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, FxHashSet};
   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 specifing 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_set = FxHashSet::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 { res: Some(Res::SelfTy(Some(def_id), _)), .. }) = segments.first();
 102
 103                 if let Some(
 104                     Node::Item(
 105                         Item {
 106                             kind: ItemKind::Trait(_, _, _, self_bounds, _),
 107                             .. }
 108                         )
 109                     ) = cx.tcx.hir().get_if_local(*def_id);
 110                 then {
 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);
 115                         }
 116                     }
 117
 118                     bound_predicate
 119                         .bounds
 120                         .iter()
 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() {
 124                                 emit_lint(cx, span);
 125                             }
 126                         });
 127                 }
 128             }
 129         }
 130     }
 131 }
 132
 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))
 136     } else {
 137         None
 138     }
 139 }
 140
 141 impl TraitBounds {
 142     fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
 143         struct SpanlessTy<'cx, 'tcx> {
 144             ty: &'tcx Ty<'tcx>,
 145             cx: &'cx LateContext<'tcx>,
 146         }
 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)
 151             }
 152         }
 153         impl Hash for SpanlessTy<'_, '_> {
 154             fn hash<H: Hasher>(&self, h: &mut H) {
 155                 let mut t = SpanlessHash::new(self.cx);
 156                 t.hash_ty(self.ty);
 157                 h.write_u64(t.finish());
 158             }
 159         }
 160         impl Eq for SpanlessTy<'_, '_> {}
 161
 162         if gen.span.from_expansion() {
 163             return;
 164         }
 165         let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
 166         let mut applicability = Applicability::MaybeIncorrect;
 167         for bound in gen.where_clause.predicates {
 168             if_chain! {
 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<_>>()
 175                 );
 176
 177                 then {
 178                     let mut hint_string = format!(
 179                         "consider combining the bounds: `{}:",
 180                         snippet(cx, p.bounded_ty.span, "_")
 181                     );
 182                     for b in v.iter() {
 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!(
 186                                 " {} +",
 187                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 188                             ));
 189                         }
 190                     }
 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!(
 195                                 " {} +",
 196                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 197                             ));
 198                         }
 199                     }
 200                     hint_string.truncate(hint_string.len() - 2);
 201                     hint_string.push('`');
 202                     span_lint_and_help(
 203                         cx,
 204                         TYPE_REPETITION_IN_BOUNDS,
 205                         p.span,
 206                         "this type has already been used as a bound predicate",
 207                         None,
 208                         &hint_string,
 209                     );
 210                 }
 211             }
 212         }
 213     }
 214 }
 215
 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() {
 218         return;
 219     }
 220
 221     let mut map = FxHashMap::default();
 222     for param in gen.params {
 223         if let ParamName::Plain(ref ident) = param.name {
 224             let res = param
 225                 .bounds
 226                 .iter()
 227                 .filter_map(get_trait_res_span_from_bound)
 228                 .collect::<Vec<_>>();
 229             map.insert(*ident, res);
 230         }
 231     }
 232
 233     for predicate in gen.where_clause.predicates {
 234         if_chain! {
 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);
 240             then {
 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
 243                                                 .iter()
 244                                                 .find(|(res_direct, _)| *res_direct == res_where) {
 245                         emit_lint(cx, *span_direct);
 246                     }
 247                 }
 248             }
 249         }
 250     }
 251 }
 252
 253 fn emit_lint(cx: &LateContext<'_>, span: Span) {
 254     span_lint_and_help(
 255         cx,
 256         TRAIT_DUPLICATION_IN_BOUNDS,
 257         span,
 258         "this trait bound is already specified in the where clause",
 259         None,
 260         "consider removing this trait bound",
 261     );
 262 }