Depsgraph: Inform when update or tag happens during evaluation

It is not allowed to do tagging or updates while dependency graph is
in the middle of evaluation.

This is something what is simple to violate from python code. This
change adds some sanity checks.

The request to update view layer or dependency graph will raise an
exception in Python now, so it's easy for scripters to notice.

Tagging for update will do silent return unless running with debug
command line argument. This is because it's a bit tricky to know
which exact dependency graph corresponds to a context from which
an update tag was triggered.

Differential Revision: https://developer.blender.org/D6035

1 files changed, 13 insertions, 4 deletions

diff --git a/source/blender/makesrna/intern/rna_layer.c b/source/blender/makesrna/intern/rna_layer.c
index 12d89ef5deb..40c6229f9b1 100644
--- a/source/blender/makesrna/intern/rna_layer.c
+++ b/source/blender/makesrna/intern/rna_layer.c
@@ -187,15 +187,24 @@ static void rna_LayerObjects_selected_begin(CollectionPropertyIterator *iter, Po
       iter, &view_layer->object_bases, rna_ViewLayer_objects_selected_skip);
 }
 
-static void rna_ViewLayer_update_tagged(ID *id_ptr, ViewLayer *view_layer, Main *bmain)
+static void rna_ViewLayer_update_tagged(ID *id_ptr,
+                                        ViewLayer *view_layer,
+                                        Main *bmain,
+                                        ReportList *reports)
 {
+  Scene *scene = (Scene *)id_ptr;
+  Depsgraph *depsgraph = BKE_scene_get_depsgraph(bmain, scene, view_layer, true);
+
+  if (DEG_is_evaluating(depsgraph)) {
+    BKE_report(reports, RPT_ERROR, "Dependency graph update requested during evaluation");
+    return;
+  }
+
 #  ifdef WITH_PYTHON
   /* Allow drivers to be evaluated */
   BPy_BEGIN_ALLOW_THREADS;
 #  endif
 
-  Scene *scene = (Scene *)id_ptr;
-  Depsgraph *depsgraph = BKE_scene_get_depsgraph(bmain, scene, view_layer, true);
   /* NOTE: This is similar to CTX_data_depsgraph_pointer(). Ideally such access would be
    * de-duplicated across all possible cases, but for now this is safest and easiest way to go.
    *
@@ -568,7 +577,7 @@ void RNA_def_view_layer(BlenderRNA *brna)
 
   /* debug update routine */
   func = RNA_def_function(srna, "update", "rna_ViewLayer_update_tagged");
-  RNA_def_function_flag(func, FUNC_USE_SELF_ID | FUNC_USE_MAIN);
+  RNA_def_function_flag(func, FUNC_USE_SELF_ID | FUNC_USE_MAIN | FUNC_USE_REPORTS);
   RNA_def_function_ui_description(
       func, "Update data tagged to be updated from previous access to data or operators");