Deprecate and replace more qasm methods for Instruction

qiskit/circuit/instruction.py

@@ -44,6 +44,7 @@
 from qiskit.qobj.qasm_qobj import QasmQobjInstruction
 from qiskit.circuit.parameter import ParameterExpression
 from qiskit.circuit.operation import Operation
+from qiskit.utils.deprecation import deprecate_func
 from .tools import pi_check
 
 _CUTOFF_PRECISION = 1e-10
@@ -436,6 +437,39 @@ def __deepcopy__(self, _memo=None):
             cpy._definition = copy.deepcopy(self._definition, _memo)
         return cpy
 
+    def _qasmif(self, string):
+        """Print an if statement if needed."""
+        if self.condition is None:
+            return string
+        if not isinstance(self.condition[0], ClassicalRegister):
+            raise QasmError(
+                "OpenQASM 2 can only condition on registers, but got '{self.condition[0]}'"
+            )
+        return "if(%s==%d) " % (self.condition[0].name, self.condition[1]) + string
+
+    @deprecate_func(
+        additional_msg=(
+            "Correct exporting to OpenQASM 2 is the responsibility of a larger exporter; it cannot "
+            "safely be done on an object-by-object basis without context. No replacement will be "
+            "provided, because the premise is wrong."
+        ),
+        since="0.25.0",
+    )
+    def qasm(self):
+        """Return a default OpenQASM string for the instruction.
+
+        Derived instructions may override this to print in a
+        different format (e.g. measure q[0] -> c[0];).
+        """
+        name_param = self.name
+        if self.params:
+            name_param = "{}({})".format(
+                name_param,
+                ",".join([pi_check(i, output="qasm", eps=1e-12) for i in self.params]),
+            )
+
+        return self._qasmif(name_param)
+
     def broadcast_arguments(self, qargs, cargs):
         """
         Validation of the arguments.
@@ -569,5 +603,7 @@ def _qasm(operation):
             raise QasmError(
                 "OpenQASM 2 can only condition on registers, but got '{operation.condition[0]}'"
             )
-        name_param = "if(%s==%d) " % (operation.condition[0].name, operation.condition[1]) + name_param
-    return  name_param
+        name_param = (
+            "if(%s==%d) " % (operation.condition[0].name, operation.condition[1]) + name_param
+        )
+    return name_param

qiskit/circuit/library/standard_gates/x.py

@@ -15,6 +15,7 @@
 from typing import Optional, Union, Type
 from math import ceil, pi
 import numpy
+from qiskit.utils.deprecation import deprecate_func
 from qiskit.circuit.controlledgate import ControlledGate
 from qiskit.circuit.gate import Gate
 import qiskit.circuit.instruction
@@ -569,6 +570,14 @@ def _define(self):
 
         self.definition = qc
 
+    @deprecate_func(
+        additional_msg=(
+            "Correct exporting to OpenQASM 2 is the responsibility of a larger exporter; it cannot "
+            "safely be done on an object-by-object basis without context. No replacement will be "
+            "provided, because the premise is wrong."
+        ),
+        since="0.25.0",
+    )
     def qasm(self):
         # Gross hack to override the Qiskit name with the name this gate has in Terra's version of
         # 'qelib1.inc'.  In general, the larger exporter mechanism should know about this to do the

qiskit/circuit/quantumcircuit.py

@@ -1738,16 +1738,22 @@ def qasm(
             elif operation.name == "barrier":
                 qargs = ",".join(bit_labels[q] for q in instruction.qubits)
                 instruction_qasm = "barrier;" if not qargs else f"barrier {qargs};"
+            elif hasattr(operation, "has_qasm2") and not operation.has_qasm2():
+                raise CircuitError(
+                    f"No QASM 2 representation is defined for operation {operation.name}"
+                )
             else:
                 operation = _qasm2_define_custom_operation(
                     operation, existing_gate_names, gates_to_define
                 )
-
+                if not isinstance(operation, Instruction):
+                    raise Exception(f"expecting Instruction got {type(operation)}")
                 # Insert qasm representation of the original instruction
-                if hasattr(operation, "qasm"):
-                    name_param = operation.qasm()
-                else:
-                    name_param = qiskit.circuit.instruction._qasm(operation)
+                if operation.name == "c3sx":
+                    operation.name = "c3sqrtx"
+                name_param = qiskit.circuit.instruction._qasm(operation)
+                if operation.name == "c3sqrtx":
+                    operation.name = "c3sx"
                 bits_qasm = ",".join(
                     bit_labels[j] for j in itertools.chain(instruction.qubits, instruction.clbits)
                 )
@@ -2822,7 +2828,7 @@ def _unroll_param_dict(
         self, value_dict: Mapping[Parameter, ParameterValueType]
     ) -> dict[Parameter, ParameterValueType]:
         unrolled_value_dict: dict[Parameter, ParameterValueType] = {}
-        for (param, value) in value_dict.items():
+        for param, value in value_dict.items():
             if isinstance(param, ParameterVector):
                 if not len(param) == len(value):
                     raise CircuitError(

qiskit/extensions/hamiltonian_gate.py

@@ -22,6 +22,7 @@
 from qiskit.quantum_info.operators.predicates import is_hermitian_matrix
 from qiskit.extensions.exceptions import ExtensionError
 from qiskit.circuit.exceptions import CircuitError
+from qiskit.utils.deprecation import deprecate_func
 
 from .unitary import UnitaryGate
 
@@ -116,6 +117,16 @@ def _define(self):
         qc._append(UnitaryGate(self.to_matrix()), q[:], [])
         self.definition = qc
 
+    def has_qasm2(self):
+        """Return `False` because no QASM2 representation is defined for HamiltonianGate."""
+        return False
+
+    @deprecate_func(
+        additional_msg=(
+            "This method raises an error stating that HamiltonianGate has no OpenQASM 2 definition."
+        ),
+        since="0.25.0",
+    )
     def qasm(self):
         """Raise an error, as QASM is not defined for the HamiltonianGate."""
         raise ExtensionError("HamiltonianGate has no QASM definition.")

test/python/circuit/test_hamiltonian_gate.py

@@ -20,6 +20,7 @@
 import qiskit
 from qiskit.extensions.hamiltonian_gate import HamiltonianGate, UnitaryGate
 from qiskit.extensions.exceptions import ExtensionError
+from qiskit.circuit.exceptions import CircuitError
 from qiskit.test import QiskitTestCase
 from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit
 from qiskit.circuit import Parameter
@@ -97,7 +98,7 @@ def test_error_on_qasm(self):
         matrix = np.zeros((2, 2))
         qc.hamiltonian(operator=matrix, time=1, qubits=qr[0])
 
-        with self.assertRaises(ExtensionError):
+        with self.assertRaises(CircuitError):
             qc.qasm()
 
     def test_2q_hamiltonian(self):