The fixture's loop iterated `[6, 7] as (number | undefined)[]` so that
its binding kept the union layout the LLDB check reads through
`item->tag` and `item->slot.arm0`. Since (T | undefined)[] stores T
elements, an array that never holds undefined gives a `number` binding,
and the check failed with "item is not a pointer".
The loop now iterates `[6, 7, undefined]`, whose binding needs the
union, and the check also reads the undefined arm's tag.
A shorthand property and an object literal passed as an argument no
longer widen the declared record layout of the binding or parameter
that receives them. A widened layout made every existing record that
flowed into that binding or parameter convert to a copy, so later
writes through the copy were lost. Those literals keep a missing
element in their own fields and convert, with a check, into a declared
record.
The debug-variables fixture iterates an array whose elements may be
undefined, so its loop binding keeps the union layout the debugger
check inspects.
Chris Tate