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
=========================================
Testing single head enforcement: Case A-1
=========================================
A repository is set to only accept a single head per name (typically named
branch). However, obsolete changesets can make this enforcement more
complicated, because they can be kept visible by other changeset on other
branch.
This case is part of a series of tests checking this behavior.
Category A: Involving obsolescence
TestCase 1: A fully obsolete branch kept visible by another one
.. old-state:
..
.. * 2 changesets on branch default
.. * 2 changesets on branch Z on top of them
..
.. new-state:
..
.. * 2 changesets on branch Z at the same location
.. * 2 changesets on branch default superseding the other ones
..
.. expected-result:
..
.. * only one head detected
..
.. graph-summary:
..
.. D ● (branch Z)
.. |
.. C ● (branch Z)
.. |
.. B ø⇠◔ B'
.. | |
.. A ø⇠◔ A'
.. |/
.. ●
$ . $TESTDIR/testlib/push-checkheads-util.sh
$ cat >> $HGRCPATH << EOF
> [command-templates]
> log = "{node|short} [{branch}] ({phase}): {desc}\n"
> EOF
Test setup
----------
$ mkdir A1
$ cd A1
$ setuprepos single-head
creating basic server and client repo
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd client
$ mkcommit B0
$ hg branch Z
marked working directory as branch Z
(branches are permanent and global, did you want a bookmark?)
$ mkcommit C0
$ mkcommit D0
$ hg push --new-branch
pushing to $TESTTMP/A1/server
searching for changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 3 files
$ hg up 0
0 files updated, 0 files merged, 4 files removed, 0 files unresolved
$ mkcommit A1
created new head
$ mkcommit B1
$ hg debugobsolete `getid "desc(A0)"` `getid "desc(A1)"`
1 new obsolescence markers
obsoleted 1 changesets
3 new orphan changesets
$ hg debugobsolete `getid "desc(B0)"` `getid "desc(B1)"`
1 new obsolescence markers
obsoleted 1 changesets
$ hg heads
262c8c798096 [default] (draft): B1
cdf1dbb37a67 [Z] (draft): D0
$ hg log -G --hidden
@ 262c8c798096 [default] (draft): B1
|
o f6082bc4ffef [default] (draft): A1
|
| * cdf1dbb37a67 [Z] (draft): D0
| |
| * 3213e3e16c67 [Z] (draft): C0
| |
| x d73caddc5533 [default] (draft): B0
| |
| x 8aaa48160adc [default] (draft): A0
|/
o 1e4be0697311 [default] (public): root
Actual testing
--------------
$ hg push -r 'desc("B1")'
pushing to $TESTTMP/A1/server
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 2 files (+1 heads)
2 new obsolescence markers
obsoleted 2 changesets
2 new orphan changesets