When appending e.g. an object, it's generally expected that it is not just
appended but also added to the active collection. Something similar happens for
adding collections, or just geometry like a mesh data-block. This is called
"loose data instantiation" in the source code.
Which data is instantiated and how depends on context. Generally, it's best to
first do the low-level link or append operation and only afterwards do the
instantiation at a higher level where more context is known. For example, when
dragging an object asset into the 3D view, it's expected that the object is
added to the active collection. When dragging a node group into the node editor
that uses an object internally (e.g. as mesh storage), not so much.
This patch adds a new `BKE_blendfile_link_append_instantiate_loose` method that
does the "default instantiation", i.e. the one we want to happen when using the
general link/append operator to import data. Instead of calling this directly
from low level `BKE_blendfile_append`, it's now called in `wm_link_append_exec`
(and other places where desired).
Furthermore, `view3d_ob_drop_copy_external_asset` does not use this anymore, but
explicitly adds only the dragged object to the active collection. Some places,
e.g. when linking/appending using the Python API, don't do any instantiation at
all. They didn't do this before either, but it was way less obvious (it used
`BLO_library_link_params_init` instead of
`BLO_library_link_params_init_with_context`). Now there is always an explicit
call to do instantiation in higher level code.
Pull Request: https://projects.blender.org/blender/blender/pulls/125814
2858c3b287