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, ParamName, Path, PathSegment, 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
  18 declare_clippy_lint! {
  19     /// ### What it does
  20     /// This lint warns about unnecessary type repetitions in trait bounds
  21     ///
  22     /// ### Why is this bad?
  23     /// Repeating the type for every bound makes the code
  24     /// less readable than combining the bounds
  25     ///
  26     /// ### Example
  27     /// ```rust
  28     /// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
  29     /// ```
  30     ///
  31     /// Could be written as:
  32     ///
  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     pedantic,
  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     /// Could be written as:
  57     ///
  58     /// ```rust
  59     /// fn func<T: Clone + Default>(arg: T) {}
  60     /// ```
  61     /// or
  62     ///
  63     /// ```rust
  64     /// fn func<T>(arg: T) where T: Clone + Default {}
  65     /// ```
  66     #[clippy::version = "1.47.0"]
  67     pub TRAIT_DUPLICATION_IN_BOUNDS,
  68     pedantic,
  69     "Check if the same trait bounds are specified twice during a function declaration"
  70 }
  71
  72 #[derive(Copy, Clone)]
  73 pub struct TraitBounds {
  74     max_trait_bounds: u64,
  75 }
  76
  77 impl TraitBounds {
  78     #[must_use]
  79     pub fn new(max_trait_bounds: u64) -> Self {
  80         Self { max_trait_bounds }
  81     }
  82 }
  83
  84 impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
  85
  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);
  90     }
  91
  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();
  95
  96         for predicate in where_clause.predicates {
  97             if_chain! {
  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();
 104                 if let Some(
 105                     Node::Item(
 106                         Item {
 107                             kind: ItemKind::Trait(_, _, _, self_bounds, _),
 108                             .. }
 109                         )
 110                     ) = cx.tcx.hir().get_if_local(*def_id);
 111                 then {
 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);
 116                         }
 117                     }
 118
 119                     bound_predicate
 120                         .bounds
 121                         .iter()
 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) {
 126                                     span_lint_and_help(
 127                                         cx,
 128                                         TRAIT_DUPLICATION_IN_BOUNDS,
 129                                         span,
 130                                         "this trait bound is already specified in trait declaration",
 131                                         None,
 132                                         "consider removing this trait bound",
 133                                     );
 134                                 }
 135                             }
 136                         });
 137                 }
 138             }
 139         }
 140     }
 141 }
 142
 143 impl TraitBounds {
 144     fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
 145         struct SpanlessTy<'cx, 'tcx> {
 146             ty: &'tcx Ty<'tcx>,
 147             cx: &'cx LateContext<'tcx>,
 148         }
 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)
 153             }
 154         }
 155         impl Hash for SpanlessTy<'_, '_> {
 156             fn hash<H: Hasher>(&self, h: &mut H) {
 157                 let mut t = SpanlessHash::new(self.cx);
 158                 t.hash_ty(self.ty);
 159                 h.write_u64(t.finish());
 160             }
 161         }
 162         impl Eq for SpanlessTy<'_, '_> {}
 163
 164         if gen.span.from_expansion() {
 165             return;
 166         }
 167         let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
 168         let mut applicability = Applicability::MaybeIncorrect;
 169         for bound in gen.where_clause.predicates {
 170             if_chain! {
 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<_>>()
 177                 );
 178
 179                 then {
 180                     let mut hint_string = format!(
 181                         "consider combining the bounds: `{}:",
 182                         snippet(cx, p.bounded_ty.span, "_")
 183                     );
 184                     for b in v.iter() {
 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!(
 188                                 " {} +",
 189                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 190                             ));
 191                         }
 192                     }
 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!(
 197                                 " {} +",
 198                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 199                             ));
 200                         }
 201                     }
 202                     hint_string.truncate(hint_string.len() - 2);
 203                     hint_string.push('`');
 204                     span_lint_and_help(
 205                         cx,
 206                         TYPE_REPETITION_IN_BOUNDS,
 207                         p.span,
 208                         "this type has already been used as a bound predicate",
 209                         None,
 210                         &hint_string,
 211                     );
 212                 }
 213             }
 214         }
 215     }
 216 }
 217
 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() {
 220         return;
 221     }
 222
 223     let mut map = FxHashMap::default();
 224     for param in gen.params {
 225         if let ParamName::Plain(ref ident) = param.name {
 226             let res = param
 227                 .bounds
 228                 .iter()
 229                 .filter_map(get_trait_info_from_bound)
 230                 .collect::<Vec<_>>();
 231             map.insert(*ident, res);
 232         }
 233     }
 234
 235     for predicate in gen.where_clause.predicates {
 236         if_chain! {
 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);
 242             then {
 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
 245                                                 .iter()
 246                                                 .find(|(res_direct, _, _)| *res_direct == res_where) {
 247                         span_lint_and_help(
 248                             cx,
 249                             TRAIT_DUPLICATION_IN_BOUNDS,
 250                             *span_direct,
 251                             "this trait bound is already specified in the where clause",
 252                             None,
 253                             "consider removing this trait bound",
 254                         );
 255                     }
 256                 }
 257             }
 258         }
 259     }
 260 }
 261
 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))
 265     } else {
 266         None
 267     }
 268 }