The `flag_value` shadows `default` in `click.option()`

[drunkwcodes]

There are two problems:

1. The flag_value shadows default in click.option()
2. The default type is omitted, the option converts to str anyway.

About 2., The click docs says in the option section: "If no type is provided, the type of the default value is used."
But it is not True. I have to use type=frozenset to make the option's value not be "frozenset()", which breaks my function iterating it.

And the 1. is the big deal.
I provide my option code below and a minimal reproducer script.
I'm making a venv for Mojo language, and looking at new venv code on cpython.

If click can not fix this, it can not do things like Brett Cannon does in venv cli design. That's not good.
I want scm_ignore_files to be frozenset() if the flag is provided, else it is default to frozenset(["git"]).

Why is default not useful and the flag_value is always used?

@click.option(
    "--without-scm-ignore-files",
    "scm_ignore_files",
    is_flag=True,
    type=frozenset,
    flag_value=frozenset(),
    default=frozenset(["git"]),
    help="Skips adding SCM ignore files to the environment "
    "directory (Git is supported by default).",
)

Thanks for watching!

Environment:

• Python version: Python 3.10.12
• Click version: 8.1.7

[davidism]

@kdeldycke was this addressed by #2956?

[kdeldycke]

1. The flag_value shadows default in click.option()

I have a fix ready for this issue in #3030.

The case reported by the user is part of the test suite now:

click/tests/test_options.py

Lines 1697 to 1718 in 14e6cee

	def test_custom_type_frozenset_flag_value(runner):
	"""A reproduction of https://github.com/pallets/click/issues/2610"""
	@click.command()
	@click.option(
	"--without-scm-ignore-files",
	"scm_ignore_files",
	is_flag=True,
	type=frozenset,
	flag_value=frozenset(),
	default=frozenset(["git"]),
	)
	def rcli(scm_ignore_files):
	click.echo(repr(scm_ignore_files), nl=False)
	result = runner.invoke(rcli)
	assert result.stdout == "frozenset({'git'})"
	assert result.exit_code == 0
	result = runner.invoke(rcli, ["--without-scm-ignore-files"])
	assert result.stdout == "frozenset()"
	assert result.exit_code == 0

2. The default type is omitted, the option converts to str anyway.

For this issue we need to support frozenset natively as a type.

[kdeldycke]

2. The default type is omitted, the option converts to str anyway.

For this issue we need to support frozenset natively as a type.

I created a separate issue for that at: #3036