diff -r 40b51c28b242 -r 1766130fe9ba rust/hg-core/src/dirstate_tree/on_disk.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-core/src/dirstate_tree/on_disk.rs	Wed May 19 13:15:00 2021 +0200
@@ -0,0 +1,4 @@
+/// Added at the start of `.hg/dirstate` when the "v2" format is used.
+/// Acts like a "magic number". This is a sanity check, not strictly necessary
+/// since `.hg/requires` already governs which format should be used.
+pub const V2_FORMAT_MARKER: &[u8; 12] = b"dirstate-v2\n";