refactor: replace displayable_blocks with child

This removes the "displayable_blocks" property and replaces all the
usages with the "child" property.

openedx/core/djangoapps/xblock/runtime/shims.py

@@ -403,7 +403,7 @@ class XBlockShim:
         warnings.warn("get_display_blocks() is deprecated.", DeprecationWarning, stacklevel=2)
         blocks = []
         for child in self.get_children():
-            blocks.extend(child.displayable_blocks())
+            blocks.append(child)
         return blocks
 
     def displayable_items(self):

xmodule/library_content_block.py

@@ -399,13 +399,13 @@ class LibraryContentBlock(
                 # 500-response.
                 logger.error('Skipping display for child block that is None')
                 continue
-            for displayable in child.displayable_blocks():
-                rendered_child = displayable.render(STUDENT_VIEW, child_context)
-                fragment.add_fragment_resources(rendered_child)
-                contents.append({
-                    'id': str(displayable.location),
-                    'content': rendered_child.content,
-                })
+
+            rendered_child = child.render(STUDENT_VIEW, child_context)
+            fragment.add_fragment_resources(rendered_child)
+            contents.append({
+                'id': str(child.location),
+                'content': rendered_child.content,
+            })
 
         fragment.add_content(self.runtime.service(self, 'mako').render_template('vert_module.html', {
             'items': contents,

xmodule/tests/test_conditional.py

@@ -91,7 +91,6 @@ class ConditionalFactory:
         child_descriptor.visible_to_staff_only = False
         child_descriptor._xmodule.student_view.return_value = Fragment(content='<p>This is a secret</p>')  # lint-amnesty, pylint: disable=protected-access
         child_descriptor.student_view = child_descriptor._xmodule.student_view  # lint-amnesty, pylint: disable=protected-access
-        child_descriptor.displayable_blocks.return_value = [child_descriptor]
         child_descriptor.runtime = descriptor_system
         child_descriptor.xmodule_runtime = get_test_system()
         child_descriptor.render = lambda view, context=None: descriptor_system.render(child_descriptor, view, context)

xmodule/x_module.py

@@ -531,17 +531,10 @@ class XModuleMixin(XModuleFields, XBlock):
         """
         blocks = []
         for child in self.get_children():
-            blocks.extend(child.displayable_blocks())
+            blocks.append(child)
 
         return blocks
 
-    def displayable_blocks(self):
-        """
-        Returns list of displayable modules contained by this module. If this
-        module is visible, should return [self].
-        """
-        return [self]
-
     def get_child_by(self, selector):
         """
         Return a child XBlock that matches the specified selector