diff REFACTOR put diff into separate source/header
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 342e6b0..85117c3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -139,6 +139,7 @@
     src/hash_table.c
     src/set.c
     src/path.c
+    src/diff.c
     src/context.c
     src/tree_data.c
     src/tree_data_free.c