From 4f986293ea0d13b187826b7ac4a63989b8b0cff6 Mon Sep 17 00:00:00 2001
From: David Yonge-Mallo <dlyongemallo@users.noreply.github.com>
Date: Thu, 9 May 2024 08:45:21 +0200
Subject: [PATCH] Add `U` as alias for `u3` gate. Required for compatibility
 with OpenQASM 3.

Together with #218, fixes #227.
---
 pyzx/circuit/gates.py      | 1 +
 pyzx/circuit/qasmparser.py | 8 ++++----
 tests/test_qasm.py         | 3 +++
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/pyzx/circuit/gates.py b/pyzx/circuit/gates.py
index a6cf7de8..97c68b88 100644
--- a/pyzx/circuit/gates.py
+++ b/pyzx/circuit/gates.py
@@ -1288,6 +1288,7 @@ def to_graph(self, g, q_mapper, c_mapper):
     "u2": U2,
     "u3": U3,
     "u": U3,
+    "U": U3,  # needed for OpenQASM 3 in Qiskit 1.0 and up
     "cu3": CU3,
     "cu": CU,
     "cx": CNOT,
diff --git a/pyzx/circuit/qasmparser.py b/pyzx/circuit/qasmparser.py
index 8f8f5448..a92341ea 100644
--- a/pyzx/circuit/qasmparser.py
+++ b/pyzx/circuit/qasmparser.py
@@ -21,7 +21,7 @@
 from typing import List, Dict, Tuple, Optional
 
 from . import Circuit
-from .gates import Gate, qasm_gate_table, U2, U3
+from .gates import Gate, qasm_gate_table
 from ..utils import settings
 
 
@@ -193,10 +193,10 @@ def parse_command(self, c: str, registers: Dict[str,Tuple[int,int]]) -> List[Gat
                 gates.append(g)
             elif name == 'u2':
                 if len(phases) != 2: raise TypeError("Invalid specification {}".format(c))
-                gates.append(U2(argset[0],phases[0],phases[1]))
-            elif name in ('u3', 'u'):
+                gates.append(qasm_gate_table[name](argset[0], phases[0], phases[1]))  # type: ignore
+            elif name in ('u3', 'u', 'U'):
                 if len(phases) != 3: raise TypeError("Invalid specification {}".format(c))
-                gates.append(U3(argset[0],phases[0],phases[1],phases[2]))
+                gates.append(qasm_gate_table[name](argset[0], phases[0], phases[1], phases[2]))  # type: ignore
             elif name in ('cx', 'CX', 'cy', 'cz', 'ch', 'csx', 'swap'):
                 if len(phases) != 0: raise TypeError("Invalid specification {}".format(c))
                 g = qasm_gate_table[name](control=argset[0],target=argset[1])  # type: ignore
diff --git a/tests/test_qasm.py b/tests/test_qasm.py
index 07bd472c..128569f5 100644
--- a/tests/test_qasm.py
+++ b/tests/test_qasm.py
@@ -290,6 +290,9 @@ def compare_gate_matrix_with_qiskit(gates, num_qubits: int, num_angles: int, qas
         compare_gate_matrix_with_qiskit(['cu3'], 2, 3, [2])
         compare_gate_matrix_with_qiskit(['u'], 1, 3, [2])
 
+        # Test native OpenQASM 3 gate.
+        compare_gate_matrix_with_qiskit(['U'], 1, 3, [3])
+
     @unittest.skipUnless(QuantumCircuit, "qiskit needs to be installed for this test")
     def test_qiskit_transpile_pyzx_optimization_round_trip(self):
         """Regression test for issue #102.