Add reset to QasmParser

Add a test which can serve as example including the modifications to
support the `reset` keyword in the import of QASM files in the PLY based
lexer/parser.

cirq-core/cirq/contrib/qasm_import/_lexer.py

@@ -29,6 +29,7 @@ def __init__(self):
     reserved = {
         'qreg': 'QREG',
         'creg': 'CREG',
+        'reset': 'RESET',
         'measure': 'MEASURE',
         'if': 'IF',
         '->': 'ARROW',
@@ -91,6 +92,10 @@ def t_CREG(self, t):
         r"""creg"""
         return t
 
+    def t_RESET(self, t):
+        r"""reset"""
+        return t
+
     def t_MEASURE(self, t):
         r"""measure"""
         return t

cirq-core/cirq/contrib/qasm_import/_parser.py

@@ -20,7 +20,7 @@
 import sympy
 from ply import yacc
 
-from cirq import ops, Circuit, NamedQubit, CX
+from cirq import ops, Circuit, NamedQubit, CX, R
 from cirq.circuits.qasm_output import QasmUGate
 from cirq.contrib.qasm_import._lexer import QasmLexer
 from cirq.contrib.qasm_import.exception import QasmException
@@ -293,6 +293,7 @@ def p_format(self, p):
     # circuit : new_reg circuit
     #         | gate_op circuit
     #         | measurement circuit
+    #         | reset circuit
     #         | if circuit
     #         | empty
 
@@ -303,8 +304,13 @@ def p_circuit_reg(self, p):
     def p_circuit_gate_or_measurement_or_if(self, p):
         """circuit :  circuit gate_op
         |  circuit measurement
-        |  circuit if"""
-        self.circuit.append(p[2])
+        |  circuit reset
+        |  circuit if
+        |  circuit new_reg"""
+        if isinstance(p[2], list):
+            self.circuit.append(p[2])
+        else:
+            self.circuit.append([p[2]])
         p[0] = self.circuit
 
     def p_circuit_empty(self, p):
@@ -325,6 +331,7 @@ def p_new_reg(self, p):
             self.qregs[name] = length
         else:
             self.cregs[name] = length
+        print("Calling qrags to create a qubit")
         p[0] = (name, length)
 
     # gate operations
@@ -499,6 +506,17 @@ def p_measurement(self, p):
             ops.MeasurementGate(num_qubits=1, key=creg[i]).on(qreg[i]) for i in range(len(qreg))
         ]
 
+    # reset operations
+    # reset : RESET qarg
+
+    def p_reset(self, p):
+        """reset : RESET qarg ';'"""
+        qreg = p[2]
+
+        p[0] = [
+            ops.ResetChannel().on(qreg[i]) for i in range(len(qreg))
+        ]
+
     # if operations
     # if : IF '(' carg EQ NATURAL_NUMBER ')' ID qargs
 

cirq-core/cirq/contrib/qasm_import/_parser_test.py

@@ -408,6 +408,34 @@ def test_U_gate_too_much_params_error():
     with pytest.raises(QasmException, match=r"U takes 3.*got.*4.*line 3"):
         parser.parse(qasm)
 
+def test_reset():
+    qasm ="""
+     OPENQASM 2.0;
+     include "qelib1.inc";
+     qreg q[1];
+     creg c[1];
+     x q[0];
+     reset q[0];
+     measure q[0] -> c[0];
+     """
+
+    parser = QasmParser()
+
+    q_0 = cirq.NamedQubit('q_0')
+
+    expected_circuit = Circuit()
+    expected_circuit.append(cirq.X(q_0))
+    expected_circuit.append(cirq.ResetChannel().on(q_0))
+    expected_circuit.append(cirq.MeasurementGate(num_qubits=1, key='c_0').on(q_0))
+
+    parsed_qasm = parser.parse(qasm)
+
+    assert parsed_qasm.supportedFormat
+    assert parsed_qasm.qelib1Include
+
+    ct.assert_same_circuits(parsed_qasm.circuit, expected_circuit)
+    assert parsed_qasm.qregs == {'q': 1}
+    assert parsed_qasm.cregs == {'c': 1}
 
 @pytest.mark.parametrize(
     'expr',