The optional element reads these programs pin now lower to nullable pointers for class and string arms. Each program declares a Set of its element union, which keeps that union a tagged box, so the tests continue to exercise the stack-box and borrowed-payload paths.
main's optional class element test from #767 (comparisons, tests and
optional chains through stack tags) gets the same Set, plus a nullable
variant asserting that those reads build no union box at all.
Malte Ubl
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