Mercurial > hg
view tests/test-requires.t @ 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 | 7ee07e1a25c0 |
children | 42d2b31cee0b |
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$ hg init t $ cd t $ echo a > a $ hg add a $ hg commit -m test $ rm .hg/requires $ hg tip abort: unknown version (65535) in revlog 00changelog [50] $ echo indoor-pool > .hg/requires $ hg tip abort: repository requires features unknown to this Mercurial: indoor-pool (see https://mercurial-scm.org/wiki/MissingRequirement for more information) [255] $ echo outdoor-pool >> .hg/requires $ hg tip abort: repository requires features unknown to this Mercurial: indoor-pool outdoor-pool (see https://mercurial-scm.org/wiki/MissingRequirement for more information) [255] $ cd .. Test checking between features supported locally and ones required in another repository of push/pull/clone on localhost: $ mkdir supported-locally $ cd supported-locally $ hg init supported $ echo a > supported/a $ hg -R supported commit -Am '#0 at supported' adding a $ echo 'featuresetup-test' >> supported/.hg/requires $ cat > $TESTTMP/supported-locally/supportlocally.py <<EOF > from __future__ import absolute_import > from mercurial import extensions, localrepo > def featuresetup(ui, supported): > for name, module in extensions.extensions(ui): > if __name__ == module.__name__: > # support specific feature locally > supported |= {b'featuresetup-test'} > return > def uisetup(ui): > localrepo.featuresetupfuncs.add(featuresetup) > EOF $ cat > supported/.hg/hgrc <<EOF > [extensions] > # enable extension locally > supportlocally = $TESTTMP/supported-locally/supportlocally.py > EOF $ hg -R supported debugrequirements dotencode dirstate-v2 (dirstate-v2 !) featuresetup-test fncache generaldelta persistent-nodemap (rust !) revlog-compression-zstd (zstd !) revlogv1 share-safe sparserevlog store $ hg -R supported status $ hg init push-dst $ hg -R supported push push-dst pushing to push-dst abort: required features are not supported in the destination: featuresetup-test [255] $ hg init pull-src $ hg -R pull-src pull supported pulling from supported abort: required features are not supported in the destination: featuresetup-test [255] $ hg clone supported clone-dst abort: repository requires features unknown to this Mercurial: featuresetup-test (see https://mercurial-scm.org/wiki/MissingRequirement for more information) [255] $ hg clone --pull supported clone-dst abort: required features are not supported in the destination: featuresetup-test [255] $ cd ..