Return non-zero exit code on invalid commands

[neoaggelos]

Summary

Closes #4091

Replaces #4129, thanks @htdvisser for suggesting a much more elegant solution.

Changes

• If Run and RunE are empty, no sub-command has been matched, so return a non-zero exit status code.

Testing

Locally

Regressions

There should not be any

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.

[neoaggelos]

@htdvisser Added this otherwise running ttn-lw-cli --help returns a non-zero exit status code as well (which makes the CI complain).

[htdvisser]

I'm not sure that's the right solution, because now we would have inconsistent error codes when requesting help on different commands.

How about putting this in main.go:

help := commands.Root.HelpFunc()
commands.Root.SetHelpFunc(func(cmd *cobra.Command, a []string) {
	help(cmd, a)
	os.Exit(0)
})

[neoaggelos]

This will not work as expected, since the help function will be called for invalid commands as well.

[neoaggelos]

Perhaps something slightly more elaborate, like:

help := commands.Root.HelpFunc()
commands.Root.SetHelpFunc(func(cmd *cobra.Command, a []string) {
	help(cmd, a)
	for _, arg ;= range a {
	    if a == "--help" {
	         os.Exit(0)
	    }
        }
})

But this is also getting a bit messy

[htdvisser]

Okay so maybe we should just accept an exit code 2 in CI, or use a different command for testing. Perhaps have CI call ttn-lw-* config instead?

[htdvisser]

See my comment from last week.