Check if cregbundle is None to avoid warning statement

[amruthpremjith]

Summary

fixes #15949

Details and comments

Added check to see if cregbundle is set to None to avoid warning output

Tested by running the same code as the issue and didn't see the warning with the change.

• Without change

(qiskit-dev) amruthpremjith@Amruths-MacBook-Pro qiskit % python3 test.py
/Users/amruthpremjith/qiskit/fork/qiskit/qiskit/visualization/circuit/circuit_visualization.py:301: RuntimeWarning: Cregbundle set to False since an instruction needs to refer to individual classical wire
  if check_clbit_in_inst(block, cregbundle) is False:

• With change

(qiskit-dev) amruthpremjith@Amruths-MacBook-Pro qiskit % python3 test.py
(qiskit-dev) amruthpremjith@Amruths-MacBook-Pro qiskit % 

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[jakelishman]

Can you add a bugfix release note, and a test that this works? For testing: you can add a small case in test/python/visualization/test_circuit_text_drawer.py that triggers the spurious warning without your change. For the test, you can use the warnings.catch_warnings context manager, and assert that there aren't any warnings emitted by that code block (for example) - the test should fail without your code change and pass with it.

[amruthpremjith]

I used the same circuit as in the original issue but used a "text" output instead cause the "mpl" one needs matplotlib and latex dependencies to run the test cases.

Test run without changes

python3 -m stestr run --no-discover test.python.visualization.test_circuit_text_drawer.TestCircuitAnnotatedOperations.test_warning_for_none_cregbundle
{0} test.python.visualization.test_circuit_text_drawer.TestCircuitAnnotatedOperations.test_warning_for_none_cregbundle [0.005022s] ... FAILED

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):

      File "/Users/amruthpremjith/qiskit/fork/qiskit/test/python/visualization/test_circuit_text_drawer.py", line 4775, in test_warning_for_none_cregbundle
    self.assertEqual(w, [])

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 885, in assertEqual
    assertion_func(first, second, msg=msg)

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 1091, in assertListEqual
    self.assertSequenceEqual(list1, list2, msg, seq_type=list)

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 1073, in assertSequenceEqual
    self.fail(msg)

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 715, in fail
    raise self.failureException(msg)

    AssertionError: Lists differ: [<warnings.WarningMessage object at 0x107313920>] != []

First list contains 1 additional elements.
First extra element 0:
<warnings.WarningMessage object at 0x107313920>

- [<warnings.WarningMessage object at 0x107313920>]
+ []


==============================
Failed 1 tests - output below:
==============================

test.python.visualization.test_circuit_text_drawer.TestCircuitAnnotatedOperations.test_warning_for_none_cregbundle
------------------------------------------------------------------------------------------------------------------

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):

      File "/Users/amruthpremjith/qiskit/fork/qiskit/test/python/visualization/test_circuit_text_drawer.py", line 4775, in test_warning_for_none_cregbundle
    self.assertEqual(w, [])

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 885, in assertEqual
    assertion_func(first, second, msg=msg)

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 1091, in assertListEqual
    self.assertSequenceEqual(list1, list2, msg, seq_type=list)

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 1073, in assertSequenceEqual
    self.fail(msg)

      File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/unittest/case.py", line 715, in fail
    raise self.failureException(msg)

    AssertionError: Lists differ: [<warnings.WarningMessage object at 0x107313920>] != []

First list contains 1 additional elements.
First extra element 0:
<warnings.WarningMessage object at 0x107313920>

- [<warnings.WarningMessage object at 0x107313920>]
+ []



======
Totals
======
Ran: 1 tests in 0.0050 sec.
 - Passed: 0
 - Skipped: 0
 - Expected Fail: 0
 - Unexpected Success: 0
 - Failed: 1
Sum of execute time for each test: 0.0050 sec.

==============
Worker Balance
==============
 - Worker 0 (1 tests) => 0:00:00.005022

No tests were successful during the run

Test with changes

python3 -m stestr run --no-discover test.python.visualization.test_circuit_text_drawer.TestCircuitAnnotatedOperations.test_warning_for_none_cregbundle
{0} test.python.visualization.test_circuit_text_drawer.TestCircuitAnnotatedOperations.test_warning_for_none_cregbundle [0.003843s] ... ok

======
Totals
======
Ran: 1 tests in 0.0038 sec.
 - Passed: 1
 - Skipped: 0
 - Expected Fail: 0
 - Unexpected Success: 0
 - Failed: 0
Sum of execute time for each test: 0.0038 sec.

==============
Worker Balance
==============
 - Worker 0 (1 tests) => 0:00:00.003843