Manage a man page using a smart way

[majecty]

The PR #50 added a man page. We need a method to manage the man page in a smart way.

There are too many methods to create a man page. We need to research them and choose one.

[majecty]

@foriequal0 Can I try this issue?

[majecty]

Since most of the content of the man page has the same content as the help message, I'll try a solution that extracts a man page from a help message.

[majecty]

Let me summarize the possible options:

1. Generate a man page from a handwritten markup file

   • Pros: easy
   • Cons:
     • There will be duplication. If we add a new command-line argument, we should update the handwritten markup file.
     • Converting tool is a new dependency. Maybe we need Ruby or Python.

2. Generate a man page using Rust's man crate

   • Pros:
     • easy
     • We need a Rust crate dependency. It is easy to manage.
   • Cons:
     • There will be duplication. If we add a new command-line argument, we should update the handwritten markup file.

3. Generate a man page from the help message

   3.1. Parse a help text and creates a man page

   • Pros: We can minimize information duplication.
   • Cons:
     • We need to search is there a tool for it. help2man
       seems a solution.
     • There will be hidden constraints to the help message that can be hard to manage.

   3.2 Parse the doc comments of the Args struct

   • Pros:
     • We can use the rust code.
     • Writing a proc macro will be fun.
   • Cons:
     • We need to manage to much accidental code just to create a man page.

4. Use another CLI option parser library that generates man page automatically.

   • clap does it.
   • Pros: Simple and easy to manage
   • Cons: We need to change all CLI arg parsing code because of the man page.

[foriequal0]

It seems 4 is viable. structopt uses clap under the hood. You might be able to find a way to convert them to clap object.

[majecty]

A feature that generates a man page will be added in the clap's version 3 which is not available yet. Since I can get a Clap::App object from StructOpt trait, however, I'll try to generate a man page using the Clap::App object.

[majecty]

I've tried to use clap::App to get the arguments' data, and failed.
Clap is not exposing FlagBuilder type, AnyArg type, and etc that are required to extract argument value and help message easily.

[foriequal0]

Closed by #84