behavior change regarding possible_values on derived boolean args in 4.4.14

[ahl]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Rust Version

rustc 1.75.0 (82e1608df 2023-12-21)

Clap Version

4.4.14

Minimal reproducible code

use clap::{CommandFactory, Parser};

#[derive(Parser)]
pub struct Args {
    #[clap(long)]
    ok: bool,
}

fn main() {
    let values = Args::command()
        .get_arguments()
        .next()
        .expect("no arguments")
        .get_possible_values();
    println!("{:#?}", values);
}

Steps to reproduce the bug with the above code

Use 4.4.13; cargo run:

[]

Use 4.4.14; cargo run:

[
    PossibleValue {
        name: "true",
        help: None,
        aliases: [],
        hide: false,
    },
    PossibleValue {
        name: "false",
        help: None,
        aliases: [],
        hide: false,
    },
]

Actual Behaviour

Behavior change from 4.4.13 to 4.4.14

Expected Behaviour

No behavior change? Unless this was intentional. I didn't see it mentioned in the release notes.

Additional Context

No response

Debug Output

No response

[epage]

This change of behavior is expected but there is something you can do on your side to address it.

In clap, args have two settings that describe whether a value is accepted or not

• num_args
• action

When an argument doesn't take a value, we don't return the possible values.

With 4.4.14, we added support for .action(ArgAction::Set).num_args(0) which introduced a discrepancy, action only describe if an arg might take a value.

To do this, we needed to change out "takes value" tracking which is mostly unnoticeable because we auto-fill in properties when parsing.

The problem is that you are looking at the possible values without the auto-fill of properties. If you call Command::build, the problem goes away.

See

#!/usr/bin/env nargo
---
[dependencies]
clap = { path = "../clap", features = ["derive"] }
---

use clap::{CommandFactory, Parser};

#[derive(Parser)]
pub struct Args {
    #[clap(long)]
    ok: bool,
}

fn main() {
    let mut cmd = Args::command();
    cmd.build();
    let values = cmd
        .get_arguments()
        .next()
        .expect("no arguments")
        .get_possible_values();
    println!("{:#?}", values);
}

[epage]

#2911 covers some of this problem in the API

[ahl]

This is extremely helpful. Thanks very much. Feel free to close this, or leave it open if there's some work item such as updating the release notes that might be relevant.