Qiskit gates not qelib1.inc are now defined when dumped (Qiskit#9777)

* non-standard gates

* Qiskit gates not qelib1.inc are now defined when dumped

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/circuit/quantumcircuit.py

@@ -1623,7 +1623,6 @@ def qasm(
             "sx",
             "sxdg",
             "cz",
-            "ccz",
             "cy",
             "swap",
             "ch",
@@ -1636,8 +1635,6 @@ def qasm(
             "cp",
             "cu3",
             "csx",
-            "cs",
-            "csdg",
             "cu",
             "rxx",
             "rzz",

releasenotes/notes/fix_9559-ec05304e52ff841f.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    The Qiskit gates :class:`~.CCZGate`, :class:`~.CSGate`, :class:`~.CSdgGate` are not defined in
+    ``qelib1.inc`` and, therefore, when dump as OpenQASM 2.0, their definition should be inserted in the file.
+    Fixes `#9559 <https://github.com/Qiskit/qiskit-terra/issues/9559>`__,
+    `#9721 <https://github.com/Qiskit/qiskit-terra/issues/9721>`__, and
+    `#9722 <https://github.com/Qiskit/qiskit-terra/issues/9722>`__.

test/python/circuit/test_circuit_qasm.py

@@ -10,7 +10,7 @@
 # copyright notice, and modified files need to carry a notice indicating
 # that they have been altered from the originals.
 
-"""Test Qiskit's QuantumCircuit class."""
+"""Test Qiskit's gates in QASM2."""
 
 import unittest
 from math import pi
@@ -19,15 +19,15 @@
 from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit
 from qiskit.test import QiskitTestCase
 from qiskit.circuit import Parameter, Qubit, Clbit, Gate
-from qiskit.circuit.library import C3SXGate
+from qiskit.circuit.library import C3SXGate, CCZGate, CSGate, CSdgGate, RZXGate
 from qiskit.qasm.exceptions import QasmError
 
 # Regex pattern to match valid OpenQASM identifiers
 VALID_QASM2_IDENTIFIER = re.compile("[a-z][a-zA-Z_0-9]*")
 
 
 class TestCircuitQasm(QiskitTestCase):
-    """QuantumCircuit Qasm tests."""
+    """QuantumCircuit QASM2 tests."""
 
     def test_circuit_qasm(self):
         """Test circuit qasm() method."""
@@ -249,7 +249,9 @@ def test_circuit_qasm_with_composite_circuit_with_many_params_and_qubits(self):
         self.assertEqual(original_str, qc.qasm())
 
     def test_c3sxgate_roundtrips(self):
-        """Test that C3SXGate correctly round trips.  Qiskit gives this gate a different name
+        """Test that C3SXGate correctly round trips.
+
+        Qiskit gives this gate a different name
         ('c3sx') to the name in Qiskit's version of qelib1.inc ('c3sqrtx') gate, which can lead to
         resolution issues."""
         qc = QuantumCircuit(4)
@@ -264,6 +266,58 @@ def test_c3sxgate_roundtrips(self):
         parsed = QuantumCircuit.from_qasm_str(qasm)
         self.assertIsInstance(parsed.data[0].operation, C3SXGate)
 
+    def test_cczgate_qasm(self):
+        """Test that CCZ dumps definition as a non-qelib1 gate."""
+        qc = QuantumCircuit(3)
+        qc.append(CCZGate(), qc.qubits, [])
+        qasm = qc.qasm()
+        expected = """OPENQASM 2.0;
+include "qelib1.inc";
+gate ccz q0,q1,q2 { h q2; ccx q0,q1,q2; h q2; }
+qreg q[3];
+ccz q[0],q[1],q[2];
+"""
+        self.assertEqual(qasm, expected)
+
+    def test_csgate_qasm(self):
+        """Test that CS dumps definition as a non-qelib1 gate."""
+        qc = QuantumCircuit(2)
+        qc.append(CSGate(), qc.qubits, [])
+        qasm = qc.qasm()
+        expected = """OPENQASM 2.0;
+include "qelib1.inc";
+gate cs q0,q1 { p(pi/4) q0; cx q0,q1; p(-pi/4) q1; cx q0,q1; p(pi/4) q1; }
+qreg q[2];
+cs q[0],q[1];
+"""
+        self.assertEqual(qasm, expected)
+
+    def test_csdggate_qasm(self):
+        """Test that CSdg dumps definition as a non-qelib1 gate."""
+        qc = QuantumCircuit(2)
+        qc.append(CSdgGate(), qc.qubits, [])
+        qasm = qc.qasm()
+        expected = """OPENQASM 2.0;
+include "qelib1.inc";
+gate csdg q0,q1 { p(-pi/4) q0; cx q0,q1; p(pi/4) q1; cx q0,q1; p(-pi/4) q1; }
+qreg q[2];
+csdg q[0],q[1];
+"""
+        self.assertEqual(qasm, expected)
+
+    def test_rzxgate_qasm(self):
+        """Test that RZX dumps definition as a non-qelib1 gate."""
+        qc = QuantumCircuit(2)
+        qc.append(RZXGate(0), qc.qubits, [])
+        qasm = qc.qasm()
+        expected = """OPENQASM 2.0;
+include "qelib1.inc";
+gate rzx(param0) q0,q1 { h q1; cx q0,q1; rz(0) q1; cx q0,q1; h q1; }
+qreg q[2];
+rzx(0) q[0],q[1];
+"""
+        self.assertEqual(qasm, expected)
+
     def test_unbound_circuit_raises(self):
         """Test circuits with unbound parameters raises."""
         qc = QuantumCircuit(1)