Install plugins to plugin location if specified

[maximilien]

Knative plugins can be installed either in the user’s PATH or if specified in the user’s ~/.config/kn/config.yaml in the `~/.config/kn/plugins directory.

Currently the plugin formulas only install the plugin’s binary in the user’s PATH.

The formulas should check the user’s config and decide where to install the plugin according to the user’s choice.

Default location should be in PATH

[maximilien]

@navidshaikh @rhuss please comment if you disagree or have questions or want to chime in.

I will try to get to this tomorrow PM and early next week. Certainly to have this before next release

FYI: @zhanggbj @cdlliuy @zhangtbj since you all have plugins.

[navidshaikh]

I wonder if we should limit the brew installed plugins only under PATH. This way we've consistent destination for kn binaries installed via brew. User installed plugins can land in plugin's directory and we'll have clear distinction for source of plugin.

[maximilien]

I am OK with that. WDYT @rhuss?

I’ll add an issue so message the user where the plugins are installed. Independently if we decide to do PATH and / or config since that should tell user something they need to know.

[rhuss]

The only issue that I see with this approach is that we do not a default lookup in PATH, only when enabled in the configuration. So this would lead to the unexpected behaviour that you install a plugin with homebrew but it wouldn't be picked up by kn.

A solution would be to add an output while installing (but honestly, this is often overlooked) or we could check ~/.config/kn/config.yaml for that configuration and print out a big fat WARNING if 'lookupInPath' is not set.

The third option would be to change the default lookup behaviour but changing defaults is not possible in a backwards compatible way.