clippy_lints/src/trait_bounds.rs

   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;
  11 use rustc_hir::{
  12     GenericArg, GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath,
  13     TraitBoundModifier, TraitItem, TraitRef, Ty, TyKind, WherePredicate,
  14 };
  15 use rustc_lint::{LateContext, LateLintPass};
  16 use rustc_session::{declare_tool_lint, impl_lint_pass};
  17 use rustc_span::{BytePos, Span};
  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     /// Use instead:
  33     /// ```rust
  34     /// pub fn foo<T>(t: T) where T: Copy + Clone {}
  35     /// ```
  36     #[clippy::version = "1.38.0"]
  37     pub TYPE_REPETITION_IN_BOUNDS,
  38     nursery,
  39     "types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
  40 }
  41
  42 declare_clippy_lint! {
  43     /// ### What it does
  44     /// Checks for cases where generics are being used and multiple
  45     /// syntax specifications for trait bounds are used simultaneously.
  46     ///
  47     /// ### Why is this bad?
  48     /// Duplicate bounds makes the code
  49     /// less readable than specifying them only once.
  50     ///
  51     /// ### Example
  52     /// ```rust
  53     /// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
  54     /// ```
  55     ///
  56     /// Use instead:
  57     /// ```rust
  58     /// # mod hidden {
  59     /// fn func<T: Clone + Default>(arg: T) {}
  60     /// # }
  61     ///
  62     /// // or
  63     ///
  64     /// fn func<T>(arg: T) where T: Clone + Default {}
  65     /// ```
  66     ///
  67     /// ```rust
  68     /// fn foo<T: Default + Default>(bar: T) {}
  69     /// ```
  70     /// Use instead:
  71     /// ```rust
  72     /// fn foo<T: Default>(bar: T) {}
  73     /// ```
  74     ///
  75     /// ```rust
  76     /// fn foo<T>(bar: T) where T: Default + Default {}
  77     /// ```
  78     /// Use instead:
  79     /// ```rust
  80     /// fn foo<T>(bar: T) where T: Default {}
  81     /// ```
  82     #[clippy::version = "1.47.0"]
  83     pub TRAIT_DUPLICATION_IN_BOUNDS,
  84     nursery,
  85     "check if the same trait bounds are specified more than once during a generic declaration"
  86 }
  87
  88 #[derive(Copy, Clone)]
  89 pub struct TraitBounds {
  90     max_trait_bounds: u64,
  91 }
  92
  93 impl TraitBounds {
  94     #[must_use]
  95     pub fn new(max_trait_bounds: u64) -> Self {
  96         Self { max_trait_bounds }
  97     }
  98 }
  99
 100 impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
 101
 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);
 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         }
 119     }
 120
 121     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
 122         let mut self_bounds_map = FxHashMap::default();
 123
 124         for predicate in item.generics.predicates {
 125             if_chain! {
 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();
 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         }
 169     }
 170 }
 171
 172 impl TraitBounds {
 173     fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
 174         struct SpanlessTy<'cx, 'tcx> {
 175             ty: &'tcx Ty<'tcx>,
 176             cx: &'cx LateContext<'tcx>,
 177         }
 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)
 182             }
 183         }
 184         impl Hash for SpanlessTy<'_, '_> {
 185             fn hash<H: Hasher>(&self, h: &mut H) {
 186                 let mut t = SpanlessHash::new(self.cx);
 187                 t.hash_ty(self.ty);
 188                 h.write_u64(t.finish());
 189             }
 190         }
 191         impl Eq for SpanlessTy<'_, '_> {}
 192
 193         if gen.span.from_expansion() {
 194             return;
 195         }
 196         let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
 197         let mut applicability = Applicability::MaybeIncorrect;
 198         for bound in gen.predicates {
 199             if_chain! {
 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<_>>()
 207                 );
 208
 209                 then {
 210                     let trait_bounds = v
 211                         .iter()
 212                         .copied()
 213                         .chain(p.bounds.iter())
 214                         .filter_map(get_trait_info_from_bound)
 215                         .map(|(_, _, span)| snippet_with_applicability(cx, span, "..", &mut applicability))
 216                         .join(" + ");
 217                     let hint_string = format!(
 218                         "consider combining the bounds: `{}: {}`",
 219                         snippet(cx, p.bounded_ty.span, "_"),
 220                         trait_bounds,
 221                     );
 222                     span_lint_and_help(
 223                         cx,
 224                         TYPE_REPETITION_IN_BOUNDS,
 225                         p.span,
 226                         "this type has already been used as a bound predicate",
 227                         None,
 228                         &hint_string,
 229                     );
 230                 }
 231             }
 232         }
 233     }
 234 }
 235
 236 fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
 237     if gen.span.from_expansion() || gen.params.is_empty() || gen.predicates.is_empty() {
 238         return;
 239     }
 240
 241     let mut map = FxHashMap::<_, Vec<_>>::default();
 242     for predicate in gen.predicates {
 243         if_chain! {
 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();
 249             then {
 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
 253                                                 .iter()
 254                                                 .find(|(res_direct, _)| *res_direct == res_where) {
 255                         span_lint_and_help(
 256                             cx,
 257                             TRAIT_DUPLICATION_IN_BOUNDS,
 258                             *span_direct,
 259                             "this trait bound is already specified in the where clause",
 260                             None,
 261                             "consider removing this trait bound",
 262                         );
 263                     }
 264                     else {
 265                         trait_resolutions_direct.push((res_where, span_where));
 266                     }
 267                 }
 268             }
 269         }
 270     }
 271 }
 272
 273 #[derive(PartialEq, Eq, Hash, Debug)]
 274 struct ComparableTraitRef(Res, Vec<Res>);
 275
 276 fn check_bounds_or_where_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
 277     if gen.span.from_expansion() {
 278         return;
 279     }
 280
 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"
 285             } else {
 286                 "these bounds contain repeated elements"
 287             };
 288             rollup_traits(cx, bound_predicate.bounds, msg);
 289         }
 290     }
 291 }
 292
 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;
 296         let trait_span = {
 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 `?`
 300             } else {
 301                 path_span
 302             }
 303         };
 304         Some((trait_path.res, trait_path.segments, trait_span))
 305     } else {
 306         None
 307     }
 308 }
 309
 310 // FIXME: ComparableTraitRef does not support nested bounds needed for associated_type_bounds
 311 fn into_comparable_trait_ref(trait_ref: &TraitRef<'_>) -> ComparableTraitRef {
 312     ComparableTraitRef(
 313         trait_ref.path.res,
 314         trait_ref
 315             .path
 316             .segments
 317             .iter()
 318             .filter_map(|segment| {
 319                 // get trait bound type arguments
 320                 Some(segment.args?.args.iter().filter_map(|arg| {
 321                     if_chain! {
 322                         if let GenericArg::Type(ty) = arg;
 323                         if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
 324                         then { return Some(path.res) }
 325                     }
 326                     None
 327                 }))
 328             })
 329             .flatten()
 330             .collect(),
 331     )
 332 }
 333
 334 fn rollup_traits(cx: &LateContext<'_>, bounds: &[GenericBound<'_>], msg: &str) {
 335     let mut map = FxHashMap::default();
 336     let mut repeated_res = false;
 337
 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))
 341         } else {
 342             None
 343         }
 344     };
 345
 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() {
 349             repeated_res = true;
 350         }
 351     }
 352
 353     if_chain! {
 354         if repeated_res;
 355         if let [first_trait, .., last_trait] = bounds;
 356         then {
 357             let all_trait_span = first_trait.span().to(last_trait.span());
 358
 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(" + ");
 364
 365             span_lint_and_sugg(
 366                 cx,
 367                 TRAIT_DUPLICATION_IN_BOUNDS,
 368                 all_trait_span,
 369                 msg,
 370                 "try",
 371                 traits,
 372                 Applicability::MachineApplicable
 373             );
 374         }
 375     }
 376 }