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Check elaborated projections from dyn don't mention unconstrained late bound lifetimes

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This commit is contained in:
Michael Goulet 2024-09-14 15:43:03 -04:00
parent 14f303bc14
commit ae5f58d906
5 changed files with 86 additions and 14 deletions
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50
compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
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@ -174,6 +174,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
// Include projections defined on supertraits.
projection_bounds.push((pred, span));
}
self.check_elaborated_projection_mentions_input_lifetimes(pred, span);
}
_ => (),
}
@ -360,6 +362,54 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
Ty::new_dynamic(tcx, existential_predicates, region_bound, representation)
}
/// Check that elaborating the principal of a trait ref doesn't lead to projections
/// that are unconstrained. This can happen because an otherwise unconstrained
/// *type variable* can be substituted with a type that has late-bound regions. See
/// `elaborated-predicates-unconstrained-late-bound.rs` for a test.
fn check_elaborated_projection_mentions_input_lifetimes(
&self,
pred: ty::PolyProjectionPredicate<'tcx>,
span: Span,
) {
let tcx = self.tcx();
// Find any late-bound regions declared in `ty` that are not
// declared in the trait-ref or assoc_item. These are not well-formed.
//
// Example:
//
// for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
// for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
let late_bound_in_projection_term =
tcx.collect_constrained_late_bound_regions(pred.map_bound(|pred| pred.projection_term));
let late_bound_in_term =
tcx.collect_referenced_late_bound_regions(pred.map_bound(|pred| pred.term));
debug!(?late_bound_in_projection_term);
debug!(?late_bound_in_term);
// FIXME: point at the type params that don't have appropriate lifetimes:
// struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
// ---- ---- ^^^^^^^
// NOTE(associated_const_equality): This error should be impossible to trigger
// with associated const equality constraints.
self.validate_late_bound_regions(
late_bound_in_projection_term,
late_bound_in_term,
|br_name| {
let item_name = tcx.item_name(pred.projection_def_id());
struct_span_code_err!(
self.dcx(),
span,
E0582,
"binding for associated type `{}` references {}, \
which does not appear in the trait input types",
item_name,
br_name
)
},
);
}
}
fn replace_dummy_self_with_error<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(