Reject on empty fields object in PlainYearMonth::with

[nekevss]

Small fix for a bug in PlainYearMonth::with.

This can still be handled downstream in the engines, if there is careful attention to the specification steps. We should still reject here to fix bug in Rust API.

[Manishearth]

Confirming that V8 is free from this bug.

d8> a = Temporal.PlainYearMonth.from({year: 2025, month: 1})
2025-01
d8> a.with({})
(d8):1: TypeError: Temporal error: Must specify at least one calendar field.
a.with({})

Is there a test262 test for this? Should there be?

[nekevss]

There is a test262 for this test. Boa was failing it.

https://boajs.dev/conformance?version=main&testPath=built-ins%2FTemporal%2FPlainYearMonth%2Fprototype%2Fwith&selectedTest=yearmonthlike-invalid.js

[nekevss]

See boa-dev/boa#4530 for reference

[Manishearth]

Fair enough!