[Impact] * snapcraft has a schema that describes allowed snapcraft.yaml files. Part of this schema describes plugs and slots that are defined as the level of a part (so not globally and not at the level of an app). * keeping this code in the schema can create potential confusion for users who expect snapcraft to validate the input to be correct. * the change is minimal, altering the schema only [Test Case] * create a snapcrat.yaml with a part defining a plug and a slot * run snapcraft * snapcraft should complain about the plug/slot definition at a part level ... parts: foo: plugin: nil plugs: [iface1] slots: [iface2] ... [Regression Potential] * snaps that used parts defining plugs or slots will no longer build * snaps that will be built after removing the offending declarations will behave exactly as before so the regression potential is minimal [Other Info]