Command w/o args displaying usage should return non-zero

Try running git, and you will see its usage. You will also receive a non-zero return code, indicating failure. This can be vital in case arguments got truncated.

Current behavior of showing usage instructions (help_text) is great!

But it should also error out with a code 1.

Example:

➜  git
usage: git [--version] [--help] [-C <path>] [-c <name>=<value>]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p | --paginate | --no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           <command> [<args>]

(snip)

'git help -a' and 'git help -g' list available subcommands and some
concept guides. See 'git help <command>' or 'git help <concept>'
to read about a specific subcommand or concept.
➜  echo $?
1

Reference: https://github.com/learningequality/kolibri/pull/5937

[layday]

This only happens with groups - invoking a (sub-)command requiring arguments, without arguments, will raise and exit with a non-zero status code. The default behaviour of a group is not to call the callback (i.e. the wrapped function) if the argument is not supplied, which presupposes that it is required. Click should exit with a non-zero status code if invoke_without_command is false and defer to the callback if it’s true.

[benjaoming]

@davidism

so I don’t currently see a compelling reason to change this

mycommand $filename <= if $filename is empty by mistake, then it will return 0 as if execution was successful.