Is it possible to include a Prolog in --help

[AngryMaciek]

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the Typer documentation, with the integrated search.
• I already searched in Google "How to X in Typer" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to Typer but to Click.

Commit to Help

• I commit to help with one of those options 👆

Example Code

`--help`

Description

I have seen it is possible to add an epilog to the --help command, as here.

Would it be possible to add a custom Prolog above the "Usage..." line too?

Operating System

Linux

Operating System Details

No response

Typer Version

0.7.0

Python Version

Python 3.11.0

Additional Context

No response

[lazToum]

Here is one way (overriding get_usage from the default TyperGroup cls):
You could also use the format_usage.

import click
import typer
from typer.core import TyperGroup as TyperGroupBase


class TyperGroup(TyperGroupBase):
    """Custom TyperGroup class."""

    def get_usage(self, ctx: click.Context) -> str:
        """Override get_usage."""
        usage = super().get_usage(ctx)
        message = (
            'Message Above.\n'
            + usage
            + '\nMessage Below.'
        )
        return message


app = typer.Typer(
    name='myapp',
    help='MyApp cli actions.',
    no_args_is_help=True,
    context_settings={"help_option_names": ["-h", "--help"]},
    invoke_without_command=True,
    options_metavar="[OPTIONS]",
    cls=TyperGroup,
)


@app.callback(invoke_without_command=True)
def get_version(
    version: bool = typer.Option(
        False,
        "--version",
        "-v",
        help="Print version and exit.",
    ),
) -> None:
    """Display the version."""
    if version:
        typer.echo(f"myapp 0.0.1")
        raise typer.Exit()


if __name__ == '__main__':
    app()

                                                                                                                        
 Message Above.                                                                                                         
 Usage: app.py [OPTIONS] COMMAND [ARGS]...                                                                               
 Message Below.                                                                                                         
                                                                                                                        
 MyApp cli actions.                                                                                                     
                                                                                                                        
╭─ Options ────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ --version             -v        Print version and exit.                                                              │
│ --install-completion            Install completion for the current shell.                                            │
│ --show-completion               Show completion for the current shell, to copy it or customize the installation.     │
│ --help                -h        Show this message and exit.                                                          │
╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

[reubenfirmin]

Maybe this needs to be a separate ticket, but I would like to be able to call a custom function in either prolog or epilog. The reason is that I use rich to create a table of data sources that can be accessed by various commands; I can't just dump that table into a decorator (as far as I know). Ideally I could just add a @prolog or @epilog decorator to a function, and let it do whatever it wants.