Arg::value_parser does not implicitly set Arg::takes_value

[wookietreiber]

Please complete the following tasks

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

Rust Version

rustc 1.63.0 (4b91a6ea7 2022-08-08)

Clap Version

3.2.17

Minimal reproducible code

fn main() {
    let digest = clap::Arg::with_name("digest")
        .short('d')
        .long("digest")
        .help("choose digest")
        .value_parser(["md5", "sha1"]);

    let cli = clap::Command::new("cmd").arg(digest);

    dbg!(cli.get_matches());
}

Steps to reproduce the bug with the above code

$ cargo run -- --help
   Compiling clap-value-parser-takes-value v0.1.0 (/home/umcdev/src/bug-reproduction/clap-value-parser-takes-value)
    Finished dev [unoptimized + debuginfo] target(s) in 0.91s
     Running `target/debug/clap-value-parser-takes-value --help`
cmd

USAGE:
    clap-value-parser-takes-value [OPTIONS]

OPTIONS:
    -d, --digest    choose digest
    -h, --help      Print help information

$ cargo run -- --digest md5
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/clap-value-parser-takes-value --digest md5`
error: Found argument 'md5' which wasn't expected, or isn't valid in this context

USAGE:
    clap-value-parser-takes-value [OPTIONS]

For more information try --help

Actual Behaviour

Arg::value_parse does not implicitly set Arg::takes_value.

Expected Behaviour

A lot of functions, e.g. Arg::value_name set Arg::takes_value(true) that I expected Arg::value_parser to do the same.

Additional Context

I consider this to be an inconsistency, it does not follow the principle of least surprise.

Debug Output

not required.

[epage]

It might not be obvious at first but value_parser applies to flags as well as option and arguments.

The first case is defining how to parse environment variables.

The other is for non-bool flags