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clean-up future_not_send a bit #15554

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clean-up future_not_send a bit #15554

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24c34d7
extend the let-chain
ada4a Aug 25, 2025
fe86ce6
split `any` in two parts
ada4a Sep 6, 2025
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109 changes: 54 additions & 55 deletions clippy_lints/src/future_not_send.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -78,66 +78,65 @@ impl<'tcx> LateLintPass<'tcx> for FutureNotSend {
if let ty::Alias(ty::Opaque, AliasTy { def_id, args, .. }) = *ret_ty.kind()
&& let Some(future_trait) = cx.tcx.lang_items().future_trait()
&& let Some(send_trait) = cx.tcx.get_diagnostic_item(sym::Send)
&& let preds = cx.tcx.explicit_item_self_bounds(def_id)
// If is a Future
&& preds
.iter_instantiated_copied(cx.tcx, args)
.filter_map(|(p, _)| p.as_trait_clause())
.any(|trait_pred| trait_pred.skip_binder().trait_ref.def_id == future_trait)
{
let preds = cx.tcx.explicit_item_self_bounds(def_id);
let is_future = preds.iter_instantiated_copied(cx.tcx, args).any(|(p, _)| {
p.as_trait_clause()
.is_some_and(|trait_pred| trait_pred.skip_binder().trait_ref.def_id == future_trait)
});
if is_future {
let span = decl.output.span();
let infcx = cx.tcx.infer_ctxt().build(cx.typing_mode());
let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
let cause = traits::ObligationCause::misc(span, fn_def_id);
ocx.register_bound(cause, cx.param_env, ret_ty, send_trait);
let send_errors = ocx.select_all_or_error();
let span = decl.output.span();
let infcx = cx.tcx.infer_ctxt().build(cx.typing_mode());
let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
let cause = traits::ObligationCause::misc(span, fn_def_id);
ocx.register_bound(cause, cx.param_env, ret_ty, send_trait);
let send_errors = ocx.select_all_or_error();

// Allow errors that try to prove `Send` for types that "mention" a generic parameter at the "top
// level".
// For example, allow errors that `T: Send` can't be proven, but reject `Rc<T>: Send` errors,
// which is always unconditionally `!Send` for any possible type `T`.
//
// We also allow associated type projections if the self type is either itself a projection or a
// type parameter.
// This is to prevent emitting warnings for e.g. holding a `<Fut as Future>::Output` across await
// points, where `Fut` is a type parameter.
// Allow errors that try to prove `Send` for types that "mention" a generic parameter at the "top
// level".
// For example, allow errors that `T: Send` can't be proven, but reject `Rc<T>: Send` errors,
// which is always unconditionally `!Send` for any possible type `T`.
//
// We also allow associated type projections if the self type is either itself a projection or a
// type parameter.
// This is to prevent emitting warnings for e.g. holding a `<Fut as Future>::Output` across await
// points, where `Fut` is a type parameter.

let is_send = send_errors.iter().all(|err| {
err.obligation
.predicate
.as_trait_clause()
.map(Binder::skip_binder)
.is_some_and(|pred| {
pred.def_id() == send_trait
&& pred.self_ty().has_param()
&& TyParamAtTopLevelVisitor.visit_ty(pred.self_ty()) == ControlFlow::Break(true)
})
});
let is_send = send_errors.iter().all(|err| {
err.obligation
.predicate
.as_trait_clause()
.map(Binder::skip_binder)
.is_some_and(|pred| {
pred.def_id() == send_trait
&& pred.self_ty().has_param()
&& TyParamAtTopLevelVisitor.visit_ty(pred.self_ty()) == ControlFlow::Break(true)
})
});

if !is_send {
span_lint_and_then(
cx,
FUTURE_NOT_SEND,
span,
"future cannot be sent between threads safely",
|db| {
for FulfillmentError { obligation, .. } in send_errors {
infcx
.err_ctxt()
.maybe_note_obligation_cause_for_async_await(db, &obligation);
if let PredicateKind::Clause(ClauseKind::Trait(trait_pred)) =
obligation.predicate.kind().skip_binder()
{
db.note(format!(
"`{}` doesn't implement `{}`",
trait_pred.self_ty(),
trait_pred.trait_ref.print_only_trait_path(),
));
}
if !is_send {
span_lint_and_then(
cx,
FUTURE_NOT_SEND,
span,
"future cannot be sent between threads safely",
|db| {
for FulfillmentError { obligation, .. } in send_errors {
infcx
.err_ctxt()
.maybe_note_obligation_cause_for_async_await(db, &obligation);
if let PredicateKind::Clause(ClauseKind::Trait(trait_pred)) =
obligation.predicate.kind().skip_binder()
{
db.note(format!(
"`{}` doesn't implement `{}`",
trait_pred.self_ty(),
trait_pred.trait_ref.print_only_trait_path(),
));
}
},
);
}
}
},
);
}
}
}
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