view contrib/base-revsets.txt @ 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

# Base Revsets to be used with revsetbenchmarks.py script
#
# The goal of this file is to gather a limited amount of revsets that allow a
# good coverage of the internal revsets mechanisms.  Revsets included should not
# be selected for their individual implementation, but for what they reveal of
# the internal implementation of smartsets classes (and their interactions).
#
# Use and update this file when you change internal implementation of these
# smartsets classes. Please include a comment explaining what each of your
# addition is testing. Also check if your changes to the smartset class makes
# some of the tests inadequate and replace them with a new one testing the same
# behavior.
#
# If you want to benchmark revsets predicate itself, check 'all-revsets.txt'.
#
# The current content of this file is currently likely not reaching this goal
# entirely, feel free, to audit its content and comment on each revset to
# highlight what internal mechanisms they test.

all()
draft()
::tip
draft() and ::tip
::tip and draft()
0::tip
roots(0::tip)
author(lmoscovicz)
author(olivia)
author(lmoscovicz) or author(olivia)
author(olivia) or author(lmoscovicz)
tip:0
0::
# those two `roots(...)` inputs are close to what phase movement use.
roots((tip~100::) - (tip~100::tip))
roots((0::) - (0::tip))
42:68 and roots(42:tip)
::p1(p1(tip))::
public()
:10000 and public()
draft()
:10000 and draft()
roots((0:tip)::)
(not public() - obsolete())
(_intlist('20000\x0020001')) and merge()
parents(20000)
(20000::) - (20000)
# The one below is used by rebase
(children(ancestor(tip~5, tip)) and ::(tip~5))::
heads(commonancestors(last(head(), 2)))
heads(-10000:-1)
roots(-10000:-1)
only(max(head()), min(head()))