Generated bash completion script not work in POSIX mode

[hehaoqian]

Please complete the following tasks

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

Rust Version

1.70.0

Clap Version

4.3.11

Minimal reproducible code

// build.rs

use clap::{CommandFactory, Parser};
use clap_complete::{generate_to, Shell};

#[derive(Parser)]
pub struct Args {
    pub input_file: String,
}

fn main() {
    let mut cmd = Args::command();
    let out_dir = std::env::var("OUT_DIR").unwrap();
    generate_to(Shell::Bash, &mut cmd, "hello-world", out_dir).unwrap();
}

Steps to reproduce the bug with the above code

1. cd into output directory
2. run the generated script in bash posix mode

bash --posix -c "source ./hello-world.bash"

Actual Behaviour

The shell errors with the following message, with non-zero return code

./hello-world.bash: line 36: `_hello-world': not a valid identifier

Expected Behaviour

The script should work in bash posix mode.

I want to emphasize that this issue report,
does NOT request to make the script work in non-bash, POSIX only "sh" shell,
such as /bin/sh in ubuntu.
Only requesting to make the script work in POSIX mode of /bin/bash

Bash doc https://www.gnu.org/software/bash/manual/html_node/Bash-POSIX-Mode.html says

Function names must be valid shell names.
That is, they may not contain characters other than letters, digits, and underscores, and may not start with a digit.
Declaring a function with an invalid name causes a fatal syntax error in non-interactive shells.

In my example, the function name of generated script is _hello-world, which is invalid in POSIX mode

This should be simple to fix, if dash character is properly escaped

The simplest way would be replacing - by _,
but it would cause conflict if generating completion script for both hello-world and hello_world
Maybe a more complex escape is needed for robustness.
Also, additional escape needed to satisfy they may not contain characters other than letters, digits, and underscores, and may not start with a digit requirement

Additional Context

There are several ways to enter bash in posix mode:

1. If bash is compiled with --enable-strict-posix-default, then posix mode is the default
2. Environment variable POSIXLY_CORRECT is set when bash is invoked
3. Shell variable POSIXLY_CORRECT is set in bash script
4. bash is invoked with "bash --posix"
5. bash is invoked with "sh", such as invoking /bin/sh in CentOS7, which symlinks /bin/sh to /bin/bash

Debug Output

No response

[epage]

My first question is how much do we care about posix mode but then I saw

bash is invoked with "sh", such as invoking /bin/sh in CentOS7, which symlinks /bin/sh to /bin/bash

I'm fine with someone going in and fixing this with a reasonable level of care taken to avoid name conflicts.