Bug: Optional value not optional anymore

[axelbringenberg]

Outline

As stated in official documentation:

Setting is_flag=False, flag_value=value tells Click that the option can still be passed a value, but if only the flag is given, the value will be flag_value.

Since 8.3.0 this doesn't work anymore, instead SystemExit with "Error: Option '--xyz' requires an argument." is thrown.

Replication of bug

Example taken from documentation:

@click.command()
@click.option("--name", is_flag=False, flag_value="Flag", default="Default")
def hello(name):
    click.echo(f"Hello, {name}!")

$ hello --name
Error: Option '--name' requires an argument.

Expected behavior

The code example above should work as

$ hello --name
Hello, Flag!

It's not even working in the generated documentation anymore: while documentation up to Sep, 10th shows the expected and correct behavior, current documentation demonstrates the bug.

• Python version: 3.11
• Click version: 8.3.0

[Rowlando13]

Thanks for the clear report! We will work on this

[pawamoy]

MkDocs seems to be affected by this again, like with version 8.2.2. Here's how it declares its boolean flags: https://github.com/mkdocs/mkdocs/blob/f68e5fc18d3cd3811dbddfdeda1a57721f9e2e4e/mkdocs/__main__.py#L253-L264. Should MkDocs change something or is Click 8.3.0 suffering from the same kind of issue as 8.2.2?

[Rowlando13]

This is still broken in 8.3.0.