Help with click

[dullboy]

Here is the code,

#test.py
import click
def print_version(ctx, value):
   if not value or ctx.resilient_parsing:
       return
   click.echo('Version 1.0')
   ctx.exit()

@click.command()
@click.option('--version', is_flag=True, callback=print_version, expose_value=False, is_eager=True)
def main():
   click.echo('Hello world')

if __name__ == '__main__':
   main()

When I run the code with test.py --version 1.0，I got a Warning: Invoked legacy parameter callback "<function print_version at 0x0000000002BE2A58>".  The new signature for such callbacks starting with click 2.0 is (ctx, param, value).
value, args = param.handle_parse_result(ctx, opts, args)
What does it mean? Thanks.