Mercurial > hg
view tests/fakedirstatewritetime.py @ 49000:dd6b67d5c256 stable
rust: fix unsound `OwningDirstateMap`
As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.
The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.
I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.
In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.
Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.
Differential Revision: https://phab.mercurial-scm.org/D12429
author | Raphaël Gomès <rgomes@octobus.net> |
---|---|
date | Tue, 05 Apr 2022 10:55:28 +0200 |
parents | 111098af6356 |
children | 6000f5b25c9b |
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# extension to emulate invoking 'dirstate.write()' at the time # specified by '[fakedirstatewritetime] fakenow', only when # 'dirstate.write()' is invoked via functions below: # # - 'workingctx._poststatusfixup()' (= 'repo.status()') # - 'committablectx.markcommitted()' from __future__ import absolute_import from mercurial import ( context, dirstatemap as dirstatemapmod, extensions, policy, registrar, ) from mercurial.dirstateutils import timestamp from mercurial.utils import dateutil try: from mercurial import rustext rustext.__name__ # force actual import (see hgdemandimport) except ImportError: rustext = None configtable = {} configitem = registrar.configitem(configtable) configitem( b'fakedirstatewritetime', b'fakenow', default=None, ) parsers = policy.importmod('parsers') has_rust_dirstate = policy.importrust('dirstate') is not None def pack_dirstate(orig, dmap, copymap, pl): return orig(dmap, copymap, pl) def fakewrite(ui, func): # fake "now" of 'pack_dirstate' only if it is invoked while 'func' fakenow = ui.config(b'fakedirstatewritetime', b'fakenow') if not fakenow: # Execute original one, if fakenow isn't configured. This is # useful to prevent subrepos from executing replaced one, # because replacing 'parsers.pack_dirstate' is also effective # in subrepos. return func() # parsing 'fakenow' in YYYYmmddHHMM format makes comparison between # 'fakenow' value and 'touch -t YYYYmmddHHMM' argument easy fakenow = dateutil.parsedate(fakenow, [b'%Y%m%d%H%M'])[0] fakenow = timestamp.timestamp((fakenow, 0, False)) if has_rust_dirstate: # The Rust implementation does not use public parse/pack dirstate # to prevent conversion round-trips orig_dirstatemap_write = dirstatemapmod.dirstatemap.write wrapper = lambda self, tr, st: orig_dirstatemap_write(self, tr, st) dirstatemapmod.dirstatemap.write = wrapper orig_get_fs_now = timestamp.get_fs_now wrapper = lambda *args: pack_dirstate(orig_pack_dirstate, *args) orig_module = parsers orig_pack_dirstate = parsers.pack_dirstate orig_module.pack_dirstate = wrapper timestamp.get_fs_now = ( lambda *args: fakenow ) # XXX useless for this purpose now try: return func() finally: orig_module.pack_dirstate = orig_pack_dirstate timestamp.get_fs_now = orig_get_fs_now if has_rust_dirstate: dirstatemapmod.dirstatemap.write = orig_dirstatemap_write def _poststatusfixup(orig, workingctx, status, fixup): ui = workingctx.repo().ui return fakewrite(ui, lambda: orig(workingctx, status, fixup)) def markcommitted(orig, committablectx, node): ui = committablectx.repo().ui return fakewrite(ui, lambda: orig(committablectx, node)) def extsetup(ui): extensions.wrapfunction( context.workingctx, '_poststatusfixup', _poststatusfixup ) extensions.wrapfunction(context.workingctx, 'markcommitted', markcommitted)