ID-Remap - Step one: core work (cleanup and rework of generic ID datablock handling).

This commit changes a lot of how IDs are handled internally, especially the unlinking/freeing
processes. So far, this was very fuzy, to summarize cleanly deleting or replacing a datablock
was pretty much impossible, except for a few special cases.

Also, unlinking was handled by each datatype, in a rather messy and prone-to-errors way (quite
a few ID usages were missed or wrongly handled that way).

One of the main goal of id-remap branch was to cleanup this, and fatorize ID links handling
by using library_query utils to allow generic handling of those, which is now the case
(now, generic ID links handling is only "knwon" from readfile.c and library_query.c).

This commit also adds backends to allow live replacement and deletion of datablocks in Blender
(so-called 'remapping' process, where we replace all usages of a given ID pointer by a new one,
or NULL one in case of unlinking).

This will allow nice new features, like ability to easily reload or relocate libraries, real immediate
deletion of datablocks in blender, replacement of one datablock by another, etc.
Some of those are for next commits.

A word of warning: this commit is highly risky, because it affects potentially a lot in Blender core.
Though it was tested rather deeply, being totally impossible to check all possible ID usage cases,
it's likely there are some remaining issues and bugs in new code... Please report them! ;)

Review task: D2027 (https://developer.blender.org/D2027).
Reviewed by campbellbarton, thanks a bunch.

31 files changed, 383 insertions, 139 deletions

diff --git a/source/blender/editors/animation/anim_channels_edit.c b/source/blender/editors/animation/anim_channels_edit.c
index 8822c8511de..c98470fb194 100644
--- a/source/blender/editors/animation/anim_channels_edit.c
+++ b/source/blender/editors/animation/anim_channels_edit.c
@@ -2119,7 +2119,7 @@ static int animchannels_clean_empty_exec(bContext *C, wmOperator *UNUSED(op))
 		
 		/* remove AnimData? */
 		if (action_empty && nla_empty && drivers_empty) {
-			BKE_animdata_free(id);
+			BKE_animdata_free(id, true);
 		}
 	}
 	
diff --git a/source/blender/editors/include/ED_buttons.h b/source/blender/editors/include/ED_buttons.h
index 9a987d7618c..64c16605dec 100644
--- a/source/blender/editors/include/ED_buttons.h
+++ b/source/blender/editors/include/ED_buttons.h
@@ -37,6 +37,4 @@ bool ED_texture_context_check_particles(const struct bContext *C);
 bool ED_texture_context_check_linestyle(const struct bContext *C);
 bool ED_texture_context_check_others(const struct bContext *C);
 
-void ED_buttons_id_unref(struct SpaceButs *sbuts, const struct ID *id);
-
 #endif /*  __ED_BUTTONS_H__ */
diff --git a/source/blender/editors/include/ED_node.h b/source/blender/editors/include/ED_node.h
index 7fe9a0c320c..f7b9d6b4f9e 100644
--- a/source/blender/editors/include/ED_node.h
+++ b/source/blender/editors/include/ED_node.h
@@ -103,8 +103,6 @@ void ED_node_set_active(struct Main *bmain, struct bNodeTree *ntree, struct bNod
 
 void ED_node_composite_job(const struct bContext *C, struct bNodeTree *nodetree, struct Scene *scene_owner);
 
-void ED_node_id_unref(struct SpaceNode *snode, const ID *id);
-
 /* node_ops.c */
 void ED_operatormacros_node(void);
 
diff --git a/source/blender/editors/include/ED_outliner.h b/source/blender/editors/include/ED_outliner.h
index af4af8e2f5d..73ee2542247 100644
--- a/source/blender/editors/include/ED_outliner.h
+++ b/source/blender/editors/include/ED_outliner.h
@@ -27,10 +27,4 @@
 #ifndef __ED_OUTLINER_H__
 #define __ED_OUTLINER_H__
 
-struct ID;
-struct SpaceOops;
-
-/* Used to check whether a given texture context is valid in current context. */
-void ED_outliner_id_unref(struct SpaceOops *so, const struct ID *id);
-
 #endif /*  __ED_OUTLINER_H__ */
diff --git a/source/blender/editors/include/ED_util.h b/source/blender/editors/include/ED_util.h
index f143ea478c6..b6b80b93e0b 100644
--- a/source/blender/editors/include/ED_util.h
+++ b/source/blender/editors/include/ED_util.h
@@ -43,7 +43,7 @@ void    ED_editors_exit(struct bContext *C);
 
 bool    ED_editors_flush_edits(const struct bContext *C, bool for_render);
 
-void ED_spacedata_id_unref(struct SpaceLink *sl, const struct ID *id);
+void    ED_spacedata_id_remap(struct ScrArea *sa, struct SpaceLink *sl, struct ID *old_id, struct ID *new_id);
 
 void    ED_OT_flush_edits(struct wmOperatorType *ot);
 
diff --git a/source/blender/editors/include/ED_view3d.h b/source/blender/editors/include/ED_view3d.h
index c23c2eed890..baab6b6100d 100644
--- a/source/blender/editors/include/ED_view3d.h
+++ b/source/blender/editors/include/ED_view3d.h
@@ -403,4 +403,6 @@ void ED_view3d_shade_update(struct Main *bmain, struct Scene *scene, struct View
 #define V3D_IS_ZBUF(v3d) \
 	(((v3d)->flag & V3D_ZBUF_SELECT) && ((v3d)->drawtype > OB_WIRE))
 
+void ED_view3d_id_remap(struct View3D *v3d, const struct ID *old_id, struct ID *new_id);
+
 #endif /* __ED_VIEW3D_H__ */
diff --git a/source/blender/editors/mesh/editmesh_undo.c b/source/blender/editors/mesh/editmesh_undo.c
index 8b16b2a977e..62656d75b9a 100644
--- a/source/blender/editors/mesh/editmesh_undo.c
+++ b/source/blender/editors/mesh/editmesh_undo.c
@@ -637,7 +637,7 @@ static void free_undo(void *um_v)
 		MEM_freeN(me->key);
 	}
 
-	BKE_mesh_free(me, false);
+	BKE_mesh_free(me);
 	MEM_freeN(me);
 }
 
diff --git a/source/blender/editors/object/object_add.c b/source/blender/editors/object/object_add.c
index 09c9442db54..f85c76291cd 100644
--- a/source/blender/editors/object/object_add.c
+++ b/source/blender/editors/object/object_add.c
@@ -1112,7 +1112,6 @@ void ED_base_object_free_and_unlink(Main *bmain, Scene *scene, Base *base)
 	BKE_scene_base_unlink(scene, base);
 	object_delete_check_glsl_update(base->object);
 	BKE_libblock_free_us(bmain, base->object);
-	if (scene->basact == base) scene->basact = NULL;
 	MEM_freeN(base);
 }
 
@@ -1288,7 +1287,7 @@ static void make_object_duplilist_real(bContext *C, Scene *scene, Base *base,
 		basen->object = ob;
 
 		/* make sure apply works */
-		BKE_animdata_free(&ob->id);
+		BKE_animdata_free(&ob->id, true);
 		ob->adt = NULL;
 
 		/* Proxies are not to be copied. */
@@ -1380,7 +1379,6 @@ static void make_object_duplilist_real(bContext *C, Scene *scene, Base *base,
 		}
 	}
 
-	/* The same how BKE_object_unlink detects which object proxies to clear. */
 	if (base->object->transflag & OB_DUPLIGROUP && base->object->dup_group) {
 		for (object = bmain->object.first; object; object = object->id.next) {
 			if (object->proxy_group == base->object) {
diff --git a/source/blender/editors/object/object_group.c b/source/blender/editors/object/object_group.c
index 76a8a68c42d..2b87a890f0f 100644
--- a/source/blender/editors/object/object_group.c
+++ b/source/blender/editors/object/object_group.c
@@ -43,6 +43,7 @@
 #include "BKE_depsgraph.h"
 #include "BKE_group.h"
 #include "BKE_library.h"
+#include "BKE_library_remap.h"
 #include "BKE_main.h"
 #include "BKE_report.h"
 #include "BKE_object.h"
@@ -527,7 +528,8 @@ static int group_unlink_exec(bContext *C, wmOperator *UNUSED(op))
 	if (!group)
 		return OPERATOR_CANCELLED;
 
-	BKE_group_unlink(bmain, group);
+	BKE_libblock_unlink(bmain, group, false);
+	BKE_libblock_free(bmain, group);
 
 	WM_event_add_notifier(C, NC_OBJECT | ND_DRAW, NULL);
 
diff --git a/source/blender/editors/render/render_preview.c b/source/blender/editors/render/render_preview.c
index f4260a0cd33..132c3fa5438 100644
--- a/source/blender/editors/render/render_preview.c
+++ b/source/blender/editors/render/render_preview.c
@@ -70,6 +70,7 @@
 #include "BKE_icons.h"
 #include "BKE_lamp.h"
 #include "BKE_library.h"
+#include "BKE_library_remap.h"
 #include "BKE_main.h"
 #include "BKE_material.h"
 #include "BKE_node.h"
@@ -830,7 +831,7 @@ static void shader_preview_free(void *customdata)
 		/* get rid of copied material */
 		BLI_remlink(&pr_main->mat, sp->matcopy);
 		
-		BKE_material_free_ex(sp->matcopy, false);
+		BKE_material_free(sp->matcopy);
 
 		properties = IDP_GetProperties((ID *)sp->matcopy, false);
 		if (properties) {
@@ -862,7 +863,9 @@ static void shader_preview_free(void *customdata)
 		
 		/* get rid of copied world */
 		BLI_remlink(&pr_main->world, sp->worldcopy);
-		BKE_world_free_ex(sp->worldcopy, true); /* [#32865] - we need to unlink the texture copies, unlike for materials */
+		/* T32865 - we need to unlink the texture copies, unlike for materials */
+		BKE_libblock_relink_ex(sp->worldcopy, NULL, NULL, true);
+		BKE_world_free(sp->worldcopy);
 		
 		properties = IDP_GetProperties((ID *)sp->worldcopy, false);
 		if (properties) {
@@ -878,6 +881,7 @@ static void shader_preview_free(void *customdata)
 		
 		/* get rid of copied lamp */
 		BLI_remlink(&pr_main->lamp, sp->lampcopy);
+		BKE_libblock_relink_ex(sp->lampcopy, NULL, NULL, true);
 		BKE_lamp_free(sp->lampcopy);
 		
 		properties = IDP_GetProperties((ID *)sp->lampcopy, false);
diff --git a/source/blender/editors/screen/screen_edit.c b/source/blender/editors/screen/screen_edit.c
index a459f982ada..62aeca4b9d1 100644
--- a/source/blender/editors/screen/screen_edit.c
+++ b/source/blender/editors/screen/screen_edit.c
@@ -45,6 +45,7 @@
 #include "BKE_image.h"
 #include "BKE_global.h"
 #include "BKE_library.h"
+#include "BKE_library_remap.h"
 #include "BKE_main.h"
 #include "BKE_node.h"
 #include "BKE_screen.h"
@@ -1755,7 +1756,9 @@ bool ED_screen_delete_scene(bContext *C, Scene *scene)
 
 	ED_screen_set_scene(C, CTX_wm_screen(C), newscene);
 
-	BKE_scene_unlink(bmain, scene, newscene);
+	BKE_libblock_remap(bmain, scene, newscene, ID_REMAP_SKIP_INDIRECT_USAGE | ID_REMAP_SKIP_NEVER_NULL_USAGE);
+
+	BKE_libblock_free(bmain, scene);
 
 	return true;
 }
diff --git a/source/blender/editors/sound/sound_ops.c b/source/blender/editors/sound/sound_ops.c
index a4d9a920cbb..4931426d62e 100644
--- a/source/blender/editors/sound/sound_ops.c
+++ b/source/blender/editors/sound/sound_ops.c
@@ -116,7 +116,7 @@ static int sound_open_exec(bContext *C, wmOperator *op)
 	info = AUD_getInfo(sound->playback_handle);
 
 	if (info.specs.channels == AUD_CHANNELS_INVALID) {
-		BKE_sound_delete(bmain, sound);
+		BKE_libblock_free(bmain, sound);
 		if (op->customdata) MEM_freeN(op->customdata);
 		BKE_report(op->reports, RPT_ERROR, "Unsupported audio format");
 		return OPERATOR_CANCELLED;
diff --git a/source/blender/editors/space_action/space_action.c b/source/blender/editors/space_action/space_action.c
index 60240109432..671d6bb083e 100644
--- a/source/blender/editors/space_action/space_action.c
+++ b/source/blender/editors/space_action/space_action.c
@@ -33,6 +33,7 @@
 #include <stdio.h>
 
 #include "DNA_action_types.h"
+#include "DNA_group_types.h"
 #include "DNA_scene_types.h"
 
 #include "MEM_guardedalloc.h"
@@ -614,6 +615,19 @@ static void action_refresh(const bContext *C, ScrArea *sa)
 	// XXX re-sizing y-extents of tot should go here?
 }
 
+static void action_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceAction *sact = (SpaceAction *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_GR)) {
+		return;
+	}
+
+	if ((ID *)sact->ads.filter_grp == old_id) {
+		sact->ads.filter_grp = (Group *)new_id;
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_action(void)
 {
@@ -631,7 +645,8 @@ void ED_spacetype_action(void)
 	st->keymap = action_keymap;
 	st->listener = action_listener;
 	st->refresh = action_refresh;
-	
+	st->id_remap = action_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype action region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_buttons/buttons_context.c b/source/blender/editors/space_buttons/buttons_context.c
index 42e2d6b90f0..5b03bdd7761 100644
--- a/source/blender/editors/space_buttons/buttons_context.c
+++ b/source/blender/editors/space_buttons/buttons_context.c
@@ -1180,33 +1180,3 @@ ID *buttons_context_id_path(const bContext *C)
 
 	return NULL;
 }
-
-void ED_buttons_id_unref(SpaceButs *sbuts, const ID *id)
-{
-	if (sbuts->pinid == id) {
-		sbuts->pinid = NULL;
-		sbuts->flag &= ~SB_PIN_CONTEXT;
-	}
-
-	if (sbuts->path) {
-		ButsContextPath *path = sbuts->path;
-		int i;
-
-		for (i = 0; i < path->len; i++) {
-			if (path->ptr[i].id.data == id) {
-				break;
-			}
-		}
-
-		if (i == path->len) {
-			/* pass */
-		}
-		else if (i == 0) {
-			MEM_SAFE_FREE(sbuts->path);
-		}
-		else {
-			memset(&path->ptr[i], 0, sizeof(path->ptr[i]) * (path->len - i));
-			path->len = i;
-		}
-	}
-}
diff --git a/source/blender/editors/space_buttons/space_buttons.c b/source/blender/editors/space_buttons/space_buttons.c
index 126a27c36cb..e4c23ad74f8 100644
--- a/source/blender/editors/space_buttons/space_buttons.c
+++ b/source/blender/editors/space_buttons/space_buttons.c
@@ -45,6 +45,8 @@
 #include "WM_api.h"
 #include "WM_types.h"
 
+#include "RNA_access.h"
+
 #include "buttons_intern.h"  /* own include */
 
 /* ******************** default callbacks for buttons space ***************** */
@@ -389,6 +391,59 @@ static void buttons_area_listener(bScreen *UNUSED(sc), ScrArea *sa, wmNotifier *
 		ED_area_tag_redraw(sa);
 }
 
+static void buttons_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceButs *sbuts = (SpaceButs *)slink;
+
+	if (sbuts->pinid == old_id) {
+		sbuts->pinid = new_id;
+		if (new_id == NULL) {
+			sbuts->flag &= ~SB_PIN_CONTEXT;
+		}
+	}
+
+	if (sbuts->path) {
+		ButsContextPath *path = sbuts->path;
+		int i;
+
+		for (i = 0; i < path->len; i++) {
+			if (path->ptr[i].id.data == old_id) {
+				break;
+			}
+		}
+
+		if (i == path->len) {
+			/* pass */
+		}
+		else if (new_id == NULL) {
+			if (i == 0) {
+				MEM_SAFE_FREE(sbuts->path);
+			}
+			else {
+				memset(&path->ptr[i], 0, sizeof(path->ptr[i]) * (path->len - i));
+				path->len = i;
+			}
+		}
+		else {
+			RNA_id_pointer_create(new_id, &path->ptr[i]);
+			/* There is no easy way to check/make path downwards valid, just nullify it.
+			 * Next redraw will rebuild this anyway. */
+			i++;
+			memset(&path->ptr[i], 0, sizeof(path->ptr[i]) * (path->len - i));
+			path->len = i;
+		}
+	}
+
+	if (sbuts->texuser) {
+		ButsContextTexture *ct = sbuts->texuser;
+		if ((ID *)ct->texture == old_id) {
+			ct->texture = (Tex *)new_id;
+		}
+		BLI_freelistN(&ct->users);
+		ct->user = NULL;
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_buttons(void)
 {
@@ -406,7 +461,8 @@ void ED_spacetype_buttons(void)
 	st->keymap = buttons_keymap;
 	st->listener = buttons_area_listener;
 	st->context = buttons_context;
-	
+	st->id_remap = buttons_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype buttons region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_clip/space_clip.c b/source/blender/editors/space_clip/space_clip.c
index e1d4e4fabc5..415839ab761 100644
--- a/source/blender/editors/space_clip/space_clip.c
+++ b/source/blender/editors/space_clip/space_clip.c
@@ -45,6 +45,7 @@
 
 #include "BKE_context.h"
 #include "BKE_screen.h"
+#include "BKE_library.h"
 #include "BKE_movieclip.h"
 #include "BKE_tracking.h"
 
@@ -1512,6 +1513,25 @@ static void clip_properties_region_listener(bScreen *UNUSED(sc), ScrArea *UNUSED
 
 /********************* registration ********************/
 
+static void clip_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceClip *sclip = (SpaceClip *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_MC, ID_MSK)) {
+		return;
+	}
+
+	if ((ID *)sclip->clip == old_id) {
+		sclip->clip = (MovieClip *)new_id;
+		id_us_ensure_real(new_id);
+	}
+
+	if ((ID *)sclip->mask_info.mask == old_id) {
+		sclip->mask_info.mask = (Mask *)new_id;
+		id_us_ensure_real(new_id);
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_clip(void)
 {
@@ -1531,6 +1551,7 @@ void ED_spacetype_clip(void)
 	st->context = clip_context;
 	st->dropboxes = clip_dropboxes;
 	st->refresh = clip_refresh;
+	st->id_remap = clip_id_remap;
 
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype clip region");
diff --git a/source/blender/editors/space_graph/space_graph.c b/source/blender/editors/space_graph/space_graph.c
index c6a8a9753d1..a7284694f64 100644
--- a/source/blender/editors/space_graph/space_graph.c
+++ b/source/blender/editors/space_graph/space_graph.c
@@ -33,6 +33,7 @@
 #include <stdio.h>
 
 #include "DNA_anim_types.h"
+#include "DNA_group_types.h"
 #include "DNA_scene_types.h"
 
 #include "MEM_guardedalloc.h"
@@ -627,6 +628,19 @@ static void graph_refresh(const bContext *C, ScrArea *sa)
 	}
 }
 
+static void graph_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceIpo *sgraph = (SpaceIpo *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_GR)) {
+		return;
+	}
+
+	if ((ID *)sgraph->ads->filter_grp == old_id) {
+		sgraph->ads->filter_grp = (Group *)new_id;
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_ipo(void)
 {
@@ -644,7 +658,8 @@ void ED_spacetype_ipo(void)
 	st->keymap = graphedit_keymap;
 	st->listener = graph_listener;
 	st->refresh = graph_refresh;
-	
+	st->id_remap = graph_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype graphedit region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_image/space_image.c b/source/blender/editors/space_image/space_image.c
index 168f9c0dfdf..35a658eac23 100644
--- a/source/blender/editors/space_image/space_image.c
+++ b/source/blender/editors/space_image/space_image.c
@@ -28,6 +28,7 @@
  *  \ingroup spimage
  */
 
+#include "DNA_gpencil_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_mask_types.h"
 #include "DNA_meshdata_types.h"
@@ -44,6 +45,7 @@
 #include "BKE_colortools.h"
 #include "BKE_context.h"
 #include "BKE_image.h"
+#include "BKE_library.h"
 #include "BKE_scene.h"
 #include "BKE_screen.h"
 
@@ -981,6 +983,31 @@ static void image_header_region_listener(bScreen *UNUSED(sc), ScrArea *UNUSED(sa
 	}
 }
 
+static void image_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceImage *simg = (SpaceImage *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_IM, ID_GD, ID_MSK)) {
+		return;
+	}
+
+	if ((ID *)simg->image == old_id) {
+		simg->image = (Image *)new_id;
+		id_us_ensure_real(new_id);
+	}
+
+	if ((ID *)simg->gpd == old_id) {
+		simg->gpd = (bGPdata *)new_id;
+		id_us_min(old_id);
+		id_us_plus(new_id);
+	}
+
+	if ((ID *)simg->mask_info.mask == old_id) {
+		simg->mask_info.mask = (Mask *)new_id;
+		id_us_ensure_real(new_id);
+	}
+}
+
 /**************************** spacetype *****************************/
 
 /* only called once, from space/spacetypes.c */
@@ -1002,7 +1029,8 @@ void ED_spacetype_image(void)
 	st->refresh = image_refresh;
 	st->listener = image_listener;
 	st->context = image_context;
-	
+	st->id_remap = image_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype image region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_logic/space_logic.c b/source/blender/editors/space_logic/space_logic.c
index 243a522011b..69966e9bf34 100644
--- a/source/blender/editors/space_logic/space_logic.c
+++ b/source/blender/editors/space_logic/space_logic.c
@@ -38,7 +38,10 @@
 #include "BLI_blenlib.h"
 #include "BLI_utildefines.h"
 
+#include "DNA_gpencil_types.h"
+
 #include "BKE_context.h"
+#include "BKE_library.h"
 #include "BKE_screen.h"
 
 #include "ED_space_api.h"
@@ -300,6 +303,21 @@ static void logic_header_region_draw(const bContext *C, ARegion *ar)
 
 /**************************** spacetype *****************************/
 
+static void logic_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceLogic *slog = (SpaceLogic *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_GD)) {
+		return;
+	}
+
+	if ((ID *)slog->gpd == old_id) {
+		slog->gpd = (bGPdata *)new_id;
+		id_us_min(old_id);
+		id_us_plus(new_id);
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_logic(void)
 {
@@ -317,7 +335,8 @@ void ED_spacetype_logic(void)
 	st->keymap = logic_keymap;
 	st->refresh = logic_refresh;
 	st->context = logic_context;
-	
+	st->id_remap = logic_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype logic region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_nla/space_nla.c b/source/blender/editors/space_nla/space_nla.c
index e2b36c5b5ae..3b5604087b9 100644
--- a/source/blender/editors/space_nla/space_nla.c
+++ b/source/blender/editors/space_nla/space_nla.c
@@ -33,6 +33,7 @@
 #include <stdio.h>
 
 #include "DNA_anim_types.h"
+#include "DNA_group_types.h"
 #include "DNA_scene_types.h"
 
 #include "MEM_guardedalloc.h"
@@ -501,6 +502,19 @@ static void nla_listener(bScreen *UNUSED(sc), ScrArea *sa, wmNotifier *wmn)
 	}
 }
 
+static void nla_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceNla *snla = (SpaceNla *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_GR)) {
+		return;
+	}
+
+	if ((ID *)snla->ads->filter_grp == old_id) {
+		snla->ads->filter_grp = (Group *)new_id;
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_nla(void)
 {
@@ -517,7 +531,8 @@ void ED_spacetype_nla(void)
 	st->operatortypes = nla_operatortypes;
 	st->listener = nla_listener;
 	st->keymap = nla_keymap;
-	
+	st->id_remap = nla_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype nla region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_node/node_edit.c b/source/blender/editors/space_node/node_edit.c
index 6ae72e2a164..ffe510016ff 100644
--- a/source/blender/editors/space_node/node_edit.c
+++ b/source/blender/editors/space_node/node_edit.c
@@ -740,34 +740,6 @@ void ED_node_set_active(Main *bmain, bNodeTree *ntree, bNode *node)
 	}
 }
 
-void ED_node_id_unref(SpaceNode *snode, const ID *id)
-{
-	if (GS(id->name) == ID_SCE) {
-		if (snode->id == id) {
-			/* nasty DNA logic for SpaceNode:
-			 * ideally should be handled by editor code, but would be bad level call
-			 */
-			bNodeTreePath *path, *path_next;
-			for (path = snode->treepath.first; path; path = path_next) {
-				path_next = path->next;
-				MEM_freeN(path);
-			}
-			BLI_listbase_clear(&snode->treepath);
-
-			snode->id = NULL;
-			snode->from = NULL;
-			snode->nodetree = NULL;
-			snode->edittree = NULL;
-		}
-	}
-	else if (GS(id->name) == ID_OB) {
-		if (snode->from == id) {
-			snode->flag &= ~SNODE_PIN;
-			snode->from = NULL;
-		}
-	}
-}
-
 void ED_node_post_apply_transform(bContext *UNUSED(C), bNodeTree *UNUSED(ntree))
 {
 	/* XXX This does not work due to layout functions relying on node->block,
diff --git a/source/blender/editors/space_node/space_node.c b/source/blender/editors/space_node/space_node.c
index df484724fc5..4ef703c8994 100644
--- a/source/blender/editors/space_node/space_node.c
+++ b/source/blender/editors/space_node/space_node.c
@@ -28,6 +28,7 @@
  *  \ingroup spnode
  */
 
+#include "DNA_gpencil_types.h"
 #include "DNA_lamp_types.h"
 #include "DNA_material_types.h"
 #include "DNA_node_types.h"
@@ -821,6 +822,41 @@ static int node_context(const bContext *C, const char *member, bContextDataResul
 	return 0;
 }
 
+static void node_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceNode *snode = (SpaceNode *)slink;
+
+	if (GS(old_id->name) == ID_SCE) {
+		if (snode->id == old_id) {
+			/* nasty DNA logic for SpaceNode:
+			 * ideally should be handled by editor code, but would be bad level call
+			 */
+			BLI_freelistN(&snode->treepath);
+
+			/* XXX Untested in case new_id != NULL... */
+			snode->id = new_id;
+			snode->from = NULL;
+			snode->nodetree = NULL;
+			snode->edittree = NULL;
+		}
+	}
+	else if (GS(old_id->name) == ID_OB) {
+		if (snode->from == old_id) {
+			if (new_id == NULL) {
+				snode->flag &= ~SNODE_PIN;
+			}
+			snode->from = new_id;
+		}
+	}
+	else if (GS(old_id->name) == ID_GD) {
+		if ((ID *)snode->gpd == old_id) {
+			snode->gpd = (bGPdata *)new_id;
+			id_us_min(old_id);
+			id_us_plus(new_id);
+		}
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_node(void)
 {
@@ -840,6 +876,7 @@ void ED_spacetype_node(void)
 	st->refresh = node_area_refresh;
 	st->context = node_context;
 	st->dropboxes = node_dropboxes;
+	st->id_remap = node_id_remap;
 
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype node region");
diff --git a/source/blender/editors/space_outliner/outliner_draw.c b/source/blender/editors/space_outliner/outliner_draw.c
index 554009da8be..43e9c262172 100644
--- a/source/blender/editors/space_outliner/outliner_draw.c
+++ b/source/blender/editors/space_outliner/outliner_draw.c
@@ -502,6 +502,11 @@ static void namebutton_cb(bContext *C, void *tsep, char *oldname)
 					BKE_reportf(CTX_wm_reports(C), RPT_ERROR,
 					            "Library path '%s' does not exist, correct this before saving", expanded);
 				}
+				else if (lib->id.tag & LIB_TAG_MISSING) {
+					BKE_reportf(CTX_wm_reports(C), RPT_INFO,
+					            "Library path '%s' is now valid, please reload the library", expanded);
+					lib->id.tag &= ~LIB_TAG_MISSING;
+				}
 			}
 		}
 		else {
diff --git a/source/blender/editors/space_outliner/outliner_edit.c b/source/blender/editors/space_outliner/outliner_edit.c
index 2627b978b40..8cee696b2ac 100644
--- a/source/blender/editors/space_outliner/outliner_edit.c
+++ b/source/blender/editors/space_outliner/outliner_edit.c
@@ -2079,36 +2079,3 @@ void OUTLINER_OT_group_link(wmOperatorType *ot)
 	/* properties */
 	RNA_def_string(ot->srna, "object", "Object", MAX_ID_NAME, "Object", "Target Object");
 }
-
-/******** Utils to clear any ref to freed ID... **********/
-
-void ED_outliner_id_unref(SpaceOops *so, const ID *id)
-{
-	/* Some early out checks. */
-	if (!TREESTORE_ID_TYPE(id)) {
-		return;  /* ID type is not used by outilner... */
-	}
-
-	if (so->search_tse.id == id) {
-		so->search_tse.id = NULL;
-	}
-
-	if (so->treestore) {
-		TreeStoreElem *tselem;
-		BLI_mempool_iter iter;
-		bool changed = false;
-
-		BLI_mempool_iternew(so->treestore, &iter);
-		while ((tselem = BLI_mempool_iterstep(&iter))) {
-			if (tselem->id == id) {
-				tselem->id = NULL;
-				changed = true;
-			}
-		}
-		if (so->treehash && changed) {
-			/* rebuild hash table, because it depends on ids too */
-			/* postpone a full rebuild because this can be called many times on-free */
-			so->storeflag |= SO_TREESTORE_REBUILD;
-		}
-	}
-}
diff --git a/source/blender/editors/space_outliner/outliner_intern.h b/source/blender/editors/space_outliner/outliner_intern.h
index dc81be7a8e0..2e46ffa6437 100644
--- a/source/blender/editors/space_outliner/outliner_intern.h
+++ b/source/blender/editors/space_outliner/outliner_intern.h
@@ -230,6 +230,7 @@ void OUTLINER_OT_object_operation(struct wmOperatorType *ot);
 void OUTLINER_OT_group_operation(struct wmOperatorType *ot);
 void OUTLINER_OT_lib_operation(struct wmOperatorType *ot);
 void OUTLINER_OT_id_operation(struct wmOperatorType *ot);
+void OUTLINER_OT_id_remap(struct wmOperatorType *ot);
 void OUTLINER_OT_data_operation(struct wmOperatorType *ot);
 void OUTLINER_OT_animdata_operation(struct wmOperatorType *ot);
 void OUTLINER_OT_action_set(struct wmOperatorType *ot);
diff --git a/source/blender/editors/space_outliner/outliner_tools.c b/source/blender/editors/space_outliner/outliner_tools.c
index 83677b6bd86..2a210e382a2 100644
--- a/source/blender/editors/space_outliner/outliner_tools.c
+++ b/source/blender/editors/space_outliner/outliner_tools.c
@@ -57,6 +57,7 @@
 #include "BKE_fcurve.h"
 #include "BKE_group.h"
 #include "BKE_library.h"
+#include "BKE_library_remap.h"
 #include "BKE_main.h"
 #include "BKE_report.h"
 #include "BKE_scene.h"
@@ -230,7 +231,8 @@ static void unlink_group_cb(
 	}
 	else {
 		Main *bmain = CTX_data_main(C);
-		BKE_group_unlink(bmain, group);
+		BKE_libblock_unlink(bmain, group, false);
+		BKE_libblock_free(bmain, group);
 	}
 }
 
@@ -246,7 +248,7 @@ static void unlink_world_cb(bContext *UNUSED(C), Scene *UNUSED(scene), TreeEleme
 }
 
 static void outliner_do_libdata_operation(
-        bContext *C, Scene *scene, SpaceOops *soops, ListBase *lb, 
+        bContext *C, Scene *scene, SpaceOops *soops, ListBase *lb,
         void (*operation_cb)(bContext *C, Scene *scene, TreeElement *, TreeStoreElem *, TreeStoreElem *, void *),
         void *user_data)
 {
@@ -522,8 +524,7 @@ static void group_instance_cb(bContext *C, Scene *scene, TreeElement *UNUSED(te)
  */
 void outliner_do_object_operation_ex(
         bContext *C, Scene *scene_act, SpaceOops *soops, ListBase *lb,
-        void (*operation_cb)(bContext *C, Scene *scene, TreeElement *,
-                             TreeStoreElem *, TreeStoreElem *, void *),
+        void (*operation_cb)(bContext *, Scene *, TreeElement *, TreeStoreElem *, TreeStoreElem *, void *),
         bool select_recurse)
 {
 	TreeElement *te;
@@ -565,7 +566,7 @@ void outliner_do_object_operation(
 static void clear_animdata_cb(int UNUSED(event), TreeElement *UNUSED(te),
                               TreeStoreElem *tselem, void *UNUSED(arg))
 {
-	BKE_animdata_free(tselem->id);
+	BKE_animdata_free(tselem->id, true);
 }
 
 
diff --git a/source/blender/editors/space_outliner/space_outliner.c b/source/blender/editors/space_outliner/space_outliner.c
index 1dd66366e5d..76bf9c701ed 100644
--- a/source/blender/editors/space_outliner/space_outliner.c
+++ b/source/blender/editors/space_outliner/space_outliner.c
@@ -486,6 +486,39 @@ static SpaceLink *outliner_duplicate(SpaceLink *sl)
 	return (SpaceLink *)soutlinern;
 }
 
+static void outliner_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceOops *so = (SpaceOops *)slink;
+
+	/* Some early out checks. */
+	if (!TREESTORE_ID_TYPE(old_id)) {
+		return;  /* ID type is not used by outilner... */
+	}
+
+	if (so->search_tse.id == old_id) {
+		so->search_tse.id = new_id;
+	}
+
+	if (so->treestore) {
+		TreeStoreElem *tselem;
+		BLI_mempool_iter iter;
+		bool changed = false;
+
+		BLI_mempool_iternew(so->treestore, &iter);
+		while ((tselem = BLI_mempool_iterstep(&iter))) {
+			if (tselem->id == old_id) {
+				tselem->id = new_id;
+				changed = true;
+			}
+		}
+		if (so->treehash && changed) {
+			/* rebuild hash table, because it depends on ids too */
+			/* postpone a full rebuild because this can be called many times on-free */
+			so->storeflag |= SO_TREESTORE_REBUILD;
+		}
+	}
+}
+
 /* only called once, from space_api/spacetypes.c */
 void ED_spacetype_outliner(void)
 {
@@ -502,7 +535,8 @@ void ED_spacetype_outliner(void)
 	st->operatortypes = outliner_operatortypes;
 	st->keymap = outliner_keymap;
 	st->dropboxes = outliner_dropboxes;
-	
+	st->id_remap = outliner_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype outliner region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_sequencer/space_sequencer.c b/source/blender/editors/space_sequencer/space_sequencer.c
index fce40f8ca59..a2a80297041 100644
--- a/source/blender/editors/space_sequencer/space_sequencer.c
+++ b/source/blender/editors/space_sequencer/space_sequencer.c
@@ -32,6 +32,7 @@
 #include <string.h>
 #include <stdio.h>
 
+#include "DNA_gpencil_types.h"
 #include "DNA_scene_types.h"
 #include "DNA_mask_types.h"
 
@@ -41,6 +42,7 @@
 #include "BLI_utildefines.h"
 
 #include "BKE_context.h"
+#include "BKE_library.h"
 #include "BKE_screen.h"
 #include "BKE_sequencer.h"
 #include "BKE_global.h"
@@ -687,6 +689,22 @@ static void sequencer_buttons_region_listener(bScreen *UNUSED(sc), ScrArea *UNUS
 			break;
 	}
 }
+
+static void sequencer_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceSeq *sseq = (SpaceSeq *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_GD)) {
+		return;
+	}
+
+	if ((ID *)sseq->gpd == old_id) {
+		sseq->gpd = (bGPdata *)new_id;
+		id_us_min(old_id);
+		id_us_plus(new_id);
+	}
+}
+
 /* ************************************* */
 
 /* only called once, from space/spacetypes.c */
@@ -708,6 +726,7 @@ void ED_spacetype_sequencer(void)
 	st->dropboxes = sequencer_dropboxes;
 	st->refresh = sequencer_refresh;
 	st->listener = sequencer_listener;
+	st->id_remap = sequencer_id_remap;
 
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype sequencer region");
diff --git a/source/blender/editors/space_text/space_text.c b/source/blender/editors/space_text/space_text.c
index 0a6a9a81e63..0dea59fd68c 100644
--- a/source/blender/editors/space_text/space_text.c
+++ b/source/blender/editors/space_text/space_text.c
@@ -38,6 +38,7 @@
 #include "BLI_blenlib.h"
 
 #include "BKE_context.h"
+#include "BKE_library.h"
 #include "BKE_screen.h"
 #include "BKE_text.h"
 
@@ -562,6 +563,20 @@ static void text_properties_region_draw(const bContext *C, ARegion *ar)
 	}
 }
 
+static void text_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceText *stext = (SpaceText *)slink;
+
+	if (!ELEM(GS(old_id->name), ID_GD)) {
+		return;
+	}
+
+	if ((ID *)stext->text == old_id) {
+		stext->text = (Text *)new_id;
+		id_us_ensure_real(new_id);
+	}
+}
+
 /********************* registration ********************/
 
 /* only called once, from space/spacetypes.c */
@@ -582,7 +597,8 @@ void ED_spacetype_text(void)
 	st->listener = text_listener;
 	st->context = text_context;
 	st->dropboxes = text_dropboxes;
-	
+	st->id_remap = text_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype text region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/space_view3d/space_view3d.c b/source/blender/editors/space_view3d/space_view3d.c
index fa14ca96fe2..96dda65b81d 100644
--- a/source/blender/editors/space_view3d/space_view3d.c
+++ b/source/blender/editors/space_view3d/space_view3d.c
@@ -1400,6 +1400,66 @@ static int view3d_context(const bContext *C, const char *member, bContextDataRes
 	return -1; /* found but not available */
 }
 
+static void view3d_id_remap(ScrArea *sa, SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	View3D *v3d;
+	ARegion *ar;
+	bool is_local = false;
+
+	if (!ELEM(GS(old_id->name), ID_OB, ID_MA, ID_IM, ID_MC)) {
+		return;
+	}
+
+	for (v3d = (View3D *)slink; v3d; v3d = v3d->localvd, is_local = true) {
+		if ((ID *)v3d->camera == old_id) {
+			v3d->camera = (Object *)new_id;
+			if (!new_id) {
+				for (ar = sa->regionbase.first; ar; ar = ar->next) {
+					if (ar->regiontype == RGN_TYPE_WINDOW) {
+						RegionView3D *rv3d = is_local ? ((RegionView3D *)ar->regiondata)->localvd : ar->regiondata;
+						if (rv3d && (rv3d->persp == RV3D_CAMOB)) {
+							rv3d->persp = RV3D_PERSP;
+						}
+					}
+				}
+			}
+		}
+		if ((ID *)v3d->ob_centre == old_id) {
+			v3d->ob_centre = (Object *)new_id;
+			if (new_id == NULL) {  /* Otherwise, bonename may remain valid... We could be smart and check this, too? */
+				v3d->ob_centre_bone[0] = '\0';
+			}
+		}
+
+		if ((ID *)v3d->defmaterial == old_id) {
+			v3d->defmaterial = (Material *)new_id;
+		}
+#if 0  /* XXX Deprecated? */
+		if ((ID *)v3d->gpd == old_id) {
+			v3d->gpd = (bGPData *)new_id;
+		}
+#endif
+
+		if (ELEM(GS(old_id->name), ID_IM, ID_MC)) {
+			for (BGpic *bgpic = v3d->bgpicbase.first; bgpic; bgpic = bgpic->next) {
+				if ((ID *)bgpic->ima == old_id) {
+					bgpic->ima = (Image *)new_id;
+					id_us_min(old_id);
+					id_us_plus(new_id);
+				}
+				if ((ID *)bgpic->clip == old_id) {
+					bgpic->clip = (MovieClip *)new_id;
+					id_us_min(old_id);
+					id_us_plus(new_id);
+				}
+			}
+		}
+
+		if (is_local) {
+			break;
+		}
+	}
+}
 
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_view3d(void)
@@ -1419,7 +1479,8 @@ void ED_spacetype_view3d(void)
 	st->keymap = view3d_keymap;
 	st->dropboxes = view3d_dropboxes;
 	st->context = view3d_context;
-	
+	st->id_remap = view3d_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype view3d main region");
 	art->regionid = RGN_TYPE_WINDOW;
diff --git a/source/blender/editors/util/ed_util.c b/source/blender/editors/util/ed_util.c
index 1f4ce926f16..e2f60955c81 100644
--- a/source/blender/editors/util/ed_util.c
+++ b/source/blender/editors/util/ed_util.c
@@ -57,6 +57,7 @@
 #include "BKE_multires.h"
 #include "BKE_packedFile.h"
 #include "BKE_paint.h"
+#include "BKE_screen.h"
 
 #include "ED_armature.h"
 #include "ED_buttons.h"
@@ -326,22 +327,14 @@ void ED_region_draw_mouse_line_cb(const bContext *C, ARegion *ar, void *arg_info
 /**
  * Use to free ID references within runtime data (stored outside of DNA)
  *
- * \note Typically notifiers take care of this,
- * but there are times we have to free references immediately, see: T44376
+ * \param new_id may be NULL to unlink \a old_id.
  */
-void ED_spacedata_id_unref(struct SpaceLink *sl, const ID *id)
+void ED_spacedata_id_remap(struct ScrArea *sa, struct SpaceLink *sl, ID *old_id, ID *new_id)
 {
+	SpaceType *st = BKE_spacetype_from_id(sl->spacetype);
 
-	switch (sl->spacetype) {
-		case SPACE_OUTLINER:
-			ED_outliner_id_unref((SpaceOops *)sl, id);
-			break;
-		case SPACE_BUTS:
-			ED_buttons_id_unref((SpaceButs *)sl, id);
-			break;
-		case SPACE_NODE:
-			ED_node_id_unref((SpaceNode *)sl, id);
-			break;
+	if (st && st->id_remap) {
+		st->id_remap(sa, sl, old_id, new_id);
 	}
 }