Editorial: Unreachable code or testing gap in RoundDuration with undefined relativeTo and unit = weeks or months

[justingrant]

RoundDuration currently includes this text:

2. If unit is "year", "month", or "week", and relativeTo is undefined, then
  a. Throw a RangeError exception.

Looking at codecov, the "year" branch of this check is tested but the "month" and "week" branches are not.

For "month" and "week", AFAICT Temporal.Duration.prototype.total and Temporal.Duration.prototype.round are the only callers of RoundDuration which could possibly have relativeTo undefined and could use "month" or "week". And both of those callers will call UnbalanceDateDurationRelative before calling RoundDuration. UnbalanceDateDurationRelative includes the same validation and RangeError-throwing for a missing relativeTo, which explains the codecov result.

Should the test in RoundDuration be an assertion instead for "month" and "week"?

Or should UnbalanceDateDurationRelative validate "year" too and RoundDuration should change to an assertion in all cases, including "year"?

Or is there another caller of RoundDuration that doesn't call UnbalanceDateDurationRelative and which can trigger this RangeError?

[justingrant]

Meeting 2023-08-17: Let's leave this issue open until all the Duration-related outstanding changes are merged, then we can see if this is still unreachable. If it is, then change it to an assertion for "month" and "week" cases.