1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::source::{snippet, snippet_with_applicability};
3 use clippy_utils::{SpanlessEq, SpanlessHash};
4 use core::hash::{Hash, Hasher};
5 use if_chain::if_chain;
6 use rustc_data_structures::fx::FxHashMap;
7 use rustc_data_structures::unhash::UnhashMap;
8 use rustc_errors::Applicability;
9 use rustc_hir::def::Res;
11 GenericBound, Generics, Item, ItemKind, Node, ParamName, Path, PathSegment, QPath, TraitItem, Ty, TyKind,
14 use rustc_lint::{LateContext, LateLintPass};
15 use rustc_session::{declare_tool_lint, impl_lint_pass};
18 declare_clippy_lint! {
20 /// This lint warns about unnecessary type repetitions in trait bounds
22 /// ### Why is this bad?
23 /// Repeating the type for every bound makes the code
24 /// less readable than combining the bounds
28 /// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
31 /// Could be written as:
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 {}
56 /// Could be written as:
59 /// fn func<T: Clone + Default>(arg: T) {}
64 /// fn func<T>(arg: T) where T: Clone + Default {}
66 #[clippy::version = "1.47.0"]
67 pub TRAIT_DUPLICATION_IN_BOUNDS,
69 "Check if the same trait bounds are specified twice during a function declaration"
72 #[derive(Copy, Clone)]
73 pub struct TraitBounds {
74 max_trait_bounds: u64,
79 pub fn new(max_trait_bounds: u64) -> Self {
80 Self { max_trait_bounds }
84 impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
86 impl<'tcx> LateLintPass<'tcx> for TraitBounds {
87 fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
88 self.check_type_repetition(cx, gen);
89 check_trait_bound_duplication(cx, gen);
92 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
93 let Generics { where_clause, .. } = &item.generics;
94 let mut self_bounds_map = FxHashMap::default();
96 for predicate in where_clause.predicates {
98 if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
99 if !bound_predicate.span.from_expansion();
100 if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
101 if let Some(PathSegment {
102 res: Some(Res::SelfTy{ trait_: Some(def_id), alias_to: _ }), ..
103 }) = segments.first();
107 kind: ItemKind::Trait(_, _, _, self_bounds, _),
110 ) = cx.tcx.hir().get_if_local(*def_id);
112 if self_bounds_map.is_empty() {
113 for bound in self_bounds.iter() {
114 let Some((self_res, self_segments, _)) = get_trait_info_from_bound(bound) else { continue };
115 self_bounds_map.insert(self_res, self_segments);
122 .filter_map(get_trait_info_from_bound)
123 .for_each(|(trait_item_res, trait_item_segments, span)| {
124 if let Some(self_segments) = self_bounds_map.get(&trait_item_res) {
125 if SpanlessEq::new(cx).eq_path_segments(self_segments, trait_item_segments) {
128 TRAIT_DUPLICATION_IN_BOUNDS,
130 "this trait bound is already specified in trait declaration",
132 "consider removing this trait bound",
144 fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
145 struct SpanlessTy<'cx, 'tcx> {
147 cx: &'cx LateContext<'tcx>,
149 impl PartialEq for SpanlessTy<'_, '_> {
150 fn eq(&self, other: &Self) -> bool {
151 let mut eq = SpanlessEq::new(self.cx);
152 eq.inter_expr().eq_ty(self.ty, other.ty)
155 impl Hash for SpanlessTy<'_, '_> {
156 fn hash<H: Hasher>(&self, h: &mut H) {
157 let mut t = SpanlessHash::new(self.cx);
159 h.write_u64(t.finish());
162 impl Eq for SpanlessTy<'_, '_> {}
164 if gen.span.from_expansion() {
167 let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
168 let mut applicability = Applicability::MaybeIncorrect;
169 for bound in gen.where_clause.predicates {
171 if let WherePredicate::BoundPredicate(ref p) = bound;
172 if p.bounds.len() as u64 <= self.max_trait_bounds;
173 if !p.span.from_expansion();
174 if let Some(ref v) = map.insert(
175 SpanlessTy { ty: p.bounded_ty, cx },
176 p.bounds.iter().collect::<Vec<_>>()
180 let mut hint_string = format!(
181 "consider combining the bounds: `{}:",
182 snippet(cx, p.bounded_ty.span, "_")
185 if let GenericBound::Trait(ref poly_trait_ref, _) = b {
186 let path = &poly_trait_ref.trait_ref.path;
187 hint_string.push_str(&format!(
189 snippet_with_applicability(cx, path.span, "..", &mut applicability)
193 for b in p.bounds.iter() {
194 if let GenericBound::Trait(ref poly_trait_ref, _) = b {
195 let path = &poly_trait_ref.trait_ref.path;
196 hint_string.push_str(&format!(
198 snippet_with_applicability(cx, path.span, "..", &mut applicability)
202 hint_string.truncate(hint_string.len() - 2);
203 hint_string.push('`');
206 TYPE_REPETITION_IN_BOUNDS,
208 "this type has already been used as a bound predicate",
218 fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
219 if gen.span.from_expansion() || gen.params.is_empty() || gen.where_clause.predicates.is_empty() {
223 let mut map = FxHashMap::default();
224 for param in gen.params {
225 if let ParamName::Plain(ref ident) = param.name {
229 .filter_map(get_trait_info_from_bound)
230 .collect::<Vec<_>>();
231 map.insert(*ident, res);
235 for predicate in gen.where_clause.predicates {
237 if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
238 if !bound_predicate.span.from_expansion();
239 if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
240 if let Some(segment) = segments.first();
241 if let Some(trait_resolutions_direct) = map.get(&segment.ident);
243 for (res_where, _, _) in bound_predicate.bounds.iter().filter_map(get_trait_info_from_bound) {
244 if let Some((_, _, span_direct)) = trait_resolutions_direct
246 .find(|(res_direct, _, _)| *res_direct == res_where) {
249 TRAIT_DUPLICATION_IN_BOUNDS,
251 "this trait bound is already specified in the where clause",
253 "consider removing this trait bound",
262 fn get_trait_info_from_bound<'a>(bound: &'a GenericBound<'_>) -> Option<(Res, &'a [PathSegment<'a>], Span)> {
263 if let GenericBound::Trait(t, _) = bound {
264 Some((t.trait_ref.path.res, t.trait_ref.path.segments, t.span))