Mercurial > hg

--- a/hgext/eol.py	Wed Oct 16 19:14:30 2024 +0200
+++ b/hgext/eol.py	Tue Oct 01 13:49:11 2024 +0200
@@ -101,6 +101,7 @@
     error as errormod,
     extensions,
     match,
+    merge,
     pycompat,
     registrar,
     scmutil,
@@ -376,6 +377,7 @@

 def reposetup(ui, repo):
     uisetup(repo.ui)
+    merge.MAYBE_USE_RUST_UPDATE = False

     if not repo.local():
         return
--- a/hgext/journal.py	Wed Oct 16 19:14:30 2024 +0200
+++ b/hgext/journal.py	Tue Oct 01 13:49:11 2024 +0200
@@ -34,6 +34,7 @@
     localrepo,
     lock,
     logcmdutil,
+    merge,
     pycompat,
     registrar,
     util,
@@ -68,6 +69,7 @@

 # Journal recording, register hooks and storage object
 def extsetup(ui):
+    merge.MAYBE_USE_RUST_UPDATE = False
     extensions.wrapfunction(dispatch, 'runcommand', runcommand)
     extensions.wrapfunction(bookmarks.bmstore, '_write', recordbookmarks)
     extensions.wrapfilecache(
--- a/hgext/keyword.py	Wed Oct 16 19:14:30 2024 +0200
+++ b/hgext/keyword.py	Tue Oct 01 13:49:11 2024 +0200
@@ -102,6 +102,7 @@
     localrepo,
     logcmdutil,
     match,
+    merge,
     patch,
     pathutil,
     pycompat,
@@ -818,6 +819,7 @@
     extensions.wrapfunction(cmdutil, 'dorecord', kw_dorecord)
     for c in nokwwebcommands.split():
         extensions.wrapfunction(webcommands, c, kwweb_skip)
+    merge.MAYBE_USE_RUST_UPDATE = False


 def reposetup(ui, repo):
--- a/hgext/largefiles/__init__.py	Wed Oct 16 19:14:30 2024 +0200
+++ b/hgext/largefiles/__init__.py	Tue Oct 01 13:49:11 2024 +0200
@@ -114,6 +114,7 @@
     exthelper,
     hg,
     localrepo,
+    merge,
     wireprotov1server,
 )

@@ -165,6 +166,7 @@

 @eh.uisetup
 def _uisetup(ui):
+    merge.MAYBE_USE_RUST_UPDATE = False
     localrepo.featuresetupfuncs.add(featuresetup)
     hg.wirepeersetupfuncs.append(proto.wirereposetup)
--- a/hgext/lfs/__init__.py	Wed Oct 16 19:14:30 2024 +0200
+++ b/hgext/lfs/__init__.py	Tue Oct 01 13:49:11 2024 +0200
@@ -138,6 +138,7 @@
     filesetlang,
     localrepo,
     logcmdutil,
+    merge,
     minifileset,
     pycompat,
     revlog,
@@ -234,6 +235,7 @@

 @eh.uisetup
 def _uisetup(ui):
+    merge.MAYBE_USE_RUST_UPDATE = False
     localrepo.featuresetupfuncs.add(featuresetup)
--- a/mercurial/merge.py	Wed Oct 16 19:14:30 2024 +0200
+++ b/mercurial/merge.py	Tue Oct 01 13:49:11 2024 +0200
@@ -8,6 +8,7 @@
 from __future__ import annotations

 import collections
+import os
 import struct
 import typing
 from typing import Dict, Optional, Tuple
@@ -34,12 +35,15 @@
     pathutil,
     policy,
     pycompat,
+    requirements,
     scmutil,
     subrepoutil,
     util,
     worker,
 )

+rust_update_mod = policy.importrust("update")
+
 _pack = struct.pack
 _unpack = struct.unpack

@@ -147,6 +151,8 @@
     dircache = dict()
     dirstate = repo.dirstate
     wvfs = repo.wvfs
+    # wouldn't it be easier to loop over unknown files (and dirs)?
+
     if not force:

         def collectconflicts(conflicts, config):
@@ -1835,6 +1841,12 @@
 UPDATECHECK_LINEAR = b'linear'
 UPDATECHECK_NO_CONFLICT = b'noconflict'

+# Let extensions turn off any Rust code in the update code if that interferes
+# will their patching.
+# This being `True` does not mean that you have Rust extensions installed or
+# that the Rust path will be taken for any given invocation.
+MAYBE_USE_RUST_UPDATE = True
+

 def _update(
     repo,
@@ -2008,6 +2020,60 @@
         if not branchmerge and not wc.dirty(missing=True):
             followcopies = False

+        update_from_null = False
+        update_from_null_fallback = False
+        if (
+            MAYBE_USE_RUST_UPDATE
+            and rust_update_mod is not None
+            and p1.rev() == nullrev
+            and not branchmerge
+            # TODO it's probably not too hard to pass down the transaction and
+            # respect the write patterns from Rust. But since it doesn't affect
+            # a simple update from null, then it doesn't matter yet.
+            and repo.currenttransaction() is None
+            and matcher is None
+            and not wc.mergestate().active()
+            and b'.hgsubstate' not in p2
+        ):
+            working_dir_iter = os.scandir(repo.root)
+            maybe_hg_folder = next(working_dir_iter)
+            assert maybe_hg_folder is not None
+            if maybe_hg_folder.name == b".hg":
+                try:
+                    next(working_dir_iter)
+                except StopIteration:
+                    update_from_null = True
+
+        if update_from_null:
+            # Check the narrowspec and sparsespec here to display warnings
+            # more easily.
+            # TODO figure out of a way of bubbling up warnings to Python
+            # while not polluting the Rust code (probably a channel)
+            repo.narrowmatch()
+            sparse.matcher(repo, [nullrev, p2.rev()])
+            repo.hook(b'preupdate', throw=True, parent1=xp1, parent2=xp2)
+            # note that we're in the middle of an update
+            repo.vfs.write(b'updatestate', p2.hex())
+            try:
+                updated_count = rust_update_mod.update_from_null(
+                    repo.root, p2.rev()
+                )
+            except rust_update_mod.FallbackError:
+                update_from_null_fallback = True
+            else:
+                # We've changed the dirstate from Rust, we need to tell Python
+                repo.dirstate.invalidate()
+                # This includes setting the parents, since they are not read
+                # again on invalidation
+                with repo.dirstate.changing_parents(repo):
+                    repo.dirstate.setparents(fp2)
+                repo.dirstate.setbranch(p2.branch(), repo.currenttransaction())
+                sparse.prunetemporaryincludes(repo)
+                repo.hook(b'update', parent1=xp1, parent2=xp2, error=0)
+                # update completed, clear state
+                util.unlink(repo.vfs.join(b'updatestate'))
+                return updateresult(updated_count, 0, 0, 0)
+
         ### calculate phase
         mresult = calculateupdates(
             repo,
@@ -2131,11 +2197,13 @@
         # the dirstate.
         always = matcher is None or matcher.always()
         updatedirstate = updatedirstate and always and not wc.isinmemory()
-        if updatedirstate:
+        # If we're in the fallback case, we've already done this
+        if updatedirstate and not update_from_null_fallback:
             repo.hook(b'preupdate', throw=True, parent1=xp1, parent2=xp2)
             # note that we're in the middle of an update
             repo.vfs.write(b'updatestate', p2.hex())

+        # TODO don't run if Rust is available
         _advertisefsmonitor(
             repo, mresult.len((mergestatemod.ACTION_GET,)), p1.node()
         )
@@ -2172,14 +2240,14 @@
                 mergestatemod.recordupdates(
                     repo, mresult.actionsdict, branchmerge, getfiledata
                 )
-                # update completed, clear state
-                util.unlink(repo.vfs.join(b'updatestate'))
-
                 if not branchmerge:
                     repo.dirstate.setbranch(
                         p2.branch(), repo.currenttransaction()
                     )

+                # update completed, clear state
+                util.unlink(repo.vfs.join(b'updatestate'))
+
                 # If we're updating to a location, clean up any stale temporary includes
                 # (ex: this happens during hg rebase --abort).
                 if not branchmerge:
--- a/rust/Cargo.lock	Wed Oct 16 19:14:30 2024 +0200
+++ b/rust/Cargo.lock	Tue Oct 01 13:49:11 2024 +0200
@@ -650,6 +650,7 @@
  "thread_local",
  "toml",
  "twox-hash",
+ "uuid",
  "zstd",
 ]

@@ -1530,6 +1531,15 @@
 checksum = "c0edd1e5b14653f783770bce4a4dabb4a5108a5370a5f5d8cfe8710c361f6c8b"

 [[package]]
+name = "uuid"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8c5f0a0af699448548ad1a2fbf920fb4bee257eae39953ba95cb84891a0446a"
+dependencies = [
+ "getrandom 0.2.8",
+]
+
+[[package]]
 name = "vcpkg"
 version = "0.2.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
--- a/rust/hg-core/Cargo.toml	Wed Oct 16 19:14:30 2024 +0200
+++ b/rust/hg-core/Cargo.toml	Tue Oct 01 13:49:11 2024 +0200
@@ -44,6 +44,7 @@
 chrono = "0.4.34"
 dyn-clone = "1.0.16"
 filetime = "0.2.23"
+uuid = { version = "1.10", features = ["v4"] }

 # We don't use the `miniz-oxide` backend to not change rhg benchmarks and until
 # we have a clearer view of which backend is the fastest.
--- a/rust/hg-core/src/dirstate_tree/on_disk.rs	Wed Oct 16 19:14:30 2024 +0200
+++ b/rust/hg-core/src/dirstate_tree/on_disk.rs	Tue Oct 01 13:49:11 2024 +0200
@@ -8,7 +8,9 @@
     self, DirstateMap, DirstateMapWriteMode, NodeRef,
 };
 use crate::dirstate_tree::path_with_basename::WithBasename;
-use crate::errors::HgError;
+use crate::errors::{HgError, IoResultExt};
+use crate::repo::Repo;
+use crate::requirements::DIRSTATE_TRACKED_HINT_V1;
 use crate::utils::hg_path::HgPath;
 use crate::DirstateEntry;
 use crate::DirstateError;
@@ -20,6 +22,7 @@
 use rand::Rng;
 use std::borrow::Cow;
 use std::fmt::Write;
+use uuid::Uuid;

 use super::dirstate_map::DirstateIdentity;

@@ -916,3 +919,22 @@
         }
     }
 }
+
+/// Write a new tracked key to disk.
+/// See `format.use-dirstate-tracked-hint` config help for more details.
+pub fn write_tracked_key(repo: &Repo) -> Result<(), HgError> {
+    // TODO move this to the dirstate itself once it grows a `dirty` flag and
+    // can reason about which context it needs to write this in.
+    // For now, only this fast-path needs to think about the tracked hint.
+    // Use [`crate::dirstate_tree::dirstate_map::DirstateMap::
+    // use_tracked_hint`] instead of looking at the requirements once
+    // refactored.
+    if !repo.requirements().contains(DIRSTATE_TRACKED_HINT_V1) {
+        return Ok(());
+    }
+    // TODO use `hg_vfs` once the `InnerRevlog` is in.
+    let path = repo
+        .working_directory_path()
+        .join(".hg/dirstate-tracked-hint");
+    std::fs::write(&path, Uuid::new_v4().as_bytes()).when_writing_file(&path)
+}
--- a/rust/hg-core/src/lib.rs	Wed Oct 16 19:14:30 2024 +0200
+++ b/rust/hg-core/src/lib.rs	Tue Oct 01 13:49:11 2024 +0200
@@ -37,6 +37,7 @@
 pub mod operations;
 pub mod progress;
 pub mod revset;
+pub mod update;
 pub mod utils;
 pub mod vfs;
--- a/rust/hg-core/src/revlog/mod.rs	Wed Oct 16 19:14:30 2024 +0200
+++ b/rust/hg-core/src/revlog/mod.rs	Tue Oct 01 13:49:11 2024 +0200
@@ -1180,7 +1180,7 @@
         } else {
             if (self.flags & REVISION_FLAG_ELLIPSIS) != 0 {
                 return Err(HgError::unsupported(
-                    "ellipsis revisions are not supported by rhg",
+                    "support for ellipsis nodes is missing",
                 )
                 .into());
             }
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-core/src/update.rs	Tue Oct 01 13:49:11 2024 +0200
@@ -0,0 +1,491 @@
+//! Tools for moving the repository to a given revision
+
+use std::{
+    fs::Permissions,
+    io::Write,
+    os::unix::fs::{MetadataExt, PermissionsExt},
+    path::Path,
+    time::Duration,
+};
+
+use crate::{
+    dirstate::{ParentFileData, TruncatedTimestamp},
+    dirstate_tree::{
+        dirstate_map::DirstateEntryReset, on_disk::write_tracked_key,
+    },
+    errors::{HgError, IoResultExt},
+    exit_codes,
+    filelog::Filelog,
+    narrow,
+    node::NULL_NODE,
+    operations::{list_rev_tracked_files, ExpandedManifestEntry},
+    progress::Progress,
+    repo::Repo,
+    sparse,
+    utils::{
+        files::{filesystem_now, get_path_from_bytes},
+        hg_path::{hg_path_to_path_buf, HgPath, HgPathError},
+        path_auditor::PathAuditor,
+    },
+    vfs::{is_on_nfs_mount, VfsImpl},
+    DirstateParents, RevlogError, RevlogOpenOptions, UncheckedRevision,
+};
+use crossbeam_channel::{Receiver, Sender};
+use rayon::prelude::*;
+
+fn write_dirstate(repo: &Repo) -> Result<(), HgError> {
+    repo.write_dirstate()
+        .map_err(|e| HgError::abort(e.to_string(), exit_codes::ABORT, None))?;
+    write_tracked_key(repo)
+}
+
+/// Update the current working copy of `repo` to the given revision `to`, from
+/// the null revision and set + write out the dirstate to reflect that.
+///
+/// Do not call this outside of a Python context. This does *not* handle any
+/// of the checks, hooks, lock taking needed to setup and get out of this
+/// update from the null revision.
+pub fn update_from_null(
+    repo: &Repo,
+    to: UncheckedRevision,
+    progress: &dyn Progress,
+) -> Result<usize, HgError> {
+    // Ignore the warnings, they've been displayed by Python already
+    // TODO non-Python clients: display narrow warnings
+    let (narrow_matcher, _) = narrow::matcher(repo)?;
+
+    let files_for_rev = list_rev_tracked_files(repo, to, narrow_matcher)
+        .map_err(handle_revlog_error)?;
+    repo.manually_set_parents(DirstateParents {
+        p1: repo.node(to).expect("update target should exist"),
+        p2: NULL_NODE,
+    })?;
+
+    // Filter the working copy according to the sparse spec
+    let tracked_files: Result<Vec<_>, _> = if !repo.has_sparse() {
+        files_for_rev.iter().collect()
+    } else {
+        // Ignore the warnings, they've been displayed by Python already
+        // TODO non-Python clients: display sparse warnings
+        let (sparse_matcher, _) = sparse::matcher(repo)?;
+        files_for_rev
+            .iter()
+            .filter(|f| {
+                match f {
+                    Ok(f) => sparse_matcher.matches(f.0),
+                    Err(_) => true, // Errors stop the update, include them
+                }
+            })
+            .collect()
+    };
+    let tracked_files = tracked_files?;
+
+    if tracked_files.is_empty() {
+        // Still write the dirstate because we might not be in the null
+        // revision.
+        // This can happen in narrow repos where all paths are excluded in
+        // this revision.
+        write_dirstate(repo)?;
+        return Ok(0);
+    }
+    let store_vfs = &repo.store_vfs();
+    let options = repo.default_revlog_options(crate::RevlogType::Filelog)?;
+    let (errors_sender, errors_receiver) = crossbeam_channel::unbounded();
+    let (files_sender, files_receiver) = crossbeam_channel::unbounded();
+    let working_directory_path = &repo.working_directory_path();
+
+    let files_count = tracked_files.len();
+    let chunks = chunk_tracked_files(tracked_files);
+    progress.update(0, Some(files_count as u64));
+
+    create_working_copy(
+        chunks,
+        working_directory_path,
+        store_vfs,
+        options,
+        files_sender,
+        errors_sender,
+        progress,
+    );
+
+    let errors: Vec<HgError> = errors_receiver.iter().collect();
+    if !errors.is_empty() {
+        log::debug!("{} errors during update (see trace logs)", errors.len());
+        for error in errors.iter() {
+            log::trace!("{}", error);
+        }
+        // Best we can do is raise the first error (in order of the channel)
+        return Err(errors.into_iter().next().expect("can never be empty"));
+    }
+
+    // TODO try to run this concurrently to update the dirstate while we're
+    // still writing out the working copy to see if that improves performance.
+    let total = update_dirstate(repo, files_receiver)?;
+
+    write_dirstate(repo)?;
+
+    Ok(total)
+}
+
+fn handle_revlog_error(e: RevlogError) -> HgError {
+    match e {
+        crate::RevlogError::Other(hg_error) => hg_error,
+        e => HgError::abort(
+            format!("revlog error: {}", e),
+            exit_codes::ABORT,
+            None,
+        ),
+    }
+}
+
+/// Preallocated size of Vec holding directory contents. This aims at
+/// preventing the need for re-allocating the Vec in most cases.
+///
+/// The value is arbitrarily picked as a little over an average number of files
+/// per directory done by looking at a few larger open-source repos.
+/// Most of the runtime is IO anyway, so this doesn't matter too much.
+const FILES_PER_DIRECTORY: usize = 16;
+
+/// Chunk files per directory prefix, so almost every directory is handled
+/// in a separate thread, which works around the FS inode mutex.
+/// Chunking less (and doing approximately `files_count`/`threads`) actually
+/// ends up being less performant: my hypothesis is `rayon`'s work stealing
+/// being more efficient with tasks of varying lengths.
+#[logging_timer::time("trace")]
+fn chunk_tracked_files(
+    tracked_files: Vec<ExpandedManifestEntry>,
+) -> Vec<(&HgPath, Vec<ExpandedManifestEntry>)> {
+    let files_count = tracked_files.len();
+
+    let mut chunks = Vec::with_capacity(files_count / FILES_PER_DIRECTORY);
+
+    let mut current_chunk = Vec::with_capacity(FILES_PER_DIRECTORY);
+    let mut last_directory = tracked_files[0].0.parent();
+
+    for file_info in tracked_files {
+        let current_directory = file_info.0.parent();
+        let different_directory = current_directory != last_directory;
+        if different_directory {
+            chunks.push((last_directory, current_chunk));
+            current_chunk = Vec::with_capacity(FILES_PER_DIRECTORY);
+        }
+        current_chunk.push(file_info);
+        last_directory = current_directory;
+    }
+    chunks.push((last_directory, current_chunk));
+    chunks
+}
+
+#[logging_timer::time("trace")]
+fn create_working_copy<'a: 'b, 'b>(
+    chunks: Vec<(&HgPath, Vec<ExpandedManifestEntry<'a>>)>,
+    working_directory_path: &Path,
+    store_vfs: &VfsImpl,
+    options: RevlogOpenOptions,
+    files_sender: Sender<(&'b HgPath, u32, usize, TruncatedTimestamp)>,
+    error_sender: Sender<HgError>,
+    progress: &dyn Progress,
+) {
+    let auditor = PathAuditor::new(working_directory_path);
+    chunks.into_par_iter().for_each(|(dir_path, chunk)| {
+        if let Err(e) = working_copy_worker(
+            dir_path,
+            chunk,
+            working_directory_path,
+            store_vfs,
+            options,
+            &files_sender,
+            progress,
+            &auditor,
+        ) {
+            error_sender
+                .send(e)
+                .expect("channel should not be disconnected")
+        }
+    });
+}
+
+/// Represents a work unit for a single thread, responsible for this set of
+/// files and restoring them to the working copy.
+#[allow(clippy::too_many_arguments)]
+fn working_copy_worker<'a: 'b, 'b>(
+    dir_path: &HgPath,
+    chunk: Vec<ExpandedManifestEntry<'a>>,
+    working_directory_path: &Path,
+    store_vfs: &VfsImpl,
+    options: RevlogOpenOptions,
+    files_sender: &Sender<(&'b HgPath, u32, usize, TruncatedTimestamp)>,
+    progress: &dyn Progress,
+    auditor: &PathAuditor,
+) -> Result<(), HgError> {
+    let dir_path =
+        hg_path_to_path_buf(dir_path).expect("invalid path in manifest");
+    let dir_path = working_directory_path.join(dir_path);
+    std::fs::create_dir_all(&dir_path).when_writing_file(&dir_path)?;
+
+    for (file, file_node, flags) in chunk {
+        auditor.audit_path(file)?;
+        let flags = flags.map(|f| f.into());
+        let path =
+            working_directory_path.join(get_path_from_bytes(file.as_bytes()));
+
+        // Treemanifest is not supported
+        assert!(flags != Some(b't'));
+
+        let filelog = Filelog::open_vfs(store_vfs, file, options)?;
+        let filelog_revision_data = &filelog
+            .data_for_node(file_node)
+            .map_err(handle_revlog_error)?;
+        let file_data = filelog_revision_data.file_data()?;
+
+        if flags == Some(b'l') {
+            let target = get_path_from_bytes(file_data);
+            if let Err(e) = std::os::unix::fs::symlink(target, &path) {
+                // If the path already exists either:
+                //   - another process created this file while ignoring the
+                //     lock => error
+                //   - our check for the fast path is incorrect => error
+                //   - this is a malicious repo/bundle and this is symlink that
+                //     tries to write things where it shouldn't be able to.
+                match e.kind() {
+                    std::io::ErrorKind::AlreadyExists => {
+                        let metadata = std::fs::symlink_metadata(&path)
+                            .when_reading_file(&path)?;
+                        if metadata.is_dir() {
+                            return Err(HgError::Path(
+                                HgPathError::TraversesSymbolicLink {
+                                    // Technically it should be one of the
+                                    // children, but good enough
+                                    path: file
+                                        .join(HgPath::new(b"*"))
+                                        .to_owned(),
+                                    symlink: file.to_owned(),
+                                },
+                            ));
+                        }
+                        return Err(e).when_writing_file(&path);
+                    }
+                    _ => return Err(e).when_writing_file(&path),
+                }
+            }
+        } else {
+            let mut f =
+                std::fs::File::create(&path).when_writing_file(&path)?;
+            f.write_all(file_data).when_writing_file(&path)?;
+        }
+        if flags == Some(b'x') {
+            std::fs::set_permissions(&path, Permissions::from_mode(0o755))
+                .when_writing_file(&path)?;
+        }
+        let metadata =
+            std::fs::symlink_metadata(&path).when_reading_file(&path)?;
+
+        let mode = metadata.mode();
+
+        files_sender
+            .send((
+                file,
+                mode,
+                file_data.len(),
+                TruncatedTimestamp::for_mtime_of(&metadata)
+                    .when_reading_file(&path)?,
+            ))
+            .expect("channel should not be closed");
+        progress.increment(1, None);
+    }
+    Ok(())
+}
+
+#[logging_timer::time("trace")]
+fn update_dirstate(
+    repo: &Repo,
+    files_receiver: Receiver<(&HgPath, u32, usize, TruncatedTimestamp)>,
+) -> Result<usize, HgError> {
+    let mut dirstate = repo
+        .dirstate_map_mut()
+        .map_err(|e| HgError::abort(e.to_string(), exit_codes::ABORT, None))?;
+
+    // (see the comments in `filter_ambiguous_files` in `merge.py` for more)
+    // It turns out that (on Linux at least) the filesystem resolution time
+    // for most filesystems is based on the HZ kernel config. Their internal
+    // clocks do return nanoseconds if the hardware clock is precise enough,
+    // which should be the case on most recent computers but are only updated
+    // every few milliseconds at best (every "jiffy").
+    //
+    // We are still not concerned with fixing the race with other
+    // processes that might modify the working copy right after it was created
+    // within the same tick, because it is impossible to catch.
+    // However, we might as well not race with operations that could run right
+    // after this one, especially other Mercurial operations that could be
+    // waiting for the wlock to change file contents and the dirstate.
+    //
+    // Thus: wait until the filesystem clock has ticked to filter ambiguous
+    // entries and write the dirstate, but only for dirstate-v2, since v1 only
+    // has second-level granularity and waiting for a whole second is too much
+    // of a penalty in the general case.
+    // Although we're assuming that people running dirstate-v2 on Linux
+    // don't have a second-granularity FS (with the exclusion of NFS), users
+    // can be surprising, and at some point in the future dirstate-v2 will
+    // become the default. To that end, we limit the wait time to 100ms and
+    // fall back to the filter method in case of a timeout.
+    //
+    // +------------+------+--------------+
+    // |   version  | wait | filter level |
+    // +------------+------+--------------+
+    // |     V1     | No   | Second       |
+    // |     V2     | Yes  | Nanosecond   |
+    // | V2-slow-fs | No   | Second       |
+    // +------------+------+--------------+
+    let dirstate_v2 = repo.use_dirstate_v2();
+
+    // Let's ignore NFS right off the bat
+    let mut fast_enough_fs = !is_on_nfs_mount(repo.working_directory_path());
+    let fs_time_now = if dirstate_v2 && fast_enough_fs {
+        match wait_until_fs_tick(repo.working_directory_path()) {
+            None => None,
+            Some(Ok(time)) => Some(time),
+            Some(Err(time)) => {
+                fast_enough_fs = false;
+                Some(time)
+            }
+        }
+    } else {
+        filesystem_now(repo.working_directory_path())
+            .ok()
+            .map(TruncatedTimestamp::from)
+    };
+
+    let mut total = 0;
+    for (filename, mode, size, mtime) in files_receiver.into_iter() {
+        total += 1;
+        // When using dirstate-v2 on a filesystem with reasonable performance
+        // this is basically always true unless you get a mtime from the
+        // far future.
+        let has_meaningful_mtime = if let Some(fs_time) = fs_time_now {
+            mtime.for_reliable_mtime_of_self(&fs_time).is_some_and(|t| {
+                // Dirstate-v1 only has second-level information
+                !t.second_ambiguous || dirstate_v2 && fast_enough_fs
+            })
+        } else {
+            // We somehow failed to write to the filesystem, so don't store
+            // the cache information.
+            false
+        };
+        let reset = DirstateEntryReset {
+            filename,
+            wc_tracked: true,
+            p1_tracked: true,
+            p2_info: false,
+            has_meaningful_mtime,
+            parent_file_data_opt: Some(ParentFileData {
+                mode_size: Some((
+                    mode,
+                    size.try_into().expect("invalid file size in manifest"),
+                )),
+                mtime: Some(mtime),
+            }),
+            from_empty: true,
+        };
+        dirstate.reset_state(reset).map_err(|e| {
+            HgError::abort(e.to_string(), exit_codes::ABORT, None)
+        })?;
+    }
+
+    Ok(total)
+}
+
+/// Wait until the next update from the filesystem time by writing in a loop
+/// a new temporary file inside the working directory and checking if its time
+/// differs from the first one observed.
+///
+/// Returns `None` if we are unable to get the filesystem time,
+/// `Some(Err(timestamp))` if we've timed out waiting for the filesystem clock
+/// to tick, and `Some(Ok(timestamp))` if we've waited successfully.
+///
+/// On Linux, your average tick is going to be a "jiffy", or 1/HZ.
+/// HZ is your kernel's tick rate (if it has one configured) and the value
+/// is the one returned by `grep 'CONFIG_HZ=' /boot/config-$(uname -r)`,
+/// again assuming a normal setup.
+///
+/// In my case (Alphare) at the time of writing, I get `CONFIG_HZ=250`,
+/// which equates to 4ms.
+///
+/// This might change with a series that could make it to Linux 6.12:
+/// https://lore.kernel.org/all/20241002-mgtime-v10-8-d1c4717f5284@kernel.org
+fn wait_until_fs_tick(
+    working_directory_path: &Path,
+) -> Option<Result<TruncatedTimestamp, TruncatedTimestamp>> {
+    let start = std::time::Instant::now();
+    let old_fs_time = filesystem_now(working_directory_path).ok()?;
+    let mut fs_time = filesystem_now(working_directory_path).ok()?;
+
+    const FS_TICK_WAIT_TIMEOUT: Duration = Duration::from_millis(100);
+
+    while fs_time == old_fs_time {
+        if std::time::Instant::now() - start > FS_TICK_WAIT_TIMEOUT {
+            log::trace!(
+                "timed out waiting for the fs clock to tick after {:?}",
+                FS_TICK_WAIT_TIMEOUT
+            );
+            return Some(Err(TruncatedTimestamp::from(old_fs_time)));
+        }
+        fs_time = filesystem_now(working_directory_path).ok()?;
+    }
+    log::trace!(
+        "waited for {:?} before writing the dirstate",
+        fs_time.duration_since(old_fs_time)
+    );
+    Some(Ok(TruncatedTimestamp::from(fs_time)))
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn test_chunk_tracked_files() {
+        fn chunk(v: Vec<&'static str>) -> Vec<ExpandedManifestEntry> {
+            v.into_iter()
+                .map(|f| (HgPath::new(f.as_bytes()), NULL_NODE, None))
+                .collect()
+        }
+        let p = HgPath::new;
+
+        let files = chunk(vec!["a"]);
+        let expected = vec![(p(""), chunk(vec!["a"]))];
+        assert_eq!(chunk_tracked_files(files), expected);
+
+        let files = chunk(vec!["a", "b", "c"]);
+        let expected = vec![(p(""), chunk(vec!["a", "b", "c"]))];
+        assert_eq!(chunk_tracked_files(files), expected);
+
+        let files = chunk(vec![
+            "dir/a-new",
+            "dir/a/mut",
+            "dir/a/mut-mut",
+            "dir/albert",
+            "dir/b",
+            "dir/subdir/c",
+            "dir/subdir/d",
+            "file",
+        ]);
+        let expected = vec![
+            (p("dir"), chunk(vec!["dir/a-new"])),
+            (p("dir/a"), chunk(vec!["dir/a/mut", "dir/a/mut-mut"])),
+            (p("dir"), chunk(vec!["dir/albert", "dir/b"])),
+            (p("dir/subdir"), chunk(vec!["dir/subdir/c", "dir/subdir/d"])),
+            (p(""), chunk(vec!["file"])),
+        ];
+        assert_eq!(chunk_tracked_files(files), expected);
+
+        // Doesn't get split
+        let large_dir = vec![
+            "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12",
+            "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23",
+        ];
+        let files = chunk(large_dir.clone());
+        let expected = vec![(p(""), chunk(large_dir))];
+        assert_eq!(chunk_tracked_files(files), expected);
+    }
+}
--- a/rust/hg-cpython/src/lib.rs	Wed Oct 16 19:14:30 2024 +0200
+++ b/rust/hg-cpython/src/lib.rs	Tue Oct 01 13:49:11 2024 +0200
@@ -45,6 +45,7 @@
 pub mod exceptions;
 mod pybytes_deref;
 pub mod revlog;
+pub mod update;
 pub mod utils;

 /// Revision as exposed to/from the Python layer.
@@ -100,6 +101,7 @@
     m.add(py, "discovery", discovery::init_module(py, &dotted_name)?)?;
     m.add(py, "dirstate", dirstate::init_module(py, &dotted_name)?)?;
     m.add(py, "revlog", revlog::init_module(py, &dotted_name)?)?;
+    m.add(py, "update", update::init_module(py, &dotted_name)?)?;
     m.add(py, "GraphError", py.get_type::<exceptions::GraphError>())?;
     Ok(())
 });
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-cpython/src/update.rs	Tue Oct 01 13:49:11 2024 +0200
@@ -0,0 +1,53 @@
+// debug.rs
+//
+// Copyright 2024 Mercurial developers
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+//! Module for updating a repository.
+use cpython::{PyDict, PyModule, PyObject, PyResult, Python};
+use hg::{
+    progress::{HgProgressBar, Progress},
+    update::update_from_null,
+    BaseRevision,
+};
+
+use crate::{
+    exceptions::FallbackError,
+    utils::{hgerror_to_pyerr, repo_from_path},
+};
+
+pub fn update_from_null_fast_path(
+    py: Python,
+    repo_path: PyObject,
+    to: BaseRevision,
+) -> PyResult<usize> {
+    log::trace!("Using update from null fastpath");
+    let repo = repo_from_path(py, repo_path)?;
+    let progress: &dyn Progress = &HgProgressBar::new("updating");
+    hgerror_to_pyerr(py, update_from_null(&repo, to.into(), progress))
+}
+
+pub fn init_module(py: Python, package: &str) -> PyResult<PyModule> {
+    let dotted_name = &format!("{}.update", package);
+    let m = PyModule::new(py, dotted_name)?;
+
+    m.add(py, "__package__", package)?;
+    m.add(py, "__doc__", "Rust module for updating a repository")?;
+    m.add(py, "FallbackError", py.get_type::<FallbackError>())?;
+    m.add(
+        py,
+        "update_from_null",
+        py_fn!(
+            py,
+            update_from_null_fast_path(repo_path: PyObject, to: BaseRevision,)
+        ),
+    )?;
+
+    let sys = PyModule::import(py, "sys")?;
+    let sys_modules: PyDict = sys.get(py, "modules")?.extract(py)?;
+    sys_modules.set_item(py, dotted_name, &m)?;
+
+    Ok(m)
+}
--- a/tests/test-audit-path.t	Wed Oct 16 19:14:30 2024 +0200
+++ b/tests/test-audit-path.t	Tue Oct 01 13:49:11 2024 +0200
@@ -91,7 +91,8 @@
   $ hg manifest -r0
   .hg/test
   $ hg update -Cr0
-  abort: path contains illegal component: .hg/test
+  abort: path contains illegal component: .hg/test (no-rust !)
+  abort: path '.hg/test' is inside the '.hg' folder (rust !)
   [10]

 attack foo/.hg/test
@@ -107,6 +108,7 @@
   $ hg manifest -r2
   back
   back/test
+
 #if symlink
   $ hg update -Cr2
   abort: path 'back/test' traverses symbolic link 'back'
@@ -220,17 +222,30 @@
 'a' and 'a/b' are taken as good paths. still applyupdates() should fail.

   $ hg up -qC null
+#if rust
+  $ hg up 1
+  abort: path 'a/*' traverses symbolic link 'a'
+  [10]
+#endif
+
+#if no-rust
   $ hg up 1
   abort: path 'a/b' traverses symbolic link 'a'
   [255]
+#endif
   $ ls ../update-symlink-out

 try branch update replacing directory with symlink, and its content: the
 path 'a' is audited as a directory first, which should be audited again as
 a symlink.

+#if rust
+  $ rm -rf a
+#else
   $ rm -f a
+#endif
   $ hg up -qC 2
+
   $ hg up 1
   abort: path 'a/b' traverses symbolic link 'a'
   [255]
--- a/tests/test-clone.t	Wed Oct 16 19:14:30 2024 +0200
+++ b/tests/test-clone.t	Tue Oct 01 13:49:11 2024 +0200
@@ -1235,7 +1235,7 @@
 #if linuxormacos no-fsmonitor
   $ hg clone a nofsmonitor
   updating to bookmark @ on branch stable
-  (warning: large working directory being used without fsmonitor enabled; enable fsmonitor to improve performance; see "hg help -e fsmonitor")
+  (warning: large working directory being used without fsmonitor enabled; enable fsmonitor to improve performance; see "hg help -e fsmonitor") (no-rust !)
   3 files updated, 0 files merged, 0 files removed, 0 files unresolved
 #else
   $ hg clone a nofsmonitor
@@ -1284,7 +1284,7 @@

 #if linuxormacos no-fsmonitor
   $ hg up cf0fe1914066
-  (warning: large working directory being used without fsmonitor enabled; enable fsmonitor to improve performance; see "hg help -e fsmonitor")
+  (warning: large working directory being used without fsmonitor enabled; enable fsmonitor to improve performance; see "hg help -e fsmonitor") (no-rust !)
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
 #else
   $ hg up cf0fe1914066
--- a/tests/test-simple-update.t	Wed Oct 16 19:14:30 2024 +0200
+++ b/tests/test-simple-update.t	Tue Oct 01 13:49:11 2024 +0200
@@ -96,11 +96,12 @@
 #if no-windows

   $ cat <<EOF > forceworker.py
-  > from mercurial import extensions, worker
+  > from mercurial import extensions, merge, worker
   > def nocost(orig, ui, costperop, nops, threadsafe=True):
   >     return worker._numworkers(ui) > 1
   > def uisetup(ui):
   >     extensions.wrapfunction(worker, 'worthwhile', nocost)
+  >     merge.MAYBE_USE_RUST_UPDATE = False
   > EOF

   $ hg init worker
--- a/tests/test-stream-bundle-v2.t	Wed Oct 16 19:14:30 2024 +0200
+++ b/tests/test-stream-bundle-v2.t	Tue Oct 01 13:49:11 2024 +0200
@@ -152,19 +152,19 @@
   bundle2-input-bundle: 2 parts total
   checking for updated bookmarks
   updating to branch default
-  resolving manifests
-   branchmerge: False, force: False, partial: False
-   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041
-   A: remote created -> g
-  getting A
-   B: remote created -> g
-  getting B
-   C: remote created -> g
-  getting C
-   D: remote created -> g
-  getting D
-   E: remote created -> g
-  getting E
+  resolving manifests (no-rust !)
+   branchmerge: False, force: False, partial: False (no-rust !)
+   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041 (no-rust !)
+   A: remote created -> g (no-rust !)
+  getting A (no-rust !)
+   B: remote created -> g (no-rust !)
+  getting B (no-rust !)
+   C: remote created -> g (no-rust !)
+  getting C (no-rust !)
+   D: remote created -> g (no-rust !)
+  getting D (no-rust !)
+   E: remote created -> g (no-rust !)
+  getting E (no-rust !)
   5 files updated, 0 files merged, 0 files removed, 0 files unresolved
   updating the branch cache
   (sent 4 HTTP requests and * bytes; received * bytes in responses) (glob)
@@ -215,19 +215,19 @@
   bundle2-input-bundle: 2 parts total
   checking for updated bookmarks
   updating to branch default
-  resolving manifests
-   branchmerge: False, force: False, partial: False
-   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041
-   A: remote created -> g
-  getting A
-   B: remote created -> g
-  getting B
-   C: remote created -> g
-  getting C
-   D: remote created -> g
-  getting D
-   E: remote created -> g
-  getting E
+  resolving manifests (no-rust !)
+   branchmerge: False, force: False, partial: False (no-rust !)
+   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041 (no-rust !)
+   A: remote created -> g (no-rust !)
+  getting A (no-rust !)
+   B: remote created -> g (no-rust !)
+  getting B (no-rust !)
+   C: remote created -> g (no-rust !)
+  getting C (no-rust !)
+   D: remote created -> g (no-rust !)
+  getting D (no-rust !)
+   E: remote created -> g (no-rust !)
+  getting E (no-rust !)
   5 files updated, 0 files merged, 0 files removed, 0 files unresolved
   updating the branch cache
   (sent 4 HTTP requests and * bytes; received * bytes in responses) (glob)
@@ -280,19 +280,19 @@
   bundle2-input-bundle: 2 parts total
   checking for updated bookmarks
   updating to branch default
-  resolving manifests
-   branchmerge: False, force: False, partial: False
-   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041
-   A: remote created -> g
-  getting A
-   B: remote created -> g
-  getting B
-   C: remote created -> g
-  getting C
-   D: remote created -> g
-  getting D
-   E: remote created -> g
-  getting E
+  resolving manifests (no-rust !)
+   branchmerge: False, force: False, partial: False (no-rust !)
+   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041 (no-rust !)
+   A: remote created -> g (no-rust !)
+  getting A (no-rust !)
+   B: remote created -> g (no-rust !)
+  getting B (no-rust !)
+   C: remote created -> g (no-rust !)
+  getting C (no-rust !)
+   D: remote created -> g (no-rust !)
+  getting D (no-rust !)
+   E: remote created -> g (no-rust !)
+  getting E (no-rust !)
   5 files updated, 0 files merged, 0 files removed, 0 files unresolved
   updating the branch cache
   (sent 4 HTTP requests and * bytes; received * bytes in responses) (glob)
@@ -342,19 +342,19 @@
   bundle2-input-bundle: 2 parts total
   checking for updated bookmarks
   updating to branch default
-  resolving manifests
-   branchmerge: False, force: False, partial: False
-   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041
-   A: remote created -> g
-  getting A
-   B: remote created -> g
-  getting B
-   C: remote created -> g
-  getting C
-   D: remote created -> g
-  getting D
-   E: remote created -> g
-  getting E
+  resolving manifests (no-rust !)
+   branchmerge: False, force: False, partial: False (no-rust !)
+   ancestor: 000000000000, local: 000000000000+, remote: 9bc730a19041 (no-rust !)
+   A: remote created -> g (no-rust !)
+  getting A (no-rust !)
+   B: remote created -> g (no-rust !)
+  getting B (no-rust !)
+   C: remote created -> g (no-rust !)
+  getting C (no-rust !)
+   D: remote created -> g (no-rust !)
+  getting D (no-rust !)
+   E: remote created -> g (no-rust !)
+  getting E (no-rust !)
   5 files updated, 0 files merged, 0 files removed, 0 files unresolved
   updating the branch cache
   (sent 4 HTTP requests and * bytes; received * bytes in responses) (glob)
--- a/tests/test-subrepo-deep-nested-change.t	Wed Oct 16 19:14:30 2024 +0200
+++ b/tests/test-subrepo-deep-nested-change.t	Tue Oct 01 13:49:11 2024 +0200
@@ -45,9 +45,9 @@
   linking [=======================================>     ] 8/9\r (no-eol) (esc) (rust !)
   linking [============================================>] 9/9\r (no-eol) (esc) (rust !)
                                                               \r (no-eol) (esc)
-  \r (no-eol) (esc)
-  updating [===========================================>] 1/1\r (no-eol) (esc)
-                                                              \r (no-eol) (esc)
+  \r (no-eol) (esc) (no-rust !)
+  updating [===========================================>] 1/1\r (no-eol) (esc) (no-rust !)
+                                                              \r (no-eol) (esc) (no-rust !)
   updating to branch default
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg add -R sub1
@@ -89,7 +89,6 @@
   linking [==================================>          ] 7/9\r (no-eol) (esc)
   linking [=======================================>     ] 8/9\r (no-eol) (esc)
   linking [============================================>] 9/9\r (no-eol) (esc)
-  updating [===========================================>] 1/1\r (no-eol) (esc)
                                                               \r (no-eol) (esc)
   updating to branch default
   cloning subrepo sub2 from $TESTTMP/sub2
--- a/tests/test-symlink-placeholder.t	Wed Oct 16 19:14:30 2024 +0200
+++ b/tests/test-symlink-placeholder.t	Tue Oct 01 13:49:11 2024 +0200
@@ -3,12 +3,13 @@
 Create extension that can disable symlink support:

   $ cat > nolink.py <<EOF
-  > from mercurial import extensions, util
+  > from mercurial import extensions, merge, util
   > def setflags(orig, f, l, x):
   >     pass
   > def checklink(orig, path):
   >     return False
   > def extsetup(ui):
+  >     merge.MAYBE_USE_RUST_UPDATE = False
   >     extensions.wrapfunction(util, 'setflags', setflags)
   >     extensions.wrapfunction(util, 'checklink', checklink)
   > EOF