kn plugins for eventing sources should be able to extend kn source group

[maximilien]

Feature request

Current kn plugin architecture prevents plugins to extend existing command groups. This makes sense since we would not want a kn-service-create plugin that redefines the service create commands. Same for almost all other kn command groups.

But there is at least one exception. This is for command groups where we want to define sub-groups but at the same time allow extensions. One such example is the kn source eventing command group.

Use case

Kn ships with some eventing sources, e.g., ping, but we also want to have plugins be created and defined that also extends this command group, e.g., source kafka and source github and others.

These plugins are being defined in the client-contrib repo for instance the kn-source-kafka is one such example.

UI Example

kn source kafka create my-kafka-source --sink my-kafka-sink ...
...
kn source github create my-hithub-source --sink my-github-sink
...

/kind proposal
/kind bug

[maximilien]

/assign @maximilien

[rhuss]

Current kn plugin architecture prevents plugins to extend existing command groups. This makes sense since we would not want a kn-service-create plugin that redefines the service create commands. Same for almost all other kn command groups.

tbh, I thought this would be true only for case where a terminal command would overwrite an built-in command (actually the command on which an "Run" is attached).

I suggest to implement this in the generic fashion to just verify that there is no collision on the terminal (sub) command.

[maximilien]

tbh, I thought this would be true only for case where a terminal command would overwrite an built-in command (actually the command on which an "Run" is attached).

I think there is value to both. Some command group should not allow extensions. For instance adding any sub commands fo service would IMO a bad thing.

I suggest to implement this in the generic fashion to just verify that there is no collision on the terminal (sub) command.

Sure but only for allowed command groups.

[rhuss]

I think there is value to both. Some command group should not allow extensions. For instance adding any sub commands fo service would IMO a bad thing.

Why ? What's about a kn service log for showing los on a kubernetes based system (like stern does) ? or kn source apiserver log (so logs on various levels).

[rhuss]

I would allow it for every group, but forbid to override.