tests/test-http-branchmap.t

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

  $ hgserve() {
  >     hg serve -a localhost -p $HGPORT1 -d --pid-file=hg.pid \
  >       -E errors.log -v $@ > startup.log
  >     # Grepping hg serve stdout would hang on Windows
  >     grep -v 'listening at' startup.log
  >     cat hg.pid >> "$DAEMON_PIDS"
  > }
  $ hg init a
  $ hg --encoding utf-8 -R a branch æ
  marked working directory as branch \xc3\xa6 (esc)
  (branches are permanent and global, did you want a bookmark?)
  $ echo foo > a/foo
  $ hg -R a ci -Am foo
  adding foo
  $ hgserve -R a --config web.push_ssl=False --config web.allow_push=* --encoding latin1
  $ hg --encoding utf-8 clone http://localhost:$HGPORT1 b
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 867c11ce77b8
  updating to branch \xc3\xa6 (esc)
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg --encoding utf-8 -R b log
  changeset:   0:867c11ce77b8
  branch:      \xc3\xa6 (esc)
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     foo
  
  $ echo bar >> b/foo
  $ hg -R b ci -m bar
  $ hg --encoding utf-8 -R b push
  pushing to http://localhost:$HGPORT1/
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files
  $ hg -R a --encoding utf-8 log
  changeset:   1:58e7c90d67cb
  branch:      \xc3\xa6 (esc)
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     bar
  
  changeset:   0:867c11ce77b8
  branch:      \xc3\xa6 (esc)
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     foo
  
  $ killdaemons.py hg.pid

verify 7e7d56fe4833 (encoding fallback in branchmap to maintain compatibility with 1.3.x)

  $ cat <<EOF > oldhg
  > import threading
  > from mercurial import dispatch, hg, ui, wireprotoserver
  > 
  > class StdoutWrapper(object):
  >     def __init__(self, stdout):
  >         self._file = stdout
  > 
  >     def write(self, data):
  >         if data == b'47\n':
  >             # latin1 encoding is one %xx (3 bytes) shorter
  >             data = b'44\n'
  >         elif data.startswith(b'%C3%A6 '):
  >             # translate to latin1 encoding
  >             data = b'%%E6 %s' % data[7:]
  >         self._file.write(data)
  > 
  >     def __getattr__(self, name):
  >         return getattr(self._file, name)
  > 
  > dispatch.initstdio()
  > myui = ui.ui.load()
  > fout = StdoutWrapper(myui.fout)
  > myui.fout = myui.ferr
  > repo = hg.repository(myui, b'a')
  > wireprotoserver._runsshserver(myui, repo, myui.fin, fout, threading.Event())
  > EOF
  $ echo baz >> b/foo
  $ hg -R b ci -m baz
  $ hg push -R b -e "\"$PYTHON\" oldhg" ssh://dummy/ --encoding latin1
  pushing to ssh://dummy/
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files