inverse of conditional gate is not conditional

[aeddins-ibm]

Information

• Qiskit Terra version: 0.18
• Python version: 3.9.5
• Operating system: mac

What is the current behavior?

Calling the inverse method of a conditional X gate returns an unconditional X gate.

Steps to reproduce the problem

What is the expected behavior?

I'd expect the inverse of a conditional gate to have the same condition.

That way, for instance, x.c_if(bit, 1) immediately followed by its inverse operation would produce the identity, as one would expect for an inverse.

Suggested solutions

Assuming it's the desired behavior, could have inverse copy the condition from the original gate to the inverse gate before returning it.

[ewinston]

I'm just curious about when this situation comes up and why it might not just warn due to the presence of measurement?