diff rust/hg-core/src/dirstate_tree/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-core/src/dirstate_tree/dirstate_map.rs	Thu Jul 08 19:23:44 2021 +0200
+++ b/rust/hg-core/src/dirstate_tree/dirstate_map.rs	Thu Jul 15 23:02:17 2021 +0200
@@ -424,9 +424,10 @@
     pub fn new_v2(
         on_disk: &'on_disk [u8],
         data_size: usize,
+        metadata: &[u8],
     ) -> Result<Self, DirstateError> {
         if let Some(data) = on_disk.get(..data_size) {
-            Ok(on_disk::read(data)?)
+            Ok(on_disk::read(data, metadata)?)
         } else {
             Err(DirstateV2ParseError.into())
         }
@@ -1094,15 +1095,16 @@
         Ok(packed)
     }
 
-    /// Returns new data together with whether that data should be appended to
-    /// the existing data file whose content is at `self.on_disk` (true),
-    /// instead of written to a new data file (false).
+    /// Returns new data and metadata together with whether that data should be
+    /// appended to the existing data file whose content is at
+    /// `self.on_disk` (true), instead of written to a new data file
+    /// (false).
     #[timed]
     fn pack_v2(
         &mut self,
         now: Timestamp,
         can_append: bool,
-    ) -> Result<(Vec<u8>, bool), DirstateError> {
+    ) -> Result<(Vec<u8>, Vec<u8>, bool), DirstateError> {
         // TODO: how do we want to handle this in 2038?
         let now: i32 = now.0.try_into().expect("time overflow");
         let mut paths = Vec::new();