src/tools/clippy/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::SpanlessHash;
   4 use if_chain::if_chain;
   5 use rustc_data_structures::fx::FxHashMap;
   6 use rustc_data_structures::unhash::UnhashMap;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{def::Res, GenericBound, Generics, ParamName, Path, QPath, TyKind, WherePredicate};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_session::{declare_tool_lint, impl_lint_pass};
  11 use rustc_span::Span;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// This lint warns about unnecessary type repetitions in trait bounds
  16     ///
  17     /// ### Why is this bad?
  18     /// Repeating the type for every bound makes the code
  19     /// less readable than combining the bounds
  20     ///
  21     /// ### Example
  22     /// ```rust
  23     /// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
  24     /// ```
  25     ///
  26     /// Could be written as:
  27     ///
  28     /// ```rust
  29     /// pub fn foo<T>(t: T) where T: Copy + Clone {}
  30     /// ```
  31     #[clippy::version = "1.38.0"]
  32     pub TYPE_REPETITION_IN_BOUNDS,
  33     pedantic,
  34     "Types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
  35 }
  36
  37 declare_clippy_lint! {
  38     /// ### What it does
  39     /// Checks for cases where generics are being used and multiple
  40     /// syntax specifications for trait bounds are used simultaneously.
  41     ///
  42     /// ### Why is this bad?
  43     /// Duplicate bounds makes the code
  44     /// less readable than specifing them only once.
  45     ///
  46     /// ### Example
  47     /// ```rust
  48     /// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
  49     /// ```
  50     ///
  51     /// Could be written as:
  52     ///
  53     /// ```rust
  54     /// fn func<T: Clone + Default>(arg: T) {}
  55     /// ```
  56     /// or
  57     ///
  58     /// ```rust
  59     /// fn func<T>(arg: T) where T: Clone + Default {}
  60     /// ```
  61     #[clippy::version = "1.47.0"]
  62     pub TRAIT_DUPLICATION_IN_BOUNDS,
  63     pedantic,
  64     "Check if the same trait bounds are specified twice during a function declaration"
  65 }
  66
  67 #[derive(Copy, Clone)]
  68 pub struct TraitBounds {
  69     max_trait_bounds: u64,
  70 }
  71
  72 impl TraitBounds {
  73     #[must_use]
  74     pub fn new(max_trait_bounds: u64) -> Self {
  75         Self { max_trait_bounds }
  76     }
  77 }
  78
  79 impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
  80
  81 impl<'tcx> LateLintPass<'tcx> for TraitBounds {
  82     fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
  83         self.check_type_repetition(cx, gen);
  84         check_trait_bound_duplication(cx, gen);
  85     }
  86 }
  87
  88 fn get_trait_res_span_from_bound(bound: &GenericBound<'_>) -> Option<(Res, Span)> {
  89     if let GenericBound::Trait(t, _) = bound {
  90         Some((t.trait_ref.path.res, t.span))
  91     } else {
  92         None
  93     }
  94 }
  95
  96 impl TraitBounds {
  97     fn check_type_repetition(self, cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
  98         if gen.span.from_expansion() {
  99             return;
 100         }
 101         let hash = |ty| -> u64 {
 102             let mut hasher = SpanlessHash::new(cx);
 103             hasher.hash_ty(ty);
 104             hasher.finish()
 105         };
 106         let mut map: UnhashMap<u64, Vec<&GenericBound<'_>>> = UnhashMap::default();
 107         let mut applicability = Applicability::MaybeIncorrect;
 108         for bound in gen.where_clause.predicates {
 109             if_chain! {
 110                 if let WherePredicate::BoundPredicate(ref p) = bound;
 111                 if p.bounds.len() as u64 <= self.max_trait_bounds;
 112                 if !p.span.from_expansion();
 113                 let h = hash(p.bounded_ty);
 114                 if let Some(ref v) = map.insert(h, p.bounds.iter().collect::<Vec<_>>());
 115
 116                 then {
 117                     let mut hint_string = format!(
 118                         "consider combining the bounds: `{}:",
 119                         snippet(cx, p.bounded_ty.span, "_")
 120                     );
 121                     for b in v.iter() {
 122                         if let GenericBound::Trait(ref poly_trait_ref, _) = b {
 123                             let path = &poly_trait_ref.trait_ref.path;
 124                             hint_string.push_str(&format!(
 125                                 " {} +",
 126                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 127                             ));
 128                         }
 129                     }
 130                     for b in p.bounds.iter() {
 131                         if let GenericBound::Trait(ref poly_trait_ref, _) = b {
 132                             let path = &poly_trait_ref.trait_ref.path;
 133                             hint_string.push_str(&format!(
 134                                 " {} +",
 135                                 snippet_with_applicability(cx, path.span, "..", &mut applicability)
 136                             ));
 137                         }
 138                     }
 139                     hint_string.truncate(hint_string.len() - 2);
 140                     hint_string.push('`');
 141                     span_lint_and_help(
 142                         cx,
 143                         TYPE_REPETITION_IN_BOUNDS,
 144                         p.span,
 145                         "this type has already been used as a bound predicate",
 146                         None,
 147                         &hint_string,
 148                     );
 149                 }
 150             }
 151         }
 152     }
 153 }
 154
 155 fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
 156     if gen.span.from_expansion() || gen.params.is_empty() || gen.where_clause.predicates.is_empty() {
 157         return;
 158     }
 159
 160     let mut map = FxHashMap::default();
 161     for param in gen.params {
 162         if let ParamName::Plain(ref ident) = param.name {
 163             let res = param
 164                 .bounds
 165                 .iter()
 166                 .filter_map(get_trait_res_span_from_bound)
 167                 .collect::<Vec<_>>();
 168             map.insert(*ident, res);
 169         }
 170     }
 171
 172     for predicate in gen.where_clause.predicates {
 173         if_chain! {
 174             if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
 175             if !bound_predicate.span.from_expansion();
 176             if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
 177             if let Some(segment) = segments.first();
 178             if let Some(trait_resolutions_direct) = map.get(&segment.ident);
 179             then {
 180                 for (res_where, _) in bound_predicate.bounds.iter().filter_map(get_trait_res_span_from_bound) {
 181                     if let Some((_, span_direct)) = trait_resolutions_direct
 182                                                 .iter()
 183                                                 .find(|(res_direct, _)| *res_direct == res_where) {
 184                         span_lint_and_help(
 185                             cx,
 186                             TRAIT_DUPLICATION_IN_BOUNDS,
 187                             *span_direct,
 188                             "this trait bound is already specified in the where clause",
 189                             None,
 190                             "consider removing this trait bound",
 191                         );
 192                     }
 193                 }
 194             }
 195         }
 196     }
 197 }