view tests/test-dirstate-race2.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

#testcases dirstate-v1 dirstate-v2

#if dirstate-v2
  $ cat >> $HGRCPATH << EOF
  > [format]
  > use-dirstate-v2=1
  > [storage]
  > dirstate-v2.slow-path=allow
  > EOF
#endif

Checking the size/permissions/file-type of files stored in the
dirstate after an update where the files are changed concurrently
outside of hg's control.

  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg commit -qAm _
  $ echo aa > a
  $ hg commit -m _
# this sleep is there to ensure current time has -at-least- one second away
# from the current time. It ensure the mtime is not ambiguous. If the test
# "sleep" longer this will be fine.
# It is not used to synchronise parallele operation so it is "fine" to use it.
  $ sleep 1
  $ hg status

  $ hg debugdirstate --no-dates
  n 644          3 (set  |unset)               a (re)

  $ cat >> $TESTTMP/dirstaterace.py << EOF
  > import time
  > from mercurial import (
  >     commit,
  >     extensions,
  >     merge,
  > )
  > def extsetup(ui):
  >     extensions.wrapfunction(merge, 'applyupdates', wrap(0))
  >     extensions.wrapfunction(commit, 'commitctx', wrap(1))
  > def wrap(duration):
  >     def new(orig, *args, **kwargs):
  >         res = orig(*args, **kwargs)
  >         with open("a", "w"):
  >             pass # just truncate the file
  >         time.sleep(duration)
  >         return res
  >     return new
  > EOF

Do an update where file 'a' is changed between hg writing it to disk
and hg writing the dirstate. The dirstate is correct nonetheless, and
so hg status correctly shows a as clean.

  $ hg up -r 0 --config extensions.race=$TESTTMP/dirstaterace.py
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg debugdirstate --no-dates
  n 644          2 (set  |unset)               a (re)
  $ echo a > a; hg status; hg diff

Do a commit where file 'a' is changed between hg committing its new
revision into the repository, and the writing of the dirstate.

This used to results in a corrupted dirstate (size did not match committed size).

  $ echo aaa > a; hg commit -qm _
  $ hg merge -qr 1; hg resolve -m; rm a.orig
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  (no more unresolved files)
  $ cat a
  <<<<<<< working copy: be46f74ce38d - test: _
  aaa
  =======
  aa
  >>>>>>> merge rev:    eb3fc6c17aa3 - test: _
  $ hg debugdirstate --no-dates
  m   0         -2 (set  |unset)               a (re)
  $ hg commit -m _ --config extensions.race=$TESTTMP/dirstaterace.py
  $ hg debugdirstate --no-dates
  n   0         -1 unset               a
  $ cat a | wc -c
   *0 (re)
  $ hg cat -r . a | wc -c
   *105 (re)
  $ hg status; hg diff --stat
  M a
   a |  5 -----
   1 files changed, 0 insertions(+), 5 deletions(-)