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, FxHashSet};
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 specifing 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_set = FxHashSet::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 { res: Some(Res::SelfTy(Some(def_id), _)), .. }) = segments.first();
106 kind: ItemKind::Trait(_, _, _, self_bounds, _),
109 ) = cx.tcx.hir().get_if_local(*def_id);
111 if self_bounds_set.is_empty() {
112 for bound in self_bounds.iter() {
113 let Some((self_res, _)) = get_trait_res_span_from_bound(bound) else { continue };
114 self_bounds_set.insert(self_res);
121 .filter_map(get_trait_res_span_from_bound)
122 .for_each(|(trait_item_res, span)| {
123 if self_bounds_set.get(&trait_item_res).is_some() {
133 fn get_trait_res_span_from_bound(bound: &GenericBound<'_>) -> Option<(Res, Span)> {
134 if let GenericBound::Trait(t, _) = bound {
135 Some((t.trait_ref.path.res, t.span))
142 fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
143 struct SpanlessTy<'cx, 'tcx> {
145 cx: &'cx LateContext<'tcx>,
147 impl PartialEq for SpanlessTy<'_, '_> {
148 fn eq(&self, other: &Self) -> bool {
149 let mut eq = SpanlessEq::new(self.cx);
150 eq.inter_expr().eq_ty(self.ty, other.ty)
153 impl Hash for SpanlessTy<'_, '_> {
154 fn hash<H: Hasher>(&self, h: &mut H) {
155 let mut t = SpanlessHash::new(self.cx);
157 h.write_u64(t.finish());
160 impl Eq for SpanlessTy<'_, '_> {}
162 if gen.span.from_expansion() {
165 let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
166 let mut applicability = Applicability::MaybeIncorrect;
167 for bound in gen.where_clause.predicates {
169 if let WherePredicate::BoundPredicate(ref p) = bound;
170 if p.bounds.len() as u64 <= self.max_trait_bounds;
171 if !p.span.from_expansion();
172 if let Some(ref v) = map.insert(
173 SpanlessTy { ty: p.bounded_ty, cx },
174 p.bounds.iter().collect::<Vec<_>>()
178 let mut hint_string = format!(
179 "consider combining the bounds: `{}:",
180 snippet(cx, p.bounded_ty.span, "_")
183 if let GenericBound::Trait(ref poly_trait_ref, _) = b {
184 let path = &poly_trait_ref.trait_ref.path;
185 hint_string.push_str(&format!(
187 snippet_with_applicability(cx, path.span, "..", &mut applicability)
191 for b in p.bounds.iter() {
192 if let GenericBound::Trait(ref poly_trait_ref, _) = b {
193 let path = &poly_trait_ref.trait_ref.path;
194 hint_string.push_str(&format!(
196 snippet_with_applicability(cx, path.span, "..", &mut applicability)
200 hint_string.truncate(hint_string.len() - 2);
201 hint_string.push('`');
204 TYPE_REPETITION_IN_BOUNDS,
206 "this type has already been used as a bound predicate",
216 fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
217 if gen.span.from_expansion() || gen.params.is_empty() || gen.where_clause.predicates.is_empty() {
221 let mut map = FxHashMap::default();
222 for param in gen.params {
223 if let ParamName::Plain(ref ident) = param.name {
227 .filter_map(get_trait_res_span_from_bound)
228 .collect::<Vec<_>>();
229 map.insert(*ident, res);
233 for predicate in gen.where_clause.predicates {
235 if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
236 if !bound_predicate.span.from_expansion();
237 if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
238 if let Some(segment) = segments.first();
239 if let Some(trait_resolutions_direct) = map.get(&segment.ident);
241 for (res_where, _) in bound_predicate.bounds.iter().filter_map(get_trait_res_span_from_bound) {
242 if let Some((_, span_direct)) = trait_resolutions_direct
244 .find(|(res_direct, _)| *res_direct == res_where) {
245 emit_lint(cx, *span_direct);
253 fn emit_lint(cx: &LateContext<'_>, span: Span) {
256 TRAIT_DUPLICATION_IN_BOUNDS,
258 "this trait bound is already specified in the where clause",
260 "consider removing this trait bound",