rust/clippy_lints/src/trait_bounds.rs

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use crate::utils::{in_macro, SpanlessHash};
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::source::{snippet, snippet_with_applicability};
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};
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use rustc_lint::{LateContext, LateLintPass};
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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: 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: _`"
}
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<T: Clone + Default>(arg: T) where T: Clone + Default {}
/// ```
///
/// Could be written as:
///
/// ```rust
/// fn func<T: Clone + Default>(arg: T) {}
/// ```
/// or
///
/// ```rust
/// fn func<T>(arg: T) where T: Clone + Default {}
/// ```
pub TRAIT_DUPLICATION_IN_BOUNDS,
pedantic,
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"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;
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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::<Vec<_>>());
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::<Vec<_>>();
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);
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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",
);
}
}
}
}
}
}