Mercurial > hg
annotate CONTRIBUTING @ 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> |
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date | Tue, 05 Apr 2022 10:55:28 +0200 |
parents | a492610a2fc1 |
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contributing: add new file with a pointer to the wiki
Augie Fackler <augie@google.com>
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1 Our full contribution guidelines are in our wiki, please see: |
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Augie Fackler <augie@google.com>
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2 |
a492610a2fc1
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Augie Fackler <augie@google.com>
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3 https://www.mercurial-scm.org/wiki/ContributingChanges |
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Augie Fackler <augie@google.com>
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4 |
a492610a2fc1
contributing: add new file with a pointer to the wiki
Augie Fackler <augie@google.com>
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5 If you just want a checklist to follow, you can go straight to |
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Augie Fackler <augie@google.com>
parents:
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6 |
a492610a2fc1
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Augie Fackler <augie@google.com>
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7 https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist |
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Augie Fackler <augie@google.com>
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8 |
a492610a2fc1
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Augie Fackler <augie@google.com>
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9 If you can't run the entire testsuite for some reason (it can be |
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contributing: add new file with a pointer to the wiki
Augie Fackler <augie@google.com>
parents:
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10 difficult on Windows), please at least run `contrib/check-code.py` on |
a492610a2fc1
contributing: add new file with a pointer to the wiki
Augie Fackler <augie@google.com>
parents:
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11 any files you've modified and run `python contrib/check-commit` on any |
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Augie Fackler <augie@google.com>
parents:
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12 commits you've made (for example, `python contrib/check-commit |
a492610a2fc1
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Augie Fackler <augie@google.com>
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13 273ce12ad8f1` will report some style violations on a very old commit). |