feat: expand variables in help texts like argparse does

[ankostis]

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Example Code

import typer

def main(component: Annotated[
        str,
        typer.Argument(
            metavar="COMPONENT.EXT",
            help="Component template to use (issue `{rootcmd} ls` cmd to list them).",
        ),
    ],
):
    """Generate component files from templates. """
  pass


if __name__ == "__main__":
    typer.run(main)

Description

Some help texts of commands and options need to refer to other subcommands and/or their default values and choices. The argparse library supports interpolations for the main command name (%(prog)s), and arguments of its add_argument() method like %(type)s, %(default)s, %(choices)s etc.

In a potential new feature for Typer these would correspond to the typer.Option() and typer.Argument() args. I would also suggest to use str.format() syntax to expand these variables, like {cmd:30} instead of %-interpolation. Furthermore, a new typer.Option(no_help_interpolation: bool=None) argument would disable this feature in case help messages contain too many such patterns.

Operating System

Linux

Operating System Details

No response

Typer Version

0.9.0

Python Version

3.10

Additional Context

No response