Split id->flag in two, persistent flags and runtime tags.

This is purely internal sanitizing/cleanup, no change in behavior is expected at all.

This change was also needed because we were getting short on ID flags, and
future enhancement of 'user_one' ID behavior requires two new ones.

id->flag remains for persistent data (fakeuser only, so far!), this also allows us
100% backward & forward compatibility.

New id->tag is used for most flags. Though written in .blend files, its content
is cleared at read time.

Note that .blend file version was bumped, so that we can clear runtimeflags from
old .blends, important in case we add new persistent flags in future.

Also, behavior of tags (either status ones, or whether they need to be cleared before/after use)
has been added as comments to their declaration.

Reviewers: sergey, campbellbarton

Differential Revision: https://developer.blender.org/D1683

4 files changed, 125 insertions, 113 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 177055e7206..30faa3709ba 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -2158,8 +2158,8 @@ static void lib_link_brush(FileData *fd, Main *main)
 	
 	/* only link ID pointers */
 	for (brush = main->brush.first; brush; brush = brush->id.next) {
-		if (brush->id.flag & LIB_NEED_LINK) {
-			brush->id.flag -= LIB_NEED_LINK;
+		if (brush->id.tag & LIB_TAG_NEED_LINK) {
+			brush->id.tag &= ~LIB_TAG_NEED_LINK;
 			
 			brush->mtex.tex = newlibadr_us(fd, brush->id.lib, brush->mtex.tex);
 			brush->mask_mtex.tex = newlibadr_us(fd, brush->id.lib, brush->mask_mtex.tex);
@@ -2194,8 +2194,8 @@ static void lib_link_palette(FileData *UNUSED(fd), Main *main)
 
 	/* only link ID pointers */
 	for (palette = main->palettes.first; palette; palette = palette->id.next) {
-		if (palette->id.flag & LIB_NEED_LINK) {
-			palette->id.flag -= LIB_NEED_LINK;
+		if (palette->id.tag & LIB_TAG_NEED_LINK) {
+			palette->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -2212,8 +2212,8 @@ static void lib_link_paint_curve(FileData *UNUSED(fd), Main *main)
 
 	/* only link ID pointers */
 	for (pc = main->paintcurves.first; pc; pc = pc->id.next) {
-		if (pc->id.flag & LIB_NEED_LINK) {
-			pc->id.flag -= LIB_NEED_LINK;
+		if (pc->id.tag & LIB_TAG_NEED_LINK) {
+			pc->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -2246,13 +2246,13 @@ static void lib_link_ipo(FileData *fd, Main *main)
 	Ipo *ipo;
 	
 	for (ipo = main->ipo.first; ipo; ipo = ipo->id.next) {
-		if (ipo->id.flag & LIB_NEED_LINK) {
+		if (ipo->id.tag & LIB_TAG_NEED_LINK) {
 			IpoCurve *icu;
 			for (icu = ipo->curve.first; icu; icu = icu->next) {
 				if (icu->driver)
 					icu->driver->ob = newlibadr(fd, ipo->id.lib, icu->driver->ob);
 			}
-			ipo->id.flag -= LIB_NEED_LINK;
+			ipo->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -2468,8 +2468,8 @@ static void lib_link_action(FileData *fd, Main *main)
 	bActionChannel *chan;
 
 	for (act = main->action.first; act; act = act->id.next) {
-		if (act->id.flag & LIB_NEED_LINK) {
-			act->id.flag -= LIB_NEED_LINK;
+		if (act->id.tag & LIB_TAG_NEED_LINK) {
+			act->id.tag &= ~LIB_TAG_NEED_LINK;
 			
 // XXX deprecated - old animation system <<<
 			for (chan=act->chanbase.first; chan; chan=chan->next) {
@@ -2719,8 +2719,8 @@ static void lib_link_nodetree(FileData *fd, Main *main)
 	
 	/* only link ID pointers */
 	for (ntree = main->nodetree.first; ntree; ntree = ntree->id.next) {
-		if (ntree->id.flag & LIB_NEED_LINK) {
-			ntree->id.flag -= LIB_NEED_LINK;
+		if (ntree->id.tag & LIB_TAG_NEED_LINK) {
+			ntree->id.tag &= ~LIB_TAG_NEED_LINK;
 			lib_link_ntree(fd, &ntree->id, ntree);
 		}
 	}
@@ -2983,7 +2983,7 @@ static void direct_link_nodetree(FileData *fd, bNodeTree *ntree)
 	ntree->adt = newdataadr(fd, ntree->adt);
 	direct_link_animdata(fd, ntree->adt);
 	
-	ntree->id.flag &= ~(LIB_ID_RECALC|LIB_ID_RECALC_DATA);
+	ntree->id.tag &= ~(LIB_TAG_ID_RECALC|LIB_TAG_ID_RECALC_DATA);
 
 	link_list(fd, &ntree->nodes);
 	for (node = ntree->nodes.first; node; node = node->next) {
@@ -3237,9 +3237,9 @@ static void lib_link_armature(FileData *fd, Main *main)
 	bArmature *arm;
 	
 	for (arm = main->armature.first; arm; arm = arm->id.next) {
-		if (arm->id.flag & LIB_NEED_LINK) {
+		if (arm->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &arm->id, arm->adt);
-			arm->id.flag -= LIB_NEED_LINK;
+			arm->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3286,14 +3286,14 @@ static void lib_link_camera(FileData *fd, Main *main)
 	Camera *ca;
 	
 	for (ca = main->camera.first; ca; ca = ca->id.next) {
-		if (ca->id.flag & LIB_NEED_LINK) {
+		if (ca->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &ca->id, ca->adt);
 			
 			ca->ipo = newlibadr_us(fd, ca->id.lib, ca->ipo); // XXX deprecated - old animation system
 			
 			ca->dof_ob = newlibadr_us(fd, ca->id.lib, ca->dof_ob);
 			
-			ca->id.flag -= LIB_NEED_LINK;
+			ca->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3314,7 +3314,7 @@ static void lib_link_lamp(FileData *fd, Main *main)
 	int a;
 	
 	for (la = main->lamp.first; la; la = la->id.next) {
-		if (la->id.flag & LIB_NEED_LINK) {
+		if (la->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &la->id, la->adt);
 			
 			for (a = 0; a < MAX_MTEX; a++) {
@@ -3332,7 +3332,7 @@ static void lib_link_lamp(FileData *fd, Main *main)
 				la->nodetree->id.lib = la->id.lib;
 			}
 			
-			la->id.flag -= LIB_NEED_LINK;
+			la->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3383,15 +3383,15 @@ static void lib_link_key(FileData *fd, Main *main)
 			blo_do_versions_key_uidgen(key);
 		}
 		
-		BLI_assert((key->id.flag & LIB_EXTERN) == 0);
+		BLI_assert((key->id.tag & LIB_TAG_EXTERN) == 0);
 
-		if (key->id.flag & LIB_NEED_LINK) {
+		if (key->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &key->id, key->adt);
 			
 			key->ipo = newlibadr_us(fd, key->id.lib, key->ipo); // XXX deprecated - old animation system
 			key->from = newlibadr(fd, key->id.lib, key->from);
 			
-			key->id.flag -= LIB_NEED_LINK;
+			key->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3452,7 +3452,7 @@ static void lib_link_mball(FileData *fd, Main *main)
 	int a;
 	
 	for (mb = main->mball.first; mb; mb = mb->id.next) {
-		if (mb->id.flag & LIB_NEED_LINK) {
+		if (mb->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &mb->id, mb->adt);
 			
 			for (a = 0; a < mb->totcol; a++) 
@@ -3460,7 +3460,7 @@ static void lib_link_mball(FileData *fd, Main *main)
 			
 			mb->ipo = newlibadr_us(fd, mb->id.lib, mb->ipo); // XXX deprecated - old animation system
 			
-			mb->id.flag -= LIB_NEED_LINK;
+			mb->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3490,7 +3490,7 @@ static void lib_link_world(FileData *fd, Main *main)
 	int a;
 	
 	for (wrld = main->world.first; wrld; wrld = wrld->id.next) {
-		if (wrld->id.flag & LIB_NEED_LINK) {
+		if (wrld->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &wrld->id, wrld->adt);
 			
 			wrld->ipo = newlibadr_us(fd, wrld->id.lib, wrld->ipo); // XXX deprecated - old animation system
@@ -3508,7 +3508,7 @@ static void lib_link_world(FileData *fd, Main *main)
 				wrld->nodetree->id.lib = wrld->id.lib;
 			}
 			
-			wrld->id.flag -= LIB_NEED_LINK;
+			wrld->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3542,8 +3542,8 @@ static void lib_link_vfont(FileData *UNUSED(fd), Main *main)
 	VFont *vf;
 	
 	for (vf = main->vfont.first; vf; vf = vf->id.next) {
-		if (vf->id.flag & LIB_NEED_LINK) {
-			vf->id.flag -= LIB_NEED_LINK;
+		if (vf->id.tag & LIB_TAG_NEED_LINK) {
+			vf->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3562,8 +3562,8 @@ static void lib_link_text(FileData *UNUSED(fd), Main *main)
 	Text *text;
 	
 	for (text = main->text.first; text; text = text->id.next) {
-		if (text->id.flag & LIB_NEED_LINK) {
-			text->id.flag -= LIB_NEED_LINK;
+		if (text->id.tag & LIB_TAG_NEED_LINK) {
+			text->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3614,10 +3614,10 @@ static void lib_link_image(FileData *fd, Main *main)
 	Image *ima;
 	
 	for (ima = main->image.first; ima; ima = ima->id.next) {
-		if (ima->id.flag & LIB_NEED_LINK) {
+		if (ima->id.tag & LIB_TAG_NEED_LINK) {
 			IDP_LibLinkProperty(ima->id.properties, (fd->flags & FD_FLAGS_SWITCH_ENDIAN), fd);
 			
-			ima->id.flag -= LIB_NEED_LINK;
+			ima->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3682,7 +3682,7 @@ static void lib_link_curve(FileData *fd, Main *main)
 	int a;
 	
 	for (cu = main->curve.first; cu; cu = cu->id.next) {
-		if (cu->id.flag & LIB_NEED_LINK) {
+		if (cu->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &cu->id, cu->adt);
 			
 			for (a = 0; a < cu->totcol; a++) 
@@ -3699,7 +3699,7 @@ static void lib_link_curve(FileData *fd, Main *main)
 			cu->ipo = newlibadr_us(fd, cu->id.lib, cu->ipo); // XXX deprecated - old animation system
 			cu->key = newlibadr_us(fd, cu->id.lib, cu->key);
 			
-			cu->id.flag -= LIB_NEED_LINK;
+			cu->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3774,7 +3774,7 @@ static void lib_link_texture(FileData *fd, Main *main)
 	Tex *tex;
 	
 	for (tex = main->tex.first; tex; tex = tex->id.next) {
-		if (tex->id.flag & LIB_NEED_LINK) {
+		if (tex->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &tex->id, tex->adt);
 			
 			tex->ima = newlibadr_us(fd, tex->id.lib, tex->ima);
@@ -3793,7 +3793,7 @@ static void lib_link_texture(FileData *fd, Main *main)
 				tex->nodetree->id.lib = tex->id.lib;
 			}
 			
-			tex->id.flag -= LIB_NEED_LINK;
+			tex->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -3854,7 +3854,7 @@ static void lib_link_material(FileData *fd, Main *main)
 	int a;
 	
 	for (ma = main->mat.first; ma; ma = ma->id.next) {
-		if (ma->id.flag & LIB_NEED_LINK) {
+		if (ma->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &ma->id, ma->adt);
 			
 			/* Link ID Properties -- and copy this comment EXACTLY for easy finding
@@ -3877,7 +3877,7 @@ static void lib_link_material(FileData *fd, Main *main)
 				ma->nodetree->id.lib = ma->id.lib;
 			}
 			
-			ma->id.flag -= LIB_NEED_LINK;
+			ma->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -4002,7 +4002,7 @@ static void lib_link_particlesettings(FileData *fd, Main *main)
 	int a;
 	
 	for (part = main->particle.first; part; part = part->id.next) {
-		if (part->id.flag & LIB_NEED_LINK) {
+		if (part->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &part->id, part->adt);
 			part->ipo = newlibadr_us(fd, part->id.lib, part->ipo); // XXX deprecated - old animation system
 			
@@ -4084,7 +4084,7 @@ static void lib_link_particlesettings(FileData *fd, Main *main)
 				}
 			}
 			
-			part->id.flag -= LIB_NEED_LINK;
+			part->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -4305,7 +4305,7 @@ static void lib_link_mesh(FileData *fd, Main *main)
 	Mesh *me;
 	
 	for (me = main->mesh.first; me; me = me->id.next) {
-		if (me->id.flag & LIB_NEED_LINK) {
+		if (me->id.tag & LIB_TAG_NEED_LINK) {
 			int i;
 			
 			/* Link ID Properties -- and copy this comment EXACTLY for easy finding
@@ -4340,7 +4340,7 @@ static void lib_link_mesh(FileData *fd, Main *main)
 	convert_tface_mt(fd, main);
 
 	for (me = main->mesh.first; me; me = me->id.next) {
-		if (me->id.flag & LIB_NEED_LINK) {
+		if (me->id.tag & LIB_TAG_NEED_LINK) {
 			/*check if we need to convert mfaces to mpolys*/
 			if (me->totface && !me->totpoly) {
 				/* temporarily switch main so that reading from
@@ -4369,7 +4369,7 @@ static void lib_link_mesh(FileData *fd, Main *main)
 			BKE_mesh_tessface_clear(me);
 #endif
 
-			me->id.flag -= LIB_NEED_LINK;
+			me->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -4586,13 +4586,13 @@ static void lib_link_latt(FileData *fd, Main *main)
 	Lattice *lt;
 	
 	for (lt = main->latt.first; lt; lt = lt->id.next) {
-		if (lt->id.flag & LIB_NEED_LINK) {
+		if (lt->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &lt->id, lt->adt);
 			
 			lt->ipo = newlibadr_us(fd, lt->id.lib, lt->ipo); // XXX deprecated - old animation system
 			lt->key = newlibadr_us(fd, lt->id.lib, lt->key);
 			
-			lt->id.flag -= LIB_NEED_LINK;
+			lt->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -4639,7 +4639,7 @@ static void lib_link_object(FileData *fd, Main *main)
 	int warn=0, a;
 	
 	for (ob = main->object.first; ob; ob = ob->id.next) {
-		if (ob->id.flag & LIB_NEED_LINK) {
+		if (ob->id.tag & LIB_TAG_NEED_LINK) {
 			IDP_LibLinkProperty(ob->id.properties, (fd->flags & FD_FLAGS_SWITCH_ENDIAN), fd);
 			lib_link_animdata(fd, &ob->id, ob->adt);
 			
@@ -4716,7 +4716,7 @@ static void lib_link_object(FileData *fd, Main *main)
 			ob->gpd = newlibadr_us(fd, ob->id.lib, ob->gpd);
 			ob->duplilist = NULL;
 			
-			ob->id.flag -= LIB_NEED_LINK;
+			ob->id.tag &= ~LIB_TAG_NEED_LINK;
 			/* if id.us==0 a new base will be created later on */
 			
 			/* WARNING! Also check expand_object(), should reflect the stuff below. */
@@ -5235,7 +5235,7 @@ static void direct_link_object(FileData *fd, Object *ob)
 	 * Also when linking in a file don't allow edit and pose modes.
 	 * See [#34776, #42780] for more information.
 	 */
-	if (fd->memfile || (ob->id.flag & (LIB_EXTERN | LIB_INDIRECT))) {
+	if (fd->memfile || (ob->id.tag & (LIB_TAG_EXTERN | LIB_TAG_INDIRECT))) {
 		ob->mode &= ~(OB_MODE_EDIT | OB_MODE_PARTICLE_EDIT);
 		if (!fd->memfile) {
 			ob->mode &= ~OB_MODE_POSE;
@@ -5505,7 +5505,7 @@ static bool scene_validate_setscene__liblink(Scene *sce, const int totscene)
 	if (sce->set == NULL) return 1;
 
 	for (a = 0, sce_iter = sce; sce_iter->set; sce_iter = sce_iter->set, a++) {
-		if (sce_iter->id.flag & LIB_NEED_LINK) {
+		if (sce_iter->id.tag & LIB_TAG_NEED_LINK) {
 			return 1;
 		}
 
@@ -5535,7 +5535,7 @@ static void lib_link_scene(FileData *fd, Main *main)
 #endif
 	
 	for (sce = main->scene.first; sce; sce = sce->id.next) {
-		if (sce->id.flag & LIB_NEED_LINK) {
+		if (sce->id.tag & LIB_TAG_NEED_LINK) {
 			/* Link ID Properties -- and copy this comment EXACTLY for easy finding
 			 * of library blocks that implement this.*/
 			IDP_LibLinkProperty(sce->id.properties, (fd->flags & FD_FLAGS_SWITCH_ENDIAN), fd);
@@ -5684,10 +5684,10 @@ static void lib_link_scene(FileData *fd, Main *main)
 			}
 			else {
 				/* postpone un-setting the flag until we've checked the set-scene */
-				sce->id.flag &= ~LIB_NEED_LINK;
+				sce->id.tag &= ~LIB_TAG_NEED_LINK;
 			}
 #else
-			sce->id.flag &= ~LIB_NEED_LINK;
+			sce->id.tag &= ~LIB_TAG_NEED_LINK;
 #endif
 		}
 
@@ -5699,8 +5699,8 @@ static void lib_link_scene(FileData *fd, Main *main)
 #ifdef USE_SETSCENE_CHECK
 	if (need_check_set) {
 		for (sce = main->scene.first; sce; sce = sce->id.next) {
-			if (sce->id.flag & LIB_NEED_LINK) {
-				sce->id.flag &= ~LIB_NEED_LINK;
+			if (sce->id.tag & LIB_TAG_NEED_LINK) {
+				sce->id.tag &= ~LIB_TAG_NEED_LINK;
 				if (!scene_validate_setscene__liblink(sce, totscene)) {
 					printf("Found cyclic background scene when linking %s\n", sce->id.name + 2);
 				}
@@ -6081,11 +6081,11 @@ static void lib_link_windowmanager(FileData *fd, Main *main)
 	wmWindow *win;
 	
 	for (wm = main->wm.first; wm; wm = wm->id.next) {
-		if (wm->id.flag & LIB_NEED_LINK) {
+		if (wm->id.tag & LIB_TAG_NEED_LINK) {
 			for (win = wm->windows.first; win; win = win->next)
 				win->screen = newlibadr(fd, NULL, win->screen);
 			
-			wm->id.flag -= LIB_NEED_LINK;
+			wm->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -6098,8 +6098,8 @@ static void lib_link_gpencil(FileData *fd, Main *main)
 	bGPdata *gpd;
 	
 	for (gpd = main->gpencil.first; gpd; gpd = gpd->id.next) {
-		if (gpd->id.flag & LIB_NEED_LINK) {
-			gpd->id.flag -= LIB_NEED_LINK;
+		if (gpd->id.tag & LIB_TAG_NEED_LINK) {
+			gpd->id.tag &= ~LIB_TAG_NEED_LINK;
 			
 			lib_link_animdata(fd, &gpd->id, gpd->adt);
 		}
@@ -6150,7 +6150,7 @@ static void lib_link_screen(FileData *fd, Main *main)
 	ScrArea *sa;
 	
 	for (sc = main->screen.first; sc; sc = sc->id.next) {
-		if (sc->id.flag & LIB_NEED_LINK) {
+		if (sc->id.tag & LIB_TAG_NEED_LINK) {
 			id_us_ensure_real(&sc->id);
 			sc->scene = newlibadr(fd, sc->id.lib, sc->scene);
 
@@ -6340,7 +6340,7 @@ static void lib_link_screen(FileData *fd, Main *main)
 					}
 				}
 			}
-			sc->id.flag -= LIB_NEED_LINK;
+			sc->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -7184,11 +7184,11 @@ static void lib_link_speaker(FileData *fd, Main *main)
 	Speaker *spk;
 	
 	for (spk = main->speaker.first; spk; spk = spk->id.next) {
-		if (spk->id.flag & LIB_NEED_LINK) {
+		if (spk->id.tag & LIB_TAG_NEED_LINK) {
 			lib_link_animdata(fd, &spk->id, spk->adt);
 			
 			spk->sound = newlibadr_us(fd, spk->id.lib, spk->sound);
-			spk->id.flag -= LIB_NEED_LINK;
+			spk->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -7240,8 +7240,8 @@ static void lib_link_sound(FileData *fd, Main *main)
 	bSound *sound;
 	
 	for (sound = main->sound.first; sound; sound = sound->id.next) {
-		if (sound->id.flag & LIB_NEED_LINK) {
-			sound->id.flag -= LIB_NEED_LINK;
+		if (sound->id.tag & LIB_TAG_NEED_LINK) {
+			sound->id.tag &= ~LIB_TAG_NEED_LINK;
 			sound->ipo = newlibadr_us(fd, sound->id.lib, sound->ipo); // XXX deprecated - old animation system
 			
 			BKE_sound_load(main, sound);
@@ -7264,8 +7264,8 @@ static void lib_link_group(FileData *fd, Main *main)
 	bool add_us;
 	
 	for (group = main->group.first; group; group = group->id.next) {
-		if (group->id.flag & LIB_NEED_LINK) {
-			group->id.flag -= LIB_NEED_LINK;
+		if (group->id.tag & LIB_TAG_NEED_LINK) {
+			group->id.tag &= ~LIB_TAG_NEED_LINK;
 			
 			add_us = false;
 			
@@ -7389,7 +7389,7 @@ static void lib_link_movieclip(FileData *fd, Main *main)
 	MovieClip *clip;
 	
 	for (clip = main->movieclip.first; clip; clip = clip->id.next) {
-		if (clip->id.flag & LIB_NEED_LINK) {
+		if (clip->id.tag & LIB_TAG_NEED_LINK) {
 			MovieTracking *tracking = &clip->tracking;
 			MovieTrackingObject *object;
 
@@ -7404,7 +7404,7 @@ static void lib_link_movieclip(FileData *fd, Main *main)
 				lib_link_movieTracks(fd, clip, &object->tracks);
 			}
 
-			clip->id.flag -= LIB_NEED_LINK;
+			clip->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 	}
 }
@@ -7468,7 +7468,7 @@ static void lib_link_mask(FileData *fd, Main *main)
 
 	mask = main->mask.first;
 	while (mask) {
-		if (mask->id.flag & LIB_NEED_LINK) {
+		if (mask->id.tag & LIB_TAG_NEED_LINK) {
 			MaskLayer *masklay;
 
 			lib_link_animdata(fd, &mask->id, mask->adt);
@@ -7492,7 +7492,7 @@ static void lib_link_mask(FileData *fd, Main *main)
 				}
 			}
 
-			mask->id.flag -= LIB_NEED_LINK;
+			mask->id.tag &= ~LIB_TAG_NEED_LINK;
 		}
 		mask = mask->id.next;
 	}
@@ -7509,8 +7509,8 @@ static void lib_link_linestyle(FileData *fd, Main *main)
 
 	linestyle = main->linestyle.first;
 	while (linestyle) {
-		if (linestyle->id.flag & LIB_NEED_LINK) {
-			linestyle->id.flag -= LIB_NEED_LINK;
+		if (linestyle->id.tag & LIB_TAG_NEED_LINK) {
+			linestyle->id.tag &= ~LIB_TAG_NEED_LINK;
 
 			IDP_LibLinkProperty(linestyle->id.properties, (fd->flags & FD_FLAGS_SWITCH_ENDIAN), fd);
 			lib_link_animdata(fd, &linestyle->id, linestyle->adt);
@@ -7921,12 +7921,10 @@ static BHead *read_libblock(FileData *fd, Main *main, BHead *bhead, int flag, ID
 	if (!id)
 		return blo_nextbhead(fd, bhead);
 	
-	/* clear first 8 bits */
-	id->flag = (id->flag & 0xFF00) | flag | LIB_NEED_LINK;
+	id->tag = flag | LIB_TAG_NEED_LINK;
 	id->lib = main->curlib;
 	id->us = ID_FAKE_USERS(id);
 	id->icon_id = 0;
-	id->flag &= ~(LIB_ID_RECALC | LIB_ID_RECALC_DATA | LIB_DOIT | LIB_MISSING);
 	
 	/* this case cannot be direct_linked: it's just the ID part */
 	if (bhead->code == ID_ID) {
@@ -8371,7 +8369,7 @@ BlendFileData *blo_read_file_internal(FileData *fd, const char *filepath)
 		case ID_ID:
 			/* Always adds to the most recently loaded ID_LI block, see direct_link_library.
 			 * This is part of the file format definition. */
-			bhead = read_libblock(fd, mainlist.last, bhead, LIB_READ | LIB_EXTERN, NULL);
+			bhead = read_libblock(fd, mainlist.last, bhead, LIB_TAG_READ | LIB_TAG_EXTERN, NULL);
 			break;
 			
 			/* in 2.50+ files, the file identifier for screens is patched, forward compatibility */
@@ -8379,7 +8377,7 @@ BlendFileData *blo_read_file_internal(FileData *fd, const char *filepath)
 			bhead->code = ID_SCR;
 			/* deliberate pass on to default */
 		default:
-			bhead = read_libblock(fd, bfd->main, bhead, LIB_LOCAL, NULL);
+			bhead = read_libblock(fd, bfd->main, bhead, LIB_TAG_LOCAL, NULL);
 		}
 	}
 	
@@ -8559,7 +8557,7 @@ static void expand_doit_library(void *fdhandle, Main *mainvar, void *old)
 					id = is_yet_read(fd, ptr, bhead);
 				
 				if (id == NULL) {
-					read_libblock(fd, ptr, bhead, LIB_READ+LIB_INDIRECT, NULL);
+					read_libblock(fd, ptr, bhead, LIB_TAG_READ | LIB_TAG_INDIRECT, NULL);
 					// commented because this can print way too much
 					// if (G.debug & G_DEBUG) printf("expand_doit: other lib %s\n", lib->name);
 					
@@ -8577,10 +8575,10 @@ static void expand_doit_library(void *fdhandle, Main *mainvar, void *old)
 					/* Update: the issue is that in file reading, the oldnewmap is OK, but for existing data, it has to be
 					 * inserted in the map to be found! */
 					
-					/* Update: previously it was checking for id->flag & LIB_PRE_EXISTING, however that does not affect file
-					 * reading. For file reading we may need to insert it into the libmap as well, because you might have
-					 * two files indirectly linking the same datablock, and in that case we need this in the libmap for the
-					 * fd of both those files.
+					/* Update: previously it was checking for id->tag & LIB_TAG_PRE_EXISTING, however that
+					 * does not affect file reading. For file reading we may need to insert it into the libmap as well,
+					 * because you might have two files indirectly linking the same datablock, and in that case
+					 * we need this in the libmap for the fd of both those files.
 					 *
 					 * The crash that this check avoided earlier was because bhead->code wasn't properly passed in, making
 					 * change_idid_adr not detect the mapping was for an ID_ID datablock. */
@@ -8597,7 +8595,7 @@ static void expand_doit_library(void *fdhandle, Main *mainvar, void *old)
 		else {
 			id = is_yet_read(fd, mainvar, bhead);
 			if (id == NULL) {
-				read_libblock(fd, mainvar, bhead, LIB_TESTIND, NULL);
+				read_libblock(fd, mainvar, bhead, LIB_TAG_TESTIND, NULL);
 			}
 			else {
 				/* this is actually only needed on UI call? when ID was already read before, and another append
@@ -9397,7 +9395,7 @@ void BLO_main_expander(BLOExpandDoitCallback expand_doit_func)
 
 /**
  * Loop over all ID data in Main to mark relations.
- * Set (id->flag & LIB_NEED_EXPAND) to mark expanding. Flags get cleared after expanding.
+ * Set (id->tag & LIB_TAG_NEED_EXPAND) to mark expanding. Flags get cleared after expanding.
  *
  * \param fdhandle usually filedata, or own handle.
  * \param mainvar the Main database to expand.
@@ -9417,7 +9415,7 @@ void BLO_expand_main(void *fdhandle, Main *mainvar)
 		while (a--) {
 			id = lbarray[a]->first;
 			while (id) {
-				if (id->flag & LIB_NEED_EXPAND) {
+				if (id->tag & LIB_TAG_NEED_EXPAND) {
 					switch (GS(id->name)) {
 					case ID_OB:
 						expand_object(fd, mainvar, (Object *)id);
@@ -9497,7 +9495,7 @@ void BLO_expand_main(void *fdhandle, Main *mainvar)
 					}
 					
 					do_it = true;
-					id->flag -= LIB_NEED_EXPAND;
+					id->tag &= ~LIB_TAG_NEED_EXPAND;
 					
 				}
 				id = id->next;
@@ -9531,9 +9529,9 @@ static void give_base_to_objects(Main *mainvar, Scene *scene, View3D *v3d, Libra
 
 	BLI_assert(scene);
 
-	/* give all objects which are LIB_INDIRECT a base, or for a group when *lib has been set */
+	/* 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) {
-		if ((ob->id.flag & LIB_INDIRECT) && (ob->id.flag & LIB_PRE_EXISTING) == 0) {
+		if ((ob->id.tag & LIB_TAG_INDIRECT) && (ob->id.tag & LIB_TAG_PRE_EXISTING) == 0) {
 			bool do_it = false;
 
 			if (ob->id.us == 0) {
@@ -9560,8 +9558,8 @@ static void give_base_to_objects(Main *mainvar, Scene *scene, View3D *v3d, Libra
 				CLAMP_MIN(ob->id.us, 0);
 				ob->id.us += 1;
 
-				ob->id.flag &= ~LIB_INDIRECT;
-				ob->id.flag |= LIB_EXTERN;
+				ob->id.tag &= ~LIB_TAG_INDIRECT;
+				ob->id.tag |= LIB_TAG_EXTERN;
 			}
 		}
 	}
@@ -9577,9 +9575,9 @@ static void give_base_to_groups(
 
 	/* give all objects which are tagged a base */
 	for (group = mainvar->group.first; group; group = group->id.next) {
-		if (group->id.flag & LIB_DOIT) {
+		if (group->id.tag & LIB_TAG_DOIT) {
 			/* any indirect group should not have been tagged */
-			BLI_assert((group->id.flag & LIB_INDIRECT) == 0);
+			BLI_assert((group->id.tag & LIB_TAG_INDIRECT) == 0);
 
 			/* BKE_object_add(...) messes with the selection */
 			ob = BKE_object_add_only_object(mainvar, OB_EMPTY, group->id.name + 2);
@@ -9610,7 +9608,7 @@ static ID *create_placeholder(Main *mainvar, const char *idname, const short fla
 	memcpy(ph_id->name, idname, sizeof(ph_id->name));
 	BKE_libblock_init_empty(ph_id);
 	ph_id->lib = mainvar->curlib;
-	ph_id->flag = flag | LIB_MISSING;
+	ph_id->tag = flag | LIB_TAG_MISSING;
 	ph_id->us = ID_FAKE_USERS(ph_id);
 	ph_id->icon_id = 0;
 
@@ -9633,7 +9631,7 @@ static ID *link_named_part(Main *mainl, FileData *fd, const short idcode, const
 		id = is_yet_read(fd, mainl, bhead);
 		if (id == NULL) {
 			/* not read yet */
-			read_libblock(fd, mainl, bhead, LIB_TESTEXT, &id);
+			read_libblock(fd, mainl, bhead, LIB_TAG_TESTEXT, &id);
 
 			if (id) {
 				/* sort by name in list */
@@ -9646,9 +9644,9 @@ static ID *link_named_part(Main *mainl, FileData *fd, const short idcode, const
 			if (G.debug)
 				printf("append: already linked\n");
 			oldnewmap_insert(fd->libmap, bhead->old, id, bhead->code);
-			if (id->flag & LIB_INDIRECT) {
-				id->flag -= LIB_INDIRECT;
-				id->flag |= LIB_EXTERN;
+			if (id->tag & LIB_TAG_INDIRECT) {
+				id->tag &= ~LIB_TAG_INDIRECT;
+				id->tag |= LIB_TAG_EXTERN;
 			}
 		}
 	}
@@ -9675,7 +9673,7 @@ void BLO_library_link_all(Main *mainl, BlendHandle *bh)
 		if (bhead->code == ENDB)
 			break;
 		if (bhead->code == ID_OB)
-			read_libblock(fd, mainl, bhead, LIB_TESTIND, &id);
+			read_libblock(fd, mainl, bhead, LIB_TAG_TESTIND, &id);
 			
 		if (id) {
 			/* sort by name in list */
@@ -9722,7 +9720,7 @@ static ID *link_named_part_ex(
 	else if (id && (GS(id->name) == ID_GR)) {
 		/* tag as needing to be instantiated */
 		if (flag & FILE_GROUP_INSTANCE)
-			id->flag |= LIB_DOIT;
+			id->tag |= LIB_TAG_DOIT;
 	}
 
 	return id;
@@ -9768,13 +9766,13 @@ ID *BLO_library_link_named_part_ex(
 static void link_id_part(ReportList *reports, FileData *fd, Main *mainvar, ID *id, ID **r_id)
 {
 	BHead *bhead = NULL;
-	const bool is_valid = BKE_idcode_is_linkable(GS(id->name)) || ((id->flag & LIB_EXTERN) == 0);
+	const bool is_valid = BKE_idcode_is_linkable(GS(id->name)) || ((id->tag & LIB_TAG_EXTERN) == 0);
 
 	if (fd) {
 		bhead = find_bhead_from_idname(fd, id->name);
 	}
 
-	id->flag &= ~LIB_READ;
+	id->tag &= ~LIB_TAG_READ;
 
 	if (!is_valid) {
 		blo_reportf_wrap(
@@ -9787,9 +9785,9 @@ static void link_id_part(ReportList *reports, FileData *fd, Main *mainvar, ID *i
 	}
 
 	if (bhead) {
-		id->flag |= LIB_NEED_EXPAND;
+		id->tag |= LIB_TAG_NEED_EXPAND;
 		// printf("read lib block %s\n", id->name);
-		read_libblock(fd, mainvar, bhead, id->flag, r_id);
+		read_libblock(fd, mainvar, bhead, id->tag, r_id);
 	}
 	else {
 		blo_reportf_wrap(
@@ -9802,7 +9800,7 @@ static void link_id_part(ReportList *reports, FileData *fd, Main *mainvar, ID *i
 
 		/* Generate a placeholder for this ID (simplified version of read_libblock actually...). */
 		if (r_id) {
-			*r_id = is_valid ? create_placeholder(mainvar, id->name, id->flag) : NULL;
+			*r_id = is_valid ? create_placeholder(mainvar, id->name, id->tag) : NULL;
 		}
 	}
 }
@@ -9942,7 +9940,7 @@ static int mainvar_count_libread_blocks(Main *mainvar)
 		ID *id;
 		
 		for (id = lbarray[a]->first; id; id = id->next) {
-			if (id->flag & LIB_READ)
+			if (id->tag & LIB_TAG_READ)
 				tot++;
 		}
 	}
@@ -9968,7 +9966,7 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 		while (mainptr) {
 			int tot = mainvar_count_libread_blocks(mainptr);
 			
-			// printf("found LIB_READ %s\n", mainptr->curlib->name);
+			// printf("found LIB_TAG_READ %s\n", mainptr->curlib->name);
 			if (tot) {
 				FileData *fd = mainptr->curlib->filedata;
 				
@@ -10049,7 +10047,7 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 					}
 					else {
 						mainptr->curlib->filedata = NULL;
-						mainptr->curlib->id.flag |= LIB_MISSING;
+						mainptr->curlib->id.tag |= LIB_TAG_MISSING;
 					}
 					
 					if (fd == NULL) {
@@ -10066,7 +10064,7 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 
 					while (id) {
 						ID *idn = id->next;
-						if (id->flag & LIB_READ) {
+						if (id->tag & LIB_TAG_READ) {
 							ID *realid = NULL;
 							BLI_remlink(lbarray[a], id);
 
@@ -10099,7 +10097,7 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 			
 			for (id = lbarray[a]->first; id; id = idn) {
 				idn = id->next;
-				if (id->flag & LIB_READ) {
+				if (id->tag & LIB_TAG_READ) {
 					BLI_assert(0);
 					BLI_remlink(lbarray[a], id);
 					blo_reportf_wrap(
diff --git a/source/blender/blenloader/intern/versioning_270.c b/source/blender/blenloader/intern/versioning_270.c
index 816eb879015..b975a39a301 100644
--- a/source/blender/blenloader/intern/versioning_270.c
+++ b/source/blender/blenloader/intern/versioning_270.c
@@ -55,6 +55,7 @@
 #include "DNA_genfile.h"
 
 #include "BKE_colortools.h"
+#include "BKE_library.h"
 #include "BKE_main.h"
 #include "BKE_modifier.h"
 #include "BKE_node.h"
@@ -1036,4 +1037,17 @@ void blo_do_versions_270(FileData *fd, Library *UNUSED(lib), Main *main)
 			}
 		}
 	}
+	if (!MAIN_VERSION_ATLEAST(main, 276, 5)) {
+		ListBase *lbarray[MAX_LIBARRAY];
+		int a;
+
+		/* Important to clear all non-persistent flags from older versions here, otherwise they could collide
+		 * with any new persistent flag we may add in the future. */
+		a = set_listbasepointers(main, lbarray);
+		while (a--) {
+			for (ID *id = lbarray[a]->first; id; id = id->next) {
+				id->flag &= LIB_FAKEUSER;
+			}
+		}
+	}
 }
diff --git a/source/blender/blenloader/intern/versioning_legacy.c b/source/blender/blenloader/intern/versioning_legacy.c
index 635df922c11..ac7b7b11b61 100644
--- a/source/blender/blenloader/intern/versioning_legacy.c
+++ b/source/blender/blenloader/intern/versioning_legacy.c
@@ -589,7 +589,7 @@ void blo_do_versions_pre250(FileData *fd, Library *lib, Main *main)
 		/* tex->extend and tex->imageflag have changed: */
 		Tex *tex = main->tex.first;
 		while (tex) {
-			if (tex->id.flag & LIB_NEED_LINK) {
+			if (tex->id.tag & LIB_TAG_NEED_LINK) {
 
 				if (tex->extend == 0) {
 					if (tex->xrepeat || tex->yrepeat) {
@@ -3043,7 +3043,7 @@ void blo_do_versions_pre250(FileData *fd, Library *lib, Main *main)
 				part->id.lib = ob->id.lib;
 
 				part->id.us--;
-				part->id.flag |= (ob->id.flag & LIB_NEED_LINK);
+				part->id.tag |= (ob->id.tag & LIB_TAG_NEED_LINK);
 
 				psys->totpart = 0;
 				psys->flag = PSYS_CURRENT;
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index 4643d2e5642..a2802db0802 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -2897,7 +2897,7 @@ static void write_libraries(WriteData *wd, Main *main)
 			found_one = false;
 			while (tot--) {
 				for (id= lbarray[tot]->first; id; id= id->next) {
-					if (id->us>0 && (id->flag & LIB_EXTERN)) {
+					if (id->us > 0 && (id->tag & LIB_TAG_EXTERN)) {
 						found_one = true;
 						break;
 					}
@@ -2922,7 +2922,7 @@ static void write_libraries(WriteData *wd, Main *main)
 			
 			while (a--) {
 				for (id= lbarray[a]->first; id; id= id->next) {
-					if (id->us>0 && (id->flag & LIB_EXTERN)) {
+					if (id->us > 0 && (id->tag & LIB_TAG_EXTERN)) {
 						if (!BKE_idcode_is_linkable(GS(id->name))) {
 							printf("ERROR: write file: datablock '%s' from lib '%s' is not linkable "
 							       "but is flagged as directly linked", id->name, main->curlib->filepath);