clippy_lints/src/trait_bounds.rs

   1 use crate::utils::{in_macro, span_help_and_lint, SpanlessHash};
   2 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   3 use rustc::{declare_tool_lint, lint_array};
   4 use rustc_data_structures::fx::FxHashMap;
   5 use rustc::hir::*;
   6
   7 declare_clippy_lint! {
   8     pub TYPE_REPETITION_IN_BOUNDS,
   9     complexity,
  10     "Types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
  11 }
  12
  13 #[derive(Copy, Clone)]
  14 pub struct TraitBounds;
  15
  16 impl LintPass for TraitBounds {
  17     fn get_lints(&self) -> LintArray {
  18         lint_array!(TYPE_REPETITION_IN_BOUNDS)
  19     }
  20
  21     fn name(&self) -> &'static str {
  22         "TypeRepetitionInBounds"
  23     }
  24 }
  25
  26
  27
  28 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TraitBounds {
  29     fn check_generics(&mut self, cx: &LateContext<'a, 'tcx>, gen: &'tcx Generics) {
  30         if in_macro(gen.span) {
  31             return;
  32         }
  33         let hash = | ty | -> u64 {
  34             let mut hasher = SpanlessHash::new(cx, cx.tables);
  35             hasher.hash_ty(ty);
  36             hasher.finish()
  37         };
  38         let mut map = FxHashMap::default();
  39         for bound in &gen.where_clause.predicates {
  40             if let WherePredicate::BoundPredicate(ref p) = bound {
  41                 let h = hash(&p.bounded_ty);
  42                 if let Some(ref v) = map.insert(h, p.bounds) {
  43                     let mut hint_string = format!("consider combining the bounds: `{:?}: ", p.bounded_ty);
  44                     for &b in v.iter() {
  45                         hint_string.push_str(&format!("{:?}, ", b));
  46                     }
  47                     for &b in p.bounds.iter() {
  48                         hint_string.push_str(&format!("{:?}, ", b));
  49                     }
  50                     hint_string.truncate(hint_string.len() - 2);
  51                     hint_string.push('`');
  52                     span_help_and_lint(
  53                         cx,
  54                         TYPE_REPETITION_IN_BOUNDS,
  55                         p.span,
  56                         "this type has already been used as a bound predicate",
  57                         &hint_string,
  58                     );
  59                 }
  60             }
  61         }
  62     }
  63 }