right click with an unit ("smart") on a destructable == "attack", in all case ?

In order to determine which order, an unit get, when we are ordering it with a right click, i need to know if a right click on a destructable == "attack" for each destructable type, or if depends the type of the destructable.

I think the order for right click is always "smart", what the unit does is up to it (or to you, if you decide to JASS its AI).

Yes it is, but that's not the question.

I mean if we right click with an unit on a destructable and the unit has an activate valid attack, the unit will always attack the destructable, or sometimes depends the destructable type, the unit will simply move to him ?

As far i tested the unit always attack the destructable, but i didn't try with all rawcode ...
And ofc i don't ask it for destructables witch can't be targeted.

no

if you have harvest or pickup tree skills (also huntress spirit owl) unit will cast them, not attack.

Ok for harvest, i knew that but forgotten to said.
But you can't cast a destructable target spell with the order "smart", can you ?

For a unit you can if "kaboom" is on, but the target must be an unit.

Check the Huntress Spirit Owl or Pickup Tree, then, as he said (also, Eat Tree)