Collection Manager: Add Operator. Task: T69577

Adds a Remove Empty Collections operator in a new specials menu
in the main Collection Manager popup.

This operator has two modes:
Mode one only removes collections if they don't have subcollections
or objects.
Mode two removes all collections that don't contain objects.

Both of these modes are accessible via the new specials menu.

4 files changed, 161 insertions, 70 deletions

diff --git a/object_collection_manager/__init__.py b/object_collection_manager/__init__.py
index f6a31695..90783e7e 100644
--- a/object_collection_manager/__init__.py
+++ b/object_collection_manager/__init__.py
@@ -22,7 +22,7 @@ bl_info = {
     "name": "Collection Manager",
     "description": "Manage collections and their objects",
     "author": "Ryan Inch",
-    "version": (2, 9, 5),
+    "version": (2, 10, 0),
     "blender": (2, 80, 0),
     "location": "View3D - Object Mode (Shortcut - M)",
     "warning": '',  # used for warning icon and text in addons panel
@@ -110,12 +110,14 @@ classes = (
     operators.CMUnDisableRenderAllOperator,
     operators.CMNewCollectionOperator,
     operators.CMRemoveCollectionOperator,
+    operators.CMRemoveEmptyCollectionsOperator,
     operators.CMSetCollectionOperator,
     operators.CMPhantomModeOperator,
     preferences.CMPreferences,
     ui.CM_UL_items,
     ui.CollectionManager,
     ui.CMDisplayOptionsPanel,
+    ui.SpecialsMenu,
     CollectionManagerProperties,
     )
 
diff --git a/object_collection_manager/operator_utils.py b/object_collection_manager/operator_utils.py
index f99d870b..d86a534f 100644
--- a/object_collection_manager/operator_utils.py
+++ b/object_collection_manager/operator_utils.py
@@ -17,12 +17,17 @@
 # ##### END GPL LICENSE BLOCK #####
 
 # Copyright 2011, Ryan Inch
+import bpy
 
 from .internals import (
     layer_collections,
+    qcd_slots,
+    expanded,
+    expand_history,
     rto_history,
     copy_buffer,
     swap_buffer,
+    update_property_group,
 )
 
 rto_path = {
@@ -289,3 +294,80 @@ def clear_swap(rto):
         swap_buffer["A"]["values"].clear()
         swap_buffer["B"]["RTO"] = ""
         swap_buffer["B"]["values"].clear()
+
+
+def link_child_collections_to_parent(laycol, collection, parent_collection):
+    # store view layer RTOs for all children of the to be deleted collection
+    child_states = {}
+    def get_child_states(layer_collection):
+        child_states[layer_collection.name] = (layer_collection.exclude,
+                                               layer_collection.hide_viewport,
+                                               layer_collection.holdout,
+                                               layer_collection.indirect_only)
+
+    apply_to_children(laycol["ptr"], get_child_states)
+
+    # link any subcollections of the to be deleted collection to it's parent
+    for subcollection in collection.children:
+        if not subcollection.name in parent_collection.children:
+            parent_collection.children.link(subcollection)
+
+    # apply the stored view layer RTOs to the newly linked collections and their
+    # children
+    def restore_child_states(layer_collection):
+        state = child_states.get(layer_collection.name)
+
+        if state:
+            layer_collection.exclude = state[0]
+            layer_collection.hide_viewport = state[1]
+            layer_collection.holdout = state[2]
+            layer_collection.indirect_only = state[3]
+
+    apply_to_children(laycol["parent"]["ptr"], restore_child_states)
+
+
+def remove_collection(laycol, collection, context):
+    # get selected row
+    cm = context.scene.collection_manager
+    selected_row_name = cm.cm_list_collection[cm.cm_list_index].name
+
+    # delete collection
+    bpy.data.collections.remove(collection)
+
+    # update references
+    expanded.discard(laycol["name"])
+
+    if expand_history["target"] == laycol["name"]:
+        expand_history["target"] = ""
+
+    if laycol["name"] in expand_history["history"]:
+        expand_history["history"].remove(laycol["name"])
+
+    if qcd_slots.contains(name=laycol["name"]):
+        qcd_slots.del_slot(name=laycol["name"])
+
+    if laycol["name"] in qcd_slots.overrides:
+        qcd_slots.overrides.remove(laycol["name"])
+
+    # reset history
+    for rto in rto_history.values():
+        rto.clear()
+
+    # update tree view
+    update_property_group(context)
+
+    # update selected row
+    laycol = layer_collections.get(selected_row_name, None)
+    if laycol:
+        cm.cm_list_index = laycol["row_index"]
+
+    elif len(cm.cm_list_collection) <= cm.cm_list_index:
+        cm.cm_list_index =  len(cm.cm_list_collection) - 1
+
+        if cm.cm_list_index > -1:
+            name = cm.cm_list_collection[cm.cm_list_index].name
+            laycol = layer_collections[name]
+            while not laycol["visible"]:
+                laycol = laycol["parent"]
+
+            cm.cm_list_index = laycol["row_index"]
diff --git a/object_collection_manager/operators.py b/object_collection_manager/operators.py
index 77882c97..642860fa 100644
--- a/object_collection_manager/operators.py
+++ b/object_collection_manager/operators.py
@@ -63,6 +63,8 @@ from .operator_utils import (
     swap_rtos,
     clear_copy,
     clear_swap,
+    link_child_collections_to_parent,
+    remove_collection,
 )
 
 class SetActiveCollection(Operator):
@@ -869,12 +871,9 @@ class CMRemoveCollectionOperator(Operator):
         global expand_history
         global qcd_slots
 
-        cm = context.scene.collection_manager
-
         laycol = layer_collections[self.collection_name]
         collection = laycol["ptr"].collection
         parent_collection = laycol["parent"]["ptr"].collection
-        selected_row_name = cm.cm_list_collection[cm.cm_list_index].name
 
 
         # shift all objects in this collection to the parent collection
@@ -885,78 +884,69 @@ class CMRemoveCollectionOperator(Operator):
 
         # shift all child collections to the parent collection preserving view layer RTOs
         if collection.children:
-            # store view layer RTOs for all children of the to be deleted collection
-            child_states = {}
-            def get_child_states(layer_collection):
-                child_states[layer_collection.name] = (layer_collection.exclude,
-                                                       layer_collection.hide_viewport,
-                                                       layer_collection.holdout,
-                                                       layer_collection.indirect_only)
-
-            apply_to_children(laycol["ptr"], get_child_states)
-
-            # link any subcollections of the to be deleted collection to it's parent
-            for subcollection in collection.children:
-                if not subcollection.name in parent_collection.children:
-                    parent_collection.children.link(subcollection)
+            link_child_collections_to_parent(laycol, collection, parent_collection)
 
-            # apply the stored view layer RTOs to the newly linked collections and their
-            # children
-            def restore_child_states(layer_collection):
-                state = child_states.get(layer_collection.name)
-
-                if state:
-                    layer_collection.exclude = state[0]
-                    layer_collection.hide_viewport = state[1]
-                    layer_collection.holdout = state[2]
-                    layer_collection.indirect_only = state[3]
-
-            apply_to_children(laycol["parent"]["ptr"], restore_child_states)
+        # remove collection, update references, and update tree view
+        remove_collection(laycol, collection, context)
 
+        return {'FINISHED'}
 
-        # remove collection, update expanded, and update tree view
-        bpy.data.collections.remove(collection)
-        expanded.discard(self.collection_name)
 
-        if expand_history["target"] == self.collection_name:
-            expand_history["target"] = ""
-
-        if self.collection_name in expand_history["history"]:
-            expand_history["history"].remove(self.collection_name)
+class CMRemoveEmptyCollectionsOperator(Operator):
+    bl_label = "Remove Empty Collections"
+    bl_idname = "view3d.remove_empty_collections"
+    bl_options = {'UNDO'}
 
-        update_property_group(context)
+    without_objects: BoolProperty()
 
+    @classmethod
+    def description(cls, context, properties):
+        if properties.without_objects:
+            tooltip = (
+                "Purge All Collections Without Objects.\n"
+                "Deletes all collections that don't contain objects even if they have subcollections"
+                )
 
-        # update selected row
-        laycol = layer_collections.get(selected_row_name, None)
-        if laycol:
-            cm.cm_list_index = laycol["row_index"]
+        else:
+            tooltip = (
+                "Remove Empty Collections.\n"
+                "Delete collections that don't have any subcollections or objects"
+                )
 
-        elif len(cm.cm_list_collection) == cm.cm_list_index:
-            cm.cm_list_index -=  1
+        return tooltip
 
-            if cm.cm_list_index > -1:
-                name = cm.cm_list_collection[cm.cm_list_index].name
-                laycol = layer_collections[name]
-                while not laycol["visible"]:
-                    laycol = laycol["parent"]
+    def execute(self, context):
+        global rto_history
+        global expand_history
+        global qcd_slots
 
-                cm.cm_list_index = laycol["row_index"]
+        if self.without_objects:
+            empty_collections = [laycol["name"]
+                                for laycol in layer_collections.values()
+                                if not laycol["ptr"].collection.objects]
+        else:
+            empty_collections = [laycol["name"]
+                                for laycol in layer_collections.values()
+                                if not laycol["children"] and
+                                not laycol["ptr"].collection.objects]
 
+        for name in empty_collections:
+            laycol = layer_collections[name]
+            collection = laycol["ptr"].collection
+            parent_collection = laycol["parent"]["ptr"].collection
 
-        # update qcd
-        if qcd_slots.contains(name=self.collection_name):
-            qcd_slots.del_slot(name=self.collection_name)
+            # link all child collections to the parent collection preserving view layer RTOs
+            if collection.children:
+                link_child_collections_to_parent(laycol, collection, parent_collection)
 
-        if self.collection_name in qcd_slots.overrides:
-            qcd_slots.overrides.remove(self.collection_name)
+            # remove collection, update references, and update tree view
+            remove_collection(laycol, collection, context)
 
-        # reset history
-        for rto in rto_history.values():
-            rto.clear()
+        self.report({"INFO"}, f"Removed {len(empty_collections)} collections")
 
         return {'FINISHED'}
 
+
 rename = [False]
 class CMNewCollectionOperator(Operator):
     bl_label = "Add New Collection"
diff --git a/object_collection_manager/ui.py b/object_collection_manager/ui.py
index 838c5d18..fab65c67 100644
--- a/object_collection_manager/ui.py
+++ b/object_collection_manager/ui.py
@@ -21,6 +21,7 @@
 import bpy
 
 from bpy.types import (
+    Menu,
     Operator,
     Panel,
     UIList,
@@ -112,9 +113,9 @@ class CollectionManager(Operator):
         layout.row().separator()
 
         # buttons
-        button_row = layout.row()
+        button_row_1 = layout.row()
 
-        op_sec = button_row.row()
+        op_sec = button_row_1.row()
         op_sec.alignment = 'LEFT'
 
         collapse_sec = op_sec.row()
@@ -138,11 +139,12 @@ class CollectionManager(Operator):
             renum_sec.alignment = 'LEFT'
             renum_sec.operator("view3d.renumerate_qcd_slots")
 
-        # filter
-        filter_sec = button_row.row()
-        filter_sec.alignment = 'RIGHT'
+        # menu & filter
+        right_sec = button_row_1.row()
+        right_sec.alignment = 'RIGHT'
 
-        filter_sec.popover(panel="COLLECTIONMANAGER_PT_display_options",
+        right_sec.menu("VIEW3D_MT_CM_specials_menu")
+        right_sec.popover(panel="COLLECTIONMANAGER_PT_display_options",
                            text="", icon='FILTER')
 
         mc_box = layout.box()
@@ -304,19 +306,19 @@ class CollectionManager(Operator):
                                    sort_lock=True)
 
         # add collections
-        addcollec_row = layout.row()
-        prop = addcollec_row.operator("view3d.add_collection", text="Add Collection",
+        button_row_2 = layout.row()
+        prop = button_row_2.operator("view3d.add_collection", text="Add Collection",
                                icon='COLLECTION_NEW')
         prop.child = False
 
-        prop = addcollec_row.operator("view3d.add_collection", text="Add SubCollection",
+        prop = button_row_2.operator("view3d.add_collection", text="Add SubCollection",
                                icon='COLLECTION_NEW')
         prop.child = True
 
         # phantom mode
-        phantom_row = layout.row()
+        button_row_3 = layout.row()
         toggle_text = "Disable " if cm.in_phantom_mode else "Enable "
-        phantom_row.operator("view3d.toggle_phantom_mode", text=toggle_text+"Phantom Mode")
+        button_row_3.operator("view3d.toggle_phantom_mode", text=toggle_text+"Phantom Mode")
 
         if cm.in_phantom_mode:
             view.enabled = False
@@ -748,6 +750,21 @@ class CMDisplayOptionsPanel(Panel):
         row.prop(cm, "align_local_ops")
 
 
+class SpecialsMenu(Menu):
+    bl_label = "Specials"
+    bl_idname = "VIEW3D_MT_CM_specials_menu"
+
+    def draw(self, context):
+        layout = self.layout
+
+        prop = layout.operator("view3d.remove_empty_collections")
+        prop.without_objects = False
+
+        prop = layout.operator("view3d.remove_empty_collections",
+                               text="Purge All Collections Without Objects")
+        prop.without_objects = True
+
+
 def view3d_header_qcd_slots(self, context):
     layout = self.layout