# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@octobus.net>
# Date 1677780172 -3600
# Node ID a6b8b1ab9116d4d87cfedbe0cea566f46ddec13d
# Parent  2fbc109fd58a44475ad5fa5fea66a6ae74e93e4b# Parent  1ded5b48b8aa01eb5917edb35d2ff282cdf363ad
branching: merge stable into default

The clippy god had to be appeased on some aspect.

diff -r 2fbc109fd58a -r a6b8b1ab9116 .hgsigs
--- a/.hgsigs	Thu Mar 02 04:16:47 2023 +0100
+++ b/.hgsigs	Thu Mar 02 19:02:52 2023 +0100
@@ -238,3 +238,4 @@
 04f1dba53c961dfdb875c8469adc96fa999cfbed 0 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
 c890d8b8bc59b18e5febf60caada629df5356ee2 0 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
 59466b13a3ae0e29a5d4f485393e516cfbb057d0 0 iQHNBAABCgA3FiEEH2b4zfZU6QXBHaBhoR4BzQ4F2VYFAmO1XgoZHGFscGhhcmVAcmFwaGFlbGdvbWVzLmRldgAKCRChHgHNDgXZVn8nDACU04KbPloLl+if6DQYreESnF9LU8C+qnLC/j5RRuaFNh/ec6C3DzLWqWdmnWA/siV3nUR1bXHfTui95azxJfYvWoXH2R2yam+YhE256B4rDDYWS1LI9kNNM+A33xcPS2HxVowkByhjB5FPKR6I90dX42BYJpTS5s/VPx63wXLznjFWuD7XJ3P0VI7D72j/+6EQCmHaAUEE5bO00Ob2JxmzJlaP+02fYc814PAONE2/ocfR0aExAVS3VA+SJGXnXTVpoaHr7NJKC2sBLFsdnhIRwtCf3rtGEvIJ5v2U2xx0ZEz/mimtGzW5ovkthobV4mojk0DRz7xBtA96pOGSRTD8QndIsdMCUipo8zZ/AGAMByCtsQOX7OYhR6gp+I6+iPh8fTR5oCbkO7cizDDQtXcrR5OT/BDH9xkAF1ghNL8o23a09/wfZ9NPg5zrh/4T/dFfoe2COlkAJJ1ttDPYyQkCfMsoWm3OXk6xJ3ExVbwkZzUDQSzsxGS+oxbFDWJZ64Q=
+8830004967ad865ead89c28a410405a6e71e0796 0 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
diff -r 2fbc109fd58a -r a6b8b1ab9116 .hgtags
--- a/.hgtags	Thu Mar 02 04:16:47 2023 +0100
+++ b/.hgtags	Thu Mar 02 19:02:52 2023 +0100
@@ -254,3 +254,4 @@
 0000000000000000000000000000000000000000 6.3.0
 c890d8b8bc59b18e5febf60caada629df5356ee2 6.3.1
 59466b13a3ae0e29a5d4f485393e516cfbb057d0 6.3.2
+8830004967ad865ead89c28a410405a6e71e0796 6.3.3
diff -r 2fbc109fd58a -r a6b8b1ab9116 hgext/patchbomb.py
--- a/hgext/patchbomb.py	Thu Mar 02 04:16:47 2023 +0100
+++ b/hgext/patchbomb.py	Thu Mar 02 19:02:52 2023 +0100
@@ -361,7 +361,12 @@
             ui.warn(_(b'warning: working directory has uncommitted changes\n'))
         output = stringio()
         cmdutil.exportfile(
-            repo, [r], output, opts=patch.difffeatureopts(ui, opts, git=True)
+            repo,
+            [r],
+            output,
+            opts=patch.difffeatureopts(
+                ui, pycompat.byteskwargs(opts), git=True
+            ),
         )
         yield output.getvalue().split(b'\n')
 
diff -r 2fbc109fd58a -r a6b8b1ab9116 mercurial/configitems.py
--- a/mercurial/configitems.py	Thu Mar 02 04:16:47 2023 +0100
+++ b/mercurial/configitems.py	Thu Mar 02 19:02:52 2023 +0100
@@ -652,6 +652,15 @@
     b'deprec-warn',
     default=False,
 )
+# possible values:
+# - auto (the default)
+# - force-append
+# - force-new
+coreconfigitem(
+    b'devel',
+    b'dirstate.v2.data_update_mode',
+    default="auto",
+)
 coreconfigitem(
     b'devel',
     b'disableloaddefaultcerts',
@@ -689,6 +698,42 @@
     b'serverrequirecert',
     default=False,
 )
+# Makes the status algorithm wait for the existence of this file
+# (or until a timeout of `devel.sync.status.pre-dirstate-write-file-timeout`
+# seconds) before taking the lock and writing the dirstate.
+# Status signals that it's ready to wait by creating a file
+# with the same name + `.waiting`.
+# Useful when testing race conditions.
+coreconfigitem(
+    b'devel',
+    b'sync.status.pre-dirstate-write-file',
+    default=None,
+)
+coreconfigitem(
+    b'devel',
+    b'sync.status.pre-dirstate-write-file-timeout',
+    default=2,
+)
+coreconfigitem(
+    b'devel',
+    b'sync.dirstate.post-docket-read-file',
+    default=None,
+)
+coreconfigitem(
+    b'devel',
+    b'sync.dirstate.post-docket-read-file-timeout',
+    default=2,
+)
+coreconfigitem(
+    b'devel',
+    b'sync.dirstate.pre-read-file',
+    default=None,
+)
+coreconfigitem(
+    b'devel',
+    b'sync.dirstate.pre-read-file-timeout',
+    default=2,
+)
 coreconfigitem(
     b'devel',
     b'strip-obsmarkers',
diff -r 2fbc109fd58a -r a6b8b1ab9116 mercurial/context.py
--- a/mercurial/context.py	Thu Mar 02 04:16:47 2023 +0100
+++ b/mercurial/context.py	Thu Mar 02 19:02:52 2023 +0100
@@ -36,6 +36,7 @@
     sparse,
     subrepo,
     subrepoutil,
+    testing,
     util,
 )
 from .utils import (
@@ -1854,6 +1855,7 @@
 
     def _poststatusfixup(self, status, fixup):
         """update dirstate for files that are actually clean"""
+        testing.wait_on_cfg(self._repo.ui, b'status.pre-dirstate-write-file')
         dirstate = self._repo.dirstate
         poststatus = self._repo.postdsstatus()
         if fixup:
diff -r 2fbc109fd58a -r a6b8b1ab9116 mercurial/diffutil.py
--- a/mercurial/diffutil.py	Thu Mar 02 04:16:47 2023 +0100
+++ b/mercurial/diffutil.py	Thu Mar 02 19:02:52 2023 +0100
@@ -7,6 +7,13 @@
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
+import typing
+
+from typing import (
+    Any,
+    Dict,
+    Optional,
+)
 
 from .i18n import _
 
@@ -15,10 +22,20 @@
     pycompat,
 )
 
+if typing.TYPE_CHECKING:
+    from . import ui as uimod
+
+# TODO: narrow the value after the config module is typed
+_Opts = Dict[bytes, Any]
+
 
 def diffallopts(
-    ui, opts=None, untrusted=False, section=b'diff', configprefix=b''
-):
+    ui: "uimod.ui",
+    opts: Optional[_Opts] = None,
+    untrusted: bool = False,
+    section: bytes = b'diff',
+    configprefix: bytes = b'',
+) -> mdiff.diffopts:
     '''return diffopts with all features supported and parsed'''
     return difffeatureopts(
         ui,
@@ -33,15 +50,15 @@
 
 
 def difffeatureopts(
-    ui,
-    opts=None,
-    untrusted=False,
-    section=b'diff',
-    git=False,
-    whitespace=False,
-    formatchanging=False,
-    configprefix=b'',
-):
+    ui: "uimod.ui",
+    opts: Optional[_Opts] = None,
+    untrusted: bool = False,
+    section: bytes = b'diff',
+    git: bool = False,
+    whitespace: bool = False,
+    formatchanging: bool = False,
+    configprefix: bytes = b'',
+) -> mdiff.diffopts:
     """return diffopts with only opted-in features parsed
 
     Features:
@@ -51,7 +68,12 @@
       with most diff parsers
     """
 
-    def get(key, name=None, getter=ui.configbool, forceplain=None):
+    def get(
+        key: bytes,
+        name: Optional[bytes] = None,
+        getter=ui.configbool,
+        forceplain: Optional[bool] = None,
+    ) -> Any:
         if opts:
             v = opts.get(key)
             # diffopts flags are either None-default (which is passed
diff -r 2fbc109fd58a -r a6b8b1ab9116 mercurial/dirstatemap.py
--- a/mercurial/dirstatemap.py	Thu Mar 02 04:16:47 2023 +0100
+++ b/mercurial/dirstatemap.py	Thu Mar 02 19:02:52 2023 +0100
@@ -10,6 +10,7 @@
     error,
     pathutil,
     policy,
+    testing,
     txnutil,
     util,
 )
@@ -31,6 +32,13 @@
 
 rangemask = 0x7FFFFFFF
 
+WRITE_MODE_AUTO = 0
+WRITE_MODE_FORCE_NEW = 1
+WRITE_MODE_FORCE_APPEND = 2
+
+
+V2_MAX_READ_ATTEMPTS = 5
+
 
 class _dirstatemapcommon:
     """
@@ -54,6 +62,16 @@
         self._parents = None
         self._dirtyparents = False
         self._docket = None
+        write_mode = ui.config(b"devel", b"dirstate.v2.data_update_mode")
+        if write_mode == b"auto":
+            self._write_mode = WRITE_MODE_AUTO
+        elif write_mode == b"force-append":
+            self._write_mode = WRITE_MODE_FORCE_APPEND
+        elif write_mode == b"force-new":
+            self._write_mode = WRITE_MODE_FORCE_NEW
+        else:
+            # unknown value, fallback to default
+            self._write_mode = WRITE_MODE_AUTO
 
         # for consistent view between _pl() and _read() invocations
         self._pendingmode = None
@@ -132,11 +150,31 @@
                 raise error.ProgrammingError(
                     b'dirstate only has a docket in v2 format'
                 )
+            self._set_identity()
             self._docket = docketmod.DirstateDocket.parse(
                 self._readdirstatefile(), self._nodeconstants
             )
         return self._docket
 
+    def _read_v2_data(self):
+        data = None
+        attempts = 0
+        while attempts < V2_MAX_READ_ATTEMPTS:
+            attempts += 1
+            try:
+                # TODO: use mmap when possible
+                data = self._opener.read(self.docket.data_filename())
+            except FileNotFoundError:
+                # read race detected between docket and data file
+                # reload the docket and retry
+                self._docket = None
+        if data is None:
+            assert attempts >= V2_MAX_READ_ATTEMPTS
+            msg = b"dirstate read race happened %d times in a row"
+            msg %= attempts
+            raise error.Abort(msg)
+        return self._opener.read(self.docket.data_filename())
+
     def write_v2_no_append(self, tr, st, meta, packed):
         old_docket = self.docket
         new_docket = docketmod.DirstateDocket.with_new_uuid(
@@ -290,14 +328,15 @@
     ### disk interaction
 
     def read(self):
-        # ignore HG_PENDING because identity is used only for writing
-        self._set_identity()
+        testing.wait_on_cfg(self._ui, b'dirstate.pre-read-file')
+        if self._use_dirstate_v2:
 
-        if self._use_dirstate_v2:
             if not self.docket.uuid:
                 return
-            st = self._opener.read(self.docket.data_filename())
+            testing.wait_on_cfg(self._ui, b'dirstate.post-docket-read-file')
+            st = self._read_v2_data()
         else:
+            self._set_identity()
             st = self._readdirstatefile()
 
         if not st:
@@ -556,19 +595,39 @@
             # ignore HG_PENDING because identity is used only for writing
             self._set_identity()
 
+            testing.wait_on_cfg(self._ui, b'dirstate.pre-read-file')
             if self._use_dirstate_v2:
-                if self.docket.uuid:
-                    # TODO: use mmap when possible
-                    data = self._opener.read(self.docket.data_filename())
+                self.docket  # load the data if needed
+                inode = (
+                    self.identity.stat.st_ino
+                    if self.identity is not None
+                    and self.identity.stat is not None
+                    else None
+                )
+                testing.wait_on_cfg(self._ui, b'dirstate.post-docket-read-file')
+                if not self.docket.uuid:
+                    data = b''
+                    self._map = rustmod.DirstateMap.new_empty()
                 else:
-                    data = b''
-                self._map = rustmod.DirstateMap.new_v2(
-                    data, self.docket.data_size, self.docket.tree_metadata
-                )
+                    data = self._read_v2_data()
+                    self._map = rustmod.DirstateMap.new_v2(
+                        data,
+                        self.docket.data_size,
+                        self.docket.tree_metadata,
+                        self.docket.uuid,
+                        inode,
+                    )
                 parents = self.docket.parents
             else:
+                self._set_identity()
+                inode = (
+                    self.identity.stat.st_ino
+                    if self.identity is not None
+                    and self.identity.stat is not None
+                    else None
+                )
                 self._map, parents = rustmod.DirstateMap.new_v1(
-                    self._readdirstatefile()
+                    self._readdirstatefile(), inode
                 )
 
             if parents and not self._dirtyparents:
@@ -638,8 +697,10 @@
                 return
 
             # We can only append to an existing data file if there is one
-            can_append = self.docket.uuid is not None
-            packed, meta, append = self._map.write_v2(can_append)
+            write_mode = self._write_mode
+            if self.docket.uuid is None:
+                write_mode = WRITE_MODE_FORCE_NEW
+            packed, meta, append = self._map.write_v2(write_mode)
             if append:
                 docket = self.docket
                 data_filename = docket.data_filename()
diff -r 2fbc109fd58a -r a6b8b1ab9116 mercurial/testing/__init__.py
--- a/mercurial/testing/__init__.py	Thu Mar 02 04:16:47 2023 +0100
+++ b/mercurial/testing/__init__.py	Thu Mar 02 19:02:52 2023 +0100
@@ -9,6 +9,21 @@
 environ = getattr(os, 'environ')
 
 
+def wait_on_cfg(ui, cfg, timeout=10):
+    """synchronize on the `cfg` config path
+
+    Use this to synchronize commands during race tests.
+    """
+    full_config = b'sync.' + cfg
+    wait_config = full_config + b'-timeout'
+    sync_path = ui.config(b'devel', full_config)
+    if sync_path is not None:
+        timeout = ui.config(b'devel', wait_config)
+        ready_path = sync_path + b'.waiting'
+        write_file(ready_path)
+        wait_file(sync_path, timeout=timeout)
+
+
 def _timeout_factor():
     """return the current modification to timeout"""
     default = int(environ.get('HGTEST_TIMEOUT_DEFAULT', 360))
diff -r 2fbc109fd58a -r a6b8b1ab9116 relnotes/6.3
--- a/relnotes/6.3	Thu Mar 02 04:16:47 2023 +0100
+++ b/relnotes/6.3	Thu Mar 02 19:02:52 2023 +0100
@@ -1,3 +1,51 @@
+= Mercurial 6.3.3 =
+
+ * tests: filter out PEP 657 error locations in tracebacks (issue6780)
+ * tests: optional PEP 657 error location in test-extension.t (issue6781)
+ * tests: optional PEP 657 error location in test-lfs-serve-access.t (issue6782)
+ * histedit: byteify the help for the multifold action
+ * sparse: fix a py2 based usage of `map()`
+ * convert: stop passing str to the dateutil API in darcs
+ * convert: turn the last str regex into bytes in cvs.py (issue6789)
+ * convert: change socket mode from b'r+' to 'rwb' in cvs.py (issue6789)
+ * convert: replace repr() by pycompat.byterepr() in cvsps.py (issue6789)
+ * tests: os module is frozen in Python 3.11 (issue6786)
+ * hgweb: unbyteify the 100-continue check
+ * resourceutil: start using importlib.resources.files() when possible
+ * revset: the `random` sort should not depend on sys.maxsize (issue6770)
+ * tests: make sure pygments can detect python script without extension
+ * convert: brz 3.3.0 moved NoSuchFile exception to breezy.transport
+ * tests: pygments 2.14+ highlight whitespace in python code
+ * hghave: make different has_pyoxidizer functions have different names
+ * hghave: refactor checks for pygments versions using checkvers()
+ * rust-narrow: fix loop that never loops
+ * scmutil: make checknewlabel() allow "_" in otherwise numeric names (issue6737)
+ * bundlerepo: enforce the requirements declared by the underlying repository
+ * setup: make the version computation process more resistant
+ * fix: add more information to the debug output
+ * tag: disallow tagging the working directory
+ * dirstate: handle missing backup file on restoration
+ * dirstate-v2: complain early on docket name collision
+ * rust: upgrade minimum `rayon` dependency
+ * setup: support building from an ongoing merge
+ * rust: add debug log about skipping dirstate update
+ * rust-dirstate: trace append/no append to help debugging
+ * dirstate-v2: don't mmap the data file when on NFS
+ * run-tests: make it possible to nest conditionals
+ * dirstate: add some debug output when writing the dirstate
+ * testing: introduce util function to synchronize concurrent commands on files
+ * dirstate: add a way to test races happening during status
+ * dirstate: use more than a bool to control append behavior
+ * dirstate-v2: add devel config option to control write behavior
+ * rhg: fix race when a fixup file is deleted on disk
+ * rhg: fix race when an ambiguous file is deleted on disk
+ * dirstate: deal with read-race for pure python code
+ * dirstate: deal with read-race for python code using rust object
+ * dirstate: deal with read-race for pure rust code path (rhg)
+ * dirstate: set identity whenever we read the dirstate's v2 docket
+ * rust-dirstate-v2: don't write dirstate if data file has changed
+ * rhg: remember the inode of .hg/dirstate
+
 = Mercurial 6.3.2 =
 
  * [ecfc84b956a8] tests: expect the message from 1baf0fffd82f in test-hghave.t (issue6762)
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/dirstate_tree/dirstate_map.rs
--- a/rust/hg-core/src/dirstate_tree/dirstate_map.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-core/src/dirstate_tree/dirstate_map.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -38,6 +38,13 @@
     V2,
 }
 
+#[derive(Debug, PartialEq, Eq)]
+pub enum DirstateMapWriteMode {
+    Auto,
+    ForceNewDataFile,
+    ForceAppend,
+}
+
 #[derive(Debug)]
 pub struct DirstateMap<'on_disk> {
     /// Contents of the `.hg/dirstate` file
@@ -59,10 +66,28 @@
     pub(super) unreachable_bytes: u32,
 
     /// Size of the data used to first load this `DirstateMap`. Used in case
-    /// we need to write some new metadata, but no new data on disk.
+    /// we need to write some new metadata, but no new data on disk,
+    /// as well as to detect writes that have happened in another process
+    /// since first read.
     pub(super) old_data_size: usize,
 
+    /// UUID used when first loading this `DirstateMap`. Used to check if
+    /// the UUID has been changed by another process since first read.
+    /// Can be `None` if using dirstate v1 or if it's a brand new dirstate.
+    pub(super) old_uuid: Option<Vec<u8>>,
+
+    /// Identity of the dirstate file (for dirstate-v1) or the docket file
+    /// (v2). Used to detect if the file has changed from another process.
+    /// Since it's always written atomically, we can compare the inode to
+    /// check the file identity.
+    ///
+    /// TODO On non-Unix systems, something like hashing is a possibility?
+    pub(super) identity: Option<u64>,
+
     pub(super) dirstate_version: DirstateVersion,
+
+    /// Controlled by config option `devel.dirstate.v2.data_update_mode`
+    pub(super) write_mode: DirstateMapWriteMode,
 }
 
 /// Using a plain `HgPathBuf` of the full path from the repository root as a
@@ -445,7 +470,10 @@
             ignore_patterns_hash: [0; on_disk::IGNORE_PATTERNS_HASH_LEN],
             unreachable_bytes: 0,
             old_data_size: 0,
+            old_uuid: None,
+            identity: None,
             dirstate_version: DirstateVersion::V1,
+            write_mode: DirstateMapWriteMode::Auto,
         }
     }
 
@@ -454,9 +482,11 @@
         on_disk: &'on_disk [u8],
         data_size: usize,
         metadata: &[u8],
+        uuid: Vec<u8>,
+        identity: Option<u64>,
     ) -> Result<Self, DirstateError> {
         if let Some(data) = on_disk.get(..data_size) {
-            Ok(on_disk::read(data, metadata)?)
+            Ok(on_disk::read(data, metadata, uuid, identity)?)
         } else {
             Err(DirstateV2ParseError::new("not enough bytes on disk").into())
         }
@@ -465,6 +495,7 @@
     #[logging_timer::time("trace")]
     pub fn new_v1(
         on_disk: &'on_disk [u8],
+        identity: Option<u64>,
     ) -> Result<(Self, Option<DirstateParents>), DirstateError> {
         let mut map = Self::empty(on_disk);
         if map.on_disk.is_empty() {
@@ -506,6 +537,7 @@
             },
         )?;
         let parents = Some(*parents);
+        map.identity = identity;
 
         Ok((map, parents))
     }
@@ -514,8 +546,15 @@
     /// append to the existing data file that contains `self.on_disk` (true),
     /// or create a new data file from scratch (false).
     pub(super) fn write_should_append(&self) -> bool {
-        let ratio = self.unreachable_bytes as f32 / self.on_disk.len() as f32;
-        ratio < ACCEPTABLE_UNREACHABLE_BYTES_RATIO
+        match self.write_mode {
+            DirstateMapWriteMode::ForceAppend => true,
+            DirstateMapWriteMode::ForceNewDataFile => false,
+            DirstateMapWriteMode::Auto => {
+                let ratio =
+                    self.unreachable_bytes as f32 / self.on_disk.len() as f32;
+                ratio < ACCEPTABLE_UNREACHABLE_BYTES_RATIO
+            }
+        }
     }
 
     fn get_node<'tree>(
@@ -911,6 +950,10 @@
             *unreachable_bytes += path.len() as u32
         }
     }
+
+    pub(crate) fn set_write_mode(&mut self, write_mode: DirstateMapWriteMode) {
+        self.write_mode = write_mode;
+    }
 }
 
 type DebugDirstateTuple<'a> = (&'a HgPath, (u8, i32, i32, i32));
@@ -1230,11 +1273,11 @@
     #[logging_timer::time("trace")]
     pub fn pack_v2(
         &self,
-        can_append: bool,
+        write_mode: DirstateMapWriteMode,
     ) -> Result<(Vec<u8>, on_disk::TreeMetadata, bool, usize), DirstateError>
     {
         let map = self.get_map();
-        on_disk::write(map, can_append)
+        on_disk::write(map, write_mode)
     }
 
     /// `callback` allows the caller to process and do something with the
@@ -1794,7 +1837,7 @@
         )?;
 
         let (packed, metadata, _should_append, _old_data_size) =
-            map.pack_v2(false)?;
+            map.pack_v2(DirstateMapWriteMode::ForceNewDataFile)?;
         let packed_len = packed.len();
         assert!(packed_len > 0);
 
@@ -1803,6 +1846,8 @@
             packed,
             packed_len,
             metadata.as_bytes(),
+            vec![],
+            None,
         )?;
 
         // Check that everything is accounted for
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/dirstate_tree/on_disk.rs
--- a/rust/hg-core/src/dirstate_tree/on_disk.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-core/src/dirstate_tree/on_disk.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -4,7 +4,9 @@
 
 use crate::dirstate::{DirstateV2Data, TruncatedTimestamp};
 use crate::dirstate_tree::dirstate_map::DirstateVersion;
-use crate::dirstate_tree::dirstate_map::{self, DirstateMap, NodeRef};
+use crate::dirstate_tree::dirstate_map::{
+    self, DirstateMap, DirstateMapWriteMode, NodeRef,
+};
 use crate::dirstate_tree::path_with_basename::WithBasename;
 use crate::errors::HgError;
 use crate::utils::hg_path::HgPath;
@@ -285,6 +287,8 @@
 pub(super) fn read<'on_disk>(
     on_disk: &'on_disk [u8],
     metadata: &[u8],
+    uuid: Vec<u8>,
+    identity: Option<u64>,
 ) -> Result<DirstateMap<'on_disk>, DirstateV2ParseError> {
     if on_disk.is_empty() {
         let mut map = DirstateMap::empty(on_disk);
@@ -307,7 +311,10 @@
         ignore_patterns_hash: meta.ignore_patterns_hash,
         unreachable_bytes: meta.unreachable_bytes.get(),
         old_data_size: on_disk.len(),
+        old_uuid: Some(uuid),
+        identity,
         dirstate_version: DirstateVersion::V2,
+        write_mode: DirstateMapWriteMode::Auto,
     };
     Ok(dirstate_map)
 }
@@ -605,9 +612,18 @@
 /// (false), and the previous size of data on disk.
 pub(super) fn write(
     dirstate_map: &DirstateMap,
-    can_append: bool,
+    write_mode: DirstateMapWriteMode,
 ) -> Result<(Vec<u8>, TreeMetadata, bool, usize), DirstateError> {
-    let append = can_append && dirstate_map.write_should_append();
+    let append = match write_mode {
+        DirstateMapWriteMode::Auto => dirstate_map.write_should_append(),
+        DirstateMapWriteMode::ForceNewDataFile => false,
+        DirstateMapWriteMode::ForceAppend => true,
+    };
+    if append {
+        log::trace!("appending to the dirstate data file");
+    } else {
+        log::trace!("creating new dirstate data file");
+    }
 
     // This ignores the space for paths, and for nodes without an entry.
     // TODO: better estimate? Skip the `Vec` and write to a file directly?
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/dirstate_tree/owning.rs
--- a/rust/hg-core/src/dirstate_tree/owning.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-core/src/dirstate_tree/owning.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -31,6 +31,7 @@
 
     pub fn new_v1<OnDisk>(
         on_disk: OnDisk,
+        identity: Option<u64>,
     ) -> Result<(Self, DirstateParents), DirstateError>
     where
         OnDisk: Deref<Target = [u8]> + Send + 'static,
@@ -42,7 +43,7 @@
             OwningDirstateMapTryBuilder {
                 on_disk,
                 map_builder: |bytes| {
-                    DirstateMap::new_v1(bytes).map(|(dmap, p)| {
+                    DirstateMap::new_v1(bytes, identity).map(|(dmap, p)| {
                         parents = p.unwrap_or(DirstateParents::NULL);
                         dmap
                     })
@@ -57,6 +58,8 @@
         on_disk: OnDisk,
         data_size: usize,
         metadata: &[u8],
+        uuid: Vec<u8>,
+        identity: Option<u64>,
     ) -> Result<Self, DirstateError>
     where
         OnDisk: Deref<Target = [u8]> + Send + 'static,
@@ -66,7 +69,7 @@
         OwningDirstateMapTryBuilder {
             on_disk,
             map_builder: |bytes| {
-                DirstateMap::new_v2(bytes, data_size, metadata)
+                DirstateMap::new_v2(bytes, data_size, metadata, uuid, identity)
             },
         }
         .try_build()
@@ -86,4 +89,16 @@
     pub fn on_disk(&self) -> &[u8] {
         self.borrow_on_disk()
     }
+
+    pub fn old_uuid(&self) -> Option<&[u8]> {
+        self.get_map().old_uuid.as_deref()
+    }
+
+    pub fn old_identity(&self) -> Option<u64> {
+        self.get_map().identity
+    }
+
+    pub fn old_data_size(&self) -> usize {
+        self.get_map().old_data_size
+    }
 }
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/errors.rs
--- a/rust/hg-core/src/errors.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-core/src/errors.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -46,6 +46,9 @@
 
     /// Censored revision data.
     CensoredNodeError,
+    /// A race condition has been detected. This *must* be handled locally
+    /// and not directly surface to the user.
+    RaceDetected(String),
 }
 
 /// Details about where an I/O error happened
@@ -111,6 +114,9 @@
                 write!(f, "encountered a censored node")
             }
             HgError::ConfigValueParseError(error) => error.fmt(f),
+            HgError::RaceDetected(context) => {
+                write!(f, "encountered a race condition {context}")
+            }
         }
     }
 }
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/repo.rs
--- a/rust/hg-core/src/repo.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-core/src/repo.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -1,6 +1,7 @@
 use crate::changelog::Changelog;
 use crate::config::{Config, ConfigError, ConfigParseError};
 use crate::dirstate::DirstateParents;
+use crate::dirstate_tree::dirstate_map::DirstateMapWriteMode;
 use crate::dirstate_tree::on_disk::Docket as DirstateDocket;
 use crate::dirstate_tree::owning::OwningDirstateMap;
 use crate::errors::HgResultExt;
@@ -9,6 +10,7 @@
 use crate::manifest::{Manifest, Manifestlog};
 use crate::revlog::filelog::Filelog;
 use crate::revlog::RevlogError;
+use crate::utils::debug::debug_wait_for_file_or_print;
 use crate::utils::files::get_path_from_bytes;
 use crate::utils::hg_path::HgPath;
 use crate::utils::SliceExt;
@@ -22,6 +24,10 @@
 use std::io::Write as IoWrite;
 use std::path::{Path, PathBuf};
 
+const V2_MAX_READ_ATTEMPTS: usize = 5;
+
+type DirstateMapIdentity = (Option<u64>, Option<Vec<u8>>, usize);
+
 /// A repository on disk
 pub struct Repo {
     working_directory: PathBuf,
@@ -30,7 +36,6 @@
     requirements: HashSet<String>,
     config: Config,
     dirstate_parents: LazyCell<DirstateParents>,
-    dirstate_data_file_uuid: LazyCell<Option<Vec<u8>>>,
     dirstate_map: LazyCell<OwningDirstateMap>,
     changelog: LazyCell<Changelog>,
     manifestlog: LazyCell<Manifestlog>,
@@ -180,7 +185,6 @@
             dot_hg,
             config: repo_config,
             dirstate_parents: LazyCell::new(),
-            dirstate_data_file_uuid: LazyCell::new(),
             dirstate_map: LazyCell::new(),
             changelog: LazyCell::new(),
             manifestlog: LazyCell::new(),
@@ -254,6 +258,15 @@
             .unwrap_or_default())
     }
 
+    fn dirstate_identity(&self) -> Result<Option<u64>, HgError> {
+        use std::os::unix::fs::MetadataExt;
+        Ok(self
+            .hg_vfs()
+            .symlink_metadata("dirstate")
+            .io_not_found_as_none()?
+            .map(|meta| meta.ino()))
+    }
+
     pub fn dirstate_parents(&self) -> Result<DirstateParents, HgError> {
         Ok(*self
             .dirstate_parents
@@ -263,15 +276,10 @@
     fn read_dirstate_parents(&self) -> Result<DirstateParents, HgError> {
         let dirstate = self.dirstate_file_contents()?;
         let parents = if dirstate.is_empty() {
-            if self.has_dirstate_v2() {
-                self.dirstate_data_file_uuid.set(None);
-            }
             DirstateParents::NULL
         } else if self.has_dirstate_v2() {
             let docket =
                 crate::dirstate_tree::on_disk::read_docket(&dirstate)?;
-            self.dirstate_data_file_uuid
-                .set(Some(docket.uuid.to_owned()));
             docket.parents()
         } else {
             *crate::dirstate::parsers::parse_dirstate_parents(&dirstate)?
@@ -280,57 +288,179 @@
         Ok(parents)
     }
 
-    fn read_dirstate_data_file_uuid(
+    /// Returns the information read from the dirstate docket necessary to
+    /// check if the data file has been updated/deleted by another process
+    /// since we last read the dirstate.
+    /// Namely, the inode, data file uuid and the data size.
+    fn get_dirstate_data_file_integrity(
         &self,
-    ) -> Result<Option<Vec<u8>>, HgError> {
+    ) -> Result<DirstateMapIdentity, HgError> {
         assert!(
             self.has_dirstate_v2(),
             "accessing dirstate data file ID without dirstate-v2"
         );
+        // Get the identity before the contents since we could have a race
+        // between the two. Having an identity that is too old is fine, but
+        // one that is younger than the content change is bad.
+        let identity = self.dirstate_identity()?;
         let dirstate = self.dirstate_file_contents()?;
         if dirstate.is_empty() {
             self.dirstate_parents.set(DirstateParents::NULL);
-            Ok(None)
+            Ok((identity, None, 0))
         } else {
             let docket =
                 crate::dirstate_tree::on_disk::read_docket(&dirstate)?;
             self.dirstate_parents.set(docket.parents());
-            Ok(Some(docket.uuid.to_owned()))
+            Ok((identity, Some(docket.uuid.to_owned()), docket.data_size()))
         }
     }
 
     fn new_dirstate_map(&self) -> Result<OwningDirstateMap, DirstateError> {
+        if self.has_dirstate_v2() {
+            // The v2 dirstate is split into a docket and a data file.
+            // Since we don't always take the `wlock` to read it
+            // (like in `hg status`), it is susceptible to races.
+            // A simple retry method should be enough since full rewrites
+            // only happen when too much garbage data is present and
+            // this race is unlikely.
+            let mut tries = 0;
+
+            while tries < V2_MAX_READ_ATTEMPTS {
+                tries += 1;
+                match self.read_docket_and_data_file() {
+                    Ok(m) => {
+                        return Ok(m);
+                    }
+                    Err(e) => match e {
+                        DirstateError::Common(HgError::RaceDetected(
+                            context,
+                        )) => {
+                            log::info!(
+                                "dirstate read race detected {} (retry {}/{})",
+                                context,
+                                tries,
+                                V2_MAX_READ_ATTEMPTS,
+                            );
+                            continue;
+                        }
+                        _ => return Err(e),
+                    },
+                }
+            }
+            let error = HgError::abort(
+                format!("dirstate read race happened {tries} times in a row"),
+                255,
+                None,
+            );
+            Err(DirstateError::Common(error))
+        } else {
+            debug_wait_for_file_or_print(
+                self.config(),
+                "dirstate.pre-read-file",
+            );
+            let identity = self.dirstate_identity()?;
+            let dirstate_file_contents = self.dirstate_file_contents()?;
+            if dirstate_file_contents.is_empty() {
+                self.dirstate_parents.set(DirstateParents::NULL);
+                Ok(OwningDirstateMap::new_empty(Vec::new()))
+            } else {
+                let (map, parents) = OwningDirstateMap::new_v1(
+                    dirstate_file_contents,
+                    identity,
+                )?;
+                self.dirstate_parents.set(parents);
+                Ok(map)
+            }
+        }
+    }
+
+    fn read_docket_and_data_file(
+        &self,
+    ) -> Result<OwningDirstateMap, DirstateError> {
+        debug_wait_for_file_or_print(self.config(), "dirstate.pre-read-file");
         let dirstate_file_contents = self.dirstate_file_contents()?;
+        let identity = self.dirstate_identity()?;
         if dirstate_file_contents.is_empty() {
             self.dirstate_parents.set(DirstateParents::NULL);
-            if self.has_dirstate_v2() {
-                self.dirstate_data_file_uuid.set(None);
-            }
-            Ok(OwningDirstateMap::new_empty(Vec::new()))
-        } else if self.has_dirstate_v2() {
-            let docket = crate::dirstate_tree::on_disk::read_docket(
-                &dirstate_file_contents,
-            )?;
-            self.dirstate_parents.set(docket.parents());
-            self.dirstate_data_file_uuid
-                .set(Some(docket.uuid.to_owned()));
-            let data_size = docket.data_size();
-            let metadata = docket.tree_metadata();
-            if let Some(data_mmap) = self
+            return Ok(OwningDirstateMap::new_empty(Vec::new()));
+        }
+        let docket = crate::dirstate_tree::on_disk::read_docket(
+            &dirstate_file_contents,
+        )?;
+        debug_wait_for_file_or_print(
+            self.config(),
+            "dirstate.post-docket-read-file",
+        );
+        self.dirstate_parents.set(docket.parents());
+        let uuid = docket.uuid.to_owned();
+        let data_size = docket.data_size();
+
+        let context = "between reading dirstate docket and data file";
+        let race_error = HgError::RaceDetected(context.into());
+        let metadata = docket.tree_metadata();
+
+        let mut map = if crate::vfs::is_on_nfs_mount(docket.data_filename()) {
+            // Don't mmap on NFS to prevent `SIGBUS` error on deletion
+            let contents = self.hg_vfs().read(docket.data_filename());
+            let contents = match contents {
+                Ok(c) => c,
+                Err(HgError::IoError { error, context }) => {
+                    match error.raw_os_error().expect("real os error") {
+                        // 2 = ENOENT, No such file or directory
+                        // 116 = ESTALE, Stale NFS file handle
+                        //
+                        // TODO match on `error.kind()` when
+                        // `ErrorKind::StaleNetworkFileHandle` is stable.
+                        2 | 116 => {
+                            // Race where the data file was deleted right after
+                            // we read the docket, try again
+                            return Err(race_error.into());
+                        }
+                        _ => {
+                            return Err(
+                                HgError::IoError { error, context }.into()
+                            )
+                        }
+                    }
+                }
+                Err(e) => return Err(e.into()),
+            };
+            OwningDirstateMap::new_v2(
+                contents, data_size, metadata, uuid, identity,
+            )
+        } else {
+            match self
                 .hg_vfs()
                 .mmap_open(docket.data_filename())
-                .io_not_found_as_none()?
+                .io_not_found_as_none()
             {
-                OwningDirstateMap::new_v2(data_mmap, data_size, metadata)
-            } else {
-                OwningDirstateMap::new_v2(Vec::new(), data_size, metadata)
+                Ok(Some(data_mmap)) => OwningDirstateMap::new_v2(
+                    data_mmap, data_size, metadata, uuid, identity,
+                ),
+                Ok(None) => {
+                    // Race where the data file was deleted right after we
+                    // read the docket, try again
+                    return Err(race_error.into());
+                }
+                Err(e) => return Err(e.into()),
             }
-        } else {
-            let (map, parents) =
-                OwningDirstateMap::new_v1(dirstate_file_contents)?;
-            self.dirstate_parents.set(parents);
-            Ok(map)
-        }
+        }?;
+
+        let write_mode_config = self
+            .config()
+            .get_str(b"devel", b"dirstate.v2.data_update_mode")
+            .unwrap_or(Some("auto"))
+            .unwrap_or("auto"); // don't bother for devel options
+        let write_mode = match write_mode_config {
+            "auto" => DirstateMapWriteMode::Auto,
+            "force-new" => DirstateMapWriteMode::ForceNewDataFile,
+            "force-append" => DirstateMapWriteMode::ForceAppend,
+            _ => DirstateMapWriteMode::Auto,
+        };
+
+        map.with_dmap_mut(|m| m.set_write_mode(write_mode));
+
+        Ok(map)
     }
 
     pub fn dirstate_map(
@@ -421,13 +551,37 @@
         // it’s unset
         let parents = self.dirstate_parents()?;
         let (packed_dirstate, old_uuid_to_remove) = if self.has_dirstate_v2() {
-            let uuid_opt = self
-                .dirstate_data_file_uuid
-                .get_or_init(|| self.read_dirstate_data_file_uuid())?;
-            let uuid_opt = uuid_opt.as_ref();
-            let can_append = uuid_opt.is_some();
+            let (identity, uuid, data_size) =
+                self.get_dirstate_data_file_integrity()?;
+            let identity_changed = identity != map.old_identity();
+            let uuid_changed = uuid.as_deref() != map.old_uuid();
+            let data_length_changed = data_size != map.old_data_size();
+
+            if identity_changed || uuid_changed || data_length_changed {
+                // If any of identity, uuid or length have changed since
+                // last disk read, don't write.
+                // This is fine because either we're in a command that doesn't
+                // write anything too important (like `hg status`), or we're in
+                // `hg add` and we're supposed to have taken the lock before
+                // reading anyway.
+                //
+                // TODO complain loudly if we've changed anything important
+                // without taking the lock.
+                // (see `hg help config.format.use-dirstate-tracked-hint`)
+                log::debug!(
+                    "dirstate has changed since last read, not updating."
+                );
+                return Ok(());
+            }
+
+            let uuid_opt = map.old_uuid();
+            let write_mode = if uuid_opt.is_some() {
+                DirstateMapWriteMode::Auto
+            } else {
+                DirstateMapWriteMode::ForceNewDataFile
+            };
             let (data, tree_metadata, append, old_data_size) =
-                map.pack_v2(can_append)?;
+                map.pack_v2(write_mode)?;
 
             // Reuse the uuid, or generate a new one, keeping the old for
             // deletion.
@@ -470,7 +624,10 @@
             //   https://github.com/openzfs/zfs/issues/13370
             //
             if !append {
+                log::trace!("creating a new dirstate data file");
                 options.create_new(true);
+            } else {
+                log::trace!("appending to the dirstate data file");
             }
 
             let data_size = (|| {
@@ -499,6 +656,22 @@
 
             (packed_dirstate, old_uuid)
         } else {
+            let identity = self.dirstate_identity()?;
+            if identity != map.old_identity() {
+                // If identity changed since last disk read, don't write.
+                // This is fine because either we're in a command that doesn't
+                // write anything too important (like `hg status`), or we're in
+                // `hg add` and we're supposed to have taken the lock before
+                // reading anyway.
+                //
+                // TODO complain loudly if we've changed anything important
+                // without taking the lock.
+                // (see `hg help config.format.use-dirstate-tracked-hint`)
+                log::debug!(
+                    "dirstate has changed since last read, not updating."
+                );
+                return Ok(());
+            }
             (map.pack_v1(parents)?, None)
         };
 
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/utils.rs
--- a/rust/hg-core/src/utils.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-core/src/utils.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -15,6 +15,7 @@
 use std::fmt;
 use std::{io::Write, ops::Deref};
 
+pub mod debug;
 pub mod files;
 pub mod hg_path;
 pub mod path_auditor;
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/utils/debug.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-core/src/utils/debug.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -0,0 +1,87 @@
+//! Utils for debugging hg-core
+
+use crate::config::Config;
+
+/// Write the file path given by the config option `devel.<config_option>` with
+/// the suffix `.waiting`, then wait for the file path given by the
+/// config option `devel.<config_option>` to appear on disk
+/// up to `devel.<config_option>-timeout` seconds.
+/// Note that the timeout may be higher because we scale it if global
+/// `run-tests` timeouts are raised to prevent flakiness on slower hardware.
+///
+/// Useful for testing race conditions.
+pub fn debug_wait_for_file(
+    config: &Config,
+    config_option: &str,
+) -> Result<(), String> {
+    let path_opt = format!("sync.{config_option}");
+    let file_path = match config.get_str(b"devel", path_opt.as_bytes()).ok() {
+        Some(Some(file_path)) => file_path,
+        _ => return Ok(()),
+    };
+
+    // TODO make it so `configitems` is shared between Rust and Python so that
+    // defaults work out of the box, etc.
+    let default_timeout = 2;
+    let timeout_opt = format!("sync.{config_option}-timeout");
+    let timeout_seconds =
+        match config.get_u32(b"devel", timeout_opt.as_bytes()) {
+            Ok(Some(timeout)) => timeout,
+            Err(e) => {
+                log::debug!("{e}");
+                default_timeout
+            }
+            _ => default_timeout,
+        };
+    let timeout_seconds = timeout_seconds as u64;
+
+    log::debug!(
+        "Config option `{config_option}` found, \
+             waiting for file `{file_path}` to be created"
+    );
+    std::fs::File::create(format!("{file_path}.waiting")).ok();
+    // If the test timeout have been extended, scale the timer relative
+    // to the normal timing.
+    let global_default_timeout: u64 = std::env::var("HGTEST_TIMEOUT_DEFAULT")
+        .map(|t| t.parse())
+        .unwrap_or(Ok(0))
+        .unwrap();
+    let global_timeout_override: u64 = std::env::var("HGTEST_TIMEOUT")
+        .map(|t| t.parse())
+        .unwrap_or(Ok(0))
+        .unwrap();
+    let timeout_seconds = if global_default_timeout < global_timeout_override {
+        timeout_seconds * global_timeout_override / global_default_timeout
+    } else {
+        timeout_seconds
+    };
+    let timeout = std::time::Duration::from_secs(timeout_seconds);
+
+    let start = std::time::Instant::now();
+    let path = std::path::Path::new(file_path);
+    let mut found = false;
+    while start.elapsed() < timeout {
+        if path.exists() {
+            log::debug!("File `{file_path}` was created");
+            found = true;
+            break;
+        } else {
+            std::thread::sleep(std::time::Duration::from_millis(10));
+        }
+    }
+    if !found {
+        let msg = format!(
+            "File `{file_path}` set by `{config_option}` was not found \
+            within the allocated {timeout_seconds} seconds timeout"
+        );
+        Err(msg)
+    } else {
+        Ok(())
+    }
+}
+
+pub fn debug_wait_for_file_or_print(config: &Config, config_option: &str) {
+    if let Err(e) = debug_wait_for_file(config, config_option) {
+        eprintln!("{e}");
+    };
+}
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-core/src/vfs.rs
--- a/rust/hg-core/src/vfs.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-core/src/vfs.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -172,3 +172,24 @@
 pub(crate) fn is_file(path: impl AsRef<Path>) -> Result<bool, HgError> {
     Ok(fs_metadata(path)?.map_or(false, |meta| meta.is_file()))
 }
+
+/// Returns whether the given `path` is on a network file system.
+/// Taken from `cargo`'s codebase.
+#[cfg(target_os = "linux")]
+pub(crate) fn is_on_nfs_mount(path: impl AsRef<Path>) -> bool {
+    use std::ffi::CString;
+    use std::mem;
+    use std::os::unix::prelude::*;
+
+    let path = match CString::new(path.as_ref().as_os_str().as_bytes()) {
+        Ok(path) => path,
+        Err(_) => return false,
+    };
+
+    unsafe {
+        let mut buf: libc::statfs = mem::zeroed();
+        let r = libc::statfs(path.as_ptr(), &mut buf);
+
+        r == 0 && buf.f_type as u32 == libc::NFS_SUPER_MAGIC as u32
+    }
+}
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/hg-cpython/src/dirstate/dirstate_map.rs
--- a/rust/hg-cpython/src/dirstate/dirstate_map.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/hg-cpython/src/dirstate/dirstate_map.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -22,7 +22,8 @@
     pybytes_deref::PyBytesDeref,
 };
 use hg::{
-    dirstate::StateMapIter, dirstate_tree::on_disk::DirstateV2ParseError,
+    dirstate::StateMapIter, dirstate_tree::dirstate_map::DirstateMapWriteMode,
+    dirstate_tree::on_disk::DirstateV2ParseError,
     dirstate_tree::owning::OwningDirstateMap, revlog::Node,
     utils::files::normalize_case, utils::hg_path::HgPath, DirstateEntry,
     DirstateError, DirstateParents,
@@ -47,9 +48,10 @@
     @staticmethod
     def new_v1(
         on_disk: PyBytes,
+        identity: Option<u64>,
     ) -> PyResult<PyObject> {
         let on_disk = PyBytesDeref::new(py, on_disk);
-        let (map, parents) = OwningDirstateMap::new_v1(on_disk)
+        let (map, parents) = OwningDirstateMap::new_v1(on_disk, identity)
             .map_err(|e| dirstate_error(py, e))?;
         let map = Self::create_instance(py, map)?;
         let p1 = PyBytes::new(py, parents.p1.as_bytes());
@@ -64,18 +66,33 @@
         on_disk: PyBytes,
         data_size: usize,
         tree_metadata: PyBytes,
+        uuid: PyBytes,
+        identity: Option<u64>,
     ) -> PyResult<PyObject> {
         let dirstate_error = |e: DirstateError| {
             PyErr::new::<exc::OSError, _>(py, format!("Dirstate error: {:?}", e))
         };
         let on_disk = PyBytesDeref::new(py, on_disk);
+        let uuid = uuid.data(py);
         let map = OwningDirstateMap::new_v2(
-            on_disk, data_size, tree_metadata.data(py),
+            on_disk,
+            data_size,
+            tree_metadata.data(py),
+            uuid.to_owned(),
+            identity,
         ).map_err(dirstate_error)?;
         let map = Self::create_instance(py, map)?;
         Ok(map.into_object())
     }
 
+    /// Returns an empty DirstateMap. Only used for a new dirstate.
+    @staticmethod
+    def new_empty() -> PyResult<PyObject> {
+        let map = OwningDirstateMap::new_empty(vec![]);
+        let map = Self::create_instance(py, map)?;
+        Ok(map.into_object())
+    }
+
     def clear(&self) -> PyResult<PyObject> {
         self.inner(py).borrow_mut().clear();
         Ok(py.None())
@@ -236,10 +253,16 @@
     /// instead of written to a new data file (False).
     def write_v2(
         &self,
-        can_append: bool,
+        write_mode: usize,
     ) -> PyResult<PyObject> {
         let inner = self.inner(py).borrow();
-        let result = inner.pack_v2(can_append);
+        let rust_write_mode = match write_mode {
+            0 => DirstateMapWriteMode::Auto,
+            1 => DirstateMapWriteMode::ForceNewDataFile,
+            2 => DirstateMapWriteMode::ForceAppend,
+            _ => DirstateMapWriteMode::Auto, // XXX should we error out?
+        };
+        let result = inner.pack_v2(rust_write_mode);
         match result {
             Ok((packed, tree_metadata, append, _old_data_size)) => {
                 let packed = PyBytes::new(py, &packed);
diff -r 2fbc109fd58a -r a6b8b1ab9116 rust/rhg/src/commands/status.rs
--- a/rust/rhg/src/commands/status.rs	Thu Mar 02 04:16:47 2023 +0100
+++ b/rust/rhg/src/commands/status.rs	Thu Mar 02 19:02:52 2023 +0100
@@ -21,6 +21,7 @@
 use hg::manifest::Manifest;
 use hg::matchers::{AlwaysMatcher, IntersectionMatcher};
 use hg::repo::Repo;
+use hg::utils::debug::debug_wait_for_file;
 use hg::utils::files::get_bytes_from_os_string;
 use hg::utils::files::get_path_from_bytes;
 use hg::utils::hg_path::{hg_path_to_path_buf, HgPath};
@@ -308,26 +309,46 @@
                 .unsure
                 .into_par_iter()
                 .map(|to_check| {
-                    unsure_is_modified(
+                    // The compiler seems to get a bit confused with complex
+                    // inference when using a parallel iterator + map
+                    // + map_err + collect, so let's just inline some of the
+                    // logic.
+                    match unsure_is_modified(
                         working_directory_vfs,
                         store_vfs,
                         check_exec,
                         &manifest,
                         &to_check.path,
-                    )
-                    .map(|modified| (to_check, modified))
+                    ) {
+                        Err(HgError::IoError { .. }) => {
+                            // IO errors most likely stem from the file being
+                            // deleted even though we know it's in the
+                            // dirstate.
+                            Ok((to_check, UnsureOutcome::Deleted))
+                        }
+                        Ok(outcome) => Ok((to_check, outcome)),
+                        Err(e) => Err(e),
+                    }
                 })
                 .collect::<Result<_, _>>()?;
-            for (status_path, is_modified) in res.into_iter() {
-                if is_modified {
-                    if display_states.modified {
-                        ds_status.modified.push(status_path);
+            for (status_path, outcome) in res.into_iter() {
+                match outcome {
+                    UnsureOutcome::Clean => {
+                        if display_states.clean {
+                            ds_status.clean.push(status_path.clone());
+                        }
+                        fixup.push(status_path.path.into_owned())
                     }
-                } else {
-                    if display_states.clean {
-                        ds_status.clean.push(status_path.clone());
+                    UnsureOutcome::Modified => {
+                        if display_states.modified {
+                            ds_status.modified.push(status_path);
+                        }
                     }
-                    fixup.push(status_path.path.into_owned())
+                    UnsureOutcome::Deleted => {
+                        if display_states.deleted {
+                            ds_status.deleted.push(status_path);
+                        }
+                    }
                 }
             }
         }
@@ -401,6 +422,13 @@
             after_status,
         )?;
 
+    // Development config option to test write races
+    if let Err(e) =
+        debug_wait_for_file(config, "status.pre-dirstate-write-file")
+    {
+        ui.write_stderr(e.as_bytes()).ok();
+    }
+
     if (fixup.is_empty() || filesystem_time_at_status_start.is_none())
         && !dirstate_write_needed
     {
@@ -420,9 +448,21 @@
                     // `unsure_is_clean` which was needed before reading
                     // contents. Here we access metadata again after reading
                     // content, in case it changed in the meantime.
-                    let fs_metadata = repo
+                    let metadata_res = repo
                         .working_directory_vfs()
-                        .symlink_metadata(&fs_path)?;
+                        .symlink_metadata(&fs_path);
+                    let fs_metadata = match metadata_res {
+                        Ok(meta) => meta,
+                        Err(err) => match err {
+                            HgError::IoError { .. } => {
+                                // The file has probably been deleted. In any
+                                // case, it was in the dirstate before, so
+                                // let's ignore the error.
+                                continue;
+                            }
+                            _ => return Err(err.into()),
+                        },
+                    };
                     if let Some(mtime) =
                         TruncatedTimestamp::for_reliable_mtime_of(
                             &fs_metadata,
@@ -449,6 +489,7 @@
             // Not updating the dirstate is not ideal but not critical:
             // don’t keep our caller waiting until some other Mercurial
             // process releases the lock.
+            log::info!("not writing dirstate from `status`: lock is held")
         }
         Err(LockError::Other(HgError::IoError { error, .. }))
             if error.kind() == io::ErrorKind::PermissionDenied =>
@@ -528,6 +569,16 @@
     }
 }
 
+/// Outcome of the additional check for an ambiguous tracked file
+enum UnsureOutcome {
+    /// The file is actually clean
+    Clean,
+    /// The file has been modified
+    Modified,
+    /// The file was deleted on disk (or became another type of fs entry)
+    Deleted,
+}
+
 /// Check if a file is modified by comparing actual repo store and file system.
 ///
 /// This meant to be used for those that the dirstate cannot resolve, due
@@ -538,7 +589,7 @@
     check_exec: bool,
     manifest: &Manifest,
     hg_path: &HgPath,
-) -> Result<bool, HgError> {
+) -> Result<UnsureOutcome, HgError> {
     let vfs = working_directory_vfs;
     let fs_path = hg_path_to_path_buf(hg_path).expect("HgPath conversion");
     let fs_metadata = vfs.symlink_metadata(&fs_path)?;
@@ -567,7 +618,7 @@
     };
 
     if entry_flags != fs_flags {
-        return Ok(true);
+        return Ok(UnsureOutcome::Modified);
     }
     let filelog = hg::filelog::Filelog::open_vfs(&store_vfs, hg_path)?;
     let fs_len = fs_metadata.len();
@@ -581,7 +632,7 @@
     if filelog_entry.file_data_len_not_equal_to(fs_len) {
         // No need to read file contents:
         // it cannot be equal if it has a different length.
-        return Ok(true);
+        return Ok(UnsureOutcome::Modified);
     }
 
     let p1_filelog_data = filelog_entry.data()?;
@@ -589,7 +640,7 @@
     if p1_contents.len() as u64 != fs_len {
         // No need to read file contents:
         // it cannot be equal if it has a different length.
-        return Ok(true);
+        return Ok(UnsureOutcome::Modified);
     }
 
     let fs_contents = if is_symlink {
@@ -597,5 +648,10 @@
     } else {
         vfs.read(fs_path)?
     };
-    Ok(p1_contents != &*fs_contents)
+
+    Ok(if p1_contents != &*fs_contents {
+        UnsureOutcome::Modified
+    } else {
+        UnsureOutcome::Clean
+    })
 }
diff -r 2fbc109fd58a -r a6b8b1ab9116 tests/run-tests.py
--- a/tests/run-tests.py	Thu Mar 02 04:16:47 2023 +0100
+++ b/tests/run-tests.py	Thu Mar 02 19:02:52 2023 +0100
@@ -1831,8 +1831,44 @@
 
         pos = prepos = -1
 
-        # True or False when in a true or false conditional section
-        skipping = None
+        # The current stack of conditionnal section.
+        # Each relevant conditionnal section can have the following value:
+        #  - True:  we should run this block
+        #  - False: we should skip this block
+        #  - None:  The parent block is skipped,
+        #           (no branch of this one will ever run)
+        condition_stack = []
+
+        def run_line():
+            """return True if the current line should be run"""
+            if not condition_stack:
+                return True
+            return bool(condition_stack[-1])
+
+        def push_conditional_block(should_run):
+            """Push a new conditional context, with its initial state
+
+            i.e. entry a #if block"""
+            if not run_line():
+                condition_stack.append(None)
+            else:
+                condition_stack.append(should_run)
+
+        def flip_conditional():
+            """reverse the current condition state
+
+            i.e. enter a #else
+            """
+            assert condition_stack
+            if condition_stack[-1] is not None:
+                condition_stack[-1] = not condition_stack[-1]
+
+        def pop_conditional():
+            """exit the current skipping context
+
+            i.e. reach the #endif"""
+            assert condition_stack
+            condition_stack.pop()
 
         # We keep track of whether or not we're in a Python block so we
         # can generate the surrounding doctest magic.
@@ -1888,7 +1924,7 @@
                     after.setdefault(pos, []).append(
                         b'  !!! invalid #require\n'
                     )
-                if not skipping:
+                if run_line():
                     haveresult, message = self._hghave(lsplit[1:])
                     if not haveresult:
                         script = [b'echo "%s"\nexit 80\n' % message]
@@ -1898,21 +1934,19 @@
                 lsplit = l.split()
                 if len(lsplit) < 2 or lsplit[0] != b'#if':
                     after.setdefault(pos, []).append(b'  !!! invalid #if\n')
-                if skipping is not None:
-                    after.setdefault(pos, []).append(b'  !!! nested #if\n')
-                skipping = not self._iftest(lsplit[1:])
+                push_conditional_block(self._iftest(lsplit[1:]))
                 after.setdefault(pos, []).append(l)
             elif l.startswith(b'#else'):
-                if skipping is None:
+                if not condition_stack:
                     after.setdefault(pos, []).append(b'  !!! missing #if\n')
-                skipping = not skipping
+                flip_conditional()
                 after.setdefault(pos, []).append(l)
             elif l.startswith(b'#endif'):
-                if skipping is None:
+                if not condition_stack:
                     after.setdefault(pos, []).append(b'  !!! missing #if\n')
-                skipping = None
+                pop_conditional()
                 after.setdefault(pos, []).append(l)
-            elif skipping:
+            elif not run_line():
                 after.setdefault(pos, []).append(l)
             elif l.startswith(b'  >>> '):  # python inlines
                 after.setdefault(pos, []).append(l)
@@ -1957,7 +1991,7 @@
 
         if inpython:
             script.append(b'EOF\n')
-        if skipping is not None:
+        if condition_stack:
             after.setdefault(pos, []).append(b'  !!! missing #endif\n')
         addsalt(n + 1, False)
         # Need to end any current per-command trace
diff -r 2fbc109fd58a -r a6b8b1ab9116 tests/test-dirstate-read-race.t
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-dirstate-read-race.t	Thu Mar 02 19:02:52 2023 +0100
@@ -0,0 +1,410 @@
+==============================================================================
+Check potential race conditions between a dirstate's read and other operations
+==============================================================================
+
+#testcases dirstate-v1 dirstate-v2-append dirstate-v2-rewrite
+#testcases pre-all-read pre-some-read
+
+Some commands, like `hg status`, do not need to take the wlock but need to
+access dirstate data.
+Other commands might update the dirstate data while this happens.
+
+This can create issues if repository data is read in the wrong order, or for
+the dirstate-v2 format where the data is contained in multiple files.
+
+This test file is meant to test various cases where such parallel operations
+happen and make sure the reading process behaves fine. We do so with a `hg
+status` command since it is probably the most advanced of such read-only
+command.
+
+It bears simililarity with `tests/test-dirstate-status-race.t ` but tests a
+different type of race.
+
+Setup
+=====
+
+  $ cat >> $HGRCPATH << EOF
+  > [storage]
+  > dirstate-v2.slow-path=allow
+  > EOF
+
+#if no-dirstate-v1
+  $ cat >> $HGRCPATH << EOF
+  > [format]
+  > use-dirstate-v2=yes
+  > EOF
+#else
+  $ cat >> $HGRCPATH << EOF
+  > [format]
+  > use-dirstate-v2=no
+  > EOF
+#endif
+
+#if dirstate-v2-rewrite
+  $ d2args="--config devel.dirstate.v2.data_update_mode=force-new"
+#endif
+#if dirstate-v2-append
+  $ d2args="--config devel.dirstate.v2.data_update_mode=force-append"
+#endif
+
+
+#if dirstate-v1
+  $ cfg="devel.sync.dirstate.pre-read-file"
+#else
+#if pre-all-read
+  $ cfg="devel.sync.dirstate.pre-read-file"
+#else
+  $ cfg="devel.sync.dirstate.post-docket-read-file"
+#endif
+#endif
+
+  $ directories="dir dir/nested dir2"
+  $ first_files="dir/nested/a dir/b dir/c dir/d dir2/e f"
+  $ second_files="g dir/nested/h dir/i dir/j dir2/k dir2/l dir/nested/m"
+  $ extra_files="dir/n dir/o p q"
+
+  $ hg init reference-repo
+  $ cd reference-repo
+  $ mkdir -p dir/nested dir2
+  $ touch -t 200001010000 $first_files $directories
+  $ hg commit -Aqm "recreate a bunch of files to facilitate dirstate-v2 append"
+  $ touch -t 200001010010 $second_files $directories
+  $ hg commit -Aqm "more files to have two commit"
+  $ hg log -G -v
+  @  changeset:   1:9a86dcbfb938
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  files:       dir/i dir/j dir/nested/h dir/nested/m dir2/k dir2/l g
+  |  description:
+  |  more files to have two commit
+  |
+  |
+  o  changeset:   0:4f23db756b09
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     files:       dir/b dir/c dir/d dir/nested/a dir2/e f
+     description:
+     recreate a bunch of files to facilitate dirstate-v2 append
+  
+  
+  $ hg manifest
+  dir/b
+  dir/c
+  dir/d
+  dir/i
+  dir/j
+  dir/nested/a
+  dir/nested/h
+  dir/nested/m
+  dir2/e
+  dir2/k
+  dir2/l
+  f
+  g
+
+Add some unknown files and refresh the dirstate
+
+  $ touch -t 200001010020 $extra_files
+  $ hg add dir/o
+  $ hg remove dir/nested/m
+
+  $ hg st --config devel.dirstate.v2.data_update_mode=force-new
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ hg debugstate
+  n 644          0 2000-01-01 00:00:00 dir/b
+  n 644          0 2000-01-01 00:00:00 dir/c
+  n 644          0 2000-01-01 00:00:00 dir/d
+  n 644          0 2000-01-01 00:10:00 dir/i
+  n 644          0 2000-01-01 00:10:00 dir/j
+  n 644          0 2000-01-01 00:00:00 dir/nested/a
+  n 644          0 2000-01-01 00:10:00 dir/nested/h
+  r ?????????????????????????????????? dir/nested/m (glob)
+  a ?????????????????????????????????? dir/o (glob)
+  n 644          0 2000-01-01 00:00:00 dir2/e
+  n 644          0 2000-01-01 00:10:00 dir2/k
+  n 644          0 2000-01-01 00:10:00 dir2/l
+  n 644          0 2000-01-01 00:00:00 f
+  n 644          0 2000-01-01 00:10:00 g
+  $ hg debugstate > ../reference
+  $ cd ..
+
+Actual Testing
+==============
+
+Race with a `hg add`
+-------------------
+
+  $ cp -a reference-repo race-with-add
+  $ cd race-with-add
+
+spin a `hg status` with some caches to update
+
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config ${cfg}=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+Add a file
+
+  $ hg $d2args add dir/n
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+The file should in a "added" state
+
+  $ hg status
+  A dir/n
+  A dir/o
+  R dir/nested/m
+  ? p
+  ? q
+
+The status process should return a consistent result and not crash.
+
+#if dirstate-v1
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/n
+  A dir/o
+  R dir/nested/m
+  ? p
+  ? q
+#else
+#if rhg pre-some-read dirstate-v2-append
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+#else
+#if rust no-rhg dirstate-v2-append
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+#else
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/n
+  A dir/o
+  R dir/nested/m
+  ? p
+  ? q
+#endif
+#endif
+#endif
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Race with a `hg commit`
+-----------------------
+
+  $ cp -a reference-repo race-with-commit
+  $ cd race-with-commit
+
+spin a `hg status with some cache to update
+
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config ${cfg}=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+Add a do a commit
+
+  $ hg status
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ hg $d2args commit -m 'racing commit'
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+commit was created, and status is now clean
+
+  $ hg log -GT '{node|short} {desc}\n'
+  @  02a67a77ee9b racing commit
+  |
+  o  9a86dcbfb938 more files to have two commit
+  |
+  o  4f23db756b09 recreate a bunch of files to facilitate dirstate-v2 append
+  
+  $ hg status
+  ? dir/n
+  ? p
+  ? q
+
+The status process should return a consistent result and not crash.
+
+#if rust no-rhg dirstate-v2-append
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+#else
+#if rhg pre-some-read dirstate-v2-append
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+#else
+  $ cat $TESTTMP/status-race-lock.out
+  M dir/o (no-rhg known-bad-output !)
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+  warning: ignoring unknown working parent 02a67a77ee9b! (no-rhg !)
+#endif
+#endif
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Race with a `hg update`
+-----------------------
+
+  $ cp -a reference-repo race-with-update
+  $ cd race-with-update
+
+spin a `hg status` with some caches to update
+
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config ${cfg}=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+do an update
+
+  $ hg status
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ hg log -GT '{node|short} {desc}\n'
+  @  9a86dcbfb938 more files to have two commit
+  |
+  o  4f23db756b09 recreate a bunch of files to facilitate dirstate-v2 append
+  
+  $ hg $d2args update --merge ".~1"
+  0 files updated, 0 files merged, 6 files removed, 0 files unresolved
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+  $ hg log -GT '{node|short} {desc}\n'
+  o  9a86dcbfb938 more files to have two commit
+  |
+  @  4f23db756b09 recreate a bunch of files to facilitate dirstate-v2 append
+  
+  $ hg status
+  A dir/o
+  ? dir/n
+  ? p
+  ? q
+
+The status process should return a consistent result and not crash.
+
+#if rhg dirstate-v2-append pre-some-read
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ! dir/i
+  ! dir/j
+  ! dir/nested/h
+  ! dir2/k
+  ! dir2/l
+  ! g
+  ? dir/n
+  ? p
+  ? q
+#else
+#if rust no-rhg dirstate-v2-append
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ! dir/i
+  ! dir/j
+  ! dir/nested/h
+  ! dir2/k
+  ! dir2/l
+  ! g
+  ? dir/n
+  ? p
+  ? q
+#else
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  ? dir/n
+  ? p
+  ? q
+#endif
+#endif
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Race with a cache updating `hg status`
+--------------------------------------
+
+It is interesting to race with "read-only" operation (that still update its cache)
+
+  $ cp -a reference-repo race-with-status
+  $ cd race-with-status
+
+spin a `hg status` with some caches to update
+
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config ${cfg}=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+do an update
+
+  $ touch -t 200001020006 f
+  $ hg $d2args status
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+The status process should return a consistent result and not crash.
+
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
diff -r 2fbc109fd58a -r a6b8b1ab9116 tests/test-dirstate-status-write-race.t
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-dirstate-status-write-race.t	Thu Mar 02 19:02:52 2023 +0100
@@ -0,0 +1,460 @@
+=====================================================================
+Check potential race conditions between a status and other operations
+=====================================================================
+
+#testcases dirstate-v1 dirstate-v2-append dirstate-v2-rewrite
+
+The `hg status` command can run without the wlock, however it might end up
+having to update the on-disk dirstate files, for example to mark ambiguous
+files as clean, or to update directory caches information with dirstate-v2.
+
+
+If another process updates the dirstate in the meantime we might run into
+trouble. Especially, commands doing semantic changes like `hg add` or
+ `hg commit` should not see their update erased by a concurrent status.
+
+Unlike commands like `add` or `commit`, `status` only writes the dirstate
+to update caches, no actual information is lost if we fail to write to disk.
+
+
+This test file is meant to test various cases where such parallel operations
+between a status with reasons to update the dirstate and another semantic
+changes happen.
+
+
+Setup
+=====
+
+  $ cat >> $HGRCPATH << EOF
+  > [storage]
+  > dirstate-v2.slow-path=allow
+  > EOF
+
+#if no-dirstate-v1
+  $ cat >> $HGRCPATH << EOF
+  > [format]
+  > use-dirstate-v2=yes
+  > EOF
+#else
+  $ cat >> $HGRCPATH << EOF
+  > [format]
+  > use-dirstate-v2=no
+  > EOF
+#endif
+
+#if dirstate-v2-rewrite
+  $ d2args="--config devel.dirstate.v2.data_update_mode=force-new"
+#endif
+#if dirstate-v2-append
+  $ d2args="--config devel.dirstate.v2.data_update_mode=force-append"
+#endif
+
+  $ directories="dir dir/nested dir2"
+  $ first_files="dir/nested/a dir/b dir/c dir/d dir2/e f"
+  $ second_files="g dir/nested/h dir/i dir/j dir2/k dir2/l dir/nested/m"
+  $ extra_files="dir/n dir/o p q"
+
+  $ hg init reference-repo
+  $ cd reference-repo
+  $ mkdir -p dir/nested dir2
+  $ touch -t 200001010000 $first_files $directories
+  $ hg commit -Aqm "recreate a bunch of files to facilitate dirstate-v2 append"
+  $ touch -t 200001010010 $second_files $directories
+  $ hg commit -Aqm "more files to have two commits"
+  $ hg log -G -v
+  @  changeset:   1:c349430a1631
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  files:       dir/i dir/j dir/nested/h dir/nested/m dir2/k dir2/l g
+  |  description:
+  |  more files to have two commits
+  |
+  |
+  o  changeset:   0:4f23db756b09
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     files:       dir/b dir/c dir/d dir/nested/a dir2/e f
+     description:
+     recreate a bunch of files to facilitate dirstate-v2 append
+  
+  
+  $ hg manifest
+  dir/b
+  dir/c
+  dir/d
+  dir/i
+  dir/j
+  dir/nested/a
+  dir/nested/h
+  dir/nested/m
+  dir2/e
+  dir2/k
+  dir2/l
+  f
+  g
+
+Add some unknown files and refresh the dirstate
+
+  $ touch -t 200001010020 $extra_files
+  $ hg add dir/o
+  $ hg remove dir/nested/m
+
+  $ hg st --config devel.dirstate.v2.data_update_mode=force-new
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ hg debugstate
+  n 644          0 2000-01-01 00:00:00 dir/b
+  n 644          0 2000-01-01 00:00:00 dir/c
+  n 644          0 2000-01-01 00:00:00 dir/d
+  n 644          0 2000-01-01 00:10:00 dir/i
+  n 644          0 2000-01-01 00:10:00 dir/j
+  n 644          0 2000-01-01 00:00:00 dir/nested/a
+  n 644          0 2000-01-01 00:10:00 dir/nested/h
+  r ?????????????????????????????????? dir/nested/m (glob)
+  a ?????????????????????????????????? dir/o (glob)
+  n 644          0 2000-01-01 00:00:00 dir2/e
+  n 644          0 2000-01-01 00:10:00 dir2/k
+  n 644          0 2000-01-01 00:10:00 dir2/l
+  n 644          0 2000-01-01 00:00:00 f
+  n 644          0 2000-01-01 00:10:00 g
+  $ hg debugstate > ../reference
+  $ cd ..
+
+Explain / verify the test principles
+------------------------------------
+
+First, we can properly copy the reference
+
+  $ cp -a reference-repo sanity-check
+  $ cd sanity-check
+  $ hg debugstate
+  n 644          0 2000-01-01 00:00:00 dir/b
+  n 644          0 2000-01-01 00:00:00 dir/c
+  n 644          0 2000-01-01 00:00:00 dir/d
+  n 644          0 2000-01-01 00:10:00 dir/i
+  n 644          0 2000-01-01 00:10:00 dir/j
+  n 644          0 2000-01-01 00:00:00 dir/nested/a
+  n 644          0 2000-01-01 00:10:00 dir/nested/h
+  r ?????????????????????????????????? dir/nested/m (glob)
+  a ?????????????????????????????????? dir/o (glob)
+  n 644          0 2000-01-01 00:00:00 dir2/e
+  n 644          0 2000-01-01 00:10:00 dir2/k
+  n 644          0 2000-01-01 00:10:00 dir2/l
+  n 644          0 2000-01-01 00:00:00 f
+  n 644          0 2000-01-01 00:10:00 g
+  $ hg debugstate > ../post-copy
+  $ diff ../reference ../post-copy
+
+And status thinks the cache is in a proper state
+
+  $ hg st
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ hg debugstate
+  n 644          0 2000-01-01 00:00:00 dir/b
+  n 644          0 2000-01-01 00:00:00 dir/c
+  n 644          0 2000-01-01 00:00:00 dir/d
+  n 644          0 2000-01-01 00:10:00 dir/i
+  n 644          0 2000-01-01 00:10:00 dir/j
+  n 644          0 2000-01-01 00:00:00 dir/nested/a
+  n 644          0 2000-01-01 00:10:00 dir/nested/h
+  r ?????????????????????????????????? dir/nested/m (glob)
+  a ?????????????????????????????????? dir/o (glob)
+  n 644          0 2000-01-01 00:00:00 dir2/e
+  n 644          0 2000-01-01 00:10:00 dir2/k
+  n 644          0 2000-01-01 00:10:00 dir2/l
+  n 644          0 2000-01-01 00:00:00 f
+  n 644          0 2000-01-01 00:10:00 g
+  $ hg debugstate > ../post-status
+  $ diff ../reference ../post-status
+
+Then we can start a status that:
+- has some update to do (the touch call)
+- will wait AFTER running status, but before updating the cache on disk
+
+  $ touch -t 200001010001 dir/c
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.sync.status.pre-dirstate-write-file=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+We check it runs the status first by modifying a file and updating another timestamp
+
+  $ touch -t 200001010003 dir/i
+  $ echo babar > dir/j
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+The test process should have reported a status before the change we made,
+and should have missed the timestamp update
+
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+  $ hg debugstate | grep dir/c
+  n 644          0 2000-01-01 00:01:00 dir/c
+  $ hg debugstate | grep dir/i
+  n 644          0 2000-01-01 00:10:00 dir/i
+  $ hg debugstate | grep dir/j
+  n 644          0 2000-01-01 00:10:00 dir/j
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Actual Testing
+==============
+
+Race with a `hg add`
+-------------------
+
+  $ cp -a reference-repo race-with-add
+  $ cd race-with-add
+
+spin a `hg status` with some caches to update
+
+  $ touch -t 200001020001 f
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.sync.status.pre-dirstate-write-file=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+Add a file
+
+  $ hg $d2args add dir/n
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+The file should in a "added" state
+
+  $ hg status
+  A dir/n
+  A dir/o
+  R dir/nested/m
+  ? p
+  ? q
+
+The status process should return a consistent result and not crash.
+
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Race with a `hg commit`
+----------------------
+
+  $ cp -a reference-repo race-with-commit
+  $ cd race-with-commit
+
+spin a `hg status` with some caches to update
+
+  $ touch -t 200001020001 dir/j
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.sync.status.pre-dirstate-write-file=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+Add a file and force the data file rewrite
+
+  $ hg $d2args commit -m created-during-status dir/o
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+The parent must change and the status should be clean
+
+  $ hg summary
+  parent: 2:2e3b442a2fd4 tip
+   created-during-status
+  branch: default
+  commit: 1 removed, 3 unknown
+  update: (current)
+  phases: 3 draft
+  $ hg status
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+
+The status process should return a consistent result and not crash.
+
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Race with a `hg update`
+----------------------
+
+  $ cp -a reference-repo race-with-update
+  $ cd race-with-update
+
+spin a `hg status` with some caches to update
+
+  $ touch -t 200001020001 dir2/k
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.sync.status.pre-dirstate-write-file=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+Add a file and force the data file rewrite
+
+  $ hg $d2args update ".~1"
+  0 files updated, 0 files merged, 6 files removed, 0 files unresolved
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+The parent must change and the status should be clean
+
+  $ hg summary
+  parent: 0:4f23db756b09 
+   recreate a bunch of files to facilitate dirstate-v2 append
+  branch: default
+  commit: 1 added, 3 unknown (new branch head)
+  update: 1 new changesets (update)
+  phases: 2 draft
+  $ hg status
+  A dir/o
+  ? dir/n
+  ? p
+  ? q
+
+The status process should return a consistent result and not crash.
+
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Race with another status
+------------------------
+
+  $ cp -a reference-repo race-with-status
+  $ cd race-with-status
+
+spin a `hg status` with some caches to update
+
+  $ touch -t 200001010030 dir/nested/h
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.sync.status.pre-dirstate-write-file=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+touch g
+
+  $ touch -t 200001010025 g
+  $ hg $d2args status
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+the first update should be on disk
+
+  $ hg debugstate --all | grep "g"
+  n 644          0 2000-01-01 00:25:00 g
+
+The status process should return a consistent result and not crash.
+
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
+
+Race with the removal of an ambiguous file
+----------------------è-------------------
+
+  $ cp -a reference-repo race-with-remove
+  $ cd race-with-remove
+
+spin a `hg status` with some caches to update
+
+  $ touch -t 200001010035 dir2/l
+  $ hg st >$TESTTMP/status-race-lock.out 2>$TESTTMP/status-race-lock.log \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.sync.status.pre-dirstate-write-file=$TESTTMP/status-race-lock \
+  > &
+  $ $RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/status-race-lock.waiting
+
+remove that same file
+
+  $ hg $d2args remove dir2/l
+  $ touch $TESTTMP/status-race-lock
+  $ wait
+
+file should be marked as removed
+
+  $ hg status
+  A dir/o
+  R dir/nested/m
+  R dir2/l
+  ? dir/n
+  ? p
+  ? q
+
+The status process should return a consistent result and not crash.
+
+  $ cat $TESTTMP/status-race-lock.out
+  A dir/o
+  R dir/nested/m
+  ? dir/n
+  ? p
+  ? q
+  $ cat $TESTTMP/status-race-lock.log
+
+final cleanup
+
+  $ rm $TESTTMP/status-race-lock $TESTTMP/status-race-lock.waiting
+  $ cd ..
diff -r 2fbc109fd58a -r a6b8b1ab9116 tests/test-dirstate.t
--- a/tests/test-dirstate.t	Thu Mar 02 04:16:47 2023 +0100
+++ b/tests/test-dirstate.t	Thu Mar 02 19:02:52 2023 +0100
@@ -148,7 +148,7 @@
   $ hg init append-mostly
   $ cd append-mostly
   $ mkdir dir dir2
-  $ touch dir/a dir/b dir/c dir/d dir/e dir2/f
+  $ touch -t 200001010000 dir/a dir/b dir/c dir/d dir/e dir2/f dir dir2
   $ hg commit -Aqm initial
   $ hg st
   $ dirstate_data_files | wc -l
@@ -163,12 +163,11 @@
   $ dirstate_uuid_has_not_changed
   not testing because using Python implementation (no-rust no-rhg !)
 
-Trigger an append with a small change
+Trigger an append with a small change to directory mtime
 
   $ current_data_size=$(find_dirstate_data_size)
-  $ rm dir2/f
+  $ touch -t 201001010000 dir2
   $ hg st
-  ! dir2/f
   $ dirstate_data_files | wc -l
    *1 (re)
   $ dirstate_uuid_has_not_changed
@@ -187,7 +186,6 @@
 Trigger a rust/rhg run which updates the unused bytes value
   $ hg st
   A file
-  ! dir2/f
   $ dirstate_data_files | wc -l
    *1 (re)
   $ dirstate_uuid_has_not_changed
@@ -213,8 +211,223 @@
 
 #endif
 
+(non-Rust always rewrites)
+
+Test the devel option to control write behavior
+==============================================
+
+Sometimes, debugging or testing the dirstate requires making sure that we have
+done a complete rewrite of the data file and have no unreachable data around,
+sometimes it requires we ensure we don't.
+
+We test the option to force this rewrite by creating the situation where an
+append would happen and check that it doesn't happen.
+
+  $ cd ..
+  $ hg init force-base
+  $ cd force-base
+  $ mkdir -p dir/nested dir2
+  $ touch -t 200001010000 f dir/nested/a dir/b dir/c dir/d dir2/e dir/nested dir dir2
+  $ hg commit -Aqm "recreate a bunch of files to facilitate append"
+  $ hg st --config devel.dirstate.v2.data_update_mode=force-new
+  $ cd ..
+
+#if dirstate-v2
+  $ hg -R force-base debugstate --docket | grep unused
+  number of unused bytes: 0
+
+Check with the option in "auto" mode
+------------------------------------
+  $ cp -a force-base append-mostly-no-force-rewrite
+  $ cd append-mostly-no-force-rewrite
+  $ current_uid=$(find_dirstate_uuid)
+
+Change mtime of dir on disk which will be recorded, causing a small enough change
+to warrant only an append
+
+  $ touch -t 202212010000 dir2
+  $ hg st \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.dirstate.v2.data_update_mode=auto
+
+UUID hasn't changed and a non-zero number of unused bytes means we've appended
+
+  $ dirstate_uuid_has_not_changed
+  not testing because using Python implementation (no-rust no-rhg !)
+
+#if no-rust no-rhg
+The pure python implementation never appends at the time this is written.
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: 0 (known-bad-output !)
+#else
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: [1-9]\d* (re)
+#endif
+  $ cd ..
+
+Check the same scenario with the option set to "force-new"
+---------------------------------------------------------
+
+  $ cp -a force-base append-mostly-force-rewrite
+  $ cd append-mostly-force-rewrite
+  $ current_uid=$(find_dirstate_uuid)
+
+Change mtime of dir on disk which will be recorded, causing a small enough change
+to warrant only an append, but we force the rewrite
+
+  $ touch -t 202212010000 dir2
+  $ hg st \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.dirstate.v2.data_update_mode=force-new
+
+UUID has changed and zero unused bytes means a full-rewrite happened
+
+
+#if no-rust no-rhg
+  $ dirstate_uuid_has_not_changed
+  not testing because using Python implementation
+#else
+  $ dirstate_uuid_has_not_changed
+  [1]
+#endif
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: 0
+  $ cd ..
+
+
+Check the same scenario with the option set to "force-append"
+-------------------------------------------------------------
+
+(should behave the same as "auto" here)
+
+  $ cp -a force-base append-mostly-force-append
+  $ cd append-mostly-force-append
+  $ current_uid=$(find_dirstate_uuid)
+
+Change mtime of dir on disk which will be recorded, causing a small enough change
+to warrant only an append, which we are forcing here anyway.
+
+  $ touch -t 202212010000 dir2
+  $ hg st \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.dirstate.v2.data_update_mode=force-append
+
+UUID has not changed and some unused bytes exist in the data file
+
+  $ dirstate_uuid_has_not_changed
+  not testing because using Python implementation (no-rust no-rhg !)
+
+#if no-rust no-rhg
+The pure python implementation never appends at the time this is written.
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: 0 (known-bad-output !)
+#else
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: [1-9]\d* (re)
+#endif
+  $ cd ..
+
+Check with the option in "auto" mode
+------------------------------------
+  $ cp -a force-base append-mostly-no-force-rewrite
+  $ cd append-mostly-no-force-rewrite
+  $ current_uid=$(find_dirstate_uuid)
+
+Change mtime of everything on disk causing a full rewrite
+
+  $ touch -t 202212010005 `hg files`
+  $ hg st \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.dirstate.v2.data_update_mode=auto
+
+UUID has changed and zero unused bytes means we've rewritten.
+
+#if no-rust no-rhg
+  $ dirstate_uuid_has_not_changed
+  not testing because using Python implementation
+#else
+  $ dirstate_uuid_has_not_changed
+  [1]
+#endif
+
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: 0 (known-bad-output !)
+  $ cd ..
+
+Check the same scenario with the option set to "force-new"
+---------------------------------------------------------
+
+(should be the same as auto)
+
+  $ cp -a force-base append-mostly-force-rewrite
+  $ cd append-mostly-force-rewrite
+  $ current_uid=$(find_dirstate_uuid)
+
+Change mtime of everything on disk causing a full rewrite
+
+  $ touch -t 202212010005 `hg files`
+  $ hg st \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.dirstate.v2.data_update_mode=force-new
+
+UUID has changed and a zero number unused bytes means we've rewritten.
+
+
+#if no-rust no-rhg
+  $ dirstate_uuid_has_not_changed
+  not testing because using Python implementation
+#else
+  $ dirstate_uuid_has_not_changed
+  [1]
+#endif
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: 0
+  $ cd ..
+
+
+Check the same scenario with the option set to "force-append"
+-------------------------------------------------------------
+
+Should append even if "auto" did not
+
+  $ cp -a force-base append-mostly-force-append
+  $ cd append-mostly-force-append
+  $ current_uid=$(find_dirstate_uuid)
+
+Change mtime of everything on disk causing a full rewrite
+
+  $ touch -t 202212010005 `hg files`
+  $ hg st \
+  > --config rhg.on-unsupported=abort \
+  > --config devel.dirstate.v2.data_update_mode=force-append
+
+UUID has not changed and some unused bytes exist in the data file
+
+  $ dirstate_uuid_has_not_changed
+  not testing because using Python implementation (no-rust no-rhg !)
+
+#if no-rust no-rhg
+The pure python implementation is never appending at the time this is written.
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: 0 (known-bad-output !)
+#else
+  $ hg debugstate --docket | grep unused
+  number of unused bytes: [1-9]\d* (re)
+#endif
+  $ cd ..
+
+
+
+Get back into a state suitable for the test of the file.
+
+  $ cd ./append-mostly
+
+#else
+  $ cd ./u
+#endif
+
 Transaction compatibility
--------------------------
+=========================
 
 The transaction preserves the dirstate.
 We should make sure all of it (docket + data) is preserved
diff -r 2fbc109fd58a -r a6b8b1ab9116 tests/test-patchbomb.t
--- a/tests/test-patchbomb.t	Thu Mar 02 04:16:47 2023 +0100
+++ b/tests/test-patchbomb.t	Thu Mar 02 19:02:52 2023 +0100
@@ -183,6 +183,43 @@
   +a
   
 
+Test --git is respected
+  $ hg email --git --date '1970-1-1 0:1' -n -f quux -t foo -c bar -r tip
+  this patch series consists of 1 patches.
+  
+  
+  displaying [PATCH] a ...
+  MIME-Version: 1.0
+  Content-Type: text/plain; charset="us-ascii"
+  Content-Transfer-Encoding: 7bit
+  Subject: [PATCH] a
+  X-Mercurial-Node: 8580ff50825a50c8f716709acdf8de0deddcd6ab
+  X-Mercurial-Series-Index: 1
+  X-Mercurial-Series-Total: 1
+  Message-Id: <8580ff50825a50c8f716.60@test-hostname>
+  X-Mercurial-Series-Id: <8580ff50825a50c8f716.60@test-hostname>
+  User-Agent: Mercurial-patchbomb/* (glob)
+  Date: Thu, 01 Jan 1970 00:01:00 +0000
+  From: quux
+  To: foo
+  Cc: bar
+  
+  # HG changeset patch
+  # User test
+  # Date 1 0
+  #      Thu Jan 01 00:00:01 1970 +0000
+  # Node ID 8580ff50825a50c8f716709acdf8de0deddcd6ab
+  # Parent  0000000000000000000000000000000000000000
+  a
+  
+  diff --git a/a b/a
+  new file mode 100644
+  --- /dev/null
+  +++ b/a
+  @@ -0,0 +1,1 @@
+  +a
+  
+
 
 Test breaking format changes aren't
   $ hg --config diff.noprefix=True email --date '1970-1-1 0:1' -n -f quux -t foo -c bar -r tip