diff rust/hg-cpython/src/dirstate/dirstate_map.rs @ 47682:78f7f0d490ee

dirstate-v2: Move fixed-size tree metadata into the docket file

Before this changeset, the dirstate-v2 data file contained not only nodes
and paths that may be reused when appending to an existing file,
but also some fixed-size metadata that applies to the entire tree
and was added at the end of the data file for every append.

This moves that metadata into the docket file, so that repeated "append"
operations without meaningful changes don’t actually need to grow any file.

Differential Revision: https://phab.mercurial-scm.org/D11098

--- a/rust/hg-cpython/src/dirstate/dirstate_map.rs	Thu Jul 08 19:23:44 2021 +0200
+++ b/rust/hg-cpython/src/dirstate/dirstate_map.rs	Thu Jul 15 23:02:17 2021 +0200
@@ -84,12 +84,14 @@
     def new_v2(
         on_disk: PyBytes,
         data_size: usize,
+        tree_metadata: PyBytes,
     ) -> PyResult<PyObject> {
         let dirstate_error = |e: DirstateError| {
             PyErr::new::<exc::OSError, _>(py, format!("Dirstate error: {:?}", e))
         };
-        let inner = OwningDirstateMap::new_v2(py, on_disk, data_size)
-                .map_err(dirstate_error)?;
+        let inner = OwningDirstateMap::new_v2(
+            py, on_disk, data_size, tree_metadata,
+        ).map_err(dirstate_error)?;
         let map = Self::create_instance(py, Box::new(inner))?;
         Ok(map.into_object())
     }
@@ -353,9 +355,11 @@
         let mut inner = self.inner(py).borrow_mut();
         let result = inner.pack_v2(now, can_append);
         match result {
-            Ok((packed, append)) => {
+            Ok((packed, tree_metadata, append)) => {
                 let packed = PyBytes::new(py, &packed);
-                Ok((packed, append).to_py_object(py).into_object())
+                let tree_metadata = PyBytes::new(py, &tree_metadata);
+                let tuple = (packed, tree_metadata, append);
+                Ok(tuple.to_py_object(py).into_object())
             },
             Err(_) => Err(PyErr::new::<exc::OSError, _>(
                 py,