debug-only assertions in rotational inertia are hostile to uses in parsing

[rpoyner-tri]

What happened?

Debug-only error checking behavior in RotationalInertia:

• forces me to bifurcate tests on compilation mode
• is generally hostile to the rule that errors in parsing flow to a diagnostic policy, rather than just throwing.

TBD: example of a split test, investigation into execution paths and alternatives.
Victory condition: parser unit tests don't need to use #ifdef to capture divergent behavior based on compilation mode.

Version

No response

What operating system are you using?

Ubuntu 22.04

What installation option are you using?

compiled from source code using Bazel

Relevant log output

No response

[jwnimmer-tri]

Yup, I've been pondering this, too.

The purpose of DRAKE_ASSERT is to identify bugs inside Drake (in our Debug CI jobs). Using DRAKE_ASSERT to sanitize data from users is wholly inappropriate.

(It is particularly relevant to parser, but even without any parsing involved -- having users call a RotationMatrix constructor that uses DRAKE_ASSERT for validating its arguments is wrong in the first place.)

[rpoyner-tri]

Example of a split test case is in #22414 .

[rpoyner-tri]

The problem seen in early revisions of #22414 was able to be avoided, but the potential for surprises remains. I'll need to study this a bit more to better reframe the problem.