Fix #147978: Missed conversion to SystemProperties for children bones.

Forgot that the Armature's bones list only contain root bones...

Fix the versioning code.

Also adding a 'recovery' extra versioning step for files that may have
already been opened and re-saved in Blender 5.0 (though this step is
not 100% handling all cases, in case some script or add-on already
created some system properties in a bone in 5.0, the existing user
properties from 4.5 and before won't be copied over anymore).

Pull Request: https://projects.blender.org/blender/blender/pulls/148125

source/blender/blenkernel/BKE_blender_version.h

@@ -27,7 +27,7 @@
 
 /* Blender file format version. */
 #define BLENDER_FILE_VERSION BLENDER_VERSION
-#define BLENDER_FILE_SUBVERSION 109
+#define BLENDER_FILE_SUBVERSION 110
 
 /* Minimum Blender version that supports reading file written with the current
  * version. Older Blender versions will test this and cancel loading the file, showing a warning to

source/blender/blenloader/intern/readfile.cc

@@ -3501,6 +3501,11 @@ static void do_versions(FileData *fd, Library *lib, Main *main)
      * later during 5.0 development process. */
     version_system_idprops_nodes_generate(main);
   }
+  if (!MAIN_VERSION_FILE_ATLEAST(main, 500, 110)) {
+    /* Same as above, but children bones were missed by initial versioning code, attempt to
+     * transfer idprops data still in case they have no system properties defined yet. */
+    version_system_idprops_children_bones_generate(main);
+  }
 
   if (G.debug & G_DEBUG) {
     char build_commit_datetime[32];

source/blender/blenloader/intern/versioning_500.cc

@@ -130,8 +130,16 @@ void version_system_idprops_generate(Main *bmain)
     for (BoneCollection *bcoll : armature->collections_span()) {
       idprops_process(bcoll->prop, &bcoll->system_properties);
     }
-    LISTBASE_FOREACH (Bone *, bone, &armature->bonebase) {
+    /* There is no way to iterate directly over all bones of an armature currently, use a recursive
+     * approach instead. */
+    auto process_bone_recursive = [](const auto &process_bone_recursive, Bone *bone) -> void {
       idprops_process(bone->prop, &bone->system_properties);
+      LISTBASE_FOREACH (Bone *, bone_it, &bone->childbase) {
+        process_bone_recursive(process_bone_recursive, bone_it);
+      }
+    };
+    LISTBASE_FOREACH (Bone *, bone_it, &armature->bonebase) {
+      process_bone_recursive(process_bone_recursive, bone_it);
     }
   }
 }
@@ -145,6 +153,29 @@ void version_system_idprops_nodes_generate(Main *bmain)
   }
   FOREACH_NODETREE_END;
 }
+/* Separate callback for non-root bones, because they were missed in the initial implementation. */
+void version_system_idprops_children_bones_generate(Main *bmain)
+{
+  LISTBASE_FOREACH (bArmature *, armature, &bmain->armatures) {
+    /* There is no way to iterate directly over all bones of an armature currently, use a recursive
+     * approach instead. */
+    auto process_bone_recursive = [](const auto &process_bone_recursive, Bone *bone) -> void {
+      /* Do not overwrite children bones' system properties if they were already defined by some
+       * scripts or add-on e.g. */
+      if (bone->system_properties == nullptr) {
+        idprops_process(bone->prop, &bone->system_properties);
+      }
+      LISTBASE_FOREACH (Bone *, bone_it, &bone->childbase) {
+        process_bone_recursive(process_bone_recursive, bone_it);
+      }
+    };
+    LISTBASE_FOREACH (Bone *, bone_it, &armature->bonebase) {
+      LISTBASE_FOREACH (Bone *, bone_child_it, &bone_it->childbase) {
+        process_bone_recursive(process_bone_recursive, bone_child_it);
+      }
+    }
+  }
+}
 
 static CustomDataLayer *find_old_seam_layer(CustomData &custom_data, const blender::StringRef name)
 {

source/blender/blenloader/intern/versioning_common.hh

@@ -218,6 +218,7 @@ bNode *version_eevee_output_node_get(bNodeTree *ntree, int16_t node_type);
  */
 void version_system_idprops_generate(Main *bmain);
 void version_system_idprops_nodes_generate(Main *bmain);
+void version_system_idprops_children_bones_generate(Main *bmain);
 
 bool all_scenes_use(Main *bmain, const blender::Span<const char *> engines);