composite gates do not have definition when qasm()'d

Information

• Qiskit Terra version: master
• Python version: 3.7

What is the current behavior?

from qiskit import QuantumCircuit, QuantumRegister

rinv_q = QuantumRegister(1, name='q')
rinv_gate = QuantumCircuit(rinv_q, name='rinv')
rinv_gate.sdg(rinv_q)
rinv_gate.h(rinv_q)
rinv_gate.sdg(rinv_q)
rinv_gate.h(rinv_q)
rinv = rinv_gate.to_instruction() 

qr = QuantumRegister(1, name='qr') 
circuit = QuantumCircuit(qr, name='circuit') 
circuit.append(rinv, [qr[0]])

print(circuit.qasm())

OPENQASM 2.0;
include "qelib1.inc";
qreg qr[1];
rinv qr[0];

What is the expected behavior?

OPENQASM 2.0;
include "qelib1.inc";
gate rinv q {sdg q; h q; sdg q; h q; }    #  <--- the definition of rinv
qreg qr[1];
rinv qr[0];

[1ucian0]

Which part is not supported?

The QASM specification does not allow classical bits as arguments. I think. Check out if you can parse them back.

I will open a PR, but will not be able to until Jan 21st, as I am unavailable until then.

Great! We can wait until then… no worries.

[ajavadia]

A related issue that has been open for a year: https://github.com/Qiskit/qiskit-terra/issues/1566

It is the inverse of this issue. Seems there is an open PR for it but does fully work.