The file format has no `@` operator, but formulas with an explicit
implicit intersection were written with a literal `@`
(`<f>@A1:A3*2</f>`). Excel writes `@x` as `_xlfn.SINGLE(x)`, which only
dynamic-array formulas carry. The writer now does the same and marks such
formulas cm="1"; the parser reads `SINGLE(x)` back as `@x`, as it already
does for `ANCHORARRAY` and `#`.
Two cases in the #83 metadata test expected a redundant `@` (`SQRT(@A1:A3)`,
`@A1:A3*2`) to be written as an ordinary formula. Dropping the `@` there is
only lossless if the reader puts it back on legacy formulas, which it
doesn't yet (the read side of #64), so they now expect cm.
generated with Claude Code
Preserve array evaluation for non-spilling XLSX formulas
Rebased onto main with a maintainer fix-up (LET bindings via split_last/as_chunks for clippy, no slice indexing); the contributor's branch does not allow maintainer edits.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Alexander Alber