core: subcommands silently ignore non-existing flags

[l0b0]

Describe the bug

Running cdk diff with an unknown flag does not result in any kind of indication that there is a problem.

Expected Behavior

cdk diff [other options] --no-such-flag should:

• Indicate clearly that the --no-such-flag is unknown. This way users immediately recognise where their mistakes are, rather than having to correlate each flag with the documentation to detect the error. Ideally, if there are multiple unknown flags, each one of them should be printed in a similar error message.
• Exit with a unique non-zero exit code, rather than exit code 0/1. This way anyone automating CDK can tell the difference between different classes of errors.
• Not run the diffing process, since the user very likely meant for the diffing process to do something which includes another flag.

Current Behavior

cdk diff --no-such-flag runs the diff, prints no warnings related to the flag, and in fact does not indicate in any way that there is a problem.

Reproduction Steps

Run cdk diff --no-such-flag.

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.93.0 (build 724bd01)

Framework Version

No response

Node.js Version

v18.17.1

OS

NixOS

Language

Typescript

Language Version

5.2.2

Other information

No response

[indrora]

This I suspect affects much more than the diff command, as we extract the arguments and parameters from the command line through a more blanket mechanism.

[l0b0]

Fair enough. It doesn't affect the cdk command itself (try cdk --foo), so hopefully there is a mechanism already in place which can be used.