Maya check Cycle Errors more thoroughly where maya.cmds.cycleCheck(list=True) fails.

maya_cycle_evaluation_error.py

from maya import cmds
import contextlib


@contextlib.contextmanager
def capture_cycle_errors():
    """Capture the plugs in Cycle Error warnings.
    
    During this context "Cycle on 'x' may not evaluate as expected"
    are captured and 'x' is extracted as plugs in the yielded list.
    
    """
    import maya.OpenMaya as om
    
    plugs = []
    def _callback(nativeMsg, messageType, data):
        if messageType != om.MCommandMessage.kWarning:
            # We only care about warnings
            return
            
        if not nativeMsg.startswith("Cycle on '"):
            # Consider only Cycle on messages
            return
            
        plug = nativeMsg.split("'")[1]
        plugs.append(plug)
        
    id = om.MCommandMessage.addCommandOutputCallback(_callback, None)
    
    # Make sure evaluation time cycle check is enabled
    original = cmds.cycleCheck(query=True, evaluation=True)
    cmds.cycleCheck(evaluation=True)
    
    try:
        yield plugs
    finally:
        om.MMessage.removeCallback(id)
        cmds.cycleCheck(evaluation=original)
        
      
def cycle_check(nodes):
    
    # Include history for the nodes since it makes
    # the following check much more accurate to
    # correctly log during the capture block
    nodes = list(set(cmds.listHistory(nodes)))
    
    with capture_cycle_errors() as plugs:    
        # Force the full DG evaluation
        cmds.dgdirty(nodes)
        cmds.dgeval(nodes)
        
    return plugs
      

# Test    
cmds.file(new=True, force=True)
cmds.loadPlugin("matrixNodes", quiet=True)
a = cmds.createNode("transform", name="a")
b = cmds.createNode("transform", name="b")
decompose = cmds.createNode("decomposeMatrix")
cmds.connectAttr(a + ".worldMatrix[0]", decompose + ".inputMatrix")
cmds.connectAttr(decompose + ".outputTranslate", b + ".translate")
cmds.connectAttr(b + ".worldMatrix[0]", a + ".offsetParentMatrix")
    
nodes = [a, b]
plugs = cycle_check(nodes)

# Our check:
print(">> cycle_check(nodes)")
print(plugs)
# THIS FINDS THE PLUG!

# maya.cmds.cycleCheck
print(">> maya.cmds.cycleCheck(all=True, list=True)")
print(cmds.cycleCheck(all=True, list=True))
# MAYA FAILS TO FIND THE PLUG WITH THIS.

More details on the OpenPype PR where I wrote this initial version