[Bug 1059085] [NEW] Lucid: recovery silently deletes data in large files.

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You have been subscribed to a public bug by C de-Avillez (hggdh2):

This is present in vim 2:7.2.330-1ubuntu3, in Lucid. It was fixed
upstream in 7.3.216, which is in Precise and newer. To replicate the bug
(taken from
https://groups.google.com/d/topic/vim_use/CNuBWi0763I/discussion):

[Summary]

The recovery process silently deletes part of the file it's run on, when
the file is large enough (40,000 lines seems to trigger it).

[Impact]

The recovery process, while it may not recover all of the user's changes
since the process was killed, is expected to at least not destroy random
chunks of data in the middle of a large file. This bug has bitten me at
least twice--silently!--before I found out what was going on.

[Test Case]

1. Run 'vi test.txt'.
2. Type '78a-' [ESC], then 'yy', '39999p', then ':wq', to create a 40,000-line test file.
3. Run 'cp test.txt test.bak'.
4. Run 'vi test.txt'.
5. Type 'Ox' to make a small change to the file.
6. From another terminal window, run 'ps x|grep [t]est.txt' to find the PID of the running vim process.
7. Run 'kill $PID' to terminate the process.
8. Run 'vi test.txt', and type 'r' to attempt recovery, then ':wq' to save the recovered contents.
9. Run 'wc -l test.txt test.bak'.

Expected output:
$ wc -l test.txt test.bak
  40001 test.txt
  40000 test.bak

Actual output:
$ wc -l test.txt test.bak
  38629 test.txt
  40000 test.bak

[Regression Potential]

Small. The patch I'm backporting
(https://groups.google.com/d/topic/vim_dev/lTos-bGcNgU/discussion) in is
part of the new 7.3 series, and vim has a large test suite; I'm porting
and checking the patch as-is, including its tests. If this breaks the
recovery process, the regression tests will catch it.

** Affects: vim (Ubuntu)
     Importance: High
         Status: Triaged

-- 
Lucid: recovery silently deletes data in large files.
https://bugs.launchpad.net/bugs/1059085
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