use crate::utils::{in_macro, snippet, snippet_with_applicability, span_lint_and_help, SpanlessHash}; use if_chain::if_chain; use rustc_data_structures::fx::FxHashMap; use rustc_errors::Applicability; use rustc_hir::{def::Res, GenericBound, Generics, ParamName, Path, QPath, TyKind, WherePredicate}; use rustc_lint::{LateContext, LateLintPass}; use rustc_session::{declare_tool_lint, impl_lint_pass}; use rustc_span::Span; 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 /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// pub fn foo(t: T) where T: Copy, T: Clone {} /// ``` /// /// Could be written as: /// /// ```rust /// pub fn foo(t: T) where T: Copy + Clone {} /// ``` pub TYPE_REPETITION_IN_BOUNDS, pedantic, "Types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`" } declare_clippy_lint! { /// **What it does:** Checks for cases where generics are being used and multiple /// syntax specifications for trait bounds are used simultaneously. /// /// **Why is this bad?** Duplicate bounds makes the code /// less readable than specifing them only once. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// fn func(arg: T) where T: Clone + Default {} /// ``` /// /// Could be written as: /// /// ```rust /// fn func(arg: T) {} /// ``` /// or /// /// ```rust /// fn func(arg: T) where T: Clone + Default {} /// ``` pub TRAIT_DUPLICATION_IN_BOUNDS, pedantic, "Check if the same trait bounds are specified twice during a function declaration" } #[derive(Copy, Clone)] pub struct TraitBounds { max_trait_bounds: u64, } impl TraitBounds { #[must_use] pub fn new(max_trait_bounds: u64) -> Self { Self { max_trait_bounds } } } impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]); impl<'tcx> LateLintPass<'tcx> for TraitBounds { fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) { self.check_type_repetition(cx, gen); check_trait_bound_duplication(cx, gen); } } fn get_trait_res_span_from_bound(bound: &GenericBound<'_>) -> Option<(Res, Span)> { if let GenericBound::Trait(t, _) = bound { Some((t.trait_ref.path.res, t.span)) } else { None } } impl TraitBounds { fn check_type_repetition(self, cx: &LateContext<'_>, gen: &'_ Generics<'_>) { if in_macro(gen.span) { return; } let hash = |ty| -> u64 { let mut hasher = SpanlessHash::new(cx); hasher.hash_ty(ty); hasher.finish() }; let mut map = FxHashMap::default(); let mut applicability = Applicability::MaybeIncorrect; for bound in gen.where_clause.predicates { if_chain! { if let WherePredicate::BoundPredicate(ref p) = bound; if p.bounds.len() as u64 <= self.max_trait_bounds; if !in_macro(p.span); let h = hash(&p.bounded_ty); if let Some(ref v) = map.insert(h, p.bounds.iter().collect::>()); then { 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!( " {} +", snippet_with_applicability(cx, path.span, "..", &mut applicability) )); } } 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!( " {} +", snippet_with_applicability(cx, path.span, "..", &mut applicability) )); } } 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", None, &hint_string, ); } } } } } fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) { if in_macro(gen.span) || gen.params.is_empty() || gen.where_clause.predicates.is_empty() { return; } let mut map = FxHashMap::default(); for param in gen.params { if let ParamName::Plain(ref ident) = param.name { let res = param .bounds .iter() .filter_map(get_trait_res_span_from_bound) .collect::>(); map.insert(*ident, res); } } for predicate in gen.where_clause.predicates { if_chain! { if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate; if !in_macro(bound_predicate.span); if let TyKind::Path(QPath::Resolved(_, Path { ref segments, .. })) = bound_predicate.bounded_ty.kind; if let Some(segment) = segments.first(); if let Some(trait_resolutions_direct) = map.get(&segment.ident); then { for (res_where, _) in bound_predicate.bounds.iter().filter_map(get_trait_res_span_from_bound) { if let Some((_, span_direct)) = trait_resolutions_direct .iter() .find(|(res_direct, _)| *res_direct == res_where) { span_lint_and_help( cx, TRAIT_DUPLICATION_IN_BOUNDS, *span_direct, "this trait bound is already specified in the where clause", None, "consider removing this trait bound", ); } } } } } }