own: a record literal assigned to a class type is a borrow error ('this value' borrows a field) #492

Under -mm=own, a record literal with a field made at run time cannot be assigned to a class type.

class P {
    x: number;
    items: number[];
}

function g(i: number) {
    const p: P = { x: i, items: [i] };
    return p.items.length;
}

function main() {
    print(g(7));
}

error: 'this value' borrows a field and cannot be stored, returned or captured

Expected: 1, as under gc, rc and none (since #487).

A record literal with a run-time field is built in a temporary slot of its own (a ts.Variable initialised by a ts.Constant, owning nothing), and the cast to a class reads each field back out of that slot (ts.PropertyRef + ts.Load) to store it into the new instance. The own pass sees each read as a borrow of the slot, and a borrow cannot be stored. The fresh values stored into the slot (ts.CreateArray, a fresh string, a call's result) should instead move into the instance: the slot is the literal's alone.

Taking the stored values directly in castTupleToClass is not enough: the literal's store into the slot already counts as a move, so own then reports "'this value' is used here after its value was moved". The pass needs to see the slot as a temporary that hands its fresh fields on, as it already does for a whole-record move into a local or a return (holdsConstantsOrMoves / recordRetainOf).

Since #487 a constant record assigned to a class is built the same way (the literal takes the class's field types, which fixed an rc leak), so const p: P = { x: 1, items: [1, 2] }, which compiled under own before #487 because the cast copied its arrays fresh, gives the same error.

Works under own: const o = { x: i, items: [i] } (a record-typed local) and a record assigned to a tuple type, which move the whole record.

Errors as expected (the value is shared): let r = { x: i, items: [i] }; const p: P = r;.

Found while fixing #487. Test: 00record_to_class.ts (passes under gc/rc/none, fails under own).

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