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Rollup merge of #137910 - compiler-errors:async-fn-goal-error, r=oli-obk

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Improve error message for `AsyncFn` trait failure for RPIT

Use a `WellFormedDerived` obligation cause to make sure we can turn an `AsyncFnKindHelper` trait goal into its parent `AsyncFn*` goal, then fix the logic for reporting `AsyncFn*` kind mismatches.

Best reviewed without whitespace.

Fixes #137905

r? oli-obk
This commit is contained in:
Michael Goulet 2025-03-06 12:22:25 -05:00 • committed by GitHub
commit 1458b3560f
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GPG key ID: B5690EEEBB952194
5 changed files with 101 additions and 54 deletions
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115
compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
View file

@ -829,7 +829,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
&& let ty::Closure(closure_def_id, _) | ty::CoroutineClosure(closure_def_id, _) =
*typeck_results.node_type(arg_hir_id).kind()
{
// Otherwise, extract the closure kind from the obligation.
// Otherwise, extract the closure kind from the obligation,
// but only if we actually have an argument to deduce the
// closure type from...
let mut err = self.report_closure_error(
&obligation,
closure_def_id,
@ -844,63 +846,72 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
let self_ty = trait_pred.self_ty().skip_binder();
if let Some(expected_kind) = self.tcx.fn_trait_kind_from_def_id(trait_pred.def_id()) {
let (closure_def_id, found_args, by_ref_captures) = match *self_ty.kind() {
ty::Closure(def_id, args) => {
(def_id, args.as_closure().sig().map_bound(|sig| sig.inputs()[0]), None)
}
ty::CoroutineClosure(def_id, args) => (
def_id,
args.as_coroutine_closure()
.coroutine_closure_sig()
.map_bound(|sig| sig.tupled_inputs_ty),
Some(args.as_coroutine_closure().coroutine_captures_by_ref_ty()),
),
_ => return None,
let (expected_kind, trait_prefix) =
if let Some(expected_kind) = self.tcx.fn_trait_kind_from_def_id(trait_pred.def_id()) {
(expected_kind, "")
} else if let Some(expected_kind) =
self.tcx.async_fn_trait_kind_from_def_id(trait_pred.def_id())
{
(expected_kind, "Async")
} else {
return None;
};
let expected_args =
trait_pred.map_bound(|trait_pred| trait_pred.trait_ref.args.type_at(1));
// Verify that the arguments are compatible. If the signature is
// mismatched, then we have a totally different error to report.
if self.enter_forall(found_args, |found_args| {
self.enter_forall(expected_args, |expected_args| {
!self.can_eq(obligation.param_env, expected_args, found_args)
})
}) {
return None;
let (closure_def_id, found_args, by_ref_captures) = match *self_ty.kind() {
ty::Closure(def_id, args) => {
(def_id, args.as_closure().sig().map_bound(|sig| sig.inputs()[0]), None)
}
ty::CoroutineClosure(def_id, args) => (
def_id,
args.as_coroutine_closure()
.coroutine_closure_sig()
.map_bound(|sig| sig.tupled_inputs_ty),
Some(args.as_coroutine_closure().coroutine_captures_by_ref_ty()),
),
_ => return None,
};
if let Some(found_kind) = self.closure_kind(self_ty)
&& !found_kind.extends(expected_kind)
{
let mut err = self.report_closure_error(
&obligation,
closure_def_id,
found_kind,
expected_kind,
"",
);
self.note_obligation_cause(&mut err, &obligation);
return Some(err.emit());
}
let expected_args = trait_pred.map_bound(|trait_pred| trait_pred.trait_ref.args.type_at(1));
// If the closure has captures, then perhaps the reason that the trait
// is unimplemented is because async closures don't implement `Fn`/`FnMut`
// if they have captures.
if let Some(by_ref_captures) = by_ref_captures
&& let ty::FnPtr(sig_tys, _) = by_ref_captures.kind()
&& !sig_tys.skip_binder().output().is_unit()
{
let mut err = self.dcx().create_err(AsyncClosureNotFn {
span: self.tcx.def_span(closure_def_id),
kind: expected_kind.as_str(),
});
self.note_obligation_cause(&mut err, &obligation);
return Some(err.emit());
}
// Verify that the arguments are compatible. If the signature is
// mismatched, then we have a totally different error to report.
if self.enter_forall(found_args, |found_args| {
self.enter_forall(expected_args, |expected_args| {
!self.can_eq(obligation.param_env, expected_args, found_args)
})
}) {
return None;
}
if let Some(found_kind) = self.closure_kind(self_ty)
&& !found_kind.extends(expected_kind)
{
let mut err = self.report_closure_error(
&obligation,
closure_def_id,
found_kind,
expected_kind,
trait_prefix,
);
self.note_obligation_cause(&mut err, &obligation);
return Some(err.emit());
}
// If the closure has captures, then perhaps the reason that the trait
// is unimplemented is because async closures don't implement `Fn`/`FnMut`
// if they have captures.
if let Some(by_ref_captures) = by_ref_captures
&& let ty::FnPtr(sig_tys, _) = by_ref_captures.kind()
&& !sig_tys.skip_binder().output().is_unit()
{
let mut err = self.dcx().create_err(AsyncClosureNotFn {
span: self.tcx.def_span(closure_def_id),
kind: expected_kind.as_str(),
});
self.note_obligation_cause(&mut err, &obligation);
return Some(err.emit());
}
None
}

5
compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
View file

@ -3191,7 +3191,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
false
};
if !is_upvar_tys_infer_tuple {
let is_builtin_async_fn_trait =
tcx.async_fn_trait_kind_from_def_id(data.parent_trait_pred.def_id()).is_some();
if !is_upvar_tys_infer_tuple && !is_builtin_async_fn_trait {
let ty_str = tcx.short_string(ty, err.long_ty_path());
let msg = format!("required because it appears within the type `{ty_str}`");
match ty.kind() {

4
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View file

@ -983,8 +983,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
return Err(SelectionError::Unimplemented);
}
} else {
nested.push(obligation.with(
nested.push(Obligation::new(
self.tcx(),
obligation.derived_cause(ObligationCauseCode::BuiltinDerived),
obligation.param_env,
ty::TraitRef::new(
self.tcx(),
self.tcx().require_lang_item(