Should the plugin author use VOID_TRIGGER explicitly or not?

[david50407]

Originally from comment: 4b18edd#r47785876

@xatier: thought: should the plugin author use VOID_TRIGGER explicitly or not? Let's make this consistent.

[david50407]

IMO, VOID_TRIGGER should represent "no triggers needed" which has special meaning.
Since it is given by empty string '' now, I think we can change the value to unique Symbol and skip empty-string triggers in system.

That is, developers need to use VOID_TRIGGER explicitly and not to use empty-string as alternative.

[xatier]

sounds good to me.

[xatier]

Sync'd offline.

1. We should provide both explicit and implicit usage of VOID_TRIGGER.
2. The implicit behavior will be documented in the parameter type polymorphism.
3. VOID_TRIGGER will become a Symbol, so plugin authors can explicitly specify both plugin's trigger and VOID_TRIGGER. This can be helpful when the plugin author would like to register some help menu which is intended to be displayed in all cases.
4. When the explicit triggers are specified, we shall limit the search results within the engines that provides those triggers.