Only allow impl lifetimes in RPITIT hidden type that come from self type

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -1,7 +1,7 @@
 use super::potentially_plural_count;
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
 use hir::def_id::{DefId, LocalDefId};
-use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_errors::{
  pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed, MultiSpan,
 };
@@ -614,8 +614,8 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
 ) -> Result<&'tcx FxHashMap<DefId, ty::EarlyBinder<Ty<'tcx>>>, ErrorGuaranteed> {
  let impl_m = tcx.opt_associated_item(impl_m_def_id.to_def_id()).unwrap();
  let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
- let impl_trait_ref =
-  tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap().subst_identity();
+ let impl_def_id = impl_m.container_id(tcx);
+ let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().subst_identity();
  let param_env = tcx.param_env(impl_m_def_id);
 
  // First, check a few of the same things as `compare_impl_method`,
@@ -755,6 +755,14 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
  );
  ocx.resolve_regions_and_report_errors(impl_m_def_id, &outlives_env)?;
 
+ let mut self_type_regions = FxHashSet::default();
+ tcx.fold_regions(impl_trait_ref.self_ty(), |re, _| {
+ if let ty::ReEarlyBound(ebr) = *re {
+ self_type_regions.insert(ebr.def_id);
+ }
+ re
+ });
+
  let mut collected_tys = FxHashMap::default();
  for (def_id, (ty, substs)) in collected_types {
  match infcx.fully_resolve((ty, substs)) {
@@ -791,14 +799,14 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
  // since we previously enforce that the trait method and impl method have the
  // same generics.
  let num_trait_substs = trait_to_impl_substs.len();
- let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len();
+ let num_impl_substs = tcx.generics_of(impl_def_id).params.len();
  let ty = match ty.try_fold_with(&mut RemapHiddenTyRegions {
  tcx,
  map,
  num_trait_substs,
  num_impl_substs,
+ self_type_regions: &self_type_regions,
  def_id,
- impl_def_id: impl_m.container_id(tcx),
  ty,
  return_span,
  }) {
@@ -888,18 +896,18 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ImplTraitInTraitCollector<'_, 'tcx> {
  }
 }
 
-struct RemapHiddenTyRegions<'tcx> {
+struct RemapHiddenTyRegions<'a, 'tcx> {
  tcx: TyCtxt<'tcx>,
  map: FxHashMap<ty::Region<'tcx>, ty::Region<'tcx>>,
+ self_type_regions: &'a FxHashSet<DefId>,
  num_trait_substs: usize,
  num_impl_substs: usize,
  def_id: DefId,
- impl_def_id: DefId,
  ty: Ty<'tcx>,
  return_span: Span,
 }
 
-impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
+impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'_, 'tcx> {
  type Error = ErrorGuaranteed;
 
  fn interner(&self) -> TyCtxt<'tcx> {
@@ -929,9 +937,13 @@ impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
  match region.kind() {
  // Remap all free regions, which correspond to late-bound regions in the function.
  ty::ReFree(_) => {}
- // Remap early-bound regions as long as they don't come from the `impl` itself,
+ // Remap early-bound regions as long as they don't come from the impl Self type,
  // in which case we don't really need to renumber them.
- ty::ReEarlyBound(ebr) if self.tcx.parent(ebr.def_id) != self.impl_def_id => {}
+ ty::ReEarlyBound(ebr) => {
+ if self.self_type_regions.contains(&ebr.def_id) {
+ return Ok(region);
+ }
+ }
  _ => return Ok(region),
  }
 

tests/ui/impl-trait/in-trait/only-mentions-self-lt.bad.stderr

@@ -0,0 +1,17 @@
+error: return type captures more lifetimes than trait definition
+ --> $DIR/only-mentions-self-lt.rs:12:26
+ |
+LL | impl<'a> Foo<'a> for () {
+ | -- this lifetime was captured
+LL | fn test(&'a self) -> &'a Self { self }
+ | ^^^^^^^^
+ |
+note: hidden type must only reference lifetimes captured by this impl trait
+ --> $DIR/only-mentions-self-lt.rs:7:26
+ |
+LL | fn test(&'a self) -> impl Sized;
+ | ^^^^^^^^^^
+ = note: hidden type inferred to be `&'a ()`
+
+error: aborting due to previous error
+

tests/ui/impl-trait/in-trait/only-mentions-self-lt.rs

@@ -0,0 +1,21 @@
+// revisions: good bad
+//[good] check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+
+trait Foo<'a> {
+ fn test(&'a self) -> impl Sized;
+}
+
+#[cfg(bad)]
+impl<'a> Foo<'a> for () {
+ fn test(&'a self) -> &'a Self { self }
+ //[bad]~^ return type captures more lifetimes than trait definition
+}
+
+#[cfg(good)]
+impl<'a> Foo<'a> for &'a () {
+ fn test(&'a self) -> &'a Self { self }
+}
+
+fn main() {}

tests/ui/impl-trait/in-trait/unconstrained-lt.current.stderr

@@ -1,9 +1,17 @@
-error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
- --> $DIR/unconstrained-lt.rs:10:6
+error: return type captures more lifetimes than trait definition
+ --> $DIR/unconstrained-lt.rs:11:18
  |
 LL | impl<'a, T> Foo for T {
- | ^^ unconstrained lifetime parameter
+ | -- this lifetime was captured
+LL | fn test() -> &'a () { &() }
+ | ^^^^^^
+ |
+note: hidden type must only reference lifetimes captured by this impl trait
+ --> $DIR/unconstrained-lt.rs:7:18
+ |
+LL | fn test() -> impl Sized;
+ | ^^^^^^^^^^
+ = note: hidden type inferred to be `&'a ()`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0207`.

tests/ui/impl-trait/in-trait/unconstrained-lt.next.stderr

@@ -1,9 +1,17 @@
-error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
- --> $DIR/unconstrained-lt.rs:10:6
+error: return type captures more lifetimes than trait definition
+ --> $DIR/unconstrained-lt.rs:11:18
  |
 LL | impl<'a, T> Foo for T {
- | ^^ unconstrained lifetime parameter
+ | -- this lifetime was captured
+LL | fn test() -> &'a () { &() }
+ | ^^^^^^
+ |
+note: hidden type must only reference lifetimes captured by this impl trait
+ --> $DIR/unconstrained-lt.rs:7:18
+ |
+LL | fn test() -> impl Sized;
+ | ^^^^^^^^^^
+ = note: hidden type inferred to be `&'a ()`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0207`.

tests/ui/impl-trait/in-trait/unconstrained-lt.rs

@@ -8,9 +8,8 @@ trait Foo {
 }
 
 impl<'a, T> Foo for T {
- //~^ ERROR the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
-
  fn test() -> &'a () { &() }
+ //~^ ERROR return type captures more lifetimes than trait definition
 }
 
 fn main() {}