(Not a click developer here, just lurking around.)

This behavior seems to be in click since forever. For some unknown reason click doesn't expect that you would to this with boolean flags:

    def get_default(
        self, ctx: Context, call: bool = True
    ) -> t.Optional[t.Union[t.Any, t.Callable[[], t.Any]]]:
        # If we're a non boolean flag our default is more complex because
        # we need to look at all flags in the same group to figure out
        # if we're the default one in which case we return the flag
        # value as default.
        if self.is_flag and not self.is_bool_flag:
            for param in ctx.command.params:
                if param.name == self.name and param.default:
                    return param.flag_value  # type: ignore

            return None

        return super().get_default(ctx, call=call)

BTW, I think the comment above is misleading. It should be:

-# if we're the default one in which case we return the flag
+# which is the default one in which case we return the flag

So, for booleans we get default value of the last parameter wins behavior; if you reverse the order of --one and --two in bool.py the output will change.

Perhaps it's expected that one would just use the usual:

@click.option('--one/--two', 'flag', default=True)

The only downside is that you get one option instead of two (or more), so YMMV.

Can confirm the same behavior from my side (on 8.1.3). This was a little confusing when I discovered it the first time, since I had a different impression from reading the documentation.

Would the project be open to doing either of these two alternatives?

• Update the documentation (specifically the feature switches section) to say that setting boolean values in feature switches does not use the default keyword argument, but rather uses whatever is set last.

• Update the code so that boolean values behave the same as any other values.

I think this is a docs problem. Feature switches docs are unclear. I will investigate.