tests/test-unrelated-pull.t

worker: avoid potential partial write of pickled data

Previously, the code wrote the pickled data using os.write(). However,
os.write() can write less bytes than passed to it. To trigger the problem, the
pickled data had to be larger than 2147479552 bytes on my system.

Instead, open a file object and pass it to pickle.dump(). This also has the
advantage that it doesn’t buffer the whole pickled data in memory.

Note that the opened file must be buffered because pickle doesn’t support
unbuffered streams because unbuffered streams’ write() method might write less
bytes than passed to it (like os.write()) but pickle.dump() relies on that all
bytes are written (see https://github.com/python/cpython/issues/93050).

The side effect of using a file object and a with statement is that wfd is
explicitly closed now while it seems like before it was implicitly closed by
process exit.

  $ hg init a
  $ cd a
  $ echo 123 > a
  $ hg add a
  $ hg commit -m "a" -u a

  $ cd ..
  $ hg init b
  $ cd b
  $ echo 321 > b
  $ hg add b
  $ hg commit -m "b" -u b

  $ hg pull ../a
  pulling from ../a
  searching for changes
  abort: repository is unrelated
  [255]

  $ hg pull -f ../a
  pulling from ../a
  searching for changes
  warning: repository is unrelated
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets 9a79c33a9db3
  (run 'hg heads' to see heads, 'hg merge' to merge)

  $ hg heads
  changeset:   1:9a79c33a9db3
  tag:         tip
  parent:      -1:000000000000
  user:        a
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a
  
  changeset:   0:01f8062b2de5
  user:        b
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     b
  

  $ cd ..