title: In Python Click how do I see --help for Subcommands whose parents have required arguments?
body: <p>My program uses <a href="http://click.pocoo.org/5/" rel="noreferrer">Click</a> for command line processing. It has a main command that takes a required argument. This command has subcommands that take optional arguments. Different subcommands take different options, but they all require the same argument from their parent. I'd like to have the command line look like this:</p>
  
  <pre><code>python myprogram.py argument-value subcommand1 --option-1=value
  </code></pre>
  
  <p>I can write this using Click like so</p>
  
  <pre><code>import click
  
  @click.group()
  @click.argument("argument")
  @click.pass_context
  def main(context, argument):
      """ARGUMENT is required for both subcommands"""
      context.obj = {"argument": argument}
  
  
  @click.command()
  @click.option("--option-1", help="option for subcommand 1")
  @click.pass_context
  def subcommand1(context, option_1):
      print("subcommand 1: %s %s" % (context.obj["argument"], option_1))
  
  
  @click.command()
  @click.option("--option-2", help="option for subcommand 2")
  @click.pass_context
  def subcommand2(context, option_2):
      print("subcommand 2: %s %s" % (context.obj["argument"], option_2))
  
  
  main.add_command(subcommand1)
  main.add_command(subcommand2)
  
  if __name__ == "__main__":
      main()
  </code></pre>
  
  <p>The top-level help message is what I want.</p>
  
  <pre><code>python myprogram.py --help
  Usage: myprogram.py [OPTIONS] ARGUMENT COMMAND [ARGS]...
  
    ARGUMENT is required for both subcommands
  
  Options:
    --help  Show this message and exit.
  
  Commands:
    subcommand1
    subcommand2
  </code></pre>
  
  <p>I can get help for a subcommand if I pass in the required argument.</p>
  
  <pre><code>python myprogram.py dummy-argument subcommand1 --help
  Usage: myprogram.py subcommand1 [OPTIONS]
  
  Options:
    --option-1 TEXT  option for subcommand 1
    --help           Show this message and exit.
  </code></pre>
  
  <p>However, I'd like to get the subcommand help without requiring the user to pass in a dummy argument. I want to be able to run <code>python myprogram.py subcommand1 --help</code> and see the same output as above, but instead I just get the help text for the top level.</p>
  
  <pre><code>python myprogram.py subcommand1 --help
  Usage: myprogram.py [OPTIONS] ARGUMENT COMMAND [ARGS]...
  
    ARGUMENT is required for both subcommands
  
  Options:
    --help  Show this message and exit.
  
  Commands:
    subcommand1
    subcommand2
  </code></pre>
  
  <p>Is there a way to get the behavior I want? I realize that Click puts a premium on having each of its commands be self-contained, but this seems like a common scenario.</p>