Mercurial > hg
view tests/test-update-reverse.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 | 5c2a4f37eace |
children | 55c6ebd11cb9 |
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$ hg init $ touch a $ hg add a $ hg commit -m "Added a" $ touch main $ hg add main $ hg commit -m "Added main" $ hg checkout 0 0 files updated, 0 files merged, 1 files removed, 0 files unresolved 'main' should be gone: $ ls -A .hg a $ touch side1 $ hg add side1 $ hg commit -m "Added side1" created new head $ touch side2 $ hg add side2 $ hg commit -m "Added side2" $ hg log changeset: 3:91ebc10ed028 tag: tip user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: Added side2 changeset: 2:b932d7dbb1e1 parent: 0:c2eda428b523 user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: Added side1 changeset: 1:71a760306caf user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: Added main changeset: 0:c2eda428b523 user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: Added a $ hg heads changeset: 3:91ebc10ed028 tag: tip user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: Added side2 changeset: 1:71a760306caf user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: Added main $ ls -A .hg a side1 side2 $ hg update --debug -C 1 resolving manifests branchmerge: False, force: True, partial: False ancestor: 91ebc10ed028+, local: 91ebc10ed028+, remote: 71a760306caf side1: other deleted -> r removing side1 side2: other deleted -> r removing side2 main: remote created -> g getting main 1 files updated, 0 files merged, 2 files removed, 0 files unresolved $ ls -A .hg a main