Fix QASM2.loads without return value (#246)

Author: david-pl

src/bloqade/qasm2/parse/lowering.py

@@ -56,6 +56,7 @@ def loads(
                         raise lowering.BuildError(f"Cannot find return value {returns}")
                 else:
                     return_value = func.ConstantNone()
+                    frame.push(return_value)
 
                 return_node = frame.push(func.Return(value_or_stmt=return_value))
 

test/pyqrack/test_target.py

@@ -1,11 +1,13 @@
 import math
+import textwrap
 
 import pytest
 from kirin import ir
 from kirin.dialects import ilist
 
 from bloqade import qasm2
 from bloqade.pyqrack import PyQrack, PyQrackQubit, StackMemorySimulator, reg
+from bloqade.qasm2.parse.lowering import QASM2
 
 
 def test_target():
@@ -171,3 +173,21 @@ def parallel():
     result = target.run(parallel)
 
     assert result == [reg.Measurement.One] * 4
+
+
+def test_loads_without_return():
+    qasm2_str = textwrap.dedent(
+        """
+    OPENQASM 2.0;
+
+    qreg q[1];
+    x q[0];
+    """
+    )
+
+    main = QASM2(qasm2.main).loads(qasm2_str, "main")
+
+    sim = StackMemorySimulator(min_qubits=2)
+    ket = sim.state_vector(main)
+
+    assert ket[0] == 0