RNA: add RNA_collection_is_empty & RNA_property_collection_is_empty

Some collections needed to be iterated over to count their length.
Provide a function to check if the collection is empty to avoid this.

source/blender/editors/curve/editcurve_paint.c

@@ -577,7 +577,7 @@ static bool curve_draw_init(bContext *C, wmOperator *op, bool is_invoke)
 
     /* Using an empty stroke complicates logic later,
      * it's simplest to disallow early on (see: T94085). */
-    if (RNA_collection_length(op->ptr, "stroke") == 0) {
+    if (RNA_collection_is_empty(op->ptr, "stroke")) {
       MEM_freeN(cdd);
       BKE_report(op->reports, RPT_ERROR, "The \"stroke\" cannot be empty");
       return false;

source/blender/editors/space_clip/clip_ops.c

@@ -186,7 +186,7 @@ static int open_exec(bContext *C, wmOperator *op)
   MovieClip *clip = NULL;
   char str[FILE_MAX];
 
-  if (RNA_collection_length(op->ptr, "files")) {
+  if (!RNA_collection_is_empty(op->ptr, "files")) {
     PointerRNA fileptr;
     PropertyRNA *prop;
     char dir_only[FILE_MAX], file_only[FILE_MAX];

source/blender/editors/space_sequencer/sequencer_add.c

@@ -747,7 +747,8 @@ static int sequencer_add_movie_strip_invoke(bContext *C,
   RNA_enum_set(op->ptr, "fit_method", SEQ_tool_settings_fit_method_get(scene));
 
   /* This is for drag and drop. */
-  if ((RNA_struct_property_is_set(op->ptr, "files") && RNA_collection_length(op->ptr, "files")) ||
+  if ((RNA_struct_property_is_set(op->ptr, "files") &&
+       !RNA_collection_is_empty(op->ptr, "files")) ||
       RNA_struct_property_is_set(op->ptr, "filepath")) {
     sequencer_generic_invoke_xy__internal(C, op, SEQPROP_NOPATHS, SEQ_TYPE_MOVIE);
     return sequencer_add_movie_strip_exec(C, op);
@@ -901,7 +902,8 @@ static int sequencer_add_sound_strip_invoke(bContext *C,
                                             const wmEvent *UNUSED(event))
 {
   /* This is for drag and drop. */
-  if ((RNA_struct_property_is_set(op->ptr, "files") && RNA_collection_length(op->ptr, "files")) ||
+  if ((RNA_struct_property_is_set(op->ptr, "files") &&
+       !RNA_collection_is_empty(op->ptr, "files")) ||
       RNA_struct_property_is_set(op->ptr, "filepath")) {
     sequencer_generic_invoke_xy__internal(C, op, SEQPROP_NOPATHS, SEQ_TYPE_SOUND_RAM);
     return sequencer_add_sound_strip_exec(C, op);
@@ -1094,7 +1096,7 @@ static int sequencer_add_image_strip_invoke(bContext *C,
   RNA_enum_set(op->ptr, "fit_method", SEQ_tool_settings_fit_method_get(scene));
 
   /* Name set already by drag and drop. */
-  if (RNA_struct_property_is_set(op->ptr, "files") && RNA_collection_length(op->ptr, "files")) {
+  if (RNA_struct_property_is_set(op->ptr, "files") && !RNA_collection_is_empty(op->ptr, "files")) {
     sequencer_generic_invoke_xy__internal(
         C, op, SEQPROP_ENDFRAME | SEQPROP_NOPATHS, SEQ_TYPE_IMAGE);
     return sequencer_add_image_strip_exec(C, op);

source/blender/makesrna/RNA_access.h

@@ -1117,6 +1117,11 @@ void RNA_property_collection_next(CollectionPropertyIterator *iter);
 void RNA_property_collection_skip(CollectionPropertyIterator *iter, int num);
 void RNA_property_collection_end(CollectionPropertyIterator *iter);
 int RNA_property_collection_length(PointerRNA *ptr, PropertyRNA *prop);
+/**
+ * Return true when `RNA_property_collection_length(ptr, prop) == 0`,
+ * without having to iterate over items in the collection (needed for some kinds of collections).
+ */
+bool RNA_property_collection_is_empty(PointerRNA *ptr, PropertyRNA *prop);
 int RNA_property_collection_lookup_index(PointerRNA *ptr, PropertyRNA *prop, PointerRNA *t_ptr);
 int RNA_property_collection_lookup_int(PointerRNA *ptr,
                                        PropertyRNA *prop,
@@ -1445,6 +1450,7 @@ void RNA_pointer_add(PointerRNA *ptr, const char *name);
 
 void RNA_collection_begin(PointerRNA *ptr, const char *name, CollectionPropertyIterator *iter);
 int RNA_collection_length(PointerRNA *ptr, const char *name);
+bool RNA_collection_is_empty(PointerRNA *ptr, const char *name);
 void RNA_collection_add(PointerRNA *ptr, const char *name, PointerRNA *r_value);
 void RNA_collection_clear(PointerRNA *ptr, const char *name);
 

source/blender/makesrna/intern/rna_access.c

@@ -3753,6 +3753,16 @@ int RNA_property_collection_length(PointerRNA *ptr, PropertyRNA *prop)
   return length;
 }
 
+bool RNA_property_collection_is_empty(PointerRNA *ptr, PropertyRNA *prop)
+{
+  BLI_assert(RNA_property_type(prop) == PROP_COLLECTION);
+  CollectionPropertyIterator iter;
+  RNA_property_collection_begin(ptr, prop, &iter);
+  bool test = iter.valid;
+  RNA_property_collection_end(&iter);
+  return !test;
+}
+
 /* This helper checks whether given collection property itself is editable (we only currently
  * support a limited set of operations, insertion of new items, and re-ordering of those new items
  * exclusively). */
@@ -6417,6 +6427,17 @@ int RNA_collection_length(PointerRNA *ptr, const char *name)
   return 0;
 }
 
+bool RNA_collection_is_empty(PointerRNA *ptr, const char *name)
+{
+  PropertyRNA *prop = RNA_struct_find_property(ptr, name);
+
+  if (prop) {
+    return RNA_property_collection_is_empty(ptr, prop);
+  }
+  printf("%s: %s.%s not found.\n", __func__, ptr->type->identifier, name);
+  return false;
+}
+
 bool RNA_property_is_set_ex(PointerRNA *ptr, PropertyRNA *prop, bool use_ghost)
 {
   prop = rna_ensure_property(prop);

source/blender/nodes/shader/nodes/node_shader_vertex_color.cc

@@ -23,7 +23,7 @@ static void node_shader_buts_vertex_color(uiLayout *layout, bContext *C, Pointer
     PointerRNA dataptr = RNA_pointer_get(&obptr, "data");
 
     if (U.experimental.use_sculpt_vertex_colors &&
-        RNA_collection_length(&dataptr, "sculpt_vertex_colors")) {
+        !RNA_collection_is_empty(&dataptr, "sculpt_vertex_colors")) {
       uiItemPointerR(
           layout, ptr, "layer_name", &dataptr, "sculpt_vertex_colors", "", ICON_GROUP_VCOL);
     }

source/blender/python/intern/bpy_rna.c

@@ -2192,16 +2192,9 @@ static int pyrna_prop_array_bool(BPy_PropertyRNA *self)
 
 static int pyrna_prop_collection_bool(BPy_PropertyRNA *self)
 {
-  /* No callback defined, just iterate and find the nth item. */
-  CollectionPropertyIterator iter;
-  int test;
-
   PYRNA_PROP_CHECK_INT(self);
 
-  RNA_property_collection_begin(&self->ptr, self->prop, &iter);
-  test = iter.valid;
-  RNA_property_collection_end(&iter);
-  return test;
+  return !RNA_property_collection_is_empty(&self->ptr, self->prop);
 }
 
 /* notice getting the length of the collection is avoided unless negative