1 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
2 use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
3 use clippy_utils::{SpanlessEq, SpanlessHash};
4 use core::hash::{Hash, Hasher};
5 use if_chain::if_chain;
6 use itertools::Itertools;
7 use rustc_data_structures::fx::FxHashMap;
8 use rustc_data_structures::unhash::UnhashMap;
9 use rustc_errors::Applicability;
10 use rustc_hir::def::Res;
12 GenericArg, GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath,
13 TraitBoundModifier, TraitItem, TraitRef, Ty, TyKind, WherePredicate,
15 use rustc_lint::{LateContext, LateLintPass};
16 use rustc_session::{declare_tool_lint, impl_lint_pass};
17 use rustc_span::{BytePos, Span};
19 declare_clippy_lint! {
21 /// This lint warns about unnecessary type repetitions in trait bounds
23 /// ### Why is this bad?
24 /// Repeating the type for every bound makes the code
25 /// less readable than combining the bounds
29 /// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
34 /// pub fn foo<T>(t: T) where T: Copy + Clone {}
36 #[clippy::version = "1.38.0"]
37 pub TYPE_REPETITION_IN_BOUNDS,
39 "types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
42 declare_clippy_lint! {
44 /// Checks for cases where generics are being used and multiple
45 /// syntax specifications for trait bounds are used simultaneously.
47 /// ### Why is this bad?
48 /// Duplicate bounds makes the code
49 /// less readable than specifying them only once.
53 /// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
59 /// fn func<T: Clone + Default>(arg: T) {}
64 /// fn func<T>(arg: T) where T: Clone + Default {}
68 /// fn foo<T: Default + Default>(bar: T) {}
72 /// fn foo<T: Default>(bar: T) {}
76 /// fn foo<T>(bar: T) where T: Default + Default {}
80 /// fn foo<T>(bar: T) where T: Default {}
82 #[clippy::version = "1.47.0"]
83 pub TRAIT_DUPLICATION_IN_BOUNDS,
85 "check if the same trait bounds are specified more than once during a generic declaration"
88 #[derive(Copy, Clone)]
89 pub struct TraitBounds {
90 max_trait_bounds: u64,
95 pub fn new(max_trait_bounds: u64) -> Self {
96 Self { max_trait_bounds }
100 impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
102 impl<'tcx> LateLintPass<'tcx> for TraitBounds {
103 fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
104 self.check_type_repetition(cx, gen);
105 check_trait_bound_duplication(cx, gen);
106 check_bounds_or_where_duplication(cx, gen);
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 {}
113 kind: ItemKind::Trait(_, _, _, bounds, ..),
117 rollup_traits(cx, bounds, "these bounds contain repeated elements");
121 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
122 let mut self_bounds_map = FxHashMap::default();
124 for predicate in item.generics.predicates {
126 if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
127 if bound_predicate.origin != PredicateOrigin::ImplTrait;
128 if !bound_predicate.span.from_expansion();
129 if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
130 if let Some(PathSegment {
131 res: Some(Res::SelfTy{ trait_: Some(def_id), alias_to: _ }), ..
132 }) = segments.first();
136 kind: ItemKind::Trait(_, _, _, self_bounds, _),
139 ) = cx.tcx.hir().get_if_local(*def_id);
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);
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) {
157 TRAIT_DUPLICATION_IN_BOUNDS,
159 "this trait bound is already specified in trait declaration",
161 "consider removing this trait bound",
173 fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
174 struct SpanlessTy<'cx, 'tcx> {
176 cx: &'cx LateContext<'tcx>,
178 impl PartialEq for SpanlessTy<'_, '_> {
179 fn eq(&self, other: &Self) -> bool {
180 let mut eq = SpanlessEq::new(self.cx);
181 eq.inter_expr().eq_ty(self.ty, other.ty)
184 impl Hash for SpanlessTy<'_, '_> {
185 fn hash<H: Hasher>(&self, h: &mut H) {
186 let mut t = SpanlessHash::new(self.cx);
188 h.write_u64(t.finish());
191 impl Eq for SpanlessTy<'_, '_> {}
193 if gen.span.from_expansion() {
196 let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
197 let mut applicability = Applicability::MaybeIncorrect;
198 for bound in gen.predicates {
200 if let WherePredicate::BoundPredicate(ref p) = bound;
201 if p.origin != PredicateOrigin::ImplTrait;
202 if p.bounds.len() as u64 <= self.max_trait_bounds;
203 if !p.span.from_expansion();
204 if let Some(ref v) = map.insert(
205 SpanlessTy { ty: p.bounded_ty, cx },
206 p.bounds.iter().collect::<Vec<_>>()
213 .chain(p.bounds.iter())
214 .filter_map(get_trait_info_from_bound)
215 .map(|(_, _, span)| snippet_with_applicability(cx, span, "..", &mut applicability))
217 let hint_string = format!(
218 "consider combining the bounds: `{}: {}`",
219 snippet(cx, p.bounded_ty.span, "_"),
224 TYPE_REPETITION_IN_BOUNDS,
226 "this type has already been used as a bound predicate",
236 fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
237 if gen.span.from_expansion() || gen.params.is_empty() || gen.predicates.is_empty() {
241 let mut map = FxHashMap::<_, Vec<_>>::default();
242 for predicate in gen.predicates {
244 if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
245 if bound_predicate.origin != PredicateOrigin::ImplTrait;
246 if !bound_predicate.span.from_expansion();
247 if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
248 if let Some(segment) = segments.first();
250 for (res_where, _, span_where) in bound_predicate.bounds.iter().filter_map(get_trait_info_from_bound) {
251 let trait_resolutions_direct = map.entry(segment.ident).or_default();
252 if let Some((_, span_direct)) = trait_resolutions_direct
254 .find(|(res_direct, _)| *res_direct == res_where) {
257 TRAIT_DUPLICATION_IN_BOUNDS,
259 "this trait bound is already specified in the where clause",
261 "consider removing this trait bound",
265 trait_resolutions_direct.push((res_where, span_where));
273 #[derive(PartialEq, Eq, Hash, Debug)]
274 struct ComparableTraitRef(Res, Vec<Res>);
276 fn check_bounds_or_where_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
277 if gen.span.from_expansion() {
281 for predicate in gen.predicates {
282 if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate {
283 let msg = if predicate.in_where_clause() {
284 "these where clauses contain repeated elements"
286 "these bounds contain repeated elements"
288 rollup_traits(cx, bound_predicate.bounds, msg);
293 fn get_trait_info_from_bound<'a>(bound: &'a GenericBound<'_>) -> Option<(Res, &'a [PathSegment<'a>], Span)> {
294 if let GenericBound::Trait(t, tbm) = bound {
295 let trait_path = t.trait_ref.path;
297 let path_span = trait_path.span;
298 if let TraitBoundModifier::Maybe = tbm {
299 path_span.with_lo(path_span.lo() - BytePos(1)) // include the `?`
304 Some((trait_path.res, trait_path.segments, trait_span))
310 // FIXME: ComparableTraitRef does not support nested bounds needed for associated_type_bounds
311 fn into_comparable_trait_ref(trait_ref: &TraitRef<'_>) -> ComparableTraitRef {
318 .filter_map(|segment| {
319 // get trait bound type arguments
320 Some(segment.args?.args.iter().filter_map(|arg| {
322 if let GenericArg::Type(ty) = arg;
323 if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
324 then { return Some(path.res) }
334 fn rollup_traits(cx: &LateContext<'_>, bounds: &[GenericBound<'_>], msg: &str) {
335 let mut map = FxHashMap::default();
336 let mut repeated_res = false;
338 let only_comparable_trait_refs = |bound: &GenericBound<'_>| {
339 if let GenericBound::Trait(t, _) = bound {
340 Some((into_comparable_trait_ref(&t.trait_ref), t.span))
346 for bound in bounds.iter().filter_map(only_comparable_trait_refs) {
347 let (comparable_bound, span_direct) = bound;
348 if map.insert(comparable_bound, span_direct).is_some() {
355 if let [first_trait, .., last_trait] = bounds;
357 let all_trait_span = first_trait.span().to(last_trait.span());
359 let mut traits = map.values()
360 .filter_map(|span| snippet_opt(cx, *span))
361 .collect::<Vec<_>>();
362 traits.sort_unstable();
363 let traits = traits.join(" + ");
367 TRAIT_DUPLICATION_IN_BOUNDS,
372 Applicability::MachineApplicable