diff --git a/mercurial/commit.py b/mercurial/commit.py
--- a/mercurial/commit.py
+++ b/mercurial/commit.py
@@ -231,6 +231,9 @@
                     changeset extra as copy source of truth).
         ms:         mergestate object (None if no mergestate exists
                     while committing)
+        includecopymeta: boolean, set to False to skip storing the copy data
+                         (only used by the Google specific feature of using
+                         changeset extra as copy source of truth).
 
     output: (filenode, touched)