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Merged
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May 28, 2025
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Optimize unit_return_expecting_ord #14905

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126 changes: 79 additions & 47 deletions clippy_lints/src/unit_return_expecting_ord.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_middle::ty::{ClauseKind, GenericPredicates, ProjectionPredicate, TraitPredicate};
use rustc_session::declare_lint_pass;
use rustc_span::{BytePos, Span, sym};
use rustc_span::{BytePos, Span, Symbol, sym};

declare_clippy_lint! {
/// ### What it does
Expand Down Expand Up @@ -36,21 +36,26 @@ declare_clippy_lint! {

declare_lint_pass!(UnitReturnExpectingOrd => [UNIT_RETURN_EXPECTING_ORD]);

fn get_trait_predicates_for_trait_id<'tcx>(
// For each
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fn get_trait_predicates_for_trait_ids<'tcx>(
cx: &LateContext<'tcx>,
generics: GenericPredicates<'tcx>,
trait_id: Option<DefId>,
) -> Vec<TraitPredicate<'tcx>> {
let mut preds = Vec::new();
trait_ids: &[Option<DefId>], // At least 2 ids
) -> [Vec<TraitPredicate<'tcx>>; 3] {
debug_assert!(trait_ids.len() >= 2);
let mut preds = [Vec::new(), Vec::new(), Vec::new()];
for (pred, _) in generics.predicates {
if let ClauseKind::Trait(poly_trait_pred) = pred.kind().skip_binder()
&& let trait_pred = cx
if let ClauseKind::Trait(poly_trait_pred) = pred.kind().skip_binder() {
let trait_pred = cx
.tcx
.instantiate_bound_regions_with_erased(pred.kind().rebind(poly_trait_pred))
&& let Some(trait_def_id) = trait_id
&& trait_def_id == trait_pred.trait_ref.def_id
{
preds.push(trait_pred);
.instantiate_bound_regions_with_erased(pred.kind().rebind(poly_trait_pred));
for (i, tid) in trait_ids.iter().enumerate() {
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The slice/array approach is a bit hard to understand, you have to look at the callsite to understand it. I see you want to get the operations within the instantiate_bound_regions_with_erased call. I think you could do that by passing in three separate arguments and handling them in sequence here, instead of using a for loop? I think that would be easier to read.

if let Some(tid) = tid
&& *tid == trait_pred.trait_ref.def_id
{
preds[i].push(trait_pred);
}
}
}
}
preds
Expand All @@ -74,15 +79,24 @@ fn get_projection_pred<'tcx>(
})
}

fn get_args_to_check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Vec<(usize, String)> {
fn get_args_to_check<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'tcx>,
args_len: usize,
fn_mut_trait: DefId,
ord_trait: Option<DefId>,
partial_ord_trait: Option<DefId>,
) -> Vec<(usize, Symbol)> {
let mut args_to_check = Vec::new();
if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
let fn_sig = cx.tcx.fn_sig(def_id).instantiate_identity();
let generics = cx.tcx.predicates_of(def_id);
let fn_mut_preds = get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().fn_mut_trait());
let ord_preds = get_trait_predicates_for_trait_id(cx, generics, cx.tcx.get_diagnostic_item(sym::Ord));
let partial_ord_preds =
get_trait_predicates_for_trait_id(cx, generics, cx.tcx.lang_items().partial_ord_trait());
let [fn_mut_preds, ord_preds, partial_ord_preds] =
get_trait_predicates_for_trait_ids(cx, generics, &[Some(fn_mut_trait), ord_trait, partial_ord_trait]);
if fn_mut_preds.is_empty() {
return vec![];
}

// Trying to call instantiate_bound_regions_with_erased on fn_sig.inputs() gives the following error
// The trait `rustc::ty::TypeFoldable<'_>` is not implemented for
// `&[rustc_middle::ty::Ty<'_>]`
Expand All @@ -102,12 +116,18 @@ fn get_args_to_check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Ve
.iter()
.any(|ord| Some(ord.self_ty()) == return_ty_pred.term.as_type())
{
args_to_check.push((i, "Ord".to_string()));
args_to_check.push((i, sym::Ord));
if args_to_check.len() == args_len - 1 {
break;
}
} else if partial_ord_preds
.iter()
.any(|pord| pord.self_ty() == return_ty_pred.term.expect_type())
{
args_to_check.push((i, "PartialOrd".to_string()));
args_to_check.push((i, sym::PartialOrd));
if args_to_check.len() == args_len - 1 {
break;
}
}
}
}
Expand Down Expand Up @@ -142,38 +162,50 @@ fn check_arg<'tcx>(cx: &LateContext<'tcx>, arg: &'tcx Expr<'tcx>) -> Option<(Spa

impl<'tcx> LateLintPass<'tcx> for UnitReturnExpectingOrd {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
if let ExprKind::MethodCall(_, receiver, args, _) = expr.kind {
let arg_indices = get_args_to_check(cx, expr);
if let ExprKind::MethodCall(_, receiver, args, _) = expr.kind
&& args.iter().any(|arg| {
matches!(
arg.peel_blocks().peel_borrows().peel_drop_temps().kind,
ExprKind::Path(_) | ExprKind::Closure(_)
)
})
&& let Some(fn_mut_trait) = cx.tcx.lang_items().fn_mut_trait()
{
let ord_trait = cx.tcx.get_diagnostic_item(sym::Ord);
let partial_ord_trait = cx.tcx.lang_items().partial_ord_trait();
if (ord_trait, partial_ord_trait) == (None, None) {
return;
}

let args = std::iter::once(receiver).chain(args.iter()).collect::<Vec<_>>();
let arg_indices = get_args_to_check(cx, expr, args.len(), fn_mut_trait, ord_trait, partial_ord_trait);
for (i, trait_name) in arg_indices {
if i < args.len() {
match check_arg(cx, args[i]) {
Some((span, None)) => {
span_lint(
cx,
UNIT_RETURN_EXPECTING_ORD,
span,
format!(
"this closure returns \
match check_arg(cx, args[i]) {
Some((span, None)) => {
span_lint(
cx,
UNIT_RETURN_EXPECTING_ORD,
span,
format!(
"this closure returns \
the unit type which also implements {trait_name}"
),
);
},
Some((span, Some(last_semi))) => {
span_lint_and_help(
cx,
UNIT_RETURN_EXPECTING_ORD,
span,
format!(
"this closure returns \
),
);
},
Some((span, Some(last_semi))) => {
span_lint_and_help(
cx,
UNIT_RETURN_EXPECTING_ORD,
span,
format!(
"this closure returns \
the unit type which also implements {trait_name}"
),
Some(last_semi),
"probably caused by this trailing semicolon",
);
},
None => {},
}
),
Some(last_semi),
"probably caused by this trailing semicolon",
);
},
None => {},
}
}
}
Expand Down