view tests/test-rename-after-merge.t @ 46607:e9901d01d135

revlog: add a mechanism to verify expected file position before appending

If someone uses `hg debuglocks`, or some non-hg process writes to the .hg
directory without respecting the locks, or if the repo's on a networked
filesystem, it's possible for the revlog code to write out corrupted data.

The form of this corruption can vary depending on what data was written and how
that happened. We are in the "networked filesystem" case (though I've had users
also do this to themselves with the "`hg debuglocks`" scenario), and most often
see this with the changelog. What ends up happening is we produce two items
(let's call them rev1 and rev2) in the .i file that have the same linkrev,
baserev, and offset into the .d file, while the data in the .d file is appended
properly. rev2's compressed_size is accurate for rev2, but when we go to
decompress the data in the .d file, we use the offset that's recorded in the
index file, which is the same as rev1, and attempt to decompress
rev2.compressed_size bytes of rev1's data. This usually does not succeed. :)

When using inline data, this also fails, though I haven't investigated why too
closely. This shows up as a "patch decode" error. I believe what's happening
there is that we're basically ignoring the offset field, getting the data
properly, but since baserev != rev, it thinks this is a delta based on rev
(instead of a full text) and can't actually apply it as such.

For now, I'm going to make this an optional component and default it to entirely
off. I may increase the default severity of this in the future, once I've
enabled it for my users and we gain more experience with it. Luckily, most of my
users have a versioned filesystem and can roll back to before the corruption has
been written, it's just a hassle to do so and not everyone knows how (so it's a
support burden). Users on other filesystems will not have that luxury, and this
can cause them to have a corrupted repository that they are unlikely to know how
to resolve, and they'll see this as a data-loss event. Refusing to create the
corruption is a much better user experience.

This mechanism is not perfect. There may be false-negatives (racy writes that
are not detected). There should not be any false-positives (non-racy writes that
are detected as such). This is not a mechanism that makes putting a repo on a
networked filesystem "safe" or "supported", just *less* likely to cause
corruption.

Differential Revision: https://phab.mercurial-scm.org/D9952

Issue746: renaming files brought by the second parent of a merge was
broken.

Create source repository:

  $ hg init t
  $ cd t
  $ echo a > a
  $ hg ci -Am a
  adding a
  $ cd ..

Fork source repository:

  $ hg clone t t2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd t2
  $ echo b > b
  $ hg ci -Am b
  adding b

Update source repository:

  $ cd ../t
  $ echo a >> a
  $ hg ci -m a2

Merge repositories:

  $ hg pull ../t2
  pulling from ../t2
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets d2ae7f538514
  1 local changesets published
  (run 'hg heads' to see heads, 'hg merge' to merge)

  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg st
  M b

Rename b as c:

  $ hg mv b c
  $ hg st
  A c
  R b

Rename back c as b:

  $ hg mv c b
  $ hg st
  M b

  $ cd ..

Issue 1476: renaming a first parent file into another first parent
file while none of them belong to the second parent was broken

  $ hg init repo1476
  $ cd repo1476
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ echo b1 > b1
  $ echo b2 > b2
  $ hg ci -Am changea
  adding b1
  adding b2
  $ hg up -C 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo c1 > c1
  $ echo c2 > c2
  $ hg ci -Am addcandd
  adding c1
  adding c2
  created new head

Merge heads:

  $ hg merge
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg mv -Af c1 c2

Commit issue 1476:

  $ hg ci -m merge

  $ hg log -r tip -C -v | grep copies
  copies:      c2 (c1)

  $ hg rollback
  repository tip rolled back to revision 2 (undo commit)
  working directory now based on revisions 2 and 1

  $ hg up -C .
  2 files updated, 0 files merged, 2 files removed, 0 files unresolved

Merge heads again:

  $ hg merge
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg mv -Af b1 b2

Commit issue 1476 with a rename on the other side:

  $ hg ci -m merge

  $ hg log -r tip -C -v | grep copies
  copies:      b2 (b1)

Test marking/unmarking copies in merge commit

  $ hg copy --forget --at-rev . b2
  abort: cannot mark/unmark copy in merge commit
  [10]

  $ hg copy --after --at-rev . b1 b2
  abort: cannot mark/unmark copy in merge commit
  [10]

  $ cd ..