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Only consider auto traits empty for the purposes of omitting vptrs from subtrait vtables

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Zachary S
2025-08-23 20:48:44 -05:00
parent c5a6a7bdd8
commit 904e83c53f
5 changed files with 167 additions and 1 deletions
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7
compiler/rustc_trait_selection/src/traits/vtable.rs
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@@ -153,7 +153,12 @@ fn prepare_vtable_segments_inner<'tcx, T>(
// emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
while let Some((inner_most_trait_ref, emit_vptr, mut siblings)) = stack.pop() {
let has_entries = has_own_existential_vtable_entries(tcx, inner_most_trait_ref.def_id);
// We don't need to emit a vptr for "truly-empty" supertraits, but we *do* need to emit a
// vptr for supertraits that have no methods, but that themselves have supertraits
// with methods, so we check if any transitive supertrait has entries here (this includes
// the trait itself).
let has_entries = ty::elaborate::supertrait_def_ids(tcx, inner_most_trait_ref.def_id)
.any(|def_id| has_own_existential_vtable_entries(tcx, def_id));
segment_visitor(VtblSegment::TraitOwnEntries {
trait_ref: inner_most_trait_ref,