Better fix for T47787 - remove extra user due to 'user_one' as soon as we increase 'real' user count.

This has several benefits:
* User count remains coherent, regardless of the order in which you use 'user_one' & real refcounting users
  (i.e. if you add to group, and then link in scene, or the reverse, you now always get same final user count).
* Avoids the need to check for potential 'user_one' extra user in count in several places in code (e.g. when
  making IDs single users...).
* Users won't wonder why they cannot make 'single user' and ID even though its user count shows '2'!
* readfile.c now always uses code from BKE's library.c when modifying id->us. Which means we can consider
  (asside from assignment during initialization) that id->us is read-only outside of library.c context.

Note that this commit reverts previous one (rB6b1d77a8052b) - please **do not** backport this one in 2.77.

5 files changed, 27 insertions, 10 deletions

diff --git a/source/blender/blenkernel/BKE_library.h b/source/blender/blenkernel/BKE_library.h
index 606edd9cc3a..21585a160dd 100644
--- a/source/blender/blenkernel/BKE_library.h
+++ b/source/blender/blenkernel/BKE_library.h
@@ -73,6 +73,7 @@ void id_lib_extern(struct ID *id);
 void BKE_library_filepath_set(struct Library *lib, const char *filepath);
 void id_us_ensure_real(struct ID *id);
 void id_us_clear_real(struct ID *id);
+void id_us_plus_no_lib(struct ID *id);
 void id_us_plus(struct ID *id);
 void id_us_min(struct ID *id);
 void id_fake_user_set(struct ID *id);
diff --git a/source/blender/blenkernel/intern/library.c b/source/blender/blenkernel/intern/library.c
index c04eda00904..6d7a61534a8 100644
--- a/source/blender/blenkernel/intern/library.c
+++ b/source/blender/blenkernel/intern/library.c
@@ -194,11 +194,29 @@ void id_us_clear_real(ID *id)
 	}
 }
 
+/* Same as \a id_us_plus, but does not handle lib indirect -> extern.
+ * Only used by readfile.c so far, but simpler/safer to keep it here nontheless. */
+void id_us_plus_no_lib(ID *id)
+{
+	if (id) {
+		if ((id->tag & LIB_TAG_EXTRAUSER) && (id->tag & LIB_TAG_EXTRAUSER_SET)) {
+			BLI_assert(id->us >= 1);
+			/* No need to increase count, just tag extra user as no more set.
+			 * Avoids annoying & inconsistent +1 in user count. */
+			id->tag &= ~LIB_TAG_EXTRAUSER_SET;
+		}
+		else {
+			BLI_assert(id->us >= 0);
+			id->us++;
+		}
+	}
+}
+
+
 void id_us_plus(ID *id)
 {
 	if (id) {
-		BLI_assert(id->us >= 0);
-		id->us++;
+		id_us_plus_no_lib(id);
 		id_lib_extern(id);
 	}
 }
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 375837437d8..8b41c618c99 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -1497,8 +1497,7 @@ static void *newlibadr_us(FileData *fd, void *lib, void *adr)	/* increases user
 {
 	ID *id = newlibadr(fd, lib, adr);
 	
-	if (id)
-		id->us++;
+	id_us_plus_no_lib(id);
 	
 	return id;
 }
@@ -4640,7 +4639,7 @@ static void lib_link_modifiers__linkModifiers(
 
 	*idpoin = newlibadr(fd, ob->id.lib, *idpoin);
 	if (*idpoin != NULL && (cd_flag & IDWALK_USER) != 0) {
-		(*idpoin)->us++;
+		id_us_plus_no_lib(*idpoin);
 	}
 }
 static void lib_link_modifiers(FileData *fd, Object *ob)
@@ -5638,7 +5637,7 @@ static void lib_link_scene(FileData *fd, Main *main)
 						seq->sound = newlibadr(fd, sce->id.lib, seq->sound);
 					}
 					if (seq->sound) {
-						seq->sound->id.us++;
+						id_us_plus_no_lib((ID *)seq->sound);
 						seq->scene_sound = BKE_sound_add_scene_sound_defaults(sce, seq);
 					}
 				}
@@ -9580,7 +9579,7 @@ static void give_base_to_objects(Main *mainvar, Scene *scene, View3D *v3d, Libra
 				base->flag = ob->flag;
 
 				CLAMP_MIN(ob->id.us, 0);
-				ob->id.us += 1;
+				id_us_plus_no_lib((ID *)ob);
 
 				ob->id.tag &= ~LIB_TAG_INDIRECT;
 				ob->id.tag |= LIB_TAG_EXTERN;
@@ -9704,7 +9703,7 @@ static void link_object_postprocess(ID *id, Scene *scene, View3D *v3d, const sho
 		base->lay = ob->lay;
 		base->object = ob;
 		base->flag = ob->flag;
-		ob->id.us++;
+		id_us_plus_no_lib((ID *)ob);
 
 		if (flag & FILE_AUTOSELECT) {
 			base->flag |= SELECT;
diff --git a/source/blender/editors/object/object_relations.c b/source/blender/editors/object/object_relations.c
index 0422ac61c69..1a3209a8ca8 100644
--- a/source/blender/editors/object/object_relations.c
+++ b/source/blender/editors/object/object_relations.c
@@ -1749,7 +1749,7 @@ static void single_object_users(Main *bmain, Scene *scene, View3D *v3d, const in
 		ob = base->object;
 
 		if ((base->flag & flag) == flag) {
-			if (ob->id.lib == NULL && ID_REFCOUNT_USERS(ob) > 1) {
+			if (ob->id.lib == NULL && ob->id.us > 1) {
 				/* base gets copy of object */
 				obn = BKE_object_copy(ob);
 				base->object = obn;
diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index eff68521b76..0bf3c350263 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -260,7 +260,6 @@ typedef struct PreviewImage {
 
 #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_REFCOUNT_USERS(id) (((ID *)id)->us - ((((ID *)id)->tag & LIB_TAG_EXTRAUSER_SET) ? 1 : 0) - ID_FAKE_USERS(id))
 
 #define ID_CHECK_UNDO(id) ((GS((id)->name) != ID_SCR) && (GS((id)->name) != ID_WM))