Required value can be left blank on finalization if cleared by calculate

[lognaturel]

Software versions

all

Problem description

Users sometimes put a calculate on a visible field in an attempt to have a dynamic default. That calculate is evaluated on form finalization, replacing any user-provided value. If the calculate evaluates to blank, the form successfully finalizes even if the field is required.

Steps to reproduce the problem

See getodk/collect#4566

Expected behavior

If a calculate clears a required value, the form should fail validation. This doesn't do a lot to help users identify their misuse of calculates because more often than not a calculate will produce a value. I'm still filing the issue because it points to something not quite right about the order things are evaluated in on finalization.