view tests/test-rebase-base-flag.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

Test the "--base" flag of the rebase command. (Tests unrelated to the "--base"
flag should probably live in somewhere else)

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > drawdag=$TESTDIR/drawdag.py
  > 
  > [phases]
  > publish=False
  > 
  > [alias]
  > tglog = log -G --template "{rev}: {node|short} {desc}"
  > EOF

  $ rebasewithdag() {
  >   N=`"$PYTHON" -c "print($N+1)"`
  >   hg init repo$N && cd repo$N
  >   hg debugdrawdag
  >   hg rebase "$@" > _rebasetmp
  >   r=$?
  >   grep -v 'saved backup bundle' _rebasetmp
  >   [ $r -eq 0 ] && hg tglog
  >   cd ..
  >   return $r
  > }

Single branching point, without merge:

  $ rebasewithdag -b D -d Z <<'EOS'
  >     D E
  >     |/
  > Z B C   # C: branching point, E should be picked
  >  \|/    # B should not be picked
  >   A
  >   |
  >   R
  > EOS
  rebasing 3:d6003a550c2c C "C"
  rebasing 5:4526cf523425 D "D"
  rebasing 6:b296604d9846 E tip "E"
  o  6: 4870f5e7df37 E
  |
  | o  5: dc999528138a D
  |/
  o  4: 6b3e11729672 C
  |
  o  3: 57e70bad1ea3 Z
  |
  | o  2: c1e6b162678d B
  |/
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Multiple branching points caused by selecting a single merge changeset:

  $ rebasewithdag -b E -d Z <<'EOS'
  >     E
  >    /|
  >   B C D  # B, C: multiple branching points
  >   | |/   # D should not be picked
  > Z | /
  >  \|/
  >   A
  >   |
  >   R
  > EOS
  rebasing 2:c1e6b162678d B "B"
  rebasing 3:d6003a550c2c C "C"
  rebasing 6:54c8f00cb91c E tip "E"
  o    6: 00598421b616 E
  |\
  | o  5: 6b3e11729672 C
  | |
  o |  4: 85260910e847 B
  |/
  o  3: 57e70bad1ea3 Z
  |
  | o  2: 8924700906fe D
  |/
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Rebase should not extend the "--base" revset using "descendants":

  $ rebasewithdag -b B -d Z <<'EOS'
  >     E
  >    /|
  > Z B C  # descendants(B) = B+E. With E, C will be included incorrectly
  >  \|/
  >   A
  >   |
  >   R
  > EOS
  rebasing 2:c1e6b162678d B "B"
  rebasing 5:54c8f00cb91c E tip "E"
  o    5: e583bf3ff54c E
  |\
  | o  4: 85260910e847 B
  | |
  | o  3: 57e70bad1ea3 Z
  | |
  o |  2: d6003a550c2c C
  |/
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Rebase should not simplify the "--base" revset using "roots":

  $ rebasewithdag -b B+E -d Z <<'EOS'
  >     E
  >    /|
  > Z B C  # roots(B+E) = B. Without E, C will be missed incorrectly
  >  \|/
  >   A
  >   |
  >   R
  > EOS
  rebasing 2:c1e6b162678d B "B"
  rebasing 3:d6003a550c2c C "C"
  rebasing 5:54c8f00cb91c E tip "E"
  o    5: 00598421b616 E
  |\
  | o  4: 6b3e11729672 C
  | |
  o |  3: 85260910e847 B
  |/
  o  2: 57e70bad1ea3 Z
  |
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
The destination is one of the two branching points of a merge:

  $ rebasewithdag -b F -d Z <<'EOS'
  >     F
  >    / \
  >   E   D
  >  /   /
  > Z   C
  >  \ /
  >   B
  >   |
  >   A
  > EOS
  nothing to rebase
  [1]

Multiple branching points caused by multiple bases (issue5420):

  $ rebasewithdag -b E1+E2+C2+B1 -d Z <<'EOS'
  >   Z    E2
  >   |   /
  >   F E1 C2
  >   |/  /
  >   E C1 B2
  >   |/  /
  >   C B1
  >   |/
  >   B
  >   |
  >   A
  >   |
  >   R
  > EOS
  rebasing 3:a113dbaa660a B1 "B1"
  rebasing 5:06ce7b1cc8c2 B2 "B2"
  rebasing 6:0ac98cce32d3 C1 "C1"
  rebasing 8:781512f5e33d C2 "C2"
  rebasing 9:428d8c18f641 E1 "E1"
  rebasing 11:e1bf82f6b6df E2 "E2"
  o  12: e4a37b6fdbd2 E2
  |
  o  11: 9675bea983df E1
  |
  | o  10: 4faf5d4c80dc C2
  | |
  | o  9: d4799b1ad57d C1
  |/
  | o  8: 772732dc64d6 B2
  | |
  | o  7: ad3ac528a49f B1
  |/
  o  6: 2cbdfca6b9d5 Z
  |
  o  5: fcdb3293ec13 F
  |
  o  4: a4652bb8ac54 E
  |
  o  3: bd5548558fcf C
  |
  o  2: c1e6b162678d B
  |
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Multiple branching points with multiple merges:

  $ rebasewithdag -b G+P -d Z <<'EOS'
  > G   H   P
  > |\ /|   |\
  > F E D   M N
  >  \|/|  /| |\
  > Z C B I J K L
  >  \|/  |/  |/
  >   A   A   A
  > EOS
  rebasing 2:dc0947a82db8 C "C"
  rebasing 8:4e4f9194f9f1 D "D"
  rebasing 9:03ca77807e91 E "E"
  rebasing 10:afc707c82df0 F "F"
  rebasing 13:690dfff91e9e G "G"
  rebasing 14:2893b886bb10 H "H"
  rebasing 3:08ebfeb61bac I "I"
  rebasing 4:a0a5005cec67 J "J"
  rebasing 5:83780307a7e8 K "K"
  rebasing 6:e131637a1cb6 L "L"
  rebasing 11:d1f6d0c3c7e4 M "M"
  rebasing 12:7aaec6f81888 N "N"
  rebasing 15:325bc8f1760d P tip "P"
  o    15: 6ef6a0ea3b18 P
  |\
  | o    14: 20ba3610a7e5 N
  | |\
  o \ \    13: cd4f6c06d2ab M
  |\ \ \
  | | | o  12: bca872041455 L
  | | | |
  | | o |  11: 7bbb6c8a6ad7 K
  | | |/
  | o /  10: de0cbffe893e J
  | |/
  o /  9: 0e710f176a88 I
  |/
  | o    8: 52507bab39ca H
  | |\
  | | | o  7: bb5fe4652f0d G
  | | |/|
  | | | o  6: f4ad4b31daf4 F
  | | | |
  | | o |  5: b168f85f2e78 E
  | | |/
  | o |  4: 8d09fcdb5594 D
  | |\|
  +---o  3: ab70b4c5a9c9 C
  | |
  o |  2: 262e37e34f63 Z
  | |
  | o  1: 112478962961 B
  |/
  o  0: 426bada5c675 A
  
Slightly more complex merge case (mentioned in https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-November/091074.html):

  $ rebasewithdag -b A3+B3 -d Z <<'EOF'
  > Z     C1    A3     B3
  > |    /     / \    / \
  > M3 C0     A1  A2 B1  B2
  > | /       |   |  |   |
  > M2        M1  C1 C1  M3
  > |
  > M1
  > |
  > M0
  > EOF
  rebasing 4:8817fae53c94 C0 "C0"
  rebasing 6:06ca5dfe3b5b B2 "B2"
  rebasing 7:73508237b032 C1 "C1"
  rebasing 9:fdb955e2faed A2 "A2"
  rebasing 11:4e449bd1a643 A3 "A3"
  rebasing 10:0a33b0519128 B1 "B1"
  rebasing 12:209327807c3a B3 tip "B3"
  o    12: ceb984566332 B3
  |\
  | o  11: 19d93caac497 B1
  | |
  | | o    10: 058e73d3916b A3
  | | |\
  | +---o  9: 0ba13ad72234 A2
  | | |
  | o |  8: c122c2af10c6 C1
  | | |
  o | |  7: 74275896650e B2
  | | |
  | o |  6: 455ba9bd3ea2 C0
  |/ /
  o |  5: b3d7d2fda53b Z
  | |
  o |  4: 182ab6383dd7 M3
  | |
  o |  3: 6c3f73563d5f M2
  | |
  | o  2: 88c860fffcc2 A1
  |/
  o  1: bc852baa85dd M1
  |
  o  0: dbdfc5c9bcd5 M0
  
Disconnected graph:

  $ rebasewithdag -b B -d Z <<'EOS'
  >   B
  >   |
  > Z A
  > EOS
  nothing to rebase from 112478962961 to 48b9aae0607f
  [1]

Multiple roots. Roots are ancestors of dest:

  $ rebasewithdag -b B+D -d Z <<'EOF'
  > D Z B
  >  \|\|
  >   C A
  > EOF
  rebasing 2:112478962961 B "B"
  rebasing 3:b70f76719894 D "D"
  o  4: 511efad7bf13 D
  |
  | o  3: 25c4e279af62 B
  |/
  o    2: 3a49f54d7bb1 Z
  |\
  | o  1: 96cc3511f894 C
  |
  o  0: 426bada5c675 A
  
Multiple roots. One root is not an ancestor of dest:

  $ rebasewithdag -b B+D -d Z <<'EOF'
  > Z B D
  >  \|\|
  >   A C
  > EOF
  nothing to rebase from f675d5a1c6a4+b70f76719894 to 262e37e34f63
  [1]

Multiple roots. One root is not an ancestor of dest. Select using a merge:

  $ rebasewithdag -b E -d Z <<'EOF'
  >   E
  >   |\
  > Z B D
  >  \|\|
  >   A C
  > EOF
  rebasing 2:f675d5a1c6a4 B "B"
  rebasing 5:f68696fe6af8 E tip "E"
  o    5: f6e6f5081554 E
  |\
  | o    4: 30cabcba27be B
  | |\
  | | o  3: 262e37e34f63 Z
  | | |
  o | |  2: b70f76719894 D
  |/ /
  o /  1: 96cc3511f894 C
   /
  o  0: 426bada5c675 A
  
Multiple roots. Two children share two parents while dest has only one parent:

  $ rebasewithdag -b B+D -d Z <<'EOF'
  > Z B D
  >  \|\|\
  >   A C A
  > EOF
  rebasing 2:f675d5a1c6a4 B "B"
  rebasing 3:c2a779e13b56 D "D"
  o    4: 5eecd056b5f8 D
  |\
  +---o  3: 30cabcba27be B
  | |/
  | o  2: 262e37e34f63 Z
  | |
  o |  1: 96cc3511f894 C
   /
  o  0: 426bada5c675 A