Fix #35404: crash in file save with python code that accesses mesh from panel.

On file save the mesh gets loads from the editmesh but the derived mesh caches
wer not cleared. This usually happens through the depsgraph but it needs to be
done manually here. Most changes are some refactoring to deduplicate derived
mesh freeing code.

8 files changed, 58 insertions, 72 deletions

diff --git a/source/blender/blenkernel/BKE_object.h b/source/blender/blenkernel/BKE_object.h
index 8870355a919..db93e4f419e 100644
--- a/source/blender/blenkernel/BKE_object.h
+++ b/source/blender/blenkernel/BKE_object.h
@@ -66,7 +66,7 @@ void BKE_object_free_bulletsoftbody(struct Object *ob);
 void BKE_object_update_base_layer(struct Scene *scene, struct Object *ob);
 
 void BKE_object_free(struct Object *ob);
-void BKE_object_free_display(struct Object *ob);
+void BKE_object_free_derived_caches(struct Object *ob);
 
 bool BKE_object_support_modifier_type_check(struct Object *ob, int modifier_type);
 
diff --git a/source/blender/blenkernel/intern/DerivedMesh.c b/source/blender/blenkernel/intern/DerivedMesh.c
index 3dda6933eab..02de0ce1d40 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.c
+++ b/source/blender/blenkernel/intern/DerivedMesh.c
@@ -2163,38 +2163,6 @@ static void editbmesh_calc_modifiers(Scene *scene, Object *ob, BMEditMesh *em, D
 		MEM_freeN(deformedVerts);
 }
 
-static void clear_mesh_caches(Object *ob)
-{
-	Mesh *me = ob->data;
-
-	/* also serves as signal to remake texspace */
-	if (ob->bb) {
-		MEM_freeN(ob->bb);
-		ob->bb = NULL;
-	}
-	if (me->bb) {
-		MEM_freeN(me->bb);
-		me->bb = NULL;
-	}
-
-	BKE_displist_free(&ob->disp);
-
-	if (ob->derivedFinal) {
-		ob->derivedFinal->needsFree = 1;
-		ob->derivedFinal->release(ob->derivedFinal);
-		ob->derivedFinal = NULL;
-	}
-	if (ob->derivedDeform) {
-		ob->derivedDeform->needsFree = 1;
-		ob->derivedDeform->release(ob->derivedDeform);
-		ob->derivedDeform = NULL;
-	}
-
-	if (ob->sculpt) {
-		BKE_object_sculpt_modifiers_changed(ob);
-	}
-}
-
 static void mesh_build_data(Scene *scene, Object *ob, CustomDataMask dataMask,
                             int build_shapekey_layers)
 {
@@ -2205,7 +2173,8 @@ static void mesh_build_data(Scene *scene, Object *ob, CustomDataMask dataMask,
 
 	BLI_assert(ob->type == OB_MESH);
 
-	clear_mesh_caches(ob);
+	BKE_object_free_derived_caches(ob);
+	BKE_object_sculpt_modifiers_changed(ob);
 
 	mesh_calc_modifiers(scene, ob, NULL, &ob->derivedDeform,
 	                    &ob->derivedFinal, 0, 1,
@@ -2226,7 +2195,8 @@ static void mesh_build_data(Scene *scene, Object *ob, CustomDataMask dataMask,
 
 static void editbmesh_build_data(Scene *scene, Object *obedit, BMEditMesh *em, CustomDataMask dataMask)
 {
-	clear_mesh_caches(obedit);
+	BKE_object_free_derived_caches(obedit);
+	BKE_object_sculpt_modifiers_changed(obedit);
 
 	if (em->derivedFinal) {
 		if (em->derivedFinal != em->derivedCage) {
diff --git a/source/blender/blenkernel/intern/depsgraph.c b/source/blender/blenkernel/intern/depsgraph.c
index 86832a72b90..03891f0fed3 100644
--- a/source/blender/blenkernel/intern/depsgraph.c
+++ b/source/blender/blenkernel/intern/depsgraph.c
@@ -1511,7 +1511,7 @@ static void flush_update_node(DagNode *node, unsigned int layer, int curtime)
 		if ((all_layer & layer) == 0) { // XXX && (ob != obedit)) {
 			/* but existing displaylists or derivedmesh should be freed */
 			if (ob->recalc & OB_RECALC_DATA)
-				BKE_object_free_display(ob);
+				BKE_object_free_derived_caches(ob);
 			
 			ob->recalc &= ~OB_RECALC_ALL;
 		}
diff --git a/source/blender/blenkernel/intern/multires.c b/source/blender/blenkernel/intern/multires.c
index c1f1ca0bbaa..7bd117ef7ce 100644
--- a/source/blender/blenkernel/intern/multires.c
+++ b/source/blender/blenkernel/intern/multires.c
@@ -373,11 +373,8 @@ void multires_mark_as_modified(Object *ob, MultiresModifiedFlags flags)
 void multires_force_update(Object *ob)
 {
 	if (ob) {
-		if (ob->derivedFinal) {
-			ob->derivedFinal->needsFree = 1;
-			ob->derivedFinal->release(ob->derivedFinal);
-			ob->derivedFinal = NULL;
-		}
+		BKE_object_free_derived_caches(ob);
+
 		if (ob->sculpt && ob->sculpt->pbvh) {
 			BKE_pbvh_free(ob->sculpt->pbvh);
 			ob->sculpt->pbvh = NULL;
diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index 741c4f5429e..3779aa8cd88 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -241,20 +241,34 @@ void BKE_object_link_modifiers(struct Object *ob_dst, struct Object *ob_src)
 	/* TODO: smoke?, cloth? */
 }
 
-/* here we will collect all local displist stuff */
-/* also (ab)used in depsgraph */
-void BKE_object_free_display(Object *ob)
+/* free data derived from mesh, called when mesh changes or is freed */
+void BKE_object_free_derived_caches(Object *ob)
 {
-	if (ob->derivedDeform) {
-		ob->derivedDeform->needsFree = 1;
-		ob->derivedDeform->release(ob->derivedDeform);
-		ob->derivedDeform = NULL;
+	/* also serves as signal to remake texspace */
+	if (ob->type == OB_MESH) {
+		Mesh *me = ob->data;
+
+		if (me->bb) {
+			MEM_freeN(me->bb);
+			me->bb = NULL;
+		}
+	}
+
+	if (ob->bb) {
+		MEM_freeN(ob->bb);
+		ob->bb = NULL;
 	}
+
 	if (ob->derivedFinal) {
 		ob->derivedFinal->needsFree = 1;
 		ob->derivedFinal->release(ob->derivedFinal);
 		ob->derivedFinal = NULL;
 	}
+	if (ob->derivedDeform) {
+		ob->derivedDeform->needsFree = 1;
+		ob->derivedDeform->release(ob->derivedDeform);
+		ob->derivedDeform = NULL;
+	}
 	
 	BKE_displist_free(&ob->disp);
 }
@@ -264,7 +278,7 @@ void BKE_object_free(Object *ob)
 {
 	int a;
 	
-	BKE_object_free_display(ob);
+	BKE_object_free_derived_caches(ob);
 	
 	/* disconnect specific data, but not for lib data (might be indirect data, can get relinked) */
 	if (ob->data) {
@@ -2790,27 +2804,29 @@ void BKE_object_sculpt_modifiers_changed(Object *ob)
 {
 	SculptSession *ss = ob->sculpt;
 
-	if (!ss->cache) {
-		/* we free pbvh on changes, except during sculpt since it can't deal with
-		 * changing PVBH node organization, we hope topology does not change in
-		 * the meantime .. weak */
-		if (ss->pbvh) {
-			BKE_pbvh_free(ss->pbvh);
-			ss->pbvh = NULL;
-		}
+	if (ss) {
+		if (!ss->cache) {
+			/* we free pbvh on changes, except during sculpt since it can't deal with
+			 * changing PVBH node organization, we hope topology does not change in
+			 * the meantime .. weak */
+			if (ss->pbvh) {
+				BKE_pbvh_free(ss->pbvh);
+				ss->pbvh = NULL;
+			}
 
-		free_sculptsession_deformMats(ob->sculpt);
-	}
-	else {
-		PBVHNode **nodes;
-		int n, totnode;
+			free_sculptsession_deformMats(ob->sculpt);
+		}
+		else {
+			PBVHNode **nodes;
+			int n, totnode;
 
-		BKE_pbvh_search_gather(ss->pbvh, NULL, NULL, &nodes, &totnode);
+			BKE_pbvh_search_gather(ss->pbvh, NULL, NULL, &nodes, &totnode);
 
-		for (n = 0; n < totnode; n++)
-			BKE_pbvh_node_mark_update(nodes[n]);
+			for (n = 0; n < totnode; n++)
+				BKE_pbvh_node_mark_update(nodes[n]);
 
-		MEM_freeN(nodes);
+			MEM_freeN(nodes);
+		}
 	}
 }
 
diff --git a/source/blender/blenkernel/intern/paint.c b/source/blender/blenkernel/intern/paint.c
index 74542321a62..e8829c6216b 100644
--- a/source/blender/blenkernel/intern/paint.c
+++ b/source/blender/blenkernel/intern/paint.c
@@ -51,6 +51,7 @@
 #include "BKE_global.h"
 #include "BKE_image.h"
 #include "BKE_library.h"
+#include "BKE_object.h"
 #include "BKE_paint.h"
 #include "BKE_pbvh.h"
 #include "BKE_subsurf.h"
@@ -433,11 +434,8 @@ void sculptsession_bm_to_me_for_render(Object *object)
 			 * here because this will lead to the while object
 			 * surface to disappear, so we'll release DM in place.
 			 */
-			if (object->derivedFinal) {
-				object->derivedFinal->needsFree = 1;
-				object->derivedFinal->release(object->derivedFinal);
-				object->derivedFinal = NULL;
-			}
+			BKE_object_free_derived_caches(object);
+
 			if (object->sculpt->pbvh) {
 				BKE_pbvh_free(object->sculpt->pbvh);
 				object->sculpt->pbvh = NULL;
diff --git a/source/blender/editors/mesh/editmesh_utils.c b/source/blender/editors/mesh/editmesh_utils.c
index 719c7ab95e3..40fda072180 100644
--- a/source/blender/editors/mesh/editmesh_utils.c
+++ b/source/blender/editors/mesh/editmesh_utils.c
@@ -374,6 +374,11 @@ void EDBM_mesh_load(Object *ob)
 #ifdef USE_TESSFACE_DEFAULT
 	BKE_mesh_tessface_calc(me);
 #endif
+
+	/* free derived mesh. usually this would happen through depsgraph but there
+	 * are exceptions like file save that will not cause this, and we want to
+	 * avoid ending up with an invalid derived mesh then */
+	BKE_object_free_derived_caches(ob);
 }
 
 /**
diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index fce520d04fa..ee10adbf7db 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -4542,7 +4542,7 @@ void sculpt_pbvh_clear(Object *ob)
 	ss->pbvh = NULL;
 	if (dm)
 		dm->getPBVH(NULL, dm);
-	BKE_object_free_display(ob);
+	BKE_object_free_derived_caches(ob);
 }
 
 void sculpt_update_after_dynamic_topology_toggle(bContext *C)