Fix T50369: Objects can't be deleted from scene when using "link group objects to scene"

Main issue here was that in old usercount system 'user_real' did simply
not allow that kind of thing to work. With new pait of 'USER_EXTRA'
tags, it becomes possible to handle the case correctly, by merely refining
checks about indirectly use objects whene removing them from a scene.

Incidently, found another related bug, 'link group objects to scene' was not
incrementing objects' usercount - bad, very very bad!

4 files changed, 15 insertions, 7 deletions

diff --git a/source/blender/blenkernel/intern/library_remap.c b/source/blender/blenkernel/intern/library_remap.c
index 4f1f6d963ed..cc7de92c96a 100644
--- a/source/blender/blenkernel/intern/library_remap.c
+++ b/source/blender/blenkernel/intern/library_remap.c
@@ -883,9 +883,10 @@ void BKE_libblock_free_us(Main *bmain, void *idv)      /* test users */
 	 *     Since only 'user_one' usage of objects is groups, and only 'real user' usage of objects is scenes,
 	 *     removing that 'user_one' tag when there is no more real (scene) users of an object ensures it gets
 	 *     fully unlinked.
+	 *     But only for local objects, not linked ones!
 	 *     Otherwise, there is no real way to get rid of an object anymore - better handling of this is TODO.
 	 */
-	if ((GS(id->name) == ID_OB) && (id->us == 1)) {
+	if ((GS(id->name) == ID_OB) && (id->us == 1) && (id->lib == NULL)) {
 		id_us_clear_real(id);
 	}
 
diff --git a/source/blender/editors/object/object_add.c b/source/blender/editors/object/object_add.c
index f42dafd094c..02b2d8492b4 100644
--- a/source/blender/editors/object/object_add.c
+++ b/source/blender/editors/object/object_add.c
@@ -1111,7 +1111,9 @@ static void object_delete_check_glsl_update(Object *ob)
 /* note: now unlinks constraints as well */
 void ED_base_object_free_and_unlink(Main *bmain, Scene *scene, Base *base)
 {
-	if (BKE_library_ID_is_indirectly_used(bmain, base->object) && ID_REAL_USERS(base->object) <= 1) {
+	if (BKE_library_ID_is_indirectly_used(bmain, base->object) &&
+	    ID_REAL_USERS(base->object) <= 1 && ID_EXTRA_USERS(base->object) == 0)
+	{
 		/* We cannot delete indirectly used object... */
 		printf("WARNING, undeletable object '%s', should have been catched before reaching this function!",
 		       base->object->id.name + 2);
@@ -1145,7 +1147,7 @@ static int object_delete_exec(bContext *C, wmOperator *op)
 			BKE_reportf(op->reports, RPT_WARNING, "Cannot delete indirectly linked object '%s'", base->object->id.name + 2);
 			continue;
 		}
-		else if (is_indirectly_used && ID_REAL_USERS(base->object) <= 1) {
+		else if (is_indirectly_used && ID_REAL_USERS(base->object) <= 1 && ID_EXTRA_USERS(base->object) == 0) {
 			BKE_reportf(op->reports, RPT_WARNING,
 			        "Cannot delete object '%s' from scene '%s', indirectly used objects need at least one user",
 			        base->object->id.name + 2, scene->id.name + 2);
@@ -1179,7 +1181,7 @@ static int object_delete_exec(bContext *C, wmOperator *op)
 				if (scene_iter != scene && !ID_IS_LINKED_DATABLOCK(scene_iter)) {
 					base_other = BKE_scene_base_find(scene_iter, base->object);
 					if (base_other) {
-						if (is_indirectly_used && ID_REAL_USERS(base->object) <= 1) {
+						if (is_indirectly_used && ID_REAL_USERS(base->object) <= 1 && ID_EXTRA_USERS(base->object) == 0) {
 							BKE_reportf(op->reports, RPT_WARNING,
 							            "Cannot delete object '%s' from scene '%s', indirectly used objects need at least one user",
 							            base->object->id.name + 2, scene_iter->id.name + 2);
diff --git a/source/blender/editors/space_outliner/outliner_tools.c b/source/blender/editors/space_outliner/outliner_tools.c
index 7739d241bd3..4eda7977622 100644
--- a/source/blender/editors/space_outliner/outliner_tools.c
+++ b/source/blender/editors/space_outliner/outliner_tools.c
@@ -411,7 +411,9 @@ static void object_delete_cb(
 			BKE_reportf(reports, RPT_WARNING, "Cannot delete indirectly linked object '%s'", base->object->id.name + 2);
 			return;
 		}
-		else if (BKE_library_ID_is_indirectly_used(bmain, base->object) && ID_REAL_USERS(base->object) <= 1) {
+		else if (BKE_library_ID_is_indirectly_used(bmain, base->object) &&
+		         ID_REAL_USERS(base->object) <= 1 && ID_EXTRA_USERS(base->object) == 0)
+		{
 			BKE_reportf(reports, RPT_WARNING,
 			            "Cannot delete object '%s' from scene '%s', indirectly used objects need at least one user",
 			            base->object->id.name + 2, scene->id.name + 2);
@@ -525,7 +527,7 @@ static void group_linkobs2scene_cb(
 		if (!base) {
 			/* link to scene */
 			base = BKE_scene_base_add(scene, gob->ob);
-			id_lib_extern((ID *)gob->ob); /* in case these are from a linked group */
+			id_us_plus(&gob->ob->id);
 		}
 		base->object->flag |= SELECT;
 		base->flag |= SELECT;
@@ -842,7 +844,9 @@ static Base *outline_delete_hierarchy(bContext *C, ReportList *reports, Scene *s
 		BKE_reportf(reports, RPT_WARNING, "Cannot delete indirectly linked object '%s'", base->object->id.name + 2);
 		return base_next;
 	}
-	else if (BKE_library_ID_is_indirectly_used(bmain, base->object) && ID_REAL_USERS(base->object) <= 1) {
+	else if (BKE_library_ID_is_indirectly_used(bmain, base->object) &&
+	         ID_REAL_USERS(base->object) <= 1 && ID_EXTRA_USERS(base->object) == 0)
+	{
 		BKE_reportf(reports, RPT_WARNING,
 		            "Cannot delete object '%s' from scene '%s', indirectly used objects need at least one user",
 		            base->object->id.name + 2, scene->id.name + 2);
diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index ed719b66eb3..2c6f3d2fc66 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -277,6 +277,7 @@ typedef enum ID_Type {
 
 #define ID_FAKE_USERS(id) ((((ID *)id)->flag & LIB_FAKEUSER) ? 1 : 0)
 #define ID_REAL_USERS(id) (((ID *)id)->us - ID_FAKE_USERS(id))
+#define ID_EXTRA_USERS(id) (((ID *)id)->tag & LIB_TAG_EXTRAUSER ? 1 : 0)
 
 #define ID_CHECK_UNDO(id) ((GS((id)->name) != ID_SCR) && (GS((id)->name) != ID_WM))