click.option with a custom type and default value tries to convert the default twice in click >= 8.0.0

[mayghalV]

click.option with a custom type class and default value tries to convert the default value twice.

For this example here:

import click
from click.types import ParamType

import pytz

class TimeZone(ParamType):

    name = "timezone"

    def convert(self, value, param, ctx):
        try:
            return pytz.timezone(value)
        except pytz.exceptions.UnknownTimeZoneError:
            self.fail(f'invalid timezone: {value}')

    def __repr__(self):
        return "TimeZone"

@click.group()
def cli():
    pass


@cli.command()
@click.option('--t', '-t', type=TimeZone(), default='UTC')
def example(t):
    print(t, type(t))


if __name__ == '__main__':
    # cli.main(['example', '-t', 'UTC']) # Works
    cli.main(['example'])   # Doesn't work - tries to convert 'UTC' twice

Running
cli.main(['example', '-t', 'UTC']) works as expected and prints UTC <class 'pytz.UTC'> as the result.

However when I try to run without a default value for t: cli.main(['example']), I get the following error message:

File "../lib64/python3.6/site-packages/pytz/__init__.py", line 170, in timezone
    if zone.upper() == 'UTC':
AttributeError: 'UTC' object has no attribute 'upper'

After running the debugger and putting a breakpoint within TimeZone.convert defined above - the breakpoint is hit twice, first with the string 'UTC', followed by the timezone pytz.UTC the second time so it seems click is trying to convert the default value twice.

Environment:

• Python version: 3.6
• Click version: >=8.0.0. Works as expected on 7.1.2

[davidism]

Not a bug, see existing closed issues about this. Custom types must accept a value that is already the correct type. Duplicate of #1898.