pytype.pytd.visitors.VerifyLiterals

Visitor for verifying that Literal[object] contains an enum. Other valid Literal types are checked by the parser, e.g. to make sure no `float` values are used in Literals. Checking that an object in a Literal is an enum member is more complex, so it gets its own visitor. Because this visitor walks up the class hierarchy, it must be run after ClassType pointers are filled in.