This mainly adds bpy.data.user_map() method, which goes over the whole Main database
to build a mapping (dict) {ID: {users_of_that_ID}}.
Very handy to check and debug ID usages, but could also be really valuable for py addons
creating temporary scenes, or some exporters, etc.
Note: current code in master's libquery misses some IDs (and reports some it should not,
like nodetrees), this is fixed in id-remap but still needs serious review before going to master.
This basically means that current bpy.data.user_map() **will not** report a complete and exhaustive
state of dependencies between IDs. Should work OK in most cases though.
Original work/idea comes from id-remap branch, was heavily reworked by @campbellbarton
and myself for master.
Reviewers: campbellbarton, sergey
Differential Revision: https://developer.blender.org/D1678
Looping twice on same ID pointer may not be an issue in master currently, but with work done in id-remap
branch this should be avoided as much as possible, so for now assuming we do not need this here.
Note: if we really need this and have to add it back, then please at least use IDWALK_USER, and not
IDWALK_NOP flag!
As we can see in (original) read code, ob pointer in groupobject is actually a 'USER_ONE' case.
This was not done in 'add object to group' code, probably because we can assume objects always
have at least one user in that case? Made it explicit now. Also fixed foreach_ID_link looper.
In general we have waaayyyyyy too much 'own handling' of ID->us count in code currently,
will clean up that...
Duplicate wasn't updating links,
so duplicatinvg a objects would still point to the originals for curve-taper, texmesh, drivers.
Use generic id-looper to handle replacing data.
This func is long enough, there's no real need to make it even longer with
verbose local varnames and multi-line for loops...
Also, avoid mono-leters names as well for data pointers.
Root of the issues comes to the fact that it's possible to produce
a situation when library object data uses local object. This is
actually forbidden and not supported by .blend IO.
Made it so Make Local wouldn't produce such an unsupported states.
Reviewers: brecht
Differential Revision: https://developer.blender.org/D372
