Refactor document data cleanup

Author: st0012

rust/rubydex/src/model/declaration.rs

@@ -357,10 +357,8 @@ impl Declaration {
         all_declarations!(self, it => it.definition_ids.is_empty())
     }
 
-    /// Returns true if this declaration is no longer anchored to anything
-    /// and can be removed. For most declarations, that means having no
-    /// definitions. Singleton classes are also kept alive by members and
-    /// inbound constant references.
+    /// Returns true if this declaration has no local anchors and can be removed.
+    /// Graph-level cleanup can still keep declarations alive based on external anchors.
     #[must_use]
     pub fn is_removable(&self) -> bool {
         if let Some(ns) = self.as_singleton_class() {

rust/rubydex/src/model/definitions.rs

@@ -179,6 +179,18 @@ impl Definition {
         }
     }
 
+    #[must_use]
+    pub fn has_extend_mixin(&self) -> bool {
+        let mixins = match self {
+            Definition::Class(definition) => definition.mixins(),
+            Definition::SingletonClass(definition) => definition.mixins(),
+            Definition::Module(definition) => definition.mixins(),
+            _ => return false,
+        };
+
+        mixins.iter().any(|mixin| matches!(mixin, Mixin::Extend(_)))
+    }
+
     #[must_use]
     pub fn is_deprecated(&self) -> bool {
         all_definitions!(self, it => it.flags().is_deprecated())