rust/clippy_lints/src/trait_bounds.rs

457 lines
16 KiB
Rust

use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
use clippy_utils::{SpanlessEq, SpanlessHash};
use core::hash::{Hash, Hasher};
use if_chain::if_chain;
use itertools::Itertools;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::unhash::UnhashMap;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::{
GenericArg, GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath,
TraitBoundModifier, TraitItem, TraitRef, Ty, TyKind, WherePredicate,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{BytePos, Span};
use std::collections::hash_map::Entry;
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 {}
/// ```
///
/// Use instead:
/// ```rust
/// pub fn foo<T>(t: T) where T: Copy + Clone {}
/// ```
#[clippy::version = "1.38.0"]
pub TYPE_REPETITION_IN_BOUNDS,
nursery,
"types are repeated unnecessarily in trait bounds, use `+` instead of using `T: _, T: _`"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for cases where generics or trait objects 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 specifying them only once.
///
/// ### Example
/// ```rust
/// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
/// ```
///
/// Use instead:
/// ```rust
/// # mod hidden {
/// fn func<T: Clone + Default>(arg: T) {}
/// # }
///
/// // or
///
/// fn func<T>(arg: T) where T: Clone + Default {}
/// ```
///
/// ```rust
/// fn foo<T: Default + Default>(bar: T) {}
/// ```
/// Use instead:
/// ```rust
/// fn foo<T: Default>(bar: T) {}
/// ```
///
/// ```rust
/// fn foo<T>(bar: T) where T: Default + Default {}
/// ```
/// Use instead:
/// ```rust
/// fn foo<T>(bar: T) where T: Default {}
/// ```
#[clippy::version = "1.47.0"]
pub TRAIT_DUPLICATION_IN_BOUNDS,
nursery,
"check if the same trait bounds are specified more than once during a generic 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 check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
// special handling for self trait bounds as these are not considered generics
// ie. trait Foo: Display {}
if let Item {
kind: ItemKind::Trait(_, _, _, bounds, ..),
..
} = item
{
rollup_traits(cx, bounds, "these bounds contain repeated elements");
}
}
fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
let mut self_bounds_map = FxHashMap::default();
for predicate in item.generics.predicates {
if_chain! {
if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
if bound_predicate.origin != PredicateOrigin::ImplTrait;
if !bound_predicate.span.from_expansion();
if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
if let Some(PathSegment {
res: Res::SelfTyParam { trait_: def_id }, ..
}) = segments.first();
if let Some(
Node::Item(
Item {
kind: ItemKind::Trait(_, _, _, self_bounds, _),
.. }
)
) = cx.tcx.hir().get_if_local(*def_id);
then {
if self_bounds_map.is_empty() {
for bound in self_bounds.iter() {
let Some((self_res, self_segments, _)) = get_trait_info_from_bound(bound) else { continue };
self_bounds_map.insert(self_res, self_segments);
}
}
bound_predicate
.bounds
.iter()
.filter_map(get_trait_info_from_bound)
.for_each(|(trait_item_res, trait_item_segments, span)| {
if let Some(self_segments) = self_bounds_map.get(&trait_item_res) {
if SpanlessEq::new(cx).eq_path_segments(self_segments, trait_item_segments) {
span_lint_and_help(
cx,
TRAIT_DUPLICATION_IN_BOUNDS,
span,
"this trait bound is already specified in trait declaration",
None,
"consider removing this trait bound",
);
}
}
});
}
}
}
}
fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) {
if_chain! {
if let TyKind::Ref(.., mut_ty) = &ty.kind;
if let TyKind::TraitObject(bounds, ..) = mut_ty.ty.kind;
if bounds.len() > 2;
then {
// Build up a hash of every trait we've seen
// When we see a trait for the first time, add it to unique_traits
// so we can later use it to build a string of all traits exactly once, without duplicates
let mut seen_def_ids = FxHashSet::default();
let mut unique_traits = Vec::new();
// Iterate the bounds and add them to our seen hash
// If we haven't yet seen it, add it to the fixed traits
for bound in bounds.iter() {
let Some(def_id) = bound.trait_ref.trait_def_id() else { continue; };
let new_trait = seen_def_ids.insert(def_id);
if new_trait {
unique_traits.push(bound);
}
}
// If the number of unique traits isn't the same as the number of traits in the bounds,
// there must be 1 or more duplicates
if bounds.len() != unique_traits.len() {
let mut bounds_span = bounds[0].span;
for bound in bounds.iter().skip(1) {
bounds_span = bounds_span.to(bound.span);
}
let fixed_trait_snippet = unique_traits
.iter()
.filter_map(|b| snippet_opt(cx, b.span))
.collect::<Vec<_>>()
.join(" + ");
span_lint_and_sugg(
cx,
TRAIT_DUPLICATION_IN_BOUNDS,
bounds_span,
"this trait bound is already specified in trait declaration",
"try",
fixed_trait_snippet,
Applicability::MaybeIncorrect,
);
}
}
}
}
}
impl TraitBounds {
fn check_type_repetition<'tcx>(self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
struct SpanlessTy<'cx, 'tcx> {
ty: &'tcx Ty<'tcx>,
cx: &'cx LateContext<'tcx>,
}
impl PartialEq for SpanlessTy<'_, '_> {
fn eq(&self, other: &Self) -> bool {
let mut eq = SpanlessEq::new(self.cx);
eq.inter_expr().eq_ty(self.ty, other.ty)
}
}
impl Hash for SpanlessTy<'_, '_> {
fn hash<H: Hasher>(&self, h: &mut H) {
let mut t = SpanlessHash::new(self.cx);
t.hash_ty(self.ty);
h.write_u64(t.finish());
}
}
impl Eq for SpanlessTy<'_, '_> {}
if gen.span.from_expansion() {
return;
}
let mut map: UnhashMap<SpanlessTy<'_, '_>, Vec<&GenericBound<'_>>> = UnhashMap::default();
let mut applicability = Applicability::MaybeIncorrect;
for bound in gen.predicates {
if_chain! {
if let WherePredicate::BoundPredicate(ref p) = bound;
if p.origin != PredicateOrigin::ImplTrait;
if p.bounds.len() as u64 <= self.max_trait_bounds;
if !p.span.from_expansion();
if let Some(ref v) = map.insert(
SpanlessTy { ty: p.bounded_ty, cx },
p.bounds.iter().collect::<Vec<_>>()
);
then {
let trait_bounds = v
.iter()
.copied()
.chain(p.bounds.iter())
.filter_map(get_trait_info_from_bound)
.map(|(_, _, span)| snippet_with_applicability(cx, span, "..", &mut applicability))
.join(" + ");
let hint_string = format!(
"consider combining the bounds: `{}: {trait_bounds}`",
snippet(cx, p.bounded_ty.span, "_"),
);
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 gen.span.from_expansion() {
return;
}
// Explanation:
// fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
// where T: Clone + Default, { unimplemented!(); }
// ^^^^^^^^^^^^^^^^^^
// |
// collects each of these where clauses into a set keyed by generic name and comparable trait
// eg. (T, Clone)
let where_predicates = gen
.predicates
.iter()
.filter_map(|pred| {
if_chain! {
if pred.in_where_clause();
if let WherePredicate::BoundPredicate(bound_predicate) = pred;
if let TyKind::Path(QPath::Resolved(_, path)) = bound_predicate.bounded_ty.kind;
then {
return Some(
rollup_traits(cx, bound_predicate.bounds, "these where clauses contain repeated elements")
.into_iter().map(|(trait_ref, _)| (path.res, trait_ref)))
}
}
None
})
.flatten()
.collect::<FxHashSet<_>>();
// Explanation:
// fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z) ...
// ^^^^^^^^^^^^^^^^^^ ^^^^^^^
// |
// compare trait bounds keyed by generic name and comparable trait to collected where
// predicates eg. (T, Clone)
for predicate in gen.predicates.iter().filter(|pred| !pred.in_where_clause()) {
if_chain! {
if let WherePredicate::BoundPredicate(bound_predicate) = predicate;
if bound_predicate.origin != PredicateOrigin::ImplTrait;
if !bound_predicate.span.from_expansion();
if let TyKind::Path(QPath::Resolved(_, path)) = bound_predicate.bounded_ty.kind;
then {
let traits = rollup_traits(cx, bound_predicate.bounds, "these bounds contain repeated elements");
for (trait_ref, span) in traits {
let key = (path.res, trait_ref);
if where_predicates.contains(&key) {
span_lint_and_help(
cx,
TRAIT_DUPLICATION_IN_BOUNDS,
span,
"this trait bound is already specified in the where clause",
None,
"consider removing this trait bound",
);
}
}
}
}
}
}
#[derive(Clone, PartialEq, Eq, Hash, Debug)]
struct ComparableTraitRef(Res, Vec<Res>);
impl Default for ComparableTraitRef {
fn default() -> Self {
Self(Res::Err, Vec::new())
}
}
fn get_trait_info_from_bound<'a>(bound: &'a GenericBound<'_>) -> Option<(Res, &'a [PathSegment<'a>], Span)> {
if let GenericBound::Trait(t, tbm) = bound {
let trait_path = t.trait_ref.path;
let trait_span = {
let path_span = trait_path.span;
if let TraitBoundModifier::Maybe = tbm {
path_span.with_lo(path_span.lo() - BytePos(1)) // include the `?`
} else {
path_span
}
};
Some((trait_path.res, trait_path.segments, trait_span))
} else {
None
}
}
// FIXME: ComparableTraitRef does not support nested bounds needed for associated_type_bounds
fn into_comparable_trait_ref(trait_ref: &TraitRef<'_>) -> ComparableTraitRef {
ComparableTraitRef(
trait_ref.path.res,
trait_ref
.path
.segments
.iter()
.filter_map(|segment| {
// get trait bound type arguments
Some(segment.args?.args.iter().filter_map(|arg| {
if_chain! {
if let GenericArg::Type(ty) = arg;
if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
then { return Some(path.res) }
}
None
}))
})
.flatten()
.collect(),
)
}
fn rollup_traits(cx: &LateContext<'_>, bounds: &[GenericBound<'_>], msg: &str) -> Vec<(ComparableTraitRef, Span)> {
let mut map = FxHashMap::default();
let mut repeated_res = false;
let only_comparable_trait_refs = |bound: &GenericBound<'_>| {
if let GenericBound::Trait(t, _) = bound {
Some((into_comparable_trait_ref(&t.trait_ref), t.span))
} else {
None
}
};
let mut i = 0usize;
for bound in bounds.iter().filter_map(only_comparable_trait_refs) {
let (comparable_bound, span_direct) = bound;
match map.entry(comparable_bound) {
Entry::Occupied(_) => repeated_res = true,
Entry::Vacant(e) => {
e.insert((span_direct, i));
i += 1;
},
}
}
// Put bounds in source order
let mut comparable_bounds = vec![Default::default(); map.len()];
for (k, (v, i)) in map {
comparable_bounds[i] = (k, v);
}
if_chain! {
if repeated_res;
if let [first_trait, .., last_trait] = bounds;
then {
let all_trait_span = first_trait.span().to(last_trait.span());
let traits = comparable_bounds.iter()
.filter_map(|&(_, span)| snippet_opt(cx, span))
.collect::<Vec<_>>();
let traits = traits.join(" + ");
span_lint_and_sugg(
cx,
TRAIT_DUPLICATION_IN_BOUNDS,
all_trait_span,
msg,
"try",
traits,
Applicability::MachineApplicable
);
}
}
comparable_bounds
}