Fixes OpenQASM circuit measurements and makes the exporter more composable

.github/qasm-parser-requirements.txt

@@ -0,0 +1 @@
+graphix-qasm-parser @ git+https://github.com/TeamGraphix/graphix-qasm-parser@refs/pull/16/head

.github/workflows/cov.yml

@@ -25,7 +25,11 @@ jobs:
           python-version: ${{ env.python-version }}
 
       - name: Run pytest
-        run: uv run --extra dev pytest --cov=./graphix --cov-report=xml --cov-report=term --doctest-modules
+        run: |
+          uv run --with-requirements .github/qasm-parser-requirements.txt \
+              --extra dev \
+            pytest --cov=./graphix --cov-report=xml --cov-report=term \
+              --doctest-modules
 
       - name: Upload coverage reports to Codecov
         uses: codecov/codecov-action@v5

CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - #591: `FixedBranchSelector` now passes its RNG parameter to its `default` branch selector.
+
+- #595: `RZZ` gates are no longer incorrectly exported as `crz`; transpilation to `CNOT`-`RZ`-`CNOT` is provided.
+
 - #596, #597: Pattern's `n_node` property updated after Pauli removal.
 
 ## [0.4] - 2026-08-18

graphix/qasm3_exporter.py

@@ -62,7 +62,7 @@ def circuit_to_qasm3_lines(circuit: Circuit, *, transpile: bool = True) -> Itera
         An iterator over the OpenQASM 3.0 lines that represent the circuit.
     """
     if transpile:
-        circuit = circuit.transpile_j_to_rzh().transpile_measurements_to_z_axis()
+        circuit = circuit.transpile_rzz().transpile_j_to_rzh().transpile_measurements_to_z_axis()
     yield "OPENQASM 3;"
     yield 'include "stdgates.inc";'
     yield f"qubit[{circuit.width}] q;"
@@ -138,9 +138,8 @@ def instruction_to_qasm3(instruction: InstructionType) -> str:
         case InstructionKind.CZ:
             return qasm3_gate_call("cz", [qasm3_qubit(instruction.targets[i]) for i in (0, 1)])
         case InstructionKind.RZZ:
-            angle = angle_to_qasm3(instruction.angle)
-            return qasm3_gate_call(
-                "crz", args=[angle], operands=[qasm3_qubit(instruction.control), qasm3_qubit(instruction.target)]
+            raise ValueError(
+                "RZZ gates must be decomposed before QASM3 export using `Circuit.transpile_rzz`, or setting `transpile=True`."
             )
         case InstructionKind.CCX:
             return qasm3_gate_call(

graphix/transpiler.py

@@ -749,6 +749,17 @@ def transpile_j_to_rzh(self) -> Circuit:
                     new_circuit.add(instr)
         return new_circuit
 
+    def transpile_rzz(self) -> Circuit:
+        """Return an equivalent circuit where all RZZ gates have been replaced with OpenQASM gates."""
+        new_circuit = Circuit(self.width)
+        for instr in self.instruction:
+            match instr.kind:
+                case InstructionKind.RZZ:
+                    new_circuit.extend(decompose_rzz(instr))
+                case _:
+                    new_circuit.add(instr)
+        return new_circuit
+
 
 def decompose_rzz(instr: instruction.RZZ) -> Iterator[instruction.CNOT | instruction.RZ]:
     """Yield a decomposition of RZZ(α) gate as CNOT(control, target)·Rz(target, α)·CNOT(control, target).

noxfile.py

@@ -51,7 +51,7 @@ def tests_all(session: Session) -> None:
     """Run the test suite with all dependencies."""
     session.install(".[dev]")
     # This dependency is added here to avoid circular dependencies
-    session.install("graphix-qasm-parser>=0.1.1")
+    session.install("-r", ".github/qasm-parser-requirements.txt")
     run_pytest(session, doctest_modules=True, mpl=True)
 
 
@@ -97,7 +97,7 @@ class ReverseDependency:
     [
         ReverseDependency("https://github.com/thierry-martinez/graphix-symbolic", branch="in-place_methods"),
         ReverseDependency("https://github.com/thierry-martinez/graphix-stim-backend", branch="rename-simulate"),
-        ReverseDependency("https://github.com/TeamGraphix/graphix-qasm-parser"),
+        ReverseDependency("https://github.com/TeamGraphix/graphix-qasm-parser", branch="refs/pull/16/head"),
         ReverseDependency(
             "https://github.com/thierry-martinez/graphix-ibmq", doctest_modules=False, branch="rename-simulate"
         ),
@@ -127,11 +127,13 @@ def tests_reverse_dependencies(session: Session, package: ReverseDependency) ->
         session.install("nox")
     with TemporaryDirectory() as tmpdir:
         with session.cd(tmpdir):
-            if package.branch is None:
-                session.run("git", "clone", package.repository, external=True)
-            else:
-                session.run("git", "clone", "-b", package.branch, package.repository, external=True)
+            session.run("git", "clone", package.repository, external=True)
             with session.cd(dirname):
+                if package.branch is not None:
+                    # Use `git fetch` instead of `git clone -b` to support
+                    # special refs such as `refs/pull/N/head`
+                    session.run("git", "fetch", "origin", package.branch, external=True)
+                    session.run("git", "checkout", "--detach", "FETCH_HEAD", external=True)
                 # graphix installation fails without constraint on numba
                 session.install(package.install_target, "numba>=0.65.1")
         # Note that `session.cd` is used as a context manager above,

tests/test_qasm3_exporter.py

@@ -11,7 +11,7 @@
 import pytest
 from numpy.random import PCG64, Generator
 
-from graphix import Circuit, instruction
+from graphix import Circuit
 from graphix.fundamentals import ANGLE_PI, Axis
 from graphix.qasm3_exporter import angle_to_qasm3, circuit_to_qasm3, pattern_to_qasm3
 from graphix.random_objects import rand_circuit
@@ -23,23 +23,6 @@ def test_angle_to_qasm3(check: tuple[float, str]) -> None:
     assert angle_to_qasm3(angle) == expected
 
 
-def test_measurement() -> None:
-    # Measurements are not supported yet by the parser.
-    # https://github.com/TeamGraphix/graphix-qasm-parser/issues/3
-    # The best we can do is to check if the measurement instruction
-    # is exported as expected.
-    circuit = Circuit(1, instr=[instruction.M(target=0, axis=Axis.Z)])
-    qasm = circuit_to_qasm3(circuit)
-    assert (
-        qasm
-        == """OPENQASM 3;
-include "stdgates.inc";
-qubit[1] q;
-bit[1] b;
-b[0] = measure q[0];"""
-    )
-
-
 @pytest.mark.parametrize("jumps", range(1, 11))
 def test_to_qasm3_random_circuit(fx_bg: PCG64, jumps: int) -> None:
     """Check the export to OpenQASM 3 without validating the result.
@@ -61,13 +44,25 @@ def test_to_qasm3_random_circuit(fx_bg: PCG64, jumps: int) -> None:
     _qasm3 = pattern_to_qasm3(pattern)
 
 
-def test_to_qasm3_failures() -> None:
-    circuit = Circuit(2)
+def test_to_qasm3_measure_on_x_axis() -> None:
+    circuit = Circuit(1)
     circuit.m(0, Axis.X)
     with pytest.raises(ValueError, match="OpenQASM3 only supports measurements on Z axis"):
         circuit_to_qasm3(circuit, transpile=False)
-    circuit = circuit.transpile_measurements_to_z_axis()
-    circuit.j(1, 0.25)
+    _qasm3 = circuit_to_qasm3(circuit)
+
+
+def test_to_qasm3_j() -> None:
+    circuit = Circuit(1)
+    circuit.j(0, 0.25)
     with pytest.raises(ValueError, match="J gates must be decomposed before QASM3 export"):
         circuit_to_qasm3(circuit, transpile=False)
     _qasm3 = circuit_to_qasm3(circuit)
+
+
+def test_to_qasm3_rzz() -> None:
+    circuit = Circuit(2)
+    circuit.rzz(0, 1, 0.25)
+    with pytest.raises(ValueError, match="RZZ gates must be decomposed before QASM3 export"):
+        circuit_to_qasm3(circuit, transpile=False)
+    _qasm3 = circuit_to_qasm3(circuit)

tests/test_qasm3_exporter_to_graphix_parser.py

@@ -8,7 +8,7 @@
 from numpy.random import PCG64, Generator
 
 from graphix import Circuit, Instruction
-from graphix.fundamentals import ANGLE_PI
+from graphix.fundamentals import ANGLE_PI, Axis
 from graphix.instruction import InstructionKind
 from graphix.qasm3_exporter import circuit_to_qasm3
 from graphix.random_objects import rand_circuit
@@ -50,7 +50,7 @@ def test_circuit_to_qasm3(fx_bg: PCG64, jumps: int) -> None:
 
 @pytest.mark.parametrize("instruction", ALL_INSTRUCTIONS)
 def test_instruction_to_qasm3(instruction: InstructionType) -> None:
-    if instruction.kind == InstructionKind.M:
+    if instruction.kind in {InstructionKind.RZZ, InstructionKind.M}:
         pytest.skip()
     check_round_trip(Circuit(3, instr=[instruction]))
 
@@ -67,3 +67,8 @@ def test_j_to_qasm3_failure() -> None:
     circuit = Circuit(3, instr=[Instruction.J(target=0, angle=ANGLE_PI / 4)])
     with pytest.raises(ValueError):
         circuit_to_qasm3(circuit, transpile=False)
+
+
+def test_measurement() -> None:
+    circuit = Circuit(1, instr=[Instruction.M(target=0, axis=Axis.Z)])
+    check_round_trip(circuit)