def add_arguments(schema, kwargs):
"""
Create a new schema like ``schema`` but with the arguments given by
``kwargs`` prepended to the signature.
:param foolscap.remoteinterface.RemoteMethodSchema schema: The existing
schema.
:param list[(bytes, foolscap.IConstraint)] kwargs: The arguments to
prepend to the signature of ``schema``.
:return foolscap.remoteinterface.RemoteMethodSchema: The new schema
object.
"""
new_kwargs = dict(schema.argConstraints)
new_kwargs.update(kwargs)
modified_schema = RemoteMethodSchema(**new_kwargs)
# Initialized from **new_kwargs, RemoteMethodSchema.argumentNames is in
# some arbitrary, probably-incorrect order. This breaks user code which
# tries to use positional arguments. Put them back in the order they were
# in originally (in the input ``schema``), prepended with the newly added
# arguments.
modified_schema.argumentNames = (
# The new arguments
list(argName for (argName, _) in kwargs) +
# The original arguments in the original order
schema.argumentNames
)
return modified_schema
