A comptime record value whose union has a discriminant takes the arm its
discriminant field names, so a value that fits two arms with overlapping
shapes gets that arm's tag and layout instead of the first arm it fits.
comptimeBakeable reports a record type reachable from its own fields as
not bakeable instead of recursing without end, so such a comptime result
reports SC1090, and the message names unions and that limit.
Chris Tate
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