clippy_lints/src/trait_bounds.rs

   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;
  10 use rustc_hir::{
  11     GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath, TraitItem, Ty, TyKind,
  12     WherePredicate,
  13 };
  14 use rustc_lint::{LateContext, LateLintPass};
  15 use rustc_session::{declare_tool_lint, impl_lint_pass};
  16 use rustc_span::Span;
  17 use std::fmt::Write as _;
  18
  19 declare_clippy_lint! {
  20     /// ### What it does
  21     /// This lint warns about unnecessary type repetitions in trait bounds
  22     ///
  23     /// ### Why is this bad?
  24     /// Repeating the type for every bound makes the code
  25     /// less readable than combining the bounds
  26     ///
  27     /// ### Example
  28     /// ```rust
  29     /// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
  30     /// ```
  31     ///
  32     /// Could be written as:
  33     ///
  34     /// ```rust
  35     /// pub fn foo<T>(t: T) where T: Copy + Clone {}
  36     /// ```
  37     #[clippy::version = "1.38.0"]
  38     pub TYPE_REPETITION_IN_BOUNDS,
  39     pedantic,
  40     "Types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
  41 }
  42
  43 declare_clippy_lint! {
  44     /// ### What it does
  45     /// Checks for cases where generics are being used and multiple
  46     /// syntax specifications for trait bounds are used simultaneously.
  47     ///
  48     /// ### Why is this bad?
  49     /// Duplicate bounds makes the code
  50     /// less readable than specifying them only once.
  51     ///
  52     /// ### Example
  53     /// ```rust
  54     /// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
  55     /// ```
  56     ///
  57     /// Could be written as:
  58     ///
  59     /// ```rust
  60     /// fn func<T: Clone + Default>(arg: T) {}
  61     /// ```
  62     /// or
  63     ///
  64     /// ```rust
  65     /// fn func<T>(arg: T) where T: Clone + Default {}
  66     /// ```
  67     #[clippy::version = "1.47.0"]
  68     pub TRAIT_DUPLICATION_IN_BOUNDS,
  69     pedantic,
  70     "Check if the same trait bounds are specified twice during a function declaration"
  71 }
  72
  73 #[derive(Copy, Clone)]
  74 pub struct TraitBounds {
  75     max_trait_bounds: u64,
  76 }
  77
  78 impl TraitBounds {
  79     #[must_use]
  80     pub fn new(max_trait_bounds: u64) -> Self {
  81         Self { max_trait_bounds }
  82     }
  83 }
  84
  85 impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
  86
  87 impl<'tcx> LateLintPass<'tcx> for TraitBounds {
  88     fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
  89         self.check_type_repetition(cx, gen);
  90         check_trait_bound_duplication(cx, gen);
  91     }
  92
  93     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
  94         let mut self_bounds_map = FxHashMap::default();
  95
  96         for predicate in item.generics.predicates {
  97             if_chain! {
  98                 if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
  99                 if bound_predicate.origin != PredicateOrigin::ImplTrait;
 100                 if !bound_predicate.span.from_expansion();
 101                 if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
 102                 if let Some(PathSegment {
 103                     res: Some(Res::SelfTy{ trait_: Some(def_id), alias_to: _ }), ..
 104                 }) = segments.first();
 105                 if let Some(
 106                     Node::Item(
 107                         Item {
 108                             kind: ItemKind::Trait(_, _, _, self_bounds, _),
 109                             .. }
 110                         )
 111                     ) = cx.tcx.hir().get_if_local(*def_id);
 112                 then {
 113                     if self_bounds_map.is_empty() {
 114                         for bound in self_bounds.iter() {
 115                             let Some((self_res, self_segments, _)) = get_trait_info_from_bound(bound) else { continue };
 116                             self_bounds_map.insert(self_res, self_segments);
 117                         }
 118                     }
 119
 120                     bound_predicate
 121                         .bounds
 122                         .iter()
 123                         .filter_map(get_trait_info_from_bound)
 124                         .for_each(|(trait_item_res, trait_item_segments, span)| {
 125                             if let Some(self_segments) = self_bounds_map.get(&trait_item_res) {
 126                                 if SpanlessEq::new(cx).eq_path_segments(self_segments, trait_item_segments) {
 127                                     span_lint_and_help(
 128                                         cx,
 129                                         TRAIT_DUPLICATION_IN_BOUNDS,
 130                                         span,
 131                                         "this trait bound is already specified in trait declaration",
 132                                         None,
 133                                         "consider removing this trait bound",
 134                                     );
 135                                 }
 136                             }
 137                         });
 138                 }
 139             }
 140         }
 141     }
 142 }
 143
 144 impl TraitBounds {
 145     fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
 146         struct SpanlessTy<'cx, 'tcx> {
 147             ty: &'tcx Ty<'tcx>,
 148             cx: &'cx LateContext<'tcx>,
 149         }
 150         impl PartialEq for SpanlessTy<'_, '_> {
 151             fn eq(&self, other: &Self) -> bool {
 152                 let mut eq = SpanlessEq::new(self.cx);
 153                 eq.inter_expr().eq_ty(self.ty, other.ty)
 154             }
 155         }
 156         impl Hash for SpanlessTy<'_, '_> {
 157             fn hash<H: Hasher>(&self, h: &mut H) {
 158                 let mut t = SpanlessHash::new(self.cx);
 159                 t.hash_ty(self.ty);
 160                 h.write_u64(t.finish());
 161             }
 162         }
 163         impl Eq for SpanlessTy<'_, '_> {}
 164
 165         if gen.span.from_expansion() {
 166             return;
 167         }
 168         let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
 169         let mut applicability = Applicability::MaybeIncorrect;
 170         for bound in gen.predicates {
 171             if_chain! {
 172                 if let WherePredicate::BoundPredicate(ref p) = bound;
 173                 if p.origin != PredicateOrigin::ImplTrait;
 174                 if p.bounds.len() as u64 <= self.max_trait_bounds;
 175                 if !p.span.from_expansion();
 176                 if let Some(ref v) = map.insert(
 177                     SpanlessTy { ty: p.bounded_ty, cx },
 178                     p.bounds.iter().collect::<Vec<_>>()
 179                 );
 180
 181                 then {
 182                     let mut hint_string = format!(
 183                         "consider combining the bounds: `{}:",
 184                         snippet(cx, p.bounded_ty.span, "_")
 185                     );
 186                     for b in v.iter() {
 187                         if let GenericBound::Trait(ref poly_trait_ref, _) = b {
 188                             let path = &poly_trait_ref.trait_ref.path;
 189                             let _ = write!(hint_string,
 190                                 " {} +",
 191                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 192                             );
 193                         }
 194                     }
 195                     for b in p.bounds.iter() {
 196                         if let GenericBound::Trait(ref poly_trait_ref, _) = b {
 197                             let path = &poly_trait_ref.trait_ref.path;
 198                             let _ = write!(hint_string,
 199                                 " {} +",
 200                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 201                             );
 202                         }
 203                     }
 204                     hint_string.truncate(hint_string.len() - 2);
 205                     hint_string.push('`');
 206                     span_lint_and_help(
 207                         cx,
 208                         TYPE_REPETITION_IN_BOUNDS,
 209                         p.span,
 210                         "this type has already been used as a bound predicate",
 211                         None,
 212                         &hint_string,
 213                     );
 214                 }
 215             }
 216         }
 217     }
 218 }
 219
 220 fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
 221     if gen.span.from_expansion() || gen.params.is_empty() || gen.predicates.is_empty() {
 222         return;
 223     }
 224
 225     let mut map = FxHashMap::<_, Vec<_>>::default();
 226     for predicate in gen.predicates {
 227         if_chain! {
 228             if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
 229             if bound_predicate.origin != PredicateOrigin::ImplTrait;
 230             if !bound_predicate.span.from_expansion();
 231             if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
 232             if let Some(segment) = segments.first();
 233             then {
 234                 for (res_where, _, span_where) in bound_predicate.bounds.iter().filter_map(get_trait_info_from_bound) {
 235                     let trait_resolutions_direct = map.entry(segment.ident).or_default();
 236                     if let Some((_, span_direct)) = trait_resolutions_direct
 237                                                 .iter()
 238                                                 .find(|(res_direct, _)| *res_direct == res_where) {
 239                         span_lint_and_help(
 240                             cx,
 241                             TRAIT_DUPLICATION_IN_BOUNDS,
 242                             *span_direct,
 243                             "this trait bound is already specified in the where clause",
 244                             None,
 245                             "consider removing this trait bound",
 246                         );
 247                     }
 248                     else {
 249                         trait_resolutions_direct.push((res_where, span_where));
 250                     }
 251                 }
 252             }
 253         }
 254     }
 255 }
 256
 257 fn get_trait_info_from_bound<'a>(bound: &'a GenericBound<'_>) -> Option<(Res, &'a [PathSegment<'a>], Span)> {
 258     if let GenericBound::Trait(t, _) = bound {
 259         Some((t.trait_ref.path.res, t.trait_ref.path.segments, t.span))
 260     } else {
 261         None
 262     }
 263 }