error: vtable entries: [
           MetadataDropInPlace,
           MetadataSize,
           MetadataAlign,
           Method(<S as A>::foo_a1),
           Vacant,
       ]
  --> $DIR/vtable-vacant.rs:20:1
   |
LL | impl A for S {}
   | ^^^^^^^^^^^^

error: vtable entries: [
           MetadataDropInPlace,
           MetadataSize,
           MetadataAlign,
           Method(<S as A>::foo_a1),
           Vacant,
           Method(<S as B>::foo_b1),
           Vacant,
       ]
  --> $DIR/vtable-vacant.rs:24:1
   |
LL | impl B for S {}
   | ^^^^^^^^^^^^

error: aborting due to 2 previous errors