Collections and groups unification

OVERVIEW

* In 2.7 terminology, all layers and groups are now collection datablocks.
* These collections are nestable, linkable, instanceable, overrideable, ..
  which opens up new ways to set up scenes and link + override data.
* Viewport/render visibility and selectability are now a part of the collection
  and shared across all view layers and linkable.
* View layers define which subset of the scene collection hierarchy is excluded
  for each. For many workflows one view layer can be used, these are more of an
  advanced feature now.

OUTLINER

* The outliner now has a "View Layer" display mode instead of "Collections",
  which can display the collections and/or objects in the view layer.
* In this display mode, collections can be excluded with the right click menu.
  These will then be greyed out and their objects will be excluded.
* To view collections not linked to any scene, the "Blender File" display mode
  can be used, with the new filtering option to just see Colleciton datablocks.
* The outliner right click menus for collections and objects were reorganized.
* Drag and drop still needs to be improved. Like before, dragging the icon or
  text gives different results, we'll unify this later.

LINKING AND OVERRIDES

* Collections can now be linked into the scene without creating an instance,
  with the link/append operator or from the collections view in the outliner.
* Collections can get static overrides with the right click menu in the outliner,
  but this is rather unreliable and not clearly communicated at the moment.
* We still need to improve the make override operator to turn collection instances
  into collections with overrides directly in the scene.

PERFORMANCE

* We tried to make performance not worse than before and improve it in some
  cases. The main thing that's still a bit slower is multiple scenes, we have to
  change the layer syncing to only updated affected scenes.
* Collections keep a list of their parent collections for faster incremental
  updates in syncing and caching.
* View layer bases are now in a object -> base hash to avoid quadratic time
  lookups internally and in API functions like visible_get().

VERSIONING

* Compatibility with 2.7 files should be improved due to the new visibility
  controls. Of course users may not want to set up their scenes differently
  now to avoid having separate layers and groups.
* Compatibility with 2.8 is mostly there, and was tested on Eevee demo and Hero
  files. There's a few things which are know to be not quite compatible, like
  nested layer collections inside groups.
* The versioning code for 2.8 files is quite complicated, and isolated behind
  #ifdef so it can be removed at the end of the release cycle.

KNOWN ISSUES

* The G-key group operators in the 3D viewport were left mostly as is, they
  need to be modified still to fit better.
* Same for the groups panel in the object properties. This needs to be updated
  still, or perhaps replaced by something better.
* Collections must all have a unique name. Less restrictive namespacing is to
  be done later, we'll have to see how important this is as all objects within
  the collections must also have a unique name anyway.
* Full scene copy and delete scene are exactly doing the right thing yet.

Differential Revision: https://developer.blender.org/D3383

https://code.blender.org/2018/05/collections-and-groups/

6 files changed, 864 insertions, 644 deletions

diff --git a/source/blender/blenloader/BLO_readfile.h b/source/blender/blenloader/BLO_readfile.h
index 7b31415ddcf..8b5c64f4ecd 100644
--- a/source/blender/blenloader/BLO_readfile.h
+++ b/source/blender/blenloader/BLO_readfile.h
@@ -134,9 +134,10 @@ struct ID *BLO_library_link_named_part(struct Main *mainl, BlendHandle **bh, con
 struct ID *BLO_library_link_named_part_ex(
         struct Main *mainl, BlendHandle **bh,
         const short idcode, const char *name, const int flag,
-        struct Scene *scene, struct ViewLayer *view_layer);
+        struct Main *bmain, struct Scene *scene, struct ViewLayer *view_layer);
 void BLO_library_link_end(
-        struct Main *mainl, BlendHandle **bh, int flag, struct Scene *scene, struct ViewLayer *view_layer);
+        struct Main *mainl, BlendHandle **bh, int flag,
+        struct Main *bmain, struct Scene *scene, struct ViewLayer *view_layer);
 
 void BLO_library_link_copypaste(struct Main *mainl, BlendHandle *bh);
 
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 85c67047be0..44aa8a40993 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -123,13 +123,13 @@
 #include "BKE_brush.h"
 #include "BKE_cachefile.h"
 #include "BKE_cloth.h"
+#include "BKE_collection.h"
 #include "BKE_constraint.h"
 #include "BKE_context.h"
 #include "BKE_curve.h"
 #include "BKE_effect.h"
 #include "BKE_fcurve.h"
 #include "BKE_global.h" // for G
-#include "BKE_group.h"
 #include "BKE_layer.h"
 #include "BKE_library.h" // for which_libbase
 #include "BKE_library_idmap.h"
@@ -258,9 +258,10 @@ static void *read_struct(FileData *fd, BHead *bh, const char *blockname);
 static void direct_link_modifiers(FileData *fd, ListBase *lb);
 static BHead *find_bhead_from_code_name(FileData *fd, const short idcode, const char *name);
 static BHead *find_bhead_from_idname(FileData *fd, const char *idname);
+
+#ifdef USE_COLLECTION_COMPAT_28
 static void expand_scene_collection(FileData *fd, Main *mainvar, SceneCollection *sc);
-static SceneCollection *get_scene_collection_active_or_create(
-        struct Scene *scene, struct ViewLayer *view_layer, const int flag);
+#endif
 
 /* this function ensures that reports are printed,
  * in the case of libraray linking errors this is important!
@@ -4835,7 +4836,7 @@ static void lib_link_object(FileData *fd, Main *main)
 			}
 			else {
 				ob->dup_group = NULL;
-				ob->transflag &= ~OB_DUPLIGROUP;
+				ob->transflag &= ~OB_DUPLICOLLECTION;
 			}
 			
 			ob->proxy = newlibadr_us(fd, ob->id.lib, ob->proxy);
@@ -5343,9 +5344,6 @@ static void direct_link_object(FileData *fd, Object *ob)
 {
 	PartEff *paf;
 	
-	/* weak weak... this was only meant as draw flag, now is used in give_base_to_objects too */
-	ob->flag &= ~OB_FROMGROUP;
-
 	/* XXX This should not be needed - but seems like it can happen in some cases, so for now play safe... */
 	ob->proxy_from = NULL;
 
@@ -5543,6 +5541,208 @@ static void direct_link_object(FileData *fd, Object *ob)
 	ob->preview = direct_link_preview_image(fd, ob->preview);
 }
 
+static void direct_link_view_settings(FileData *fd, ColorManagedViewSettings *view_settings)
+{
+	view_settings->curve_mapping = newdataadr(fd, view_settings->curve_mapping);
+
+	if (view_settings->curve_mapping)
+		direct_link_curvemapping(fd, view_settings->curve_mapping);
+}
+
+/* ***************** READ VIEW LAYER *************** */
+
+static void direct_link_layer_collections(FileData *fd, ListBase *lb, bool master)
+{
+	link_list(fd, lb);
+	for (LayerCollection *lc = lb->first; lc; lc = lc->next) {
+#ifdef USE_COLLECTION_COMPAT_28
+		lc->scene_collection = newdataadr(fd, lc->scene_collection);
+#endif
+
+		/* Master collection is not a real datablock. */
+		if (master) {
+			lc->collection = newdataadr(fd, lc->collection);
+		}
+
+		direct_link_layer_collections(fd, &lc->layer_collections, false);
+	}
+}
+
+static void direct_link_view_layer(FileData *fd, ViewLayer *view_layer)
+{
+	view_layer->stats = NULL;
+	link_list(fd, &view_layer->object_bases);
+	view_layer->basact = newdataadr(fd, view_layer->basact);
+
+	direct_link_layer_collections(fd, &view_layer->layer_collections, true);
+	view_layer->active_collection = newdataadr(fd, view_layer->active_collection);
+
+	view_layer->id_properties = newdataadr(fd, view_layer->id_properties);
+	IDP_DirectLinkGroup_OrFree(&view_layer->id_properties, (fd->flags & FD_FLAGS_SWITCH_ENDIAN), fd);
+
+	link_list(fd, &(view_layer->freestyle_config.modules));
+	link_list(fd, &(view_layer->freestyle_config.linesets));
+
+	BLI_listbase_clear(&view_layer->drawdata);
+	view_layer->object_bases_array = NULL;
+	view_layer->object_bases_hash = NULL;
+}
+
+static void lib_link_layer_collection(FileData *fd, Library *lib, LayerCollection *layer_collection, bool master)
+{
+	/* Master collection is not a real datablock. */
+	if (!master) {
+		layer_collection->collection = newlibadr(fd, lib, layer_collection->collection);
+	}
+
+	for (LayerCollection *layer_collection_nested = layer_collection->layer_collections.first;
+	     layer_collection_nested != NULL;
+	     layer_collection_nested = layer_collection_nested->next)
+	{
+		lib_link_layer_collection(fd, lib, layer_collection_nested, false);
+	}
+}
+
+static void lib_link_view_layer(FileData *fd, Library *lib, ViewLayer *view_layer)
+{
+	/* tag scene layer to update for collection tree evaluation */
+	view_layer->flag |= VIEW_LAYER_ENGINE_DIRTY;
+
+	for (FreestyleModuleConfig *fmc = view_layer->freestyle_config.modules.first; fmc; fmc = fmc->next) {
+		fmc->script = newlibadr(fd, lib, fmc->script);
+	}
+
+	for (FreestyleLineSet *fls = view_layer->freestyle_config.linesets.first; fls; fls = fls->next) {
+		fls->linestyle = newlibadr_us(fd, lib, fls->linestyle);
+		fls->group = newlibadr_us(fd, lib, fls->group);
+	}
+
+	for (Base *base = view_layer->object_bases.first, *base_next = NULL; base; base = base_next) {
+		base_next = base->next;
+
+		/* we only bump the use count for the collection objects */
+		base->object = newlibadr(fd, lib, base->object);
+		base->flag |= BASE_DIRTY_ENGINE_SETTINGS;
+
+		if (base->object == NULL) {
+			/* Free in case linked object got lost. */
+			BLI_freelinkN(&view_layer->object_bases, base);
+		}
+	}
+
+	for (LayerCollection *layer_collection = view_layer->layer_collections.first;
+	     layer_collection != NULL;
+	     layer_collection = layer_collection->next)
+	{
+		lib_link_layer_collection(fd, lib, layer_collection, true);
+	}
+
+	IDP_LibLinkProperty(view_layer->id_properties, fd);
+}
+
+/* ***************** READ COLLECTION *************** */
+
+#ifdef USE_COLLECTION_COMPAT_28
+static void direct_link_scene_collection(FileData *fd, SceneCollection *sc)
+{
+	link_list(fd, &sc->objects);
+	link_list(fd, &sc->scene_collections);
+
+	for (SceneCollection *nsc = sc->scene_collections.first; nsc; nsc = nsc->next) {
+		direct_link_scene_collection(fd, nsc);
+	}
+}
+
+static void lib_link_scene_collection(FileData *fd, Library *lib, SceneCollection *sc)
+{
+	for (LinkData *link = sc->objects.first; link; link = link->next) {
+		link->data = newlibadr_us(fd, lib, link->data);
+		BLI_assert(link->data);
+	}
+
+	for (SceneCollection *nsc = sc->scene_collections.first; nsc; nsc = nsc->next) {
+		lib_link_scene_collection(fd, lib, nsc);
+	}
+}
+#endif
+
+static void direct_link_collection(FileData *fd, Collection *collection)
+{
+	link_list(fd, &collection->gobject);
+	link_list(fd, &collection->children);
+
+	collection->preview = direct_link_preview_image(fd, collection->preview);
+
+	collection->flag &= ~COLLECTION_HAS_OBJECT_CACHE;
+	BLI_listbase_clear(&collection->object_cache);
+	BLI_listbase_clear(&collection->parents);
+
+#ifdef USE_COLLECTION_COMPAT_28
+	/* This runs before the very first doversion. */
+	if (collection->collection != NULL) {
+		collection->collection = newdataadr(fd, collection->collection);
+		direct_link_scene_collection(fd, collection->collection);
+	}
+
+	if (collection->view_layer != NULL) {
+		collection->view_layer = newdataadr(fd, collection->view_layer);
+		direct_link_view_layer(fd, collection->view_layer);
+	}
+#endif
+}
+
+static void lib_link_collection_data(FileData *fd, Library *lib, Collection *collection)
+{
+	for (CollectionObject *cob = collection->gobject.first, *cob_next = NULL; cob; cob = cob_next) {
+		cob_next = cob->next;
+		cob->ob = newlibadr_us(fd, lib, cob->ob);
+
+		if (cob->ob == NULL) {
+			BLI_assert(!"Collection linked object got lost"); // TODO: remove, only for testing now
+			BLI_freelinkN(&collection->gobject, cob);
+		}
+	}
+
+	for (CollectionChild *child = collection->children.first, *child_next = NULL; child; child = child_next) {
+		child_next = child->next;
+		child->collection = newlibadr_us(fd, lib, child->collection);
+
+		if (child->collection == NULL ||
+		    BKE_collection_find_cycle(collection, child->collection))
+		{
+			BLI_assert(!"Collection child got lost"); // TODO: remove, only for testing now
+			BLI_freelinkN(&collection->children, child);
+		}
+		else {
+			CollectionParent *cparent = MEM_callocN(sizeof(CollectionParent), "CollectionParent");
+			cparent->collection = collection;
+			BLI_addtail(&child->collection->parents, cparent);
+		}
+	}
+}
+
+static void lib_link_collection(FileData *fd, Main *main)
+{
+	for (Collection *collection = main->collection.first; collection; collection = collection->id.next) {
+		if (collection->id.tag & LIB_TAG_NEED_LINK) {
+			collection->id.tag &= ~LIB_TAG_NEED_LINK;
+			IDP_LibLinkProperty(collection->id.properties, fd);
+
+#ifdef USE_COLLECTION_COMPAT_28
+			if (collection->collection) {
+				lib_link_scene_collection(fd, collection->id.lib, collection->collection);
+			}
+
+			if (collection->view_layer) {
+				lib_link_view_layer(fd, collection->id.lib, collection->view_layer);
+			}
+#endif
+
+			lib_link_collection_data(fd, collection->id.lib, collection);
+		}
+	}
+}
+
 /* ************ READ SCENE ***************** */
 
 /* patch for missing scene IDs, can't be in do-versions */
@@ -5605,41 +5805,6 @@ static bool scene_validate_setscene__liblink(Scene *sce, const int totscene)
 }
 #endif
 
-static void lib_link_scene_collection(FileData *fd, Library *lib, SceneCollection *sc)
-{
-	for (LinkData *link = sc->objects.first; link; link = link->next) {
-		link->data = newlibadr_us(fd, lib, link->data);
-		BLI_assert(link->data);
-	}
-
-	for (SceneCollection *nsc = sc->scene_collections.first; nsc; nsc = nsc->next) {
-		lib_link_scene_collection(fd, lib, nsc);
-	}
-}
-
-static void lib_link_view_layer(FileData *fd, Library *lib, ViewLayer *view_layer)
-{
-	/* tag scene layer to update for collection tree evaluation */
-	view_layer->flag |= VIEW_LAYER_ENGINE_DIRTY;
-
-	for (FreestyleModuleConfig *fmc = view_layer->freestyle_config.modules.first; fmc; fmc = fmc->next) {
-		fmc->script = newlibadr(fd, lib, fmc->script);
-	}
-
-	for (FreestyleLineSet *fls = view_layer->freestyle_config.linesets.first; fls; fls = fls->next) {
-		fls->linestyle = newlibadr_us(fd, lib, fls->linestyle);
-		fls->group = newlibadr_us(fd, lib, fls->group);
-	}
-
-	for (Base *base = view_layer->object_bases.first; base; base = base->next) {
-		/* we only bump the use count for the collection objects */
-		base->object = newlibadr(fd, lib, base->object);
-		base->flag |= BASE_DIRTY_ENGINE_SETTINGS;
-	}
-
-	IDP_LibLinkProperty(view_layer->id_properties, fd);
-}
-
 static void lib_link_scene(FileData *fd, Main *main)
 {
 #ifdef USE_SETSCENE_CHECK
@@ -5750,7 +5915,7 @@ static void lib_link_scene(FileData *fd, Main *main)
 			BKE_sequencer_update_sound_bounds_all(sce);
 			
 			
-			/* rigidbody world relies on it's linked groups */
+			/* rigidbody world relies on it's linked collections */
 			if (sce->rigidbody_world) {
 				RigidBodyWorld *rbw = sce->rigidbody_world;
 				if (rbw->group)
@@ -5780,7 +5945,15 @@ static void lib_link_scene(FileData *fd, Main *main)
 			/* Motion Tracking */
 			sce->clip = newlibadr_us(fd, sce->id.lib, sce->clip);
 
-			lib_link_scene_collection(fd, sce->id.lib, sce->collection);
+#ifdef USE_COLLECTION_COMPAT_28
+			if (sce->collection) {
+				lib_link_scene_collection(fd, sce->id.lib, sce->collection);
+			}
+#endif
+
+			if (sce->master_collection) {
+				lib_link_collection_data(fd, sce->id.lib, sce->master_collection);
+			}
 
 			for (ViewLayer *view_layer = sce->view_layers.first; view_layer; view_layer = view_layer->next) {
 				lib_link_view_layer(fd, sce->id.lib, view_layer);
@@ -5881,57 +6054,6 @@ static void direct_link_sequence_modifiers(FileData *fd, ListBase *lb)
 	}
 }
 
-static void direct_link_view_settings(FileData *fd, ColorManagedViewSettings *view_settings)
-{
-	view_settings->curve_mapping = newdataadr(fd, view_settings->curve_mapping);
-
-	if (view_settings->curve_mapping)
-		direct_link_curvemapping(fd, view_settings->curve_mapping);
-}
-
-static void direct_link_scene_collection(FileData *fd, SceneCollection *sc)
-{
-	link_list(fd, &sc->objects);
-	link_list(fd, &sc->scene_collections);
-
-	for (SceneCollection *nsc = sc->scene_collections.first; nsc; nsc = nsc->next) {
-		direct_link_scene_collection(fd, nsc);
-	}
-}
-
-static void direct_link_layer_collections(FileData *fd, ListBase *lb)
-{
-	link_list(fd, lb);
-	for (LayerCollection *lc = lb->first; lc; lc = lc->next) {
-		lc->scene_collection = newdataadr(fd, lc->scene_collection);
-
-		link_list(fd, &lc->object_bases);
-
-		for (LinkData *link = lc->object_bases.first; link; link = link->next) {
-			link->data = newdataadr(fd, link->data);
-		}
-
-		direct_link_layer_collections(fd, &lc->layer_collections);
-	}
-}
-
-static void direct_link_view_layer(FileData *fd, ViewLayer *view_layer)
-{
-	view_layer->stats = NULL;
-	link_list(fd, &view_layer->object_bases);
-	view_layer->basact = newdataadr(fd, view_layer->basact);
-	direct_link_layer_collections(fd, &view_layer->layer_collections);
-
-	view_layer->id_properties = newdataadr(fd, view_layer->id_properties);
-	IDP_DirectLinkGroup_OrFree(&view_layer->id_properties, (fd->flags & FD_FLAGS_SWITCH_ENDIAN), fd);
-
-	link_list(fd, &(view_layer->freestyle_config.modules));
-	link_list(fd, &(view_layer->freestyle_config.linesets));
-
-	BLI_listbase_clear(&view_layer->drawdata);
-	view_layer->object_bases_array = NULL;
-}
-
 /**
  * Workspaces store a render layer pointer which can only be read after scene is read.
  */
@@ -6206,11 +6328,18 @@ static void direct_link_scene(FileData *fd, Scene *sce, Main *bmain)
 
 	direct_link_curvemapping(fd, &sce->r.mblur_shutter_curve);
 
+#ifdef USE_COLLECTION_COMPAT_28
 	/* this runs before the very first doversion */
 	if (sce->collection) {
 		sce->collection = newdataadr(fd, sce->collection);
 		direct_link_scene_collection(fd, sce->collection);
 	}
+#endif
+
+	if (sce->master_collection) {
+		sce->master_collection = newdataadr(fd, sce->master_collection);
+		direct_link_collection(fd, sce->master_collection);
+	}
 
 	/* insert into global old-new map for reading without UI (link_global accesses it again) */
 	link_glob_list(fd, &sce->view_layers);
@@ -7553,71 +7682,6 @@ static void lib_link_sound(FileData *fd, Main *main)
 		}
 	}
 }
-/* ***************** READ GROUP *************** */
-
-static void direct_link_group(FileData *fd, Group *group)
-{
-	link_list(fd, &group->gobject);
-
-	group->preview = direct_link_preview_image(fd, group->preview);
-
-	/* This runs before the very first doversion. */
-	if (group->collection != NULL) {
-		group->collection = newdataadr(fd, group->collection);
-		direct_link_scene_collection(fd, group->collection);
-	}
-
-	if (group->view_layer != NULL) {
-		group->view_layer = newdataadr(fd, group->view_layer);
-		direct_link_view_layer(fd, group->view_layer);
-	}
-}
-
-static void lib_link_group(FileData *fd, Main *main)
-{
-	for (Group *group = main->group.first; group; group = group->id.next) {
-		if (group->id.tag & LIB_TAG_NEED_LINK) {
-			group->id.tag &= ~LIB_TAG_NEED_LINK;
-			IDP_LibLinkProperty(group->id.properties, fd);
-
-			if (group->view_layer == NULL) {
-				/* Old file, this is required for doversion. */
-				bool add_us = false;
-
-				GroupObject *go, *gon;
-				go = group->gobject.first;
-				while (go) {
-					gon = go->next;
-					go->ob = newlibadr_real_us(fd, group->id.lib, go->ob);
-					if (go->ob != NULL) {
-						go->ob->flag |= OB_FROMGROUP;
-						/* If group has an object, it increments user... */
-						add_us = true;
-					}
-					else {
-						/* Remove NULL objects. */
-						BLI_remlink(&group->gobject, go);
-						MEM_freeN(go);
-					}
-					go =  gon;
-				}
-
-				if (add_us) {
-					id_us_ensure_real(&group->id);
-				}
-				/* The rest of the read code is only for new files, skip it. */
-				continue;
-			}
-
-			lib_link_scene_collection(fd, group->id.lib, group->collection);
-			lib_link_view_layer(fd, group->id.lib, group->view_layer);
-
-			if (!BLI_listbase_is_empty(&group->view_layer->object_bases)) {
-				id_us_ensure_real(&group->id);
-			}
-		}
-	}
-}
 
 /* ***************** READ MOVIECLIP *************** */
 
@@ -8355,7 +8419,7 @@ static BHead *read_libblock(FileData *fd, Main *main, BHead *bhead, const short
 			direct_link_lightprobe(fd, (LightProbe *)id);
 			break;
 		case ID_GR:
-			direct_link_group(fd, (Group *)id);
+			direct_link_collection(fd, (Collection *)id);
 			break;
 		case ID_AR:
 			direct_link_armature(fd, (bArmature*)id);
@@ -8563,7 +8627,7 @@ static void lib_link_all(FileData *fd, Main *main)
 	lib_link_speaker(fd, main);
 	lib_link_lightprobe(fd, main);
 	lib_link_sound(fd, main);
-	lib_link_group(fd, main);
+	lib_link_collection(fd, main);
 	lib_link_armature(fd, main);
 	lib_link_action(fd, main);
 	lib_link_vfont(fd, main);
@@ -8774,6 +8838,7 @@ BlendFileData *blo_read_file_internal(FileData *fd, const char *filepath)
 	if (fd->memfile == NULL) {
 		/* Do not apply in undo case! */
 		BKE_main_override_static_update(bfd->main);
+		BKE_collections_after_lib_link(bfd->main);
 	}
 
 	lib_verify_nodetree(bfd->main, true);
@@ -9207,18 +9272,21 @@ static void expand_particlesettings(FileData *fd, Main *mainvar, ParticleSetting
 	}
 }
 
-static void expand_group(FileData *fd, Main *mainvar, Group *group)
+static void expand_collection(FileData *fd, Main *mainvar, Collection *collection)
 {
-	GroupObject *go;
-	
-	for (go = group->gobject.first; go; go = go->next) {
-		expand_doit(fd, mainvar, go->ob);
+	for (CollectionObject *cob = collection->gobject.first; cob; cob = cob->next) {
+		expand_doit(fd, mainvar, cob->ob);
 	}
 
-	if (group->collection != NULL) {
-		expand_scene_collection(fd, mainvar, group->collection);
+	for (CollectionChild *child = collection->children.first; child; child = child->next) {
+		expand_doit(fd, mainvar, child->collection);
 	}
 
+#ifdef USE_COLLECTION_COMPAT_28
+	if (collection->collection != NULL) {
+		expand_scene_collection(fd, mainvar, collection->collection);
+	}
+#endif
 }
 
 static void expand_key(FileData *fd, Main *mainvar, Key *key)
@@ -9531,16 +9599,18 @@ static void expand_object(FileData *fd, Main *mainvar, Object *ob)
 	}
 }
 
+#ifdef USE_COLLECTION_COMPAT_28
 static void expand_scene_collection(FileData *fd, Main *mainvar, SceneCollection *sc)
 {
 	for (LinkData *link = sc->objects.first; link; link = link->next) {
 		expand_doit(fd, mainvar, link->data);
 	}
 
-	for (SceneCollection *nsc= sc->scene_collections.first; nsc; nsc = nsc->next) {
+	for (SceneCollection *nsc = sc->scene_collections.first; nsc; nsc = nsc->next) {
 		expand_scene_collection(fd, mainvar, nsc);
 	}
 }
+#endif
 
 static void expand_scene(FileData *fd, Main *mainvar, Scene *sce)
 {
@@ -9626,7 +9696,15 @@ static void expand_scene(FileData *fd, Main *mainvar, Scene *sce)
 
 	expand_doit(fd, mainvar, sce->clip);
 
-	expand_scene_collection(fd, mainvar, sce->collection);
+#ifdef USE_COLLECTION_COMPAT_28
+	if (sce->collection) {
+		expand_scene_collection(fd, mainvar, sce->collection);
+	}
+#endif
+
+	if (sce->master_collection) {
+		expand_collection(fd, mainvar, sce->master_collection);
+	}
 }
 
 static void expand_camera(FileData *fd, Main *mainvar, Camera *ca)
@@ -9833,7 +9911,7 @@ void BLO_expand_main(void *fdhandle, Main *mainvar)
 						expand_action(fd, mainvar, (bAction *)id); // XXX deprecated - old animation system
 						break;
 					case ID_GR:
-						expand_group(fd, mainvar, (Group *)id);
+						expand_collection(fd, mainvar, (Collection *)id);
 						break;
 					case ID_NT:
 						expand_nodetree(fd, mainvar, (bNodeTree *)id);
@@ -9881,11 +9959,11 @@ void BLO_expand_main(void *fdhandle, Main *mainvar)
 
 /* ***************************** */
 	
-static bool object_in_any_scene(Main *mainvar, Object *ob)
+static bool object_in_any_scene(Main *bmain, Object *ob)
 {
 	Scene *sce;
 	
-	for (sce = mainvar->scene.first; sce; sce = sce->id.next) {
+	for (sce = bmain->scene.first; sce; sce = sce->id.next) {
 		if (BKE_scene_object_find(sce, ob)) {
 			return true;
 		}
@@ -9894,25 +9972,34 @@ static bool object_in_any_scene(Main *mainvar, Object *ob)
 	return false;
 }
 
-static void give_base_to_objects(
-        Main *mainvar, Scene *scene, ViewLayer *view_layer, Library *lib, const short flag)
+static Collection *get_collection_active(
+        Main *bmain, Scene *scene, ViewLayer *view_layer, const int flag)
+{
+	if (flag & FILE_ACTIVE_COLLECTION) {
+		LayerCollection *lc = BKE_layer_collection_get_active(view_layer);
+		return lc->collection;
+	}
+	else {
+		return BKE_collection_add(bmain, scene->master_collection, NULL);
+	}
+}
+
+static void add_loose_objects_to_scene(
+        Main *mainvar, Main *bmain, Scene *scene, ViewLayer *view_layer, Library *lib, const short flag)
 {
-	Object *ob;
-	Base *base;
-	SceneCollection *scene_collection = NULL;
 	const bool is_link = (flag & FILE_LINK) != 0;
 
 	BLI_assert(scene);
 
-	/* Give all objects which are LIB_TAG_INDIRECT a base, or for a group when *lib has been set. */
-	for (ob = mainvar->object.first; ob; ob = ob->id.next) {
+	/* Give all objects which are LIB_TAG_INDIRECT a base, or for a collection when *lib has been set. */
+	for (Object *ob = mainvar->object.first; ob; ob = ob->id.next) {
 		if ((ob->id.tag & LIB_TAG_INDIRECT) && (ob->id.tag & LIB_TAG_PRE_EXISTING) == 0) {
 			bool do_it = false;
 
 			if (ob->id.us == 0) {
 				do_it = true;
 			}
-			else if (!is_link && (ob->id.lib == lib) && (object_in_any_scene(mainvar, ob) == 0)) {
+			else if (!is_link && (ob->id.lib == lib) && (object_in_any_scene(bmain, ob) == 0)) {
 				/* When appending, make sure any indirectly loaded objects get a base, else they cant be accessed at all
 				 * (see T27437). */
 				do_it = true;
@@ -9921,17 +10008,14 @@ static void give_base_to_objects(
 			if (do_it) {
 				CLAMP_MIN(ob->id.us, 0);
 
-				if (scene_collection == NULL) {
-					scene_collection = get_scene_collection_active_or_create(scene, view_layer, FILE_ACTIVE_COLLECTION);
-				}
-
-				BKE_collection_object_add(&scene->id, scene_collection, ob);
-				base = BKE_view_layer_base_find(view_layer, ob);
+				Collection *active_collection = get_collection_active(bmain, scene, view_layer, FILE_ACTIVE_COLLECTION);
+				BKE_collection_object_add(bmain, active_collection, ob);
+				Base *base = BKE_view_layer_base_find(view_layer, ob);
 				BKE_scene_object_base_flag_sync_from_base(base);
 
 				if (flag & FILE_AUTOSELECT) {
 					/* Note that link_object_postprocess() already checks for FILE_AUTOSELECT flag,
-					 * but it will miss objects from non-instantiated groups... */
+					 * but it will miss objects from non-instantiated collections... */
 					if (base->flag & BASE_SELECTABLED) {
 						base->flag |= BASE_SELECTED;
 						BKE_scene_object_base_flag_sync_from_base(base);
@@ -9946,42 +10030,45 @@ static void give_base_to_objects(
 	}
 }
 
-static void give_base_to_groups(
-        Main *mainvar, Scene *scene, ViewLayer *view_layer, Library *UNUSED(lib), const short UNUSED(flag))
+static void add_collections_to_scene(
+        Main *mainvar, Main *bmain, Scene *scene, ViewLayer *view_layer, Library *UNUSED(lib), const short flag)
 {
-	Group *group;
-	Base *base;
-	Object *ob;
-	SceneCollection *scene_collection;
-
-	/* If the group is empty this function is not even called, so it's safe to ensure a collection at this point. */
-	scene_collection = get_scene_collection_active_or_create(scene, view_layer, FILE_ACTIVE_COLLECTION);
+	Collection *active_collection = get_collection_active(bmain, scene, view_layer, FILE_ACTIVE_COLLECTION);
 
 	/* Give all objects which are tagged a base. */
-	for (group = mainvar->group.first; group; group = group->id.next) {
-		if (group->id.tag & LIB_TAG_DOIT) {
-			/* Any indirect group should not have been tagged. */
-			BLI_assert((group->id.tag & LIB_TAG_INDIRECT) == 0);
+	for (Collection *collection = mainvar->collection.first; collection; collection = collection->id.next) {
+		if (collection->id.tag & LIB_TAG_DOIT) {
+			if (flag & FILE_GROUP_INSTANCE) {
+				/* Any indirect collection should not have been tagged. */
+				BLI_assert((collection->id.tag & LIB_TAG_INDIRECT) == 0);
+
+				/* BKE_object_add(...) messes with the selection. */
+				Object *ob = BKE_object_add_only_object(bmain, OB_EMPTY, collection->id.name + 2);
+				ob->type = OB_EMPTY;
 
-			/* BKE_object_add(...) messes with the selection. */
-			ob = BKE_object_add_only_object(mainvar, OB_EMPTY, group->id.name + 2);
-			ob->type = OB_EMPTY;
+				BKE_collection_object_add(bmain, active_collection, ob);
+				Base *base = BKE_view_layer_base_find(view_layer, ob);
 
-			BKE_collection_object_add(&scene->id, scene_collection, ob);
-			base = BKE_view_layer_base_find(view_layer, ob);
+				if (base->flag & BASE_SELECTABLED) {
+					base->flag |= BASE_SELECTED;
+				}
 
-			if (base->flag & BASE_SELECTABLED) {
-				base->flag |= BASE_SELECTED;
-			}
+				BKE_scene_object_base_flag_sync_from_base(base);
+				DEG_id_tag_update(&ob->id, OB_RECALC_OB | OB_RECALC_DATA | OB_RECALC_TIME);
+				view_layer->basact = base;
 
-			BKE_scene_object_base_flag_sync_from_base(base);
-			DEG_id_tag_update(&ob->id, OB_RECALC_OB | OB_RECALC_DATA | OB_RECALC_TIME);
-			view_layer->basact = base;
+				/* Assign the collection. */
+				ob->dup_group = collection;
+				ob->transflag |= OB_DUPLICOLLECTION;
+				copy_v3_v3(ob->loc, scene->cursor.location);
+			}
+			else {
+				/* Add collection as child of active collection. */
+				BKE_collection_child_add(bmain, active_collection, collection);
 
-			/* Assign the group. */
-			ob->dup_group = group;
-			ob->transflag |= OB_DUPLIGROUP;
-			copy_v3_v3(ob->loc, scene->cursor.location);
+				collection->id.tag &= ~LIB_TAG_INDIRECT;
+				collection->id.tag |= LIB_TAG_EXTERN;
+			}
 		}
 	}
 }
@@ -10055,35 +10142,19 @@ static ID *link_named_part(
 	return id;
 }
 
-static SceneCollection *get_scene_collection_active_or_create(
-        struct Scene *scene, struct ViewLayer *view_layer, const int flag)
-{
-	LayerCollection *lc = NULL;
-
-	if (flag & FILE_ACTIVE_COLLECTION) {
-		lc = BKE_layer_collection_get_active_ensure(scene, view_layer);
-	}
-	else {
-		SceneCollection *sc = BKE_collection_add(&scene->id, NULL, COLLECTION_TYPE_NONE, NULL);
-		lc = BKE_collection_link(view_layer, sc);
-	}
-
-	return lc->scene_collection;
-}
-
-static void link_object_postprocess(ID *id, Scene *scene, ViewLayer *view_layer, const int flag)
+static void link_object_postprocess(ID *id, Main *bmain, Scene *scene, ViewLayer *view_layer, const int flag)
 {
 	if (scene) {
 		/* link to scene */
 		Base *base;
 		Object *ob;
-		SceneCollection *sc;
+		Collection *collection;
 
 		ob = (Object *)id;
 		ob->mode = OB_MODE_OBJECT;
 
-		sc =  get_scene_collection_active_or_create(scene, view_layer, flag);
-		BKE_collection_object_add(&scene->id, sc, ob);
+		collection = get_collection_active(bmain, scene, view_layer, flag);
+		BKE_collection_object_add(bmain, collection, ob);
 		base = BKE_view_layer_base_find(view_layer, ob);
 		BKE_scene_object_base_flag_sync_from_base(base);
 
@@ -10121,11 +10192,11 @@ void BLO_library_link_copypaste(Main *mainl, BlendHandle *bh)
 			id_sort_by_name(lb, id);
 
 			if (bhead->code == ID_OB) {
-				/* Instead of instancing Base's directly, postpone until after groups are loaded
-				 * otherwise the base's flag is set incorrectly when groups are used */
+				/* Instead of instancing Base's directly, postpone until after collections are loaded
+				 * otherwise the base's flag is set incorrectly when collections are used */
 				Object *ob = (Object *)id;
 				ob->mode = OB_MODE_OBJECT;
-				/* ensure give_base_to_objects runs on this object */
+				/* ensure add_loose_objects_to_scene runs on this object */
 				BLI_assert(id->us == 0);
 			}
 		}
@@ -10134,17 +10205,16 @@ void BLO_library_link_copypaste(Main *mainl, BlendHandle *bh)
 
 static ID *link_named_part_ex(
         Main *mainl, FileData *fd, const short idcode, const char *name, const int flag,
-        Scene *scene, ViewLayer *view_layer)
+        Main *bmain, Scene *scene, ViewLayer *view_layer)
 {
 	ID *id = link_named_part(mainl, fd, idcode, name, flag);
 
 	if (id && (GS(id->name) == ID_OB)) {	/* loose object: give a base */
-		link_object_postprocess(id, scene, view_layer, flag);
+		link_object_postprocess(id, bmain, scene, view_layer, flag);
 	}
 	else if (id && (GS(id->name) == ID_GR)) {
-		/* tag as needing to be instantiated */
-		if (flag & FILE_GROUP_INSTANCE)
-			id->tag |= LIB_TAG_DOIT;
+		/* tag as needing to be instantiated or linked */
+		id->tag |= LIB_TAG_DOIT;
 	}
 
 	return id;
@@ -10167,24 +10237,24 @@ ID *BLO_library_link_named_part(Main *mainl, BlendHandle **bh, const short idcod
 
 /**
  * Link a named datablock from an external blend file.
- * Optionally instantiate the object/group in the scene when the flags are set.
+ * Optionally instantiate the object/collection in the scene when the flags are set.
  *
  * \param mainl The main database to link from (not the active one).
  * \param bh The blender file handle.
  * \param idcode The kind of datablock to link.
  * \param name The name of the datablock (without the 2 char ID prefix).
  * \param flag Options for linking, used for instantiating.
- * \param scene The scene in which to instantiate objects/groups (if NULL, no instantiation is done).
- * \param v3d The active View3D (only to define active layers for instantiated objects & groups, can be NULL).
+ * \param scene The scene in which to instantiate objects/collections (if NULL, no instantiation is done).
+ * \param v3d The active View3D (only to define active layers for instantiated objects & collections, can be NULL).
  * \return the linked ID when found.
  */
 ID *BLO_library_link_named_part_ex(
         Main *mainl, BlendHandle **bh,
         const short idcode, const char *name, const int flag,
-        Scene *scene, ViewLayer *view_layer)
+        Main *bmain, Scene *scene, ViewLayer *view_layer)
 {
 	FileData *fd = (FileData*)(*bh);
-	return link_named_part_ex(mainl, fd, idcode, name, flag, scene, view_layer);
+	return link_named_part_ex(mainl, fd, idcode, name, flag, bmain, scene, view_layer);
 }
 
 static void link_id_part(ReportList *reports, FileData *fd, Main *mainvar, ID *id, ID **r_id)
@@ -10237,8 +10307,8 @@ static Main *library_link_begin(Main *mainvar, FileData **fd, const char *filepa
 
 	(*fd)->mainlist = MEM_callocN(sizeof(ListBase), "FileData.mainlist");
 	
-	/* clear for group instantiating tag */
-	BKE_main_id_tag_listbase(&(mainvar->group), LIB_TAG_DOIT, false);
+	/* clear for collection instantiating tag */
+	BKE_main_id_tag_listbase(&(mainvar->collection), LIB_TAG_DOIT, false);
 
 	/* make mains */
 	blo_split_main((*fd)->mainlist, mainvar);
@@ -10297,7 +10367,7 @@ static void split_main_newid(Main *mainptr, Main *main_newid)
 }
 
 /* scene and v3d may be NULL. */
-static void library_link_end(Main *mainl, FileData **fd, const short flag, Scene *scene, ViewLayer *view_layer)
+static void library_link_end(Main *mainl, FileData **fd, const short flag, Main *bmain, Scene *scene, ViewLayer *view_layer)
 {
 	Main *mainvar;
 	Library *curlib;
@@ -10327,6 +10397,7 @@ static void library_link_end(Main *mainl, FileData **fd, const short flag, Scene
 	mainl = NULL; /* blo_join_main free's mainl, cant use anymore */
 
 	lib_link_all(*fd, mainvar);
+	BKE_collections_after_lib_link(mainvar);
 
 	/* Yep, second splitting... but this is a very cheap operation, so no big deal. */
 	blo_split_main((*fd)->mainlist, mainvar);
@@ -10350,22 +10421,19 @@ static void library_link_end(Main *mainl, FileData **fd, const short flag, Scene
 	lib_verify_nodetree(mainvar, false);
 	fix_relpaths_library(G.main->name, mainvar); /* make all relative paths, relative to the open blend file */
 
-	/* Give a base to loose objects. If group append, do it for objects too.
-	 * Only directly linked objects & groups are instantiated by `BLO_library_link_named_part_ex()` & co,
+	/* Give a base to loose objects and collections.
+	 * Only directly linked objects & collections are instantiated by `BLO_library_link_named_part_ex()` & co,
 	 * here we handle indirect ones and other possible edge-cases. */
 	if (scene) {
-		give_base_to_objects(mainvar, scene, view_layer, curlib, flag);
-
-		if (flag & FILE_GROUP_INSTANCE) {
-			give_base_to_groups(mainvar, scene, view_layer, curlib, flag);
-		}
+		add_collections_to_scene(mainvar, bmain, scene, view_layer, curlib, flag);
+		add_loose_objects_to_scene(mainvar, bmain, scene, view_layer, curlib, flag);
 	}
 	else {
 		/* printf("library_append_end, scene is NULL (objects wont get bases)\n"); */
 	}
 
-	/* clear group instantiating tag */
-	BKE_main_id_tag_listbase(&(mainvar->group), LIB_TAG_DOIT, false);
+	/* clear collection instantiating tag */
+	BKE_main_id_tag_listbase(&(mainvar->collection), LIB_TAG_DOIT, false);
 
 	/* patch to prevent switch_endian happens twice */
 	if ((*fd)->flags & FD_FLAGS_SWITCH_ENDIAN) {
@@ -10376,19 +10444,20 @@ static void library_link_end(Main *mainl, FileData **fd, const short flag, Scene
 
 /**
  * Finalize linking from a given .blend file (library).
- * Optionally instance the indirect object/group in the scene when the flags are set.
+ * Optionally instance the indirect object/collection in the scene when the flags are set.
  * \note Do not use \a bh after calling this function, it may frees it.
  *
  * \param mainl The main database to link from (not the active one).
  * \param bh The blender file handle (WARNING! may be freed by this function!).
  * \param flag Options for linking, used for instantiating.
- * \param scene The scene in which to instantiate objects/groups (if NULL, no instantiation is done).
- * \param view_layer The scene layer in which to instantiate objects/groups (if NULL, no instantiation is done).
+ * \param bmain The main database in which to instantiate objects/collections
+ * \param scene The scene in which to instantiate objects/collections (if NULL, no instantiation is done).
+ * \param view_layer The scene layer in which to instantiate objects/collections (if NULL, no instantiation is done).
  */
-void BLO_library_link_end(Main *mainl, BlendHandle **bh, int flag, Scene *scene, ViewLayer *view_layer)
+void BLO_library_link_end(Main *mainl, BlendHandle **bh, int flag, Main *bmain, Scene *scene, ViewLayer *view_layer)
 {
 	FileData *fd = (FileData*)(*bh);
-	library_link_end(mainl, &fd, flag, scene, view_layer);
+	library_link_end(mainl, &fd, flag, bmain, scene, view_layer);
 	*bh = (BlendHandle*)fd;
 }
 
diff --git a/source/blender/blenloader/intern/versioning_260.c b/source/blender/blenloader/intern/versioning_260.c
index 1d8bea40381..8e0795f7e34 100644
--- a/source/blender/blenloader/intern/versioning_260.c
+++ b/source/blender/blenloader/intern/versioning_260.c
@@ -2265,7 +2265,6 @@ void blo_do_versions_260(FileData *fd, Library *UNUSED(lib), Main *main)
 
 						if (!ELEM(so->outlinevis,
 						          SO_SCENES,
-						          SO_GROUPS,
 						          SO_LIBRARIES,
 						          SO_SEQUENCE,
 						          SO_DATA_API))
diff --git a/source/blender/blenloader/intern/versioning_280.c b/source/blender/blenloader/intern/versioning_280.c
index c3a634f1e74..43302408dc4 100644
--- a/source/blender/blenloader/intern/versioning_280.c
+++ b/source/blender/blenloader/intern/versioning_280.c
@@ -59,7 +59,6 @@
 #include "BKE_constraint.h"
 #include "BKE_customdata.h"
 #include "BKE_freestyle.h"
-#include "BKE_group.h"
 #include "BKE_idprop.h"
 #include "BKE_layer.h"
 #include "BKE_main.h"
@@ -75,7 +74,6 @@
 
 #include "MEM_guardedalloc.h"
 
-
 static bScreen *screen_parent_find(const bScreen *screen)
 {
 	/* can avoid lookup if screen state isn't maximized/full (parent and child store the same state) */
@@ -185,6 +183,162 @@ static void do_version_workspaces_after_lib_link(Main *bmain)
 	}
 }
 
+#ifdef USE_COLLECTION_COMPAT_28
+enum {
+	COLLECTION_DEPRECATED_VISIBLE    = (1 << 0),
+	COLLECTION_DEPRECATED_VIEWPORT   = (1 << 0),
+	COLLECTION_DEPRECATED_SELECTABLE = (1 << 1),
+	COLLECTION_DEPRECATED_DISABLED   = (1 << 2),
+	COLLECTION_DEPRECATED_RENDER     = (1 << 3),
+};
+
+static void do_version_view_layer_visibility(ViewLayer *view_layer)
+{
+	/* Convert from deprecated VISIBLE flag to DISABLED */
+	LayerCollection *lc;
+	for (lc = view_layer->layer_collections.first;
+	     lc;
+	     lc = lc->next)
+	{
+		if (lc->flag & COLLECTION_DEPRECATED_DISABLED) {
+			lc->flag &= ~COLLECTION_DEPRECATED_DISABLED;
+		}
+
+		if ((lc->flag & COLLECTION_DEPRECATED_VISIBLE) == 0) {
+			lc->flag |= COLLECTION_DEPRECATED_DISABLED;
+		}
+
+		lc->flag |= COLLECTION_DEPRECATED_VIEWPORT | COLLECTION_DEPRECATED_RENDER;
+	}
+}
+
+static void do_version_layer_collection_pre(ViewLayer *view_layer,
+                                            ListBase *lb,
+                                            GSet *enabled_set,
+                                            GSet *selectable_set)
+{
+	/* Convert from deprecated DISABLED to new layer collection and collection flags */
+	for (LayerCollection *lc = lb->first; lc; lc = lc->next) {
+		if (lc->scene_collection) {
+			if (!(lc->flag & COLLECTION_DEPRECATED_DISABLED)) {
+				BLI_gset_insert(enabled_set, lc->scene_collection);
+			}
+			if (lc->flag & COLLECTION_DEPRECATED_SELECTABLE) {
+				BLI_gset_insert(selectable_set, lc->scene_collection);
+			}
+		}
+
+		do_version_layer_collection_pre(view_layer, &lc->layer_collections, enabled_set, selectable_set);
+	}
+}
+
+static void do_version_layer_collection_post(ViewLayer *view_layer,
+                                             ListBase *lb,
+                                             GSet *enabled_set,
+                                             GSet *selectable_set,
+                                             GHash *collection_map)
+{
+	/* Apply layer collection exclude flags. */
+	for (LayerCollection *lc = lb->first; lc; lc = lc->next) {
+		if (!(lc->collection->flag & COLLECTION_IS_MASTER)) {
+			SceneCollection *sc = BLI_ghash_lookup(collection_map, lc->collection);
+			const bool enabled = (sc && BLI_gset_haskey(enabled_set, sc));
+			const bool selectable = (sc && BLI_gset_haskey(selectable_set, sc));
+
+			if (!enabled) {
+				lc->flag |= LAYER_COLLECTION_EXCLUDE;
+			}
+			if (enabled && !selectable) {
+				lc->collection->flag |= COLLECTION_RESTRICT_SELECT;
+			}
+		}
+
+		do_version_layer_collection_post(view_layer, &lc->layer_collections, enabled_set, selectable_set, collection_map);
+	}
+}
+
+static void do_version_scene_collection_convert(Main *bmain,
+                                                SceneCollection *sc,
+                                                Collection *collection,
+                                                GHash *collection_map)
+{
+	if (collection_map) {
+		BLI_ghash_insert(collection_map, collection, sc);
+	}
+
+	for (SceneCollection *nsc = sc->scene_collections.first; nsc;) {
+		SceneCollection *nsc_next = nsc->next;
+		Collection *ncollection = BKE_collection_add(bmain, collection, nsc->name);
+		do_version_scene_collection_convert(bmain, nsc, ncollection, collection_map);
+		nsc = nsc_next;
+	}
+
+	for (LinkData *link = sc->objects.first; link; link = link->next) {
+		Object *ob = link->data;
+		if (ob) {
+			BKE_collection_object_add(bmain, collection, ob);
+			id_us_min(&ob->id);
+		}
+	}
+
+	BLI_freelistN(&sc->objects);
+	MEM_freeN(sc);
+}
+
+static void do_version_group_collection_to_collection(Main *bmain, Collection *group)
+{
+	/* Convert old 2.8 group collections to new unified collections. */
+	if (group->collection) {
+		do_version_scene_collection_convert(bmain, group->collection, group, NULL);
+	}
+
+	group->collection = NULL;
+	id_fake_user_set(&group->id);
+}
+
+static void do_version_scene_collection_to_collection(Main *bmain, Scene *scene)
+{
+	/* Convert old 2.8 scene collections to new unified collections. */
+
+	/* Temporarily clear view layers so we don't do any layer collection syncing
+	 * and destroy old flags that we want to restore. */
+	ListBase view_layers = scene->view_layers;
+	BLI_listbase_clear(&scene->view_layers);
+
+	if (!scene->master_collection) {
+		scene->master_collection = BKE_collection_master_add();
+	}
+
+	/* Convert scene collections. */
+	GHash *collection_map = BLI_ghash_new(BLI_ghashutil_ptrhash, BLI_ghashutil_ptrcmp, __func__);
+	if (scene->collection) {
+		do_version_scene_collection_convert(bmain, scene->collection, scene->master_collection, collection_map);
+		scene->collection = NULL;
+	}
+
+	scene->view_layers = view_layers;
+
+	/* Convert layer collections. */
+	ViewLayer *view_layer;
+	for (view_layer = scene->view_layers.first; view_layer; view_layer = view_layer->next) {
+		GSet *enabled_set = BLI_gset_new(BLI_ghashutil_ptrhash, BLI_ghashutil_ptrcmp, __func__);
+		GSet *selectable_set = BLI_gset_new(BLI_ghashutil_ptrhash, BLI_ghashutil_ptrcmp, __func__);
+
+		do_version_layer_collection_pre(view_layer, &view_layer->layer_collections, enabled_set, selectable_set);
+		BKE_layer_collection_sync(scene, view_layer);
+		do_version_layer_collection_post(view_layer, &view_layer->layer_collections, enabled_set, selectable_set, collection_map);
+
+		BLI_gset_free(enabled_set, NULL);
+		BLI_gset_free(selectable_set, NULL);
+
+		BKE_layer_collection_sync(scene, view_layer);
+	}
+
+	BLI_ghash_free(collection_map, NULL, NULL);
+}
+#endif
+
+
 enum {
 	DO_VERSION_COLLECTION_VISIBLE     = 0,
 	DO_VERSION_COLLECTION_HIDE        = 1,
@@ -192,311 +346,348 @@ enum {
 	DO_VERSION_COLLECTION_HIDE_ALL    = 3,
 };
 
-void do_versions_after_linking_280(Main *main)
+static void do_version_layers_to_collections(Main *bmain, Scene *scene)
 {
-	if (!MAIN_VERSION_ATLEAST(main, 280, 0)) {
-		for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
-			/* since we don't have access to FileData we check the (always valid) first render layer instead */
-			if (scene->view_layers.first == NULL) {
-				SceneCollection *sc_master = BKE_collection_master(&scene->id);
-				BLI_strncpy(sc_master->name, "Master Collection", sizeof(sc_master->name));
-
-				struct DoVersionSceneCollections {
-					SceneCollection *collections[20];
-					int created;
-					const char *suffix;
-					int flag_viewport;
-					int flag_render;
-				} collections[] =
-				{
-					{
-						.collections = {NULL},
-						.created = 0,
-						.suffix = "",
-						.flag_viewport = COLLECTION_SELECTABLE,
-						.flag_render = COLLECTION_SELECTABLE
-					},
-					{
-						.collections = {NULL},
-						.created = 0,
-						.suffix = " - Hide Viewport",
-						.flag_viewport = COLLECTION_SELECTABLE,
-						.flag_render = COLLECTION_SELECTABLE
-					},
-					{
-						.collections = {NULL},
-						.created = 0,
-						.suffix = " - Hide Render",
-						.flag_viewport = COLLECTION_SELECTABLE,
-						.flag_render = COLLECTION_SELECTABLE | COLLECTION_DISABLED
-					},
-					{
-						.collections = {NULL},
-						.created = 0,
-						.suffix = " - Hide Render All",
-						.flag_viewport = COLLECTION_SELECTABLE | COLLECTION_DISABLED,
-						.flag_render = COLLECTION_SELECTABLE | COLLECTION_DISABLED
-					}
-				};
-
-				for (int layer = 0; layer < 20; layer++) {
-					for (Base *base = scene->base.first; base; base = base->next) {
-						if (base->lay & (1 << layer)) {
-							int collection_index = -1;
-							if ((base->object->restrictflag & OB_RESTRICT_VIEW) &&
-							    (base->object->restrictflag & OB_RESTRICT_RENDER))
-							{
-								collection_index = DO_VERSION_COLLECTION_HIDE_ALL;
-							}
-							else if (base->object->restrictflag & OB_RESTRICT_VIEW) {
-								collection_index = DO_VERSION_COLLECTION_HIDE;
-							}
-							else if (base->object->restrictflag & OB_RESTRICT_RENDER) {
-								collection_index = DO_VERSION_COLLECTION_HIDE_RENDER;
-							}
-							else {
-								collection_index = DO_VERSION_COLLECTION_VISIBLE;
-							}
+	/* Since we don't have access to FileData we check the (always valid) first
+	 * render layer instead. */
+	if (!scene->master_collection) {
+		scene->master_collection = BKE_collection_master_add();
+	}
 
-							/* Create collections when needed only. */
-							if ((collections[collection_index].created & (1 << layer)) == 0) {
-								char name[MAX_NAME];
-
-								if ((collections[DO_VERSION_COLLECTION_VISIBLE].created & (1 << layer)) == 0) {
-									BLI_snprintf(name,
-									             sizeof(sc_master->name),
-									             "Collection %d%s",
-									             layer + 1,
-									             collections[DO_VERSION_COLLECTION_VISIBLE].suffix);
-									collections[DO_VERSION_COLLECTION_VISIBLE].collections[layer] =
-									        BKE_collection_add(&scene->id, sc_master, COLLECTION_TYPE_NONE, name);
-									collections[DO_VERSION_COLLECTION_VISIBLE].created |= (1 << layer);
-								}
-
-								if (collection_index != DO_VERSION_COLLECTION_VISIBLE) {
-									SceneCollection *sc_parent;
-									sc_parent = collections[DO_VERSION_COLLECTION_VISIBLE].collections[layer];
-									BLI_snprintf(name,
-									             sizeof(sc_master->name),
-									             "Collection %d%s",
-									             layer + 1,
-									             collections[collection_index].suffix);
-									collections[collection_index].collections[layer] = BKE_collection_add(
-									        &scene->id,
-									        sc_parent,
-									        COLLECTION_TYPE_NONE,
-									        name);
-									collections[collection_index].created |= (1 << layer);
-								}
-							}
+	if (scene->view_layers.first) {
+		return;
+	}
 
-							BKE_collection_object_add(
-							        &scene->id, collections[collection_index].collections[layer], base->object);
-						}
+	/* Create collections from layers. */
+	Collection *collection_master = BKE_collection_master(scene);
 
-						if (base->flag & SELECT) {
-							base->object->flag |= SELECT;
-						}
-						else {
-							base->object->flag &= ~SELECT;
-						}
-					}
+	struct DoVersionSceneCollections {
+		Collection *collections[20];
+		int created;
+		const char *suffix;
+		int flag;
+	} collections[] =
+	{
+		{
+			.collections = {NULL},
+			.created = 0,
+			.suffix = "",
+			.flag = 0,
+		},
+		{
+			.collections = {NULL},
+			.created = 0,
+			.suffix = " - Hide Viewport",
+			.flag = COLLECTION_RESTRICT_VIEW,
+		},
+		{
+			.collections = {NULL},
+			.created = 0,
+			.suffix = " - Hide Render",
+			.flag = COLLECTION_RESTRICT_RENDER,
+		},
+		{
+			.collections = {NULL},
+			.created = 0,
+			.suffix = " - Hide Render All",
+			.flag = COLLECTION_RESTRICT_VIEW | COLLECTION_RESTRICT_RENDER,
+		}
+	};
+
+	for (int layer = 0; layer < 20; layer++) {
+		for (Base *base = scene->base.first; base; base = base->next) {
+			if (base->lay & (1 << layer)) {
+				int collection_index = -1;
+				if ((base->object->restrictflag & OB_RESTRICT_VIEW) &&
+				    (base->object->restrictflag & OB_RESTRICT_RENDER))
+				{
+					collection_index = DO_VERSION_COLLECTION_HIDE_ALL;
+				}
+				else if (base->object->restrictflag & OB_RESTRICT_VIEW) {
+					collection_index = DO_VERSION_COLLECTION_HIDE;
+				}
+				else if (base->object->restrictflag & OB_RESTRICT_RENDER) {
+					collection_index = DO_VERSION_COLLECTION_HIDE_RENDER;
+				}
+				else {
+					collection_index = DO_VERSION_COLLECTION_VISIBLE;
 				}
 
-				/* Re-order the nested hidden collections. */
-				SceneCollection *scene_collection_parent = sc_master->scene_collections.first;
+				/* Create collections when needed only. */
+				if ((collections[collection_index].created & (1 << layer)) == 0) {
+					char name[MAX_NAME];
 
-				for (int layer = 0; layer < 20; layer++) {
-					if (collections[DO_VERSION_COLLECTION_VISIBLE].created & (1 << layer)) {
+					if ((collections[DO_VERSION_COLLECTION_VISIBLE].created & (1 << layer)) == 0) {
+						BLI_snprintf(name,
+						             sizeof(collection_master->id.name),
+						             "Collection %d%s",
+						             layer + 1,
+						             collections[DO_VERSION_COLLECTION_VISIBLE].suffix);
 
-						if ((collections[DO_VERSION_COLLECTION_HIDE].created & (1 << layer)) &&
-						    (collections[DO_VERSION_COLLECTION_HIDE].collections[layer] !=
-						     scene_collection_parent->scene_collections.first))
-						{
-							BLI_listbase_swaplinks(
-							        &scene_collection_parent->scene_collections,
-							        collections[DO_VERSION_COLLECTION_HIDE].collections[layer],
-							        scene_collection_parent->scene_collections.first);
-						}
+						Collection *collection = BKE_collection_add(bmain, collection_master, name);
+						collection->flag |= collections[DO_VERSION_COLLECTION_VISIBLE].flag;
+						collections[DO_VERSION_COLLECTION_VISIBLE].collections[layer] = collection;
+						collections[DO_VERSION_COLLECTION_VISIBLE].created |= (1 << layer);
 
-						if ((collections[DO_VERSION_COLLECTION_HIDE_ALL].created & (1 << layer)) &&
-						    (collections[DO_VERSION_COLLECTION_HIDE_ALL].collections[layer] !=
-						     scene_collection_parent->scene_collections.last))
-						{
-							BLI_listbase_swaplinks(
-							        &scene_collection_parent->scene_collections,
-							        collections[DO_VERSION_COLLECTION_HIDE_ALL].collections[layer],
-							        scene_collection_parent->scene_collections.last);
+						if (!(scene->lay & (1 << layer))) {
+							collection->flag |= COLLECTION_RESTRICT_VIEW | COLLECTION_RESTRICT_RENDER;
 						}
+					}
 
-						scene_collection_parent = scene_collection_parent->next;
+					if (collection_index != DO_VERSION_COLLECTION_VISIBLE) {
+						Collection *collection_parent;
+						collection_parent = collections[DO_VERSION_COLLECTION_VISIBLE].collections[layer];
+						BLI_snprintf(name,
+						             sizeof(collection_master->id.name),
+						             "Collection %d%s",
+						             layer + 1,
+						             collections[collection_index].suffix);
+
+						Collection *collection = BKE_collection_add(bmain, collection_parent, name);
+						collection->flag |= collections[collection_index].flag;
+						collections[collection_index].collections[layer] = collection;
+						collections[collection_index].created |= (1 << layer);
+
+						if (!(scene->lay & (1 << layer))) {
+							collection->flag |= COLLECTION_RESTRICT_VIEW | COLLECTION_RESTRICT_RENDER;
+						}
 					}
 				}
-				BLI_assert(scene_collection_parent == NULL);
 
-				/* Handle legacy render layers. */
-				{
-					for (SceneRenderLayer *srl = scene->r.layers.first; srl; srl = srl->next) {
-
-						ViewLayer *view_layer = BKE_view_layer_add(scene, srl->name);
-
-						if (srl->samples != 0) {
-							/* It is up to the external engine to handle
-							 * its own doversion in this case. */
-							BKE_override_view_layer_int_add(
-							        view_layer,
-							        ID_SCE,
-							        "samples",
-							        srl->samples);
-						}
+				/* Note usually this would do slow collection syncing for view layers,
+				 * but since no view layers exists yet at this point it's fast. */
+				BKE_collection_object_add(bmain,
+						collections[collection_index].collections[layer], base->object);
+			}
 
-						if (srl->mat_override) {
-							BKE_override_view_layer_datablock_add(
-							        view_layer,
-							        ID_MA,
-							        "self",
-							        (ID *)srl->mat_override);
-						}
+			if (base->flag & SELECT) {
+				base->object->flag |= SELECT;
+			}
+			else {
+				base->object->flag &= ~SELECT;
+			}
+		}
+	}
 
-						if (srl->layflag & SCE_LAY_DISABLE) {
-							view_layer->flag &= ~VIEW_LAYER_RENDER;
-						}
+	/* Re-order the nested hidden collections. */
+	CollectionChild *child_parent = collection_master->children.first;
+	Collection *collection_parent = (child_parent) ? child_parent->collection : NULL;
 
-						if ((srl->layflag & SCE_LAY_FRS) == 0) {
-							view_layer->flag &= ~VIEW_LAYER_FREESTYLE;
-						}
+	for (int layer = 0; layer < 20; layer++) {
+		if (collections[DO_VERSION_COLLECTION_VISIBLE].created & (1 << layer)) {
+			CollectionChild *hide_child = BLI_findptr(&collection_parent->children, collections[DO_VERSION_COLLECTION_HIDE].collections[layer], offsetof(CollectionChild, collection));
 
-						/* XXX If we are to keep layflag it should be merged with flag (dfelinto). */
-						view_layer->layflag = srl->layflag;
-						/* XXX Not sure if we should keep the passes (dfelinto). */
-						view_layer->passflag = srl->passflag;
-						view_layer->pass_xor = srl->pass_xor;
-						view_layer->pass_alpha_threshold = srl->pass_alpha_threshold;
+			if ((collections[DO_VERSION_COLLECTION_HIDE].created & (1 << layer)) &&
+				(hide_child != collection_parent->children.first))
+			{
+				BLI_listbase_swaplinks(
+						&collection_parent->children,
+						hide_child,
+						collection_parent->children.first);
+			}
 
-						BKE_freestyle_config_free(&view_layer->freestyle_config, true);
-						view_layer->freestyle_config = srl->freestyleConfig;
-						view_layer->id_properties = srl->prop;
+			CollectionChild *hide_all_child = BLI_findptr(&collection_parent->children, collections[DO_VERSION_COLLECTION_HIDE_ALL].collections[layer], offsetof(CollectionChild, collection));
 
-						/* unlink master collection  */
-						BKE_collection_unlink(view_layer, view_layer->layer_collections.first);
+			if ((collections[DO_VERSION_COLLECTION_HIDE_ALL].created & (1 << layer)) &&
+				(hide_all_child != collection_parent->children.last))
+			{
+				BLI_listbase_swaplinks(
+						&collection_parent->children,
+						hide_all_child,
+						collection_parent->children.last);
+			}
 
-						/* Add new collection bases. */
-						for (int layer = 0; layer < 20; layer++) {
-							if ((scene->lay & srl->lay & ~(srl->lay_exclude) & (1 << layer)) ||
-							    (srl->lay_zmask & (scene->lay | srl->lay_exclude) & (1 << layer)))
-							{
-								if (collections[DO_VERSION_COLLECTION_VISIBLE].created & (1 << layer)) {
-
-									LayerCollection *layer_collection_parent;
-									layer_collection_parent = BKE_collection_link(
-									        view_layer,
-									        collections[DO_VERSION_COLLECTION_VISIBLE].collections[layer]);
-
-									if (srl->lay_zmask & (1 << layer)) {
-										BKE_override_layer_collection_boolean_add(
-										        layer_collection_parent,
-										        ID_OB,
-										        "cycles.is_holdout",
-										        true);
-									}
-
-									if ((srl->lay & (1 << layer)) == 0) {
-										BKE_override_layer_collection_boolean_add(
-										        layer_collection_parent,
-										        ID_OB,
-										        "cycles_visibility.camera",
-										        false);
-									}
-
-									LayerCollection *layer_collection_child;
-									layer_collection_child = layer_collection_parent->layer_collections.first;
-
-									for (int j = 1; j < 4; j++) {
-										if (collections[j].created & (1 << layer)) {
-											layer_collection_child->flag = COLLECTION_VIEWPORT |
-											                               COLLECTION_RENDER |
-											                               collections[j].flag_render;
-											layer_collection_child = layer_collection_child->next;
-										}
-									}
-									BLI_assert(layer_collection_child == NULL);
-								}
-							}
-						}
+			child_parent = child_parent->next;
+			collection_parent = (child_parent) ? child_parent->collection : NULL;
+		}
+	}
+	BLI_assert(collection_parent == NULL);
 
-						/* for convenience set the same active object in all the layers */
-						if (scene->basact) {
-							view_layer->basact = BKE_view_layer_base_find(view_layer, scene->basact->object);
-						}
+	/* Handle legacy render layers. */
+	bool have_override = false;
 
-						for (Base *base = view_layer->object_bases.first; base; base = base->next) {
-							if ((base->flag & BASE_SELECTABLED) && (base->object->flag & SELECT)) {
-								base->flag |= BASE_SELECTED;
-							}
-						}
-					}
-				}
-				BLI_freelistN(&scene->r.layers);
+	for (SceneRenderLayer *srl = scene->r.layers.first; srl; srl = srl->next) {
+		ViewLayer *view_layer = BKE_view_layer_add(scene, srl->name);
 
-				ViewLayer *view_layer = BKE_view_layer_add(scene, "Viewport");
-				/* If we ported all the original render layers, we don't need to make the viewport layer renderable. */
-				if (!BLI_listbase_is_single(&scene->view_layers)) {
-					view_layer->flag &= ~VIEW_LAYER_RENDER;
-				}
+		if (srl->samples != 0) {
+			have_override = true;
 
-				/* If layer was not set, disable it. */
-				LayerCollection *layer_collection_parent;
-				layer_collection_parent =
-					((LayerCollection *)view_layer->layer_collections.first)->layer_collections.first;
+			/* It is up to the external engine to handle
+			 * its own doversion in this case. */
+			BKE_override_view_layer_int_add(
+					view_layer,
+					ID_SCE,
+					"samples",
+					srl->samples);
+		}
 
-				for (int layer = 0; layer < 20; layer++) {
-					if (collections[DO_VERSION_COLLECTION_VISIBLE].created & (1 << layer)) {
-						const bool is_disabled = (scene->lay & (1 << layer)) == 0;
+		if (srl->mat_override) {
+			have_override = true;
 
-						/* We only need to disable the parent collection. */
-						if (is_disabled) {
-							layer_collection_parent->flag |= COLLECTION_DISABLED;
-						}
+			BKE_override_view_layer_datablock_add(
+					view_layer,
+					ID_MA,
+					"self",
+					(ID *)srl->mat_override);
+		}
 
-						LayerCollection *layer_collection_child;
-						layer_collection_child = layer_collection_parent->layer_collections.first;
+		if (srl->layflag & SCE_LAY_DISABLE) {
+			view_layer->flag &= ~VIEW_LAYER_RENDER;
+		}
 
-						for (int j = 1; j < 4; j++) {
-							if (collections[j].created & (1 << layer)) {
-								layer_collection_child->flag = COLLECTION_VIEWPORT |
-								                               COLLECTION_RENDER |
-								                               collections[j].flag_viewport;
-								layer_collection_child = layer_collection_child->next;
-							}
-						}
-						BLI_assert(layer_collection_child == NULL);
-						layer_collection_parent = layer_collection_parent->next;
+		if ((srl->layflag & SCE_LAY_FRS) == 0) {
+			view_layer->flag &= ~VIEW_LAYER_FREESTYLE;
+		}
+
+		/* XXX If we are to keep layflag it should be merged with flag (dfelinto). */
+		view_layer->layflag = srl->layflag;
+		/* XXX Not sure if we should keep the passes (dfelinto). */
+		view_layer->passflag = srl->passflag;
+		view_layer->pass_xor = srl->pass_xor;
+		view_layer->pass_alpha_threshold = srl->pass_alpha_threshold;
+
+		BKE_freestyle_config_free(&view_layer->freestyle_config, true);
+		view_layer->freestyle_config = srl->freestyleConfig;
+		view_layer->id_properties = srl->prop;
+
+		/* Set exclusion and overrides. */
+		for (int layer = 0; layer < 20; layer++) {
+			if (collections[DO_VERSION_COLLECTION_VISIBLE].created & (1 << layer)) {
+				Collection *collection = collections[DO_VERSION_COLLECTION_VISIBLE].collections[layer];
+				LayerCollection *lc = BKE_layer_collection_first_from_scene_collection(view_layer, collection);
+
+				if (srl->lay_exclude & (1 << layer)) {
+					/* Disable excluded layer. */
+					have_override = true;
+					lc->flag |= LAYER_COLLECTION_EXCLUDE;
+					for (LayerCollection *nlc = lc->layer_collections.first; nlc; nlc = nlc->next) {
+						nlc->flag |= LAYER_COLLECTION_EXCLUDE;
 					}
 				}
-				BLI_assert(layer_collection_parent == NULL);
+				else if ((scene->lay & srl->lay & ~(srl->lay_exclude) & (1 << layer)) ||
+					(srl->lay_zmask & (scene->lay | srl->lay_exclude) & (1 << layer)))
+				{
+					if (srl->lay_zmask & (1 << layer)) {
+						have_override = true;
+
+						BKE_override_layer_collection_boolean_add(
+								lc,
+								ID_OB,
+								"cycles.is_holdout",
+								true);
+					}
 
-				/* convert active base */
-				if (scene->basact) {
-					view_layer->basact = BKE_view_layer_base_find(view_layer, scene->basact->object);
-				}
+					if ((srl->lay & (1 << layer)) == 0) {
+						have_override = true;
 
-				/* convert selected bases */
-				for (Base *base = view_layer->object_bases.first; base; base = base->next) {
-					if ((base->flag & BASE_SELECTABLED) && (base->object->flag & SELECT)) {
-						base->flag |= BASE_SELECTED;
+						BKE_override_layer_collection_boolean_add(
+								lc,
+								ID_OB,
+								"cycles_visibility.camera",
+								false);
 					}
+				}
 
-					/* keep lay around for forward compatibility (open those files in 2.79) */
-					base->lay = base->object->lay;
+				LayerCollection *nlc = lc->layer_collections.first;
+				for (int j = 1; j < 4; j++) {
+					if (collections[j].created & (1 << layer)) {
+						nlc = nlc->next;
+					}
 				}
+				BLI_assert(nlc == NULL);
+			}
+		}
+
+		/* for convenience set the same active object in all the layers */
+		if (scene->basact) {
+			view_layer->basact = BKE_view_layer_base_find(view_layer, scene->basact->object);
+		}
+
+		for (Base *base = view_layer->object_bases.first; base; base = base->next) {
+			if ((base->flag & BASE_SELECTABLED) && (base->object->flag & SELECT)) {
+				base->flag |= BASE_SELECTED;
+			}
+		}
+	}
+
+	BLI_freelistN(&scene->r.layers);
+
+	/* If render layers included overrides, we also create a vanilla
+	 * viewport layer without them. */
+	if (have_override) {
+		ViewLayer *view_layer = BKE_view_layer_add(scene, "Viewport");
+
+		/* Make it first in the list. */
+		BLI_remlink(&scene->view_layers, view_layer);
+		BLI_addhead(&scene->view_layers, view_layer);
+
+		/* If we ported all the original render layers, we don't need to make the viewport layer renderable. */
+		if (!BLI_listbase_is_single(&scene->view_layers)) {
+			view_layer->flag &= ~VIEW_LAYER_RENDER;
+		}
+
+		/* convert active base */
+		if (scene->basact) {
+			view_layer->basact = BKE_view_layer_base_find(view_layer, scene->basact->object);
+		}
+
+		/* convert selected bases */
+		for (Base *base = view_layer->object_bases.first; base; base = base->next) {
+			if ((base->flag & BASE_SELECTABLED) && (base->object->flag & SELECT)) {
+				base->flag |= BASE_SELECTED;
+			}
 
-				/* remove bases once and for all */
-				for (Base *base = scene->base.first; base; base = base->next) {
-					id_us_min(&base->object->id);
+			/* keep lay around for forward compatibility (open those files in 2.79) */
+			base->lay = base->object->lay;
+		}
+	}
+
+	/* remove bases once and for all */
+	for (Base *base = scene->base.first; base; base = base->next) {
+		id_us_min(&base->object->id);
+	}
+
+	BLI_freelistN(&scene->base);
+	scene->basact = NULL;
+}
+
+void do_versions_after_linking_280(Main *main)
+{
+	bool use_collection_compat_28 = true;
+
+	if (!MAIN_VERSION_ATLEAST(main, 280, 0)) {
+		use_collection_compat_28 = false;
+
+		/* Convert group layer visibility flags to hidden nested collection. */
+		for (Collection *collection = main->collection.first; collection; collection = collection->id.next) {
+			Collection *collection_hidden = NULL;
+
+			if (collection->flag & (COLLECTION_RESTRICT_VIEW | COLLECTION_RESTRICT_RENDER)) {
+				continue;
+			}
+
+			for (CollectionObject *cob = collection->gobject.first, *cob_next = NULL; cob; cob = cob_next) {
+				cob_next = cob->next;
+				Object *ob = cob->ob;
+
+				if (!(ob->lay & collection->layer)) {
+					if (collection_hidden == NULL) {
+						collection_hidden = BKE_collection_add(main, collection, "Hidden");
+						collection_hidden->flag |= COLLECTION_RESTRICT_VIEW | COLLECTION_RESTRICT_RENDER;
+					}
+
+					BKE_collection_object_add(main, collection_hidden, ob);
+					BKE_collection_object_remove(main, collection, ob, true);
 				}
-				BLI_freelistN(&scene->base);
-				scene->basact = NULL;
 			}
+
+			/* Add fake user for all existing groups. */
+			id_fake_user_set(&collection->id);
+		}
+
+		/* Convert layers to collections. */
+		for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
+			do_version_layers_to_collections(main, scene);
 		}
 	}
 
@@ -507,11 +698,11 @@ void do_versions_after_linking_280(Main *main)
 			ViewLayer *layer = screen->scene->view_layers.first;
 
 			for (ScrArea *sa = screen->areabase.first; sa; sa = sa->next) {
-				for (SpaceLink *view_layer = sa->spacedata.first; view_layer; view_layer = view_layer->next) {
-					if (view_layer->spacetype == SPACE_OUTLINER) {
-						SpaceOops *soutliner = (SpaceOops *)view_layer;
+				for (SpaceLink *space = sa->spacedata.first; space; space = space->next) {
+					if (space->spacetype == SPACE_OUTLINER) {
+						SpaceOops *soutliner = (SpaceOops *)space;
 
-						soutliner->outlinevis = SO_COLLECTIONS;
+						soutliner->outlinevis = SO_VIEW_LAYER;
 
 						if (BLI_listbase_count_at_most(&layer->layer_collections, 2) == 1) {
 							if (soutliner->treestore == NULL) {
@@ -566,7 +757,7 @@ void do_versions_after_linking_280(Main *main)
 		}
 	}
 
-	{
+	if (!MAIN_VERSION_ATLEAST(main, 280, 4)) {
 		for (WorkSpace *workspace = main->workspaces.first; workspace; workspace = workspace->id.next) {
 			if (workspace->view_layer) {
 				/* During 2.8 work we temporarly stored view-layer in the
@@ -584,42 +775,7 @@ void do_versions_after_linking_280(Main *main)
 		}
 	}
 
-	{
-		/* Since we don't have access to FileData we check the (always valid) master collection of the group. */
-		for (Group *group = main->group.first; group; group = group->id.next) {
-			if (group->collection == NULL) {
-				BKE_group_init(group);
-				SceneCollection *sc = GROUP_MASTER_COLLECTION(group);
-				SceneCollection *sc_hidden = NULL;
-
-				for (GroupObject *go = group->gobject.first; go; go = go->next) {
-					if (go->ob->lay & group->layer) {
-						BKE_collection_object_add(&group->id, sc, go->ob);
-					}
-					else {
-						if (sc_hidden == NULL) {
-							sc_hidden = BKE_collection_add(&group->id, sc, COLLECTION_TYPE_GROUP_INTERNAL, "Hidden");
-						}
-						BKE_collection_object_add(&group->id, sc_hidden, go->ob);
-					}
-				}
-
-				if (sc_hidden != NULL) {
-					LayerCollection *layer_collection_master, *layer_collection_hidden;
-					layer_collection_master = group->view_layer->layer_collections.first;
-					layer_collection_hidden = layer_collection_master->layer_collections.first;
-					layer_collection_hidden->flag |= COLLECTION_DISABLED;
-				}
-			}
-
-			GroupObject *go;
-			while ((go = BLI_pophead(&group->gobject))) {
-				MEM_freeN(go);
-			}
-		}
-	}
-
-	{
+	if (!MAIN_VERSION_ATLEAST(main, 280, 4)) {
 		for (Object *object = main->object.first; object; object = object->id.next) {
 #ifndef VERSION_280_SUBVERSION_4
 			/* If any object already has an initialized value for
@@ -687,38 +843,26 @@ void do_versions_after_linking_280(Main *main)
 			}
 		}
 	}
-}
 
-static void do_version_view_layer_visibility(ViewLayer *view_layer)
-{
-	LayerCollection *layer_collection;
-	for (layer_collection = view_layer->layer_collections.first;
-	     layer_collection;
-	     layer_collection = layer_collection->next)
-	{
-		if (layer_collection->flag & COLLECTION_DISABLED) {
-			BKE_collection_enable(view_layer, layer_collection);
-			layer_collection->flag &= ~COLLECTION_DISABLED;
+#ifdef USE_COLLECTION_COMPAT_28
+	if (use_collection_compat_28 && !MAIN_VERSION_ATLEAST(main, 280, 14)) {
+		for (Collection *group = main->collection.first; group; group = group->id.next) {
+			do_version_group_collection_to_collection(main, group);
 		}
 
-		if ((layer_collection->flag & (1 << 0)) == 0) { /* !COLLECTION_VISIBLE */
-			layer_collection->flag |= COLLECTION_DISABLED;
+		for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
+			do_version_scene_collection_to_collection(main, scene);
 		}
-		layer_collection->flag |= COLLECTION_VIEWPORT | COLLECTION_RENDER;
 	}
+#endif
 }
 
 void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *main)
 {
+	bool use_collection_compat_28 = true;
 
 	if (!MAIN_VERSION_ATLEAST(main, 280, 0)) {
-		if (!DNA_struct_elem_find(fd->filesdna, "Scene", "ListBase", "view_layers")) {
-			for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
-				/* Master Collection */
-				scene->collection = MEM_callocN(sizeof(SceneCollection), "Master Collection");
-				BLI_strncpy(scene->collection->name, "Master Collection", sizeof(scene->collection->name));
-			}
-		}
+		use_collection_compat_28 = false;
 
 		for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
 			scene->r.gauss = 1.5f;
@@ -835,7 +979,9 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *main)
 			printf("You need to combine transparency and emission shaders to the converted Principled shader nodes.\n");
 		}
 
-		if ((DNA_struct_elem_find(fd->filesdna, "ViewLayer", "FreestyleConfig", "freestyle_config") == false) &&
+#ifdef USE_COLLECTION_COMPAT_28
+		if (use_collection_compat_28 &&
+		    (DNA_struct_elem_find(fd->filesdna, "ViewLayer", "FreestyleConfig", "freestyle_config") == false) &&
 		    DNA_struct_elem_find(fd->filesdna, "Scene", "ListBase", "view_layers"))
 		{
 			for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
@@ -849,9 +995,11 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *main)
 				}
 			}
 		}
+#endif
 	}
 
-	if (!MAIN_VERSION_ATLEAST(main, 280, 3)) {
+#ifdef USE_COLLECTION_COMPAT_28
+	if (use_collection_compat_28 && !MAIN_VERSION_ATLEAST(main, 280, 3)) {
 		for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
 			ViewLayer *view_layer;
 			for (view_layer = scene->view_layers.first; view_layer; view_layer = view_layer->next) {
@@ -859,12 +1007,13 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *main)
 			}
 		}
 
-		for (Group *group = main->group.first; group; group = group->id.next) {
+		for (Collection *group = main->collection.first; group; group = group->id.next) {
 			if (group->view_layer != NULL) {
 				do_version_view_layer_visibility(group->view_layer);
 			}
 		}
 	}
+#endif
 
 	if (!MAIN_VERSION_ATLEAST(main, 280, 6)) {
 		if (DNA_struct_elem_find(fd->filesdna, "SpaceOops", "int", "filter") == false) {
@@ -881,14 +1030,12 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *main)
 
 							if (!ELEM(so->outlinevis,
 							          SO_SCENES,
-							          SO_GROUPS,
 							          SO_LIBRARIES,
 							          SO_SEQUENCE,
 							          SO_DATA_API,
-							          SO_ID_ORPHANS,
-							          SO_COLLECTIONS))
+							          SO_ID_ORPHANS))
 							{
-								so->outlinevis = SO_COLLECTIONS;
+								so->outlinevis = SO_VIEW_LAYER;
 							}
 						}
 					}
@@ -1079,7 +1226,7 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *main)
 		}
 	}
 
-	{
+	if (!MAIN_VERSION_ATLEAST(main, 280, 14)) {
 		if (!DNA_struct_elem_find(fd->filesdna, "Scene", "SceneDisplay", "display")) {
 			/* Initialize new scene.SceneDisplay */
 			for (Scene *scene = main->scene.first; scene; scene = scene->id.next) {
@@ -1309,6 +1456,7 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *main)
 						if (sl->spacetype == SPACE_OUTLINER) {
 							SpaceOops *soops = (SpaceOops *)sl;
 							soops->filter_id_type = ID_GR;
+							soops->outlinevis = SO_VIEW_LAYER;
 						}
 					}
 				}
diff --git a/source/blender/blenloader/intern/versioning_legacy.c b/source/blender/blenloader/intern/versioning_legacy.c
index 57530c6a004..9e0c3f3ccdc 100644
--- a/source/blender/blenloader/intern/versioning_legacy.c
+++ b/source/blender/blenloader/intern/versioning_legacy.c
@@ -1661,7 +1661,7 @@ void blo_do_versions_pre250(FileData *fd, Library *lib, Main *main)
 		Curve *cu;
 		Material *ma;
 		Mesh *me;
-		Group *group;
+		Collection *collection;
 		Nurb *nu;
 		BezTriple *bezt;
 		BPoint *bp;
@@ -1818,9 +1818,9 @@ void blo_do_versions_pre250(FileData *fd, Library *lib, Main *main)
 		for (me = main->mesh.first; me; me = me->id.next)
 			customdata_version_242(me);
 
-		for (group = main->group.first; group; group = group->id.next)
-			if (group->layer == 0)
-				group->layer = (1 << 20) - 1;
+		for (collection = main->collection.first; collection; collection = collection->id.next)
+			if (collection->layer == 0)
+				collection->layer = (1 << 20) - 1;
 
 		/* now, subversion control! */
 		if (main->subversionfile < 3) {
@@ -2471,7 +2471,7 @@ void blo_do_versions_pre250(FileData *fd, Library *lib, Main *main)
 		idproperties_fix_group_lengths(main->vfont);
 		idproperties_fix_group_lengths(main->text);
 		idproperties_fix_group_lengths(main->sound);
-		idproperties_fix_group_lengths(main->group);
+		idproperties_fix_group_lengths(main->collection);
 		idproperties_fix_group_lengths(main->armature);
 		idproperties_fix_group_lengths(main->action);
 		idproperties_fix_group_lengths(main->nodetree);
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index 507fe2e082c..8ea1205be38 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -162,9 +162,9 @@
 #include "BKE_blender_version.h"
 #include "BKE_bpath.h"
 #include "BKE_curve.h"
+#include "BKE_collection.h"
 #include "BKE_constraint.h"
 #include "BKE_global.h" // for G
-#include "BKE_group.h"
 #include "BKE_idcode.h"
 #include "BKE_library.h" // for  set_listbasepointers
 #include "BKE_library_override.h"
@@ -1380,13 +1380,13 @@ static void write_particlesettings(WriteData *wd, ParticleSettings *part)
 			if (dw->ob != NULL) {
 				dw->index = 0;
 				if (part->dup_group) { /* can be NULL if lining fails or set to None */
-					FOREACH_GROUP_OBJECT_BEGIN(part->dup_group, object)
+					FOREACH_COLLECTION_OBJECT_RECURSIVE_BEGIN(part->dup_group, object)
 					{
 						if (object != dw->ob) {
 							dw->index++;
 						}
 					}
-					FOREACH_GROUP_OBJECT_END;
+					FOREACH_COLLECTION_OBJECT_RECURSIVE_END;
 				}
 			}
 			writestruct(wd, DATA, ParticleDupliWeight, 1, dw);
@@ -2356,6 +2356,31 @@ static void write_lamp(WriteData *wd, Lamp *la)
 	}
 }
 
+static void write_collection_nolib(WriteData *wd, Collection *collection)
+{
+	/* Shared function for collection datablocks and scene master collection. */
+	write_previews(wd, collection->preview);
+
+	for (CollectionObject *cob = collection->gobject.first; cob; cob = cob->next) {
+		writestruct(wd, DATA, CollectionObject, 1, cob);
+	}
+
+	for (CollectionChild *child = collection->children.first; child; child = child->next) {
+		writestruct(wd, DATA, CollectionChild, 1, child);
+	}
+}
+
+static void write_collection(WriteData *wd, Collection *collection)
+{
+	if (collection->id.us > 0 || wd->use_memfile) {
+		/* write LibData */
+		writestruct(wd, ID_GR, Collection, 1, collection);
+		write_iddata(wd, &collection->id);
+
+		write_collection_nolib(wd, collection);
+	}
+}
+
 static void write_sequence_modifiers(WriteData *wd, ListBase *modbase)
 {
 	SequenceModifierData *smd;
@@ -2397,24 +2422,11 @@ static void write_paint(WriteData *wd, Paint *p)
 	}
 }
 
-static void write_scene_collection(WriteData *wd, SceneCollection *sc)
-{
-	writestruct(wd, DATA, SceneCollection, 1, sc);
-
-	writelist(wd, DATA, LinkData, &sc->objects);
-
-	for (SceneCollection *nsc = sc->scene_collections.first; nsc; nsc = nsc->next) {
-		write_scene_collection(wd, nsc);
-	}
-}
-
 static void write_layer_collections(WriteData *wd, ListBase *lb)
 {
 	for (LayerCollection *lc = lb->first; lc; lc = lc->next) {
 		writestruct(wd, DATA, LayerCollection, 1, lc);
 
-		writelist(wd, DATA, LinkData, &lc->object_bases);
-
 		write_layer_collections(wd, &lc->layer_collections);
 	}
 }
@@ -2623,12 +2635,16 @@ static void write_scene(WriteData *wd, Scene *sce)
 
 	write_previews(wd, sce->preview);
 	write_curvemapping_curves(wd, &sce->r.mblur_shutter_curve);
-	write_scene_collection(wd, sce->collection);
 
 	for (ViewLayer *view_layer = sce->view_layers.first; view_layer; view_layer = view_layer->next) {
 		write_view_layer(wd, view_layer);
 	}
 
+	if (sce->master_collection) {
+		writestruct(wd, DATA, Collection, 1, sce->master_collection);
+		write_collection_nolib(wd, sce->master_collection);
+	}
+
 	/* Freed on doversion. */
 	BLI_assert(sce->layer_properties == NULL);
 }
@@ -3046,19 +3062,6 @@ static void write_probe(WriteData *wd, LightProbe *prb)
 	}
 }
 
-static void write_group(WriteData *wd, Group *group)
-{
-	if (group->id.us > 0 || wd->use_memfile) {
-		/* write LibData */
-		writestruct(wd, ID_GR, Group, 1, group);
-		write_iddata(wd, &group->id);
-
-		write_previews(wd, group->preview);
-		write_scene_collection(wd, group->collection);
-		write_view_layer(wd, group->view_layer);
-	}
-}
-
 static void write_nodetree(WriteData *wd, bNodeTree *ntree)
 {
 	if (ntree->id.us > 0 || wd->use_memfile) {
@@ -3859,7 +3862,7 @@ static bool write_file_handle(
 						write_sound(wd, (bSound *)id);
 						break;
 					case ID_GR:
-						write_group(wd, (Group *)id);
+						write_collection(wd, (Collection *)id);
 						break;
 					case ID_AR:
 						write_armature(wd, (bArmature *)id);