Provide better error when command is wrong

[TWiStErRob]

Compare these two experiences:

$ gradlew :commandLine:run --args="wrongcommandname"

Usage: commandlineapp [OPTIONS] COMMAND [ARGS]...

Error: no such subcommand: "wrongcommandname"

$ gradlew :commandLine:run --args="wrongcommandname --valid=param"

Error: no such option: "--valid"

The first one is really good, it actually tells me that there isn't a command like this, it even suggests a close-enough match in case of typos. However the second one gives a misleading error message suggesting that the parameter is wrong, when the command name is mis-spelled or otherwise non-existent.

Is it possible to get the same error message as the first one for the second case too? (i.e. validate command first, and then try parsing params)

Affected versions: 2.5.0, 3.5.0

[ajalt]

Thanks for the report!

This happens because, in order to support argument().multiple(), the parser gathers up all positional arguments (which might be subcommands) and validates them after it validates options. I think the solution will be to gather all errors instead of throwing them immediately and track which argv index they correspond to, then throw the one corresponding to the earliest index.

[TWiStErRob]

Ah, I was suspecting something like this.

Rather than choosing the "best" one after gathering all, maybe it's better to sort them by "best guess" and list all. Let the user decide how bad it is, instead of hiding.

[ajalt]

I implemented this in the 4.0 branch. It looks like there's an internal Kotlin compiler error preventing the snapshot from being published, but you can still build on JVM if you'd like to try it out.

I'm not currently reporting more than one error, since errors after the first are often spurious. As in your example, if someone mistypes a subcommand name, it's probably not helpful to report an error for every option and argument after that. But if you have a use case for it, feel free to open another issue to discuss.