Depsgraph: assert that mesh_get_eval_final/deform aren't used in eval.

Using those functions during multithreaded evaluation is a sure
way to have a race condition and crash.

source/blender/blenkernel/intern/DerivedMesh.c

@@ -2157,6 +2157,13 @@ DerivedMesh *mesh_get_derived_final(
 Mesh *mesh_get_eval_final(
         struct Depsgraph *depsgraph, Scene *scene, Object *ob, CustomDataMask dataMask)
 {
+	/* This function isn't thread-safe and can't be used during evaluation. */
+	BLI_assert(DEG_debug_is_evaluating(depsgraph) == false);
+
+	/* Evaluated meshes aren't supposed to be created on original instances. If you do,
+	 * they aren't cleaned up properly on mode switch, causing crashes, e.g T58150. */
+	BLI_assert(ob->id.tag & LIB_TAG_COPIED_ON_WRITE);
+
 	/* if there's no evaluated mesh or the last data mask used doesn't include
 	 * the data we need, rebuild the derived mesh
 	 */
@@ -2197,6 +2204,13 @@ DerivedMesh *mesh_get_derived_deform(struct Depsgraph *depsgraph, Scene *scene,
 #endif
 Mesh *mesh_get_eval_deform(struct Depsgraph *depsgraph, Scene *scene, Object *ob, CustomDataMask dataMask)
 {
+	/* This function isn't thread-safe and can't be used during evaluation. */
+	BLI_assert(DEG_debug_is_evaluating(depsgraph) == false);
+
+	/* Evaluated meshes aren't supposed to be created on original instances. If you do,
+	 * they aren't cleaned up properly on mode switch, causing crashes, e.g T58150. */
+	BLI_assert(ob->id.tag & LIB_TAG_COPIED_ON_WRITE);
+
 	/* if there's no derived mesh or the last data mask used doesn't include
 	 * the data we need, rebuild the derived mesh
 	 */

source/blender/depsgraph/DEG_depsgraph.h

@@ -237,6 +237,8 @@ void DEG_make_inactive(struct Depsgraph *depsgraph);
 
 /* Evaluation Debug ------------------------------ */
 
+bool DEG_debug_is_evaluating(struct Depsgraph *depsgraph);
+
 void DEG_debug_print_begin(struct Depsgraph *depsgraph);
 
 void DEG_debug_print_eval(struct Depsgraph *depsgraph,

source/blender/depsgraph/intern/depsgraph.cc

@@ -94,7 +94,8 @@ Depsgraph::Depsgraph(Scene *scene,
     mode(mode),
     ctime(BKE_scene_frame_get(scene)),
     scene_cow(NULL),
-    is_active(false)
+    is_active(false),
+    debug_is_evaluating(false)
 {
 	BLI_spin_init(&lock);
 	id_hash = BLI_ghash_ptr_new("Depsgraph id hash");
@@ -645,6 +646,13 @@ void DEG_make_inactive(struct Depsgraph *depsgraph)
 
 /* Evaluation and debug */
 
+bool DEG_debug_is_evaluating(struct Depsgraph *depsgraph)
+{
+	DEG::Depsgraph *deg_graph =
+	        reinterpret_cast<DEG::Depsgraph *>(depsgraph);
+	return deg_graph->debug_is_evaluating;
+}
+
 static DEG::string depsgraph_name_for_logging(struct Depsgraph *depsgraph)
 {
 	const char *name = DEG_debug_name_get(depsgraph);

source/blender/depsgraph/intern/depsgraph.h

@@ -234,6 +234,8 @@ struct Depsgraph {
 	int debug_flags;
 	string debug_name;
 
+	bool debug_is_evaluating;
+
 	/* Cached list of colliders/effectors for collections and the scene
 	 * created along with relations, for fast lookup during evaluation. */
 	GHash *physics_relations[DEG_PHYSICS_RELATIONS_NUM];

source/blender/depsgraph/intern/eval/deg_eval.cc

@@ -291,6 +291,7 @@ void deg_evaluate_on_refresh(Depsgraph *graph)
 	}
 	const bool do_time_debug = ((G.debug & G_DEBUG_DEPSGRAPH_TIME) != 0);
 	const double start_time = do_time_debug ? PIL_check_seconds_timer() : 0;
+	graph->debug_is_evaluating = true;
 	depsgraph_ensure_view_layer(graph);
 	/* Set up evaluation state. */
 	DepsgraphEvalState state;
@@ -326,6 +327,7 @@ void deg_evaluate_on_refresh(Depsgraph *graph)
 	if (need_free_scheduler) {
 		BLI_task_scheduler_free(task_scheduler);
 	}
+	graph->debug_is_evaluating = false;
 	if (do_time_debug) {
 		printf("Depsgraph updated in %f seconds.\n",
 		       PIL_check_seconds_timer() - start_time);