1 files changed, 15 insertions, 0 deletions

diff --git a/crates/ra_hir_expand/src/lib.rs b/crates/ra_hir_expand/src/lib.rs
index 51c5f9623..7cf3b59a7 100644
--- a/crates/ra_hir_expand/src/lib.rs
+++ b/crates/ra_hir_expand/src/lib.rs
@@ -112,6 +112,21 @@ impl HirFileId {
             }
         }
     }
+
+    /// Indicate it is macro file generated for builtin derive
+    pub fn is_builtin_derive(&self, db: &dyn db::AstDatabase) -> Option<InFile<ast::ModuleItem>> {
+        match self.0 {
+            HirFileIdRepr::FileId(_) => None,
+            HirFileIdRepr::MacroFile(macro_file) => {
+                let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
+                let item = match loc.def.kind {
+                    MacroDefKind::BuiltInDerive(_) => loc.kind.node(db),
+                    _ => return None,
+                };
+                Some(item.with_value(ast::ModuleItem::cast(item.value.clone())?))
+            }
+        }
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]