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