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Rollup merge of #152218 - adwinwhite:fix-mir-borrowck-opaque-handling-keep-all-errors, r=lcnr

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Report unconstrained region in hidden types lazily

Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/264

I didn't copy the mechanism of HIR typeck as I found that we just need to be lax in the unconstrained region case.
It already ignores non-defining uses and invalid params.

About tests, I'm having trouble coming up with more complex ones. 🙁

This fixes `ukanren` and `codecrafters-redis-rust` but not rust-lang/rust#151322 and rust-lang/rust#151323.
I believe they are a [different problem](https://github.com/rust-lang/rust/issues/151322#issuecomment-3864656974).

r? @lcnr
This commit is contained in:
Jonathan Brouwer 2026-02-13 13:35:00 +01:00 • committed by GitHub
commit 98e8f99bc0
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5 changed files with 198 additions and 13 deletions
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100
compiler/rustc_borrowck/src/region_infer/opaque_types/mod.rs
View file

@ -24,13 +24,13 @@ use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
use tracing::{debug, instrument};
use super::reverse_sccs::ReverseSccGraph;
use crate::BorrowckInferCtxt;
use crate::consumers::RegionInferenceContext;
use crate::session_diagnostics::LifetimeMismatchOpaqueParam;
use crate::type_check::canonical::fully_perform_op_raw;
use crate::type_check::free_region_relations::UniversalRegionRelations;
use crate::type_check::{Locations, MirTypeckRegionConstraints};
use crate::universal_regions::{RegionClassification, UniversalRegions};
use crate::{BorrowckInferCtxt, CollectRegionConstraintsResult};
mod member_constraints;
mod region_ctxt;
@ -126,6 +126,31 @@ fn nll_var_to_universal_region<'tcx>(
}
}
/// Record info needed to report the same name error later.
#[derive(Copy, Clone, Debug)]
pub(crate) struct UnexpectedHiddenRegion<'tcx> {
// The def_id of the body where this error occurs.
// Needed to handle region vars with their corresponding `infcx`.
def_id: LocalDefId,
opaque_type_key: OpaqueTypeKey<'tcx>,
hidden_type: ProvisionalHiddenType<'tcx>,
member_region: Region<'tcx>,
}
impl<'tcx> UnexpectedHiddenRegion<'tcx> {
pub(crate) fn to_error(self) -> (LocalDefId, DeferredOpaqueTypeError<'tcx>) {
let UnexpectedHiddenRegion { def_id, opaque_type_key, hidden_type, member_region } = self;
(
def_id,
DeferredOpaqueTypeError::UnexpectedHiddenRegion {
opaque_type_key,
hidden_type,
member_region,
},
)
}
}
/// Collect all defining uses of opaque types inside of this typeck root. This
/// expects the hidden type to be mapped to the definition parameters of the opaque
/// and errors if we end up with distinct hidden types.
@ -176,11 +201,13 @@ struct DefiningUse<'tcx> {
/// It also means that this whole function is not really soundness critical as we
/// recheck all uses of the opaques regardless.
pub(crate) fn compute_definition_site_hidden_types<'tcx>(
def_id: LocalDefId,
infcx: &BorrowckInferCtxt<'tcx>,
universal_region_relations: &Frozen<UniversalRegionRelations<'tcx>>,
constraints: &MirTypeckRegionConstraints<'tcx>,
location_map: Rc<DenseLocationMap>,
hidden_types: &mut FxIndexMap<LocalDefId, ty::DefinitionSiteHiddenType<'tcx>>,
unconstrained_hidden_type_errors: &mut Vec<UnexpectedHiddenRegion<'tcx>>,
opaque_types: &[(OpaqueTypeKey<'tcx>, ProvisionalHiddenType<'tcx>)],
) -> Vec<DeferredOpaqueTypeError<'tcx>> {
let mut errors = Vec::new();
@ -204,8 +231,10 @@ pub(crate) fn compute_definition_site_hidden_types<'tcx>(
// up equal to one of their choice regions and compute the actual hidden type of
// the opaque type definition. This is stored in the `root_cx`.
compute_definition_site_hidden_types_from_defining_uses(
def_id,
&rcx,
hidden_types,
unconstrained_hidden_type_errors,
&defining_uses,
&mut errors,
);
@ -274,8 +303,10 @@ fn collect_defining_uses<'tcx>(
#[instrument(level = "debug", skip(rcx, hidden_types, defining_uses, errors))]
fn compute_definition_site_hidden_types_from_defining_uses<'tcx>(
def_id: LocalDefId,
rcx: &RegionCtxt<'_, 'tcx>,
hidden_types: &mut FxIndexMap<LocalDefId, ty::DefinitionSiteHiddenType<'tcx>>,
unconstrained_hidden_type_errors: &mut Vec<UnexpectedHiddenRegion<'tcx>>,
defining_uses: &[DefiningUse<'tcx>],
errors: &mut Vec<DeferredOpaqueTypeError<'tcx>>,
) {
@ -293,16 +324,29 @@ fn compute_definition_site_hidden_types_from_defining_uses<'tcx>(
Ok(hidden_type) => hidden_type,
Err(r) => {
debug!("UnexpectedHiddenRegion: {:?}", r);
errors.push(DeferredOpaqueTypeError::UnexpectedHiddenRegion {
hidden_type,
opaque_type_key,
member_region: ty::Region::new_var(tcx, r),
});
let guar = tcx.dcx().span_delayed_bug(
hidden_type.span,
"opaque type with non-universal region args",
);
ty::ProvisionalHiddenType::new_error(tcx, guar)
// If we're using the next solver, the unconstrained region may be resolved by a
// fully defining use from another body.
// So we don't generate error eagerly here.
if rcx.infcx.tcx.use_typing_mode_borrowck() {
unconstrained_hidden_type_errors.push(UnexpectedHiddenRegion {
def_id,
hidden_type,
opaque_type_key,
member_region: ty::Region::new_var(tcx, r),
});
continue;
} else {
errors.push(DeferredOpaqueTypeError::UnexpectedHiddenRegion {
hidden_type,
opaque_type_key,
member_region: ty::Region::new_var(tcx, r),
});
let guar = tcx.dcx().span_delayed_bug(
hidden_type.span,
"opaque type with non-universal region args",
);
ty::ProvisionalHiddenType::new_error(tcx, guar)
}
}
};
@ -570,6 +614,40 @@ pub(crate) fn apply_definition_site_hidden_types<'tcx>(
errors
}
/// We handle `UnexpectedHiddenRegion` error lazily in the next solver as
/// there may be a fully defining use in another body.
///
/// In case such a defining use does not exist, we register an error here.
pub(crate) fn handle_unconstrained_hidden_type_errors<'tcx>(
tcx: TyCtxt<'tcx>,
hidden_types: &mut FxIndexMap<LocalDefId, ty::DefinitionSiteHiddenType<'tcx>>,
unconstrained_hidden_type_errors: &mut Vec<UnexpectedHiddenRegion<'tcx>>,
collect_region_constraints_results: &mut FxIndexMap<
LocalDefId,
CollectRegionConstraintsResult<'tcx>,
>,
) {
let mut unconstrained_hidden_type_errors = std::mem::take(unconstrained_hidden_type_errors);
unconstrained_hidden_type_errors
.retain(|unconstrained| !hidden_types.contains_key(&unconstrained.opaque_type_key.def_id));
unconstrained_hidden_type_errors.iter().for_each(|t| {
tcx.dcx()
.span_delayed_bug(t.hidden_type.span, "opaque type with non-universal region args");
});
// `UnexpectedHiddenRegion` error contains region var which only makes sense in the
// corresponding `infcx`.
// So we need to insert the error to the body where it originates from.
for error in unconstrained_hidden_type_errors {
let (def_id, error) = error.to_error();
let Some(result) = collect_region_constraints_results.get_mut(&def_id) else {
unreachable!("the body should depend on opaques type if it has opaque use");
};
result.deferred_opaque_type_errors.push(error);
}
}
/// In theory `apply_definition_site_hidden_types` could introduce new uses of opaque types.
/// We do not check these new uses so this could be unsound.
///

20
compiler/rustc_borrowck/src/root_cx.rs
View file

@ -12,8 +12,9 @@ use smallvec::SmallVec;
use crate::consumers::BorrowckConsumer;
use crate::nll::compute_closure_requirements_modulo_opaques;
use crate::region_infer::opaque_types::{
apply_definition_site_hidden_types, clone_and_resolve_opaque_types,
UnexpectedHiddenRegion, apply_definition_site_hidden_types, clone_and_resolve_opaque_types,
compute_definition_site_hidden_types, detect_opaque_types_added_while_handling_opaque_types,
handle_unconstrained_hidden_type_errors,
};
use crate::type_check::{Locations, constraint_conversion};
use crate::{
@ -26,7 +27,12 @@ use crate::{
pub(super) struct BorrowCheckRootCtxt<'tcx> {
pub tcx: TyCtxt<'tcx>,
root_def_id: LocalDefId,
/// This contains fully resolved hidden types or `ty::Error`.
hidden_types: FxIndexMap<LocalDefId, ty::DefinitionSiteHiddenType<'tcx>>,
/// This contains unconstrained regions in hidden types.
/// Only used for deferred error reporting. See
/// [`crate::region_infer::opaque_types::handle_unconstrained_hidden_type_errors`]
unconstrained_hidden_type_errors: Vec<UnexpectedHiddenRegion<'tcx>>,
/// The region constraints computed by [borrowck_collect_region_constraints]. This uses
/// an [FxIndexMap] to guarantee that iterating over it visits nested bodies before
/// their parents.
@ -49,6 +55,7 @@ impl<'tcx> BorrowCheckRootCtxt<'tcx> {
tcx,
root_def_id,
hidden_types: Default::default(),
unconstrained_hidden_type_errors: Default::default(),
collect_region_constraints_results: Default::default(),
propagated_borrowck_results: Default::default(),
tainted_by_errors: None,
@ -84,23 +91,32 @@ impl<'tcx> BorrowCheckRootCtxt<'tcx> {
fn handle_opaque_type_uses(&mut self) {
let mut per_body_info = Vec::new();
for input in self.collect_region_constraints_results.values_mut() {
for (def_id, input) in &mut self.collect_region_constraints_results {
let (num_entries, opaque_types) = clone_and_resolve_opaque_types(
&input.infcx,
&input.universal_region_relations,
&mut input.constraints,
);
input.deferred_opaque_type_errors = compute_definition_site_hidden_types(
*def_id,
&input.infcx,
&input.universal_region_relations,
&input.constraints,
Rc::clone(&input.location_map),
&mut self.hidden_types,
&mut self.unconstrained_hidden_type_errors,
&opaque_types,
);
per_body_info.push((num_entries, opaque_types));
}
handle_unconstrained_hidden_type_errors(
self.tcx,
&mut self.hidden_types,
&mut self.unconstrained_hidden_type_errors,
&mut self.collect_region_constraints_results,
);
for (input, (opaque_types_storage_num_entries, opaque_types)) in
self.collect_region_constraints_results.values_mut().zip(per_body_info)
{

21
tests/ui/traits/next-solver/opaques/eventually-constrained-region.rs Normal file
View file

@ -0,0 +1,21 @@
//@ check-pass
//@ compile-flags: -Znext-solver
// Regression test for trait-system-refactor-initiative#264.
//
// Some defining uses of opaque types can't constrain captured regions to universals.
// Previouly, we eagerly report error in this case.
// Now we report error only if there's no fully defining use from all bodies of the typeck root.
struct Inv<'a>(*mut &'a ());
fn mk_static() -> Inv<'static> { todo!() }
fn guide_closure_sig<'a>(f: impl FnOnce() -> Inv<'a>) {}
fn unconstrained_in_closure() -> impl Sized {
guide_closure_sig(|| unconstrained_in_closure());
mk_static()
}
fn main() {}

34
tests/ui/traits/next-solver/opaques/report-all-unexpected-hidden-errors.rs Normal file
View file

@ -0,0 +1,34 @@
//@ compile-flags: -Znext-solver
// Just for diagnostics completeness.
// This is probably unimportant as we only report one error for such case in HIR typeck.
#![feature(type_alias_impl_trait)]
struct Invar<'a>(*mut &'a ());
fn mk_invar<'a>(a: &'a i32) -> Invar<'a> {
todo!()
}
type MultiUse = impl Sized;
#[define_opaque(MultiUse)]
fn capture_different_universals_not_on_bounds<'a, 'b, 'c>(a: &'a i32, b: &'b i32, c: &'c i32) {
let _ = || -> MultiUse {
//~^ ERROR: hidden type for `MultiUse` captures lifetime that does not appear in bounds [E0700]
mk_invar(a)
};
let _ = || -> MultiUse {
//~^ ERROR: hidden type for `MultiUse` captures lifetime that does not appear in bounds [E0700]
mk_invar(b)
};
let _ = || {
let _ = || -> MultiUse {
//~^ ERROR: hidden type for `MultiUse` captures lifetime that does not appear in bounds [E0700]
mk_invar(c)
};
};
}
fn main() {}

36
tests/ui/traits/next-solver/opaques/report-all-unexpected-hidden-errors.stderr Normal file
View file

@ -0,0 +1,36 @@
error[E0700]: hidden type for `MultiUse` captures lifetime that does not appear in bounds
--> $DIR/report-all-unexpected-hidden-errors.rs:18:19
|
LL | type MultiUse = impl Sized;
| ---------- opaque type defined here
...
LL | let _ = || -> MultiUse {
| ^^^^^^^^
|
= note: hidden type `Invar<'_>` captures lifetime `'_`
error[E0700]: hidden type for `MultiUse` captures lifetime that does not appear in bounds
--> $DIR/report-all-unexpected-hidden-errors.rs:22:19
|
LL | type MultiUse = impl Sized;
| ---------- opaque type defined here
...
LL | let _ = || -> MultiUse {
| ^^^^^^^^
|
= note: hidden type `Invar<'_>` captures lifetime `'_`
error[E0700]: hidden type for `MultiUse` captures lifetime that does not appear in bounds
--> $DIR/report-all-unexpected-hidden-errors.rs:27:23
|
LL | type MultiUse = impl Sized;
| ---------- opaque type defined here
...
LL | let _ = || -> MultiUse {
| ^^^^^^^^
|
= note: hidden type `Invar<'_>` captures lifetime `'_`
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0700`.