Support default for arguments with multiple values

[tekumara]

I'd like to be able to specify a default for arguments with multiple values.

A currently failing test case:

import pytest
import click
from click.testing import CliRunner

@pytest.fixture(scope="function")
def runner(request):
    return CliRunner()

def test_multivalue_args_with_default(runner):
    @click.command()
    @click.argument('files', nargs=-1, default=['arg1'])
    def cmd(files):
        for filename in files:
            click.echo(filename)

    result = runner.invoke(cmd, ['--'])
    assert result.output == 'arg1\n'

Fails with:

TypeError: 'default' is not supported for nargs=-1.

I'm using click 8.0.3

[j7an]

@tekumara The issue with the code lies in the use of the default argument with click.argument. According to Click's documentation, the default argument is not supported for click.argument, but it is supported for click.option. Therefore, the attempt to set a default value for an argument directly leads to unexpected behavior.

To fix this, you should handle the default value within the command function itself.

import pytest
import click
from click.testing import CliRunner

@pytest.fixture(scope="function")
def runner():
    return CliRunner()

def test_multivalue_args_with_default(runner):
    @click.command()
    @click.argument('files', nargs=-1)
    def cmd(files):
        if not files:
            files = ['arg1']
        for filename in files:
            click.echo(filename)

    result = runner.invoke(cmd, ['--'])
    assert result.output == 'arg1\n'

if __name__ == "__main__":
    pytest.main()

In this version, if no files are provided, the command function sets files to ['arg1'], achieving the same effect as trying to set a default value.

[Rowlando13]

Will fix when rewrite parameter docs to show what the parameter class brings vs the option and argument sub classes.

[kdeldycke]

I'd like to be able to specify a default for arguments with multiple values.

@tekumara This has now been fixed in #3030: arguments with nargs=-1 now accepts defaults.

I made a unittest out of your falling example at: https://github.com/pallets/click/blob/3bd9e22cb7290b1e592ee1c1ed6050eea2438861/tests/test_arguments.py#L388-L392