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
#require test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ import_checker="$TESTDIR"/../contrib/import-checker.py
$ cd "$TESTDIR"/..
There are a handful of cases here that require renaming a module so it
doesn't overlap with a stdlib module name. There are also some cycles
here that we should still endeavor to fix, and some cycles will be
hidden by deduplication algorithm in the cycle detector, so fixing
these may expose other cycles.
Known-bad files are excluded by -X as some of them would produce unstable
outputs, which should be fixed later.
NOTE: the `hg locate` command here only works on files that are known to
Mercurial. If you add an import of a new file and haven't yet `hg add`ed it, you
will likely receive warnings about a direct import.
$ testrepohg locate 'set:**.py or grep(r"^#!.*?python")' \
> 'tests/**.t' \
> -X hgweb.cgi \
> -X setup.py \
> -X contrib/automation/ \
> -X contrib/debugshell.py \
> -X contrib/hgweb.fcgi \
> -X contrib/packaging/hg-docker \
> -X contrib/packaging/hgpackaging/ \
> -X contrib/packaging/inno/ \
> -X contrib/phab-clean.py \
> -X contrib/python-zstandard/ \
> -X contrib/win32/hgwebdir_wsgi.py \
> -X contrib/perf-utils/perf-revlog-write-plot.py \
> -X doc/gendoc.py \
> -X doc/hgmanpage.py \
> -X i18n/posplit \
> -X mercurial/thirdparty \
> -X tests/hypothesishelpers.py \
> -X tests/test-check-interfaces.py \
> -X tests/test-demandimport.py \
> -X tests/test-imports-checker.t \
> -X tests/test-verify-repo-operations.py \
> -X tests/test-extension.t \
> | sed 's-\\-/-g' | "$PYTHON" "$import_checker" -