Show long help message when defined

[dhiltgen]

This fixes the help template so that if a command
includes a Long form help message that is displayed instead
of ignoring it and always showing the Short message.

Signed-off-by: Daniel Hiltgen daniel.hiltgen@docker.com

For example:
https://github.com/docker/cli/blob/master/cli/command/container/cp.go#L49-L56

Before this fix:

% docker container cp --help

Usage:	docker container cp [OPTIONS] CONTAINER:SRC_PATH DEST_PATH|-
	docker cp [OPTIONS] SRC_PATH|- CONTAINER:DEST_PATH

Copy files/folders between a container and the local filesystem

Options:
  -a, --archive       Archive mode (copy all uid/gid information)
  -L, --follow-link   Always follow symbol link in SRC_PATH

After this fix

% docker container cp --help

Usage:	docker container cp [OPTIONS] CONTAINER:SRC_PATH DEST_PATH|-
	docker cp [OPTIONS] SRC_PATH|- CONTAINER:DEST_PATH

Copy files/folders between a container and the local filesystem

Use '-' as the source to read a tar archive from stdin
and extract it to a directory destination in a container.
Use '-' as the destination to stream a tar archive of a
container source to stdout.

Options:
  -a, --archive               Archive mode (copy all uid/gid information)
  -L, --follow-link           Always follow symbol link in SRC_PATH
      --orchestrator string   Orchestrator to use (swarm|kubernetes|all)

(The orchestrator flag is a bug recently introduced - unrelated to this PR)

[dhiltgen]

I should note that the --help on the parent command still lists the Short message as it should

% docker container --help

Usage:	docker container COMMAND

Manage containers

Options:
      --orchestrator string   Orchestrator to use (swarm|kubernetes|all)

Commands:
  attach      Attach local standard input, output, and error streams to a running container
  commit      Create a new image from a container's changes
  cp          Copy files/folders between a container and the local filesystem
  create      Create a new container
...

[thaJeztah]

Looks like this was changed in https://github.com/moby/moby/pull/23825/files#diff-4a2b6f090171fe18f7406cb69fb2e479R143

The original template was;

{{with or .Long .Short }}{{. | trim}}{{end}}{{if gt .Aliases 0}}

In a later PR, man-page generation was moved to external markdown files; moby/moby#26830, but the template wasn't updated with that change, so I think it's ok to use the long description again (if present)

ping @dnephin to double check

[dnephin]

Ya, seems fine to use Long now

[silvin-lubecki]

LGTM