rust/clippy_lints/src/trait_bounds.rs

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use crate::utils::{in_macro, snippet, span_lint_and_help, SpanlessHash};
use rustc_data_structures::fx::FxHashMap;
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use rustc_hir::{GenericBound, Generics, WherePredicate};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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#[derive(Copy, Clone)]
pub struct TraitBounds;
declare_clippy_lint! {
/// **What it does:** This lint warns about unnecessary type repetitions in trait bounds
///
/// **Why is this bad?** Repeating the type for every bound makes the code
/// less readable than combining the bounds
///
/// **Example:**
/// ```rust
/// pub fn foo<T>(t: T) where T: Copy, T: Clone {}
/// ```
///
/// Could be written as:
///
/// ```rust
/// pub fn foo<T>(t: T) where T: Copy + Clone {}
/// ```
pub TYPE_REPETITION_IN_BOUNDS,
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pedantic,
"Types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
}
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impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TraitBounds {
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fn check_generics(&mut self, cx: &LateContext<'a, 'tcx>, gen: &'tcx Generics<'_>) {
if in_macro(gen.span) {
return;
}
let hash = |ty| -> u64 {
let mut hasher = SpanlessHash::new(cx, cx.tables);
hasher.hash_ty(ty);
hasher.finish()
};
let mut map = FxHashMap::default();
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for bound in gen.where_clause.predicates {
if let WherePredicate::BoundPredicate(ref p) = bound {
let h = hash(&p.bounded_ty);
if let Some(ref v) = map.insert(h, p.bounds.iter().collect::<Vec<_>>()) {
let mut hint_string = format!(
"consider combining the bounds: `{}:",
snippet(cx, p.bounded_ty.span, "_")
);
for b in v.iter() {
if let GenericBound::Trait(ref poly_trait_ref, _) = b {
let path = &poly_trait_ref.trait_ref.path;
hint_string.push_str(&format!(" {} +", path));
}
}
for b in p.bounds.iter() {
if let GenericBound::Trait(ref poly_trait_ref, _) = b {
let path = &poly_trait_ref.trait_ref.path;
hint_string.push_str(&format!(" {} +", path));
}
}
hint_string.truncate(hint_string.len() - 2);
hint_string.push('`');
span_lint_and_help(
cx,
TYPE_REPETITION_IN_BOUNDS,
p.span,
"this type has already been used as a bound predicate",
&hint_string,
);
}
}
}
}
}