain! {
	390	if let GenericArg::Type(ty) = arg;
	391	if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
	392	then { return Some(path.res) }
	393	}
	394	None
	395	}))
	396	})
	397	.flatten()
	398	.collect(),
	399	)
	400	}
	401
f2b60f7d	402	fn rollup_traits(cx: &LateContext<'_>, bounds: &[GenericBound<'_>], msg: &str) -> Vec<(ComparableTraitRef, Span)> {
064997fb FG	403	let mut map = FxHashMap::default();
	404	let mut repeated_res = false;
	405
	406	let only_comparable_trait_refs = \|bound: &GenericBound<'_>\| {
	407	if let GenericBound::Trait(t, _) = bound {
	408	Some((into_comparable_trait_ref(&t.trait_ref), t.span))
	409	} else {
	410	None
	411	}
	412	};
	413
f2b60f7d	414	let mut i = 0usize;
064997fb FG	415	for bound in bounds.iter().filter_map(only_comparable_trait_refs) {
064997fb FG	416	let (comparable_bound, span_direct) = bound;
f2b60f7d FG	417	match map.entry(comparable_bound) {
	418	Entry::Occupied(_) => repeated_res = true,
	419	Entry::Vacant(e) => {
	420	e.insert((span_direct, i));
	421	i += 1;
	422	},
064997fb FG	423	}
	424	}
	425
f2b60f7d FG	426	// Put bounds in source order
	427	let mut comparable_bounds = vec![Default::default(); map.len()];
	428	for (k, (v, i)) in map {
	429	comparable_bounds[i] = (k, v);
	430	}
	431
064997fb FG	432	if_chain! {
	433	if repeated_res;
	434	if let [first_trait, .., last_trait] = bounds;
	435	then {
	436	let all_trait_span = first_trait.span().to(last_trait.span());
	437
f2b60f7d FG	438	let traits = comparable_bounds.iter()
f2b60f7d FG	439	.filter_map(\|&(_, span)\| snippet_opt(cx, span))
064997fb	440	.collect::<Vec<_>>();
064997fb FG	441	let traits = traits.join(" + ");
	442
	443	span_lint_and_sugg(
	444	cx,
	445	TRAIT_DUPLICATION_IN_BOUNDS,
	446	all_trait_span,
	447	msg,
	448	"try",
	449	traits,
	450	Applicability::MachineApplicable
	451	);
	452	}
	453	}
f2b60f7d FG	454
f2b60f7d FG	455	comparable_bounds
064997fb	456	}