--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/revlogutils/censor.py	Sat May 29 00:11:56 2021 +0200
@@ -0,0 +1,102 @@
+# censor code related to censoring revision
+#
+# Copyright 2021 Pierre-Yves David <pierre-yves.david@octobus.net>
+# Copyright 2015 Google, Inc <martinvonz@google.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from ..node import (
+    nullrev,
+)
+from ..i18n import _
+from .. import (
+    error,
+)
+from ..utils import (
+    storageutil,
+)
+from . import constants
+
+
+def v1_censor(rl, tr, censornode, tombstone=b''):
+    """censors a revision in a "version 1" revlog"""
+    assert rl._format_version == constants.REVLOGV1, rl._format_version
+
+    # avoid cycle
+    from .. import revlog
+
+    censorrev = rl.rev(censornode)
+    tombstone = storageutil.packmeta({b'censored': tombstone}, b'')
+
+    if len(tombstone) > rl.rawsize(censorrev):
+        raise error.Abort(
+            _(b'censor tombstone must be no longer than censored data')
+        )
+
+    # Rewriting the revlog in place is hard. Our strategy for censoring is
+    # to create a new revlog, copy all revisions to it, then replace the
+    # revlogs on transaction close.
+    #
+    # This is a bit dangerous. We could easily have a mismatch of state.
+    newrl = revlog.revlog(
+        rl.opener,
+        target=rl.target,
+        radix=rl.radix,
+        postfix=b'tmpcensored',
+        censorable=True,
+    )
+    newrl._format_version = rl._format_version
+    newrl._format_flags = rl._format_flags
+    newrl._generaldelta = rl._generaldelta
+    newrl._parse_index = rl._parse_index
+
+    for rev in rl.revs():
+        node = rl.node(rev)
+        p1, p2 = rl.parents(node)
+
+        if rev == censorrev:
+            newrl.addrawrevision(
+                tombstone,
+                tr,
+                rl.linkrev(censorrev),
+                p1,
+                p2,
+                censornode,
+                constants.REVIDX_ISCENSORED,
+            )
+
+            if newrl.deltaparent(rev) != nullrev:
+                m = _(b'censored revision stored as delta; cannot censor')
+                h = _(
+                    b'censoring of revlogs is not fully implemented;'
+                    b' please report this bug'
+                )
+                raise error.Abort(m, hint=h)
+            continue
+
+        if rl.iscensored(rev):
+            if rl.deltaparent(rev) != nullrev:
+                m = _(
+                    b'cannot censor due to censored '
+                    b'revision having delta stored'
+                )
+                raise error.Abort(m)
+            rawtext = rl._chunk(rev)
+        else:
+            rawtext = rl.rawdata(rev)
+
+        newrl.addrawrevision(
+            rawtext, tr, rl.linkrev(rev), p1, p2, node, rl.flags(rev)
+        )
+
+    tr.addbackup(rl._indexfile, location=b'store')
+    if not rl._inline:
+        tr.addbackup(rl._datafile, location=b'store')
+
+    rl.opener.rename(newrl._indexfile, rl._indexfile)
+    if not rl._inline:
+        rl.opener.rename(newrl._datafile, rl._datafile)
+
+    rl.clearcaches()
+    rl._loadindex()