view tests/test-tag.t @ 30155:b7a966ce89ed

changelog: disable delta chains

This patch disables delta chains on changelogs. After this patch, new
entries on changelogs - including existing changelogs - will be stored
as the fulltext of that data (likely compressed). No delta computation
will be performed.

An overview of delta chains and data justifying this change follows.

Revlogs try to store entries as a delta against a previous entry (either
a parent revision in the case of generaldelta or the previous physical
revision when not using generaldelta). Most of the time this is the
correct thing to do: it frequently results in less CPU usage and smaller
storage.

Delta chains are most effective when the base revision being deltad
against is similar to the current data. This tends to occur naturally
for manifests and file data, since only small parts of each tend to
change with each revision. Changelogs, however, are a different story.

Changelog entries represent changesets/commits. And unless commits in a
repository are homogonous (same author, changing same files, similar
commit messages, etc), a delta from one entry to the next tends to be
relatively large compared to the size of the entry. This means that
delta chains tend to be short. How short? Here is the full vs delta
revision breakdown on some real world repos:

Repo             % Full    % Delta   Max Length
hg                45.8       54.2        6
mozilla-central   42.4       57.6        8
mozilla-unified   42.5       57.5       17
pypy              46.1       53.9        6
python-zstandard  46.1       53.9        3

(I threw in python-zstandard as an example of a repo that is homogonous.
It contains a small Python project with changes all from the same
author.)

Contrast this with the manifest revlog for these repos, where 99+% of
revisions are deltas and delta chains run into the thousands.

So delta chains aren't as useful on changelogs. But even a short delta
chain may provide benefits. Let's measure that.

Delta chains may require less CPU to read revisions if the CPU time
spent reading smaller deltas is less than the CPU time used to
decompress larger individual entries. We can measure this via
`hg perfrevlog -c -d 1` to iterate a revlog to resolve each revision's
fulltext. Here are the results of that command on a repo using delta
chains in its changelog and on a repo without delta chains:

hg (forward)
! wall 0.407008 comb 0.410000 user 0.410000 sys 0.000000 (best of 25)
! wall 0.390061 comb 0.390000 user 0.390000 sys 0.000000 (best of 26)

hg (reverse)
! wall 0.515221 comb 0.520000 user 0.520000 sys 0.000000 (best of 19)
! wall 0.400018 comb 0.400000 user 0.390000 sys 0.010000 (best of 25)

mozilla-central (forward)
! wall 4.508296 comb 4.490000 user 4.490000 sys 0.000000 (best of 3)
! wall 4.370222 comb 4.370000 user 4.350000 sys 0.020000 (best of 3)

mozilla-central (reverse)
! wall 5.758995 comb 5.760000 user 5.720000 sys 0.040000 (best of 3)
! wall 4.346503 comb 4.340000 user 4.320000 sys 0.020000 (best of 3)

mozilla-unified (forward)
! wall 4.957088 comb 4.950000 user 4.940000 sys 0.010000 (best of 3)
! wall 4.660528 comb 4.650000 user 4.630000 sys 0.020000 (best of 3)

mozilla-unified (reverse)
! wall 6.119827 comb 6.110000 user 6.090000 sys 0.020000 (best of 3)
! wall 4.675136 comb 4.670000 user 4.670000 sys 0.000000 (best of 3)

pypy (forward)
! wall 1.231122 comb 1.240000 user 1.230000 sys 0.010000 (best of 8)
! wall 1.164896 comb 1.160000 user 1.160000 sys 0.000000 (best of 9)

pypy (reverse)
! wall 1.467049 comb 1.460000 user 1.460000 sys 0.000000 (best of 7)
! wall 1.160200 comb 1.170000 user 1.160000 sys 0.010000 (best of 9)

The data clearly shows that it takes less wall and CPU time to resolve
revisions when there are no delta chains in the changelogs, regardless
of the direction of traversal. Furthermore, not using a delta chain
means that fulltext resolution in reverse is as fast as iterating
forward. So not using delta chains on the changelog is a clear CPU win
for reading operations.

An example of a user-visible operation showing this speed-up is revset
evaluation. Here are results for
`hg perfrevset 'author(gps) or author(mpm)'`:

hg
! wall 1.655506 comb 1.660000 user 1.650000 sys 0.010000 (best of 6)
! wall 1.612723 comb 1.610000 user 1.600000 sys 0.010000 (best of 7)

mozilla-central
! wall 17.629826 comb 17.640000 user 17.600000 sys 0.040000 (best of 3)
! wall 17.311033 comb 17.300000 user 17.260000 sys 0.040000 (best of 3)

What about 00changelog.i size?

Repo                Delta Chains     No Delta Chains
hg                    7,033,250         6,976,771
mozilla-central      82,978,748        81,574,623
mozilla-unified      88,112,349        86,702,162
pypy                 20,740,699        20,659,741

The data shows that removing delta chains from the changelog makes the
changelog smaller.

Delta chains are also used during changegroup generation. This
operation essentially converts a series of revisions to one large
delta chain. And changegroup generation is smart: if the delta in
the revlog matches what the changegroup is emitting, it will reuse
the delta instead of recalculating it. We can measure the impact
removing changelog delta chains has on changegroup generation via
`hg perfchangegroupchangelog`:

hg
! wall 1.589245 comb 1.590000 user 1.590000 sys 0.000000 (best of 7)
! wall 1.788060 comb 1.790000 user 1.790000 sys 0.000000 (best of 6)

mozilla-central
! wall 17.382585 comb 17.380000 user 17.340000 sys 0.040000 (best of 3)
! wall 20.161357 comb 20.160000 user 20.120000 sys 0.040000 (best of 3)

mozilla-unified
! wall 18.722839 comb 18.720000 user 18.680000 sys 0.040000 (best of 3)
! wall 21.168075 comb 21.170000 user 21.130000 sys 0.040000 (best of 3)

pypy
! wall 4.828317 comb 4.830000 user 4.820000 sys 0.010000 (best of 3)
! wall 5.415455 comb 5.420000 user 5.410000 sys 0.010000 (best of 3)

The data shows eliminating delta chains makes the changelog part of
changegroup generation slower. This is expected since we now have to
compute deltas for revisions where we could recycle the delta before.

It is worth putting this regression into context of overall changegroup
times. Here is the rough total CPU time spent in changegroup generation
for various repos while using delta chains on the changelog:

Repo              CPU Time (s)    CPU Time w/ compression
hg                  4.50              7.05
mozilla-central   111.1             222.0
pypy               28.68             75.5

Before compression, removing delta chains from the changegroup adds
~4.4% overhead to hg changegroup generation, 1.3% to mozilla-central,
and 2.0% to pypy. When you factor in zlib compression, these percentages
are roughly divided by 2.

While the increased CPU usage for changegroup generation is unfortunate,
I think it is acceptable because the percentage is small, server
operators (those likely impacted most by this) have other mechanisms
to mitigate CPU consumption (namely reducing zlib compression level and
pre-generated clone bundles), and because there is room to optimize this
in the future. For example, we could use the nullid as the base revision,
effectively encoding the full revision for each entry in the changegroup.
When doing this, `hg perfchangegroupchangelog` nearly halves:

mozilla-unified
! wall 21.168075 comb 21.170000 user 21.130000 sys 0.040000 (best of 3)
! wall 11.196461 comb 11.200000 user 11.190000 sys 0.010000 (best of 3)

This looks very promising as a future optimization opportunity.

It's worth that the changes in test-acl.t to the changegroup part size.
This is because revision 6 in the changegroup had a delta chain of
length 2 before and after this patch the base revision is nullrev.
When the base revision is nullrev, cg2packer.deltaparent() hardcodes
the *previous* revision from the changegroup as the delta parent.
This caused the delta in the changegroup to switch base revisions,
the delta to change, and the size to change accordingly. While the
size increased in this case, I think sizes will remain the same
on average, as the delta base for changelog revisions doesn't matter
too much (as this patch shows). So, I don't consider this a regression.

  $ hg init test
  $ cd test

  $ echo a > a
  $ hg add a
  $ hg commit -m "test"
  $ hg history
  changeset:   0:acb14030fe0a
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     test
  

  $ hg tag ' '
  abort: tag names cannot consist entirely of whitespace
  [255]

(this tests also that editor is not invoked, if '--edit' is not
specified)

  $ HGEDITOR=cat hg tag "bleah"
  $ hg history
  changeset:   1:d4f0d2909abc
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag bleah for changeset acb14030fe0a
  
  changeset:   0:acb14030fe0a
  tag:         bleah
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     test
  

  $ echo foo >> .hgtags
  $ hg tag "bleah2"
  abort: working copy of .hgtags is changed
  (please commit .hgtags manually)
  [255]

  $ hg revert .hgtags
  $ hg tag -r 0 x y z y y z
  abort: tag names must be unique
  [255]
  $ hg tag tap nada dot tip
  abort: the name 'tip' is reserved
  [255]
  $ hg tag .
  abort: the name '.' is reserved
  [255]
  $ hg tag null
  abort: the name 'null' is reserved
  [255]
  $ hg tag "bleah"
  abort: tag 'bleah' already exists (use -f to force)
  [255]
  $ hg tag "blecch" "bleah"
  abort: tag 'bleah' already exists (use -f to force)
  [255]

  $ hg tag --remove "blecch"
  abort: tag 'blecch' does not exist
  [255]
  $ hg tag --remove "bleah" "blecch" "blough"
  abort: tag 'blecch' does not exist
  [255]

  $ hg tag -r 0 "bleah0"
  $ hg tag -l -r 1 "bleah1"
  $ hg tag gack gawk gorp
  $ hg tag -f gack
  $ hg tag --remove gack gorp

  $ hg tag "bleah "
  abort: tag 'bleah' already exists (use -f to force)
  [255]
  $ hg tag " bleah"
  abort: tag 'bleah' already exists (use -f to force)
  [255]
  $ hg tag " bleah"
  abort: tag 'bleah' already exists (use -f to force)
  [255]
  $ hg tag -r 0 "  bleahbleah  "
  $ hg tag -r 0 " bleah bleah "

  $ cat .hgtags
  acb14030fe0a21b60322c440ad2d20cf7685a376 bleah
  acb14030fe0a21b60322c440ad2d20cf7685a376 bleah0
  336fccc858a4eb69609a291105009e484a6b6b8d gack
  336fccc858a4eb69609a291105009e484a6b6b8d gawk
  336fccc858a4eb69609a291105009e484a6b6b8d gorp
  336fccc858a4eb69609a291105009e484a6b6b8d gack
  799667b6f2d9b957f73fa644a918c2df22bab58f gack
  799667b6f2d9b957f73fa644a918c2df22bab58f gack
  0000000000000000000000000000000000000000 gack
  336fccc858a4eb69609a291105009e484a6b6b8d gorp
  0000000000000000000000000000000000000000 gorp
  acb14030fe0a21b60322c440ad2d20cf7685a376 bleahbleah
  acb14030fe0a21b60322c440ad2d20cf7685a376 bleah bleah

  $ cat .hg/localtags
  d4f0d2909abc9290e2773c08837d70c1794e3f5a bleah1

tagging on a non-head revision

  $ hg update 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg tag -l localblah
  $ hg tag "foobar"
  abort: not at a branch head (use -f to force)
  [255]
  $ hg tag -f "foobar"
  $ cat .hgtags
  acb14030fe0a21b60322c440ad2d20cf7685a376 foobar
  $ cat .hg/localtags
  d4f0d2909abc9290e2773c08837d70c1794e3f5a bleah1
  acb14030fe0a21b60322c440ad2d20cf7685a376 localblah

  $ hg tag -l 'xx
  > newline'
  abort: '\n' cannot be used in a name
  [255]
  $ hg tag -l 'xx:xx'
  abort: ':' cannot be used in a name
  [255]

cloning local tags

  $ cd ..
  $ hg -R test log -r0:5
  changeset:   0:acb14030fe0a
  tag:         bleah
  tag:         bleah bleah
  tag:         bleah0
  tag:         bleahbleah
  tag:         foobar
  tag:         localblah
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     test
  
  changeset:   1:d4f0d2909abc
  tag:         bleah1
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag bleah for changeset acb14030fe0a
  
  changeset:   2:336fccc858a4
  tag:         gawk
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag bleah0 for changeset acb14030fe0a
  
  changeset:   3:799667b6f2d9
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag gack, gawk, gorp for changeset 336fccc858a4
  
  changeset:   4:154eeb7c0138
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag gack for changeset 799667b6f2d9
  
  changeset:   5:b4bb47aaff09
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Removed tag gack, gorp
  
  $ hg clone -q -rbleah1 test test1
  $ hg -R test1 parents --style=compact
  1[tip]   d4f0d2909abc   1970-01-01 00:00 +0000   test
    Added tag bleah for changeset acb14030fe0a
  
  $ hg clone -q -r5 test#bleah1 test2
  $ hg -R test2 parents --style=compact
  5[tip]   b4bb47aaff09   1970-01-01 00:00 +0000   test
    Removed tag gack, gorp
  
  $ hg clone -q -U test#bleah1 test3
  $ hg -R test3 parents --style=compact

  $ cd test

Issue601: hg tag doesn't do the right thing if .hgtags or localtags
doesn't end with EOL

  $ python << EOF
  > f = file('.hg/localtags'); last = f.readlines()[-1][:-1]; f.close()
  > f = file('.hg/localtags', 'w'); f.write(last); f.close()
  > EOF
  $ cat .hg/localtags; echo
  acb14030fe0a21b60322c440ad2d20cf7685a376 localblah
  $ hg tag -l localnewline
  $ cat .hg/localtags; echo
  acb14030fe0a21b60322c440ad2d20cf7685a376 localblah
  c2899151f4e76890c602a2597a650a72666681bf localnewline
  

  $ python << EOF
  > f = file('.hgtags'); last = f.readlines()[-1][:-1]; f.close()
  > f = file('.hgtags', 'w'); f.write(last); f.close()
  > EOF
  $ hg ci -m'broken manual edit of .hgtags'
  $ cat .hgtags; echo
  acb14030fe0a21b60322c440ad2d20cf7685a376 foobar
  $ hg tag newline
  $ cat .hgtags; echo
  acb14030fe0a21b60322c440ad2d20cf7685a376 foobar
  a0eea09de1eeec777b46f2085260a373b2fbc293 newline
  

tag and branch using same name

  $ hg branch tag-and-branch-same-name
  marked working directory as branch tag-and-branch-same-name
  (branches are permanent and global, did you want a bookmark?)
  $ hg ci -m"discouraged"
  $ hg tag tag-and-branch-same-name
  warning: tag tag-and-branch-same-name conflicts with existing branch name

test custom commit messages

  $ cat > editor.sh << '__EOF__'
  > echo "==== before editing"
  > cat "$1"
  > echo "===="
  > echo "custom tag message" > "$1"
  > echo "second line" >> "$1"
  > __EOF__

at first, test saving last-message.txt

(test that editor is not invoked before transaction starting)

  $ cat > .hg/hgrc << '__EOF__'
  > [hooks]
  > # this failure occurs before editor invocation
  > pretag.test-saving-lastmessage = false
  > __EOF__
  $ rm -f .hg/last-message.txt
  $ HGEDITOR="\"sh\" \"`pwd`/editor.sh\"" hg tag custom-tag -e
  abort: pretag.test-saving-lastmessage hook exited with status 1
  [255]
  $ test -f .hg/last-message.txt
  [1]

(test that editor is invoked and commit message is saved into
"last-message.txt")

  $ cat >> .hg/hgrc << '__EOF__'
  > [hooks]
  > pretag.test-saving-lastmessage =
  > # this failure occurs after editor invocation
  > pretxncommit.unexpectedabort = false
  > __EOF__

(this tests also that editor is invoked, if '--edit' is specified,
regardless of '--message')

  $ rm -f .hg/last-message.txt
  $ HGEDITOR="\"sh\" \"`pwd`/editor.sh\"" hg tag custom-tag -e -m "foo bar"
  ==== before editing
  foo bar
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch 'tag-and-branch-same-name'
  HG: changed .hgtags
  ====
  note: commit message saved in .hg/last-message.txt
  transaction abort!
  rollback completed
  abort: pretxncommit.unexpectedabort hook exited with status 1
  [255]
  $ cat .hg/last-message.txt
  custom tag message
  second line

  $ cat >> .hg/hgrc << '__EOF__'
  > [hooks]
  > pretxncommit.unexpectedabort =
  > __EOF__
  $ hg status .hgtags
  M .hgtags
  $ hg revert --no-backup -q .hgtags

then, test custom commit message itself

  $ HGEDITOR="\"sh\" \"`pwd`/editor.sh\"" hg tag custom-tag -e
  ==== before editing
  Added tag custom-tag for changeset 75a534207be6
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch 'tag-and-branch-same-name'
  HG: changed .hgtags
  ====
  $ hg log -l1 --template "{desc}\n"
  custom tag message
  second line


local tag with .hgtags modified

  $ hg tag hgtags-modified
  $ hg rollback
  repository tip rolled back to revision 13 (undo commit)
  working directory now based on revision 13
  $ hg st
  M .hgtags
  ? .hgtags.orig
  ? editor.sh
  $ hg tag --local baz
  $ hg revert --no-backup .hgtags


tagging when at named-branch-head that's not a topo-head

  $ hg up default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge -t internal:local
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'merge named branch'
  $ hg up 13
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg tag new-topo-head

tagging on null rev

  $ hg up null
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ hg tag nullrev
  abort: not at a branch head (use -f to force)
  [255]

  $ hg init empty
  $ hg tag -R empty nullrev
  abort: cannot tag null revision
  [255]

  $ hg tag -R empty -r 00000000000 -f nulltag
  abort: cannot tag null revision
  [255]

  $ cd ..

tagging on an uncommitted merge (issue2542)

  $ hg init repo-tag-uncommitted-merge
  $ cd repo-tag-uncommitted-merge
  $ echo c1 > f1
  $ hg ci -Am0
  adding f1
  $ echo c2 > f2
  $ hg ci -Am1
  adding f2
  $ hg co -q 0
  $ hg branch b1
  marked working directory as branch b1
  (branches are permanent and global, did you want a bookmark?)
  $ hg ci -m2
  $ hg up default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge b1
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg tag t1
  abort: uncommitted merge
  [255]
  $ hg status
  $ hg tag --rev 1 t2
  abort: uncommitted merge
  [255]
  $ hg tag --rev 1 --local t3
  $ hg tags -v
  tip                                2:2a156e8887cc
  t3                                 1:c3adabd1a5f4 local

  $ cd ..

commit hook on tag used to be run without write lock - issue3344

  $ hg init repo-tag
  $ touch repo-tag/test
  $ hg -R repo-tag commit -A -m "test"
  adding test
  $ hg init repo-tag-target
  $ cat > "$TESTTMP/issue3344.sh" <<EOF
  > hg push "$TESTTMP/repo-tag-target"
  > EOF
  $ hg -R repo-tag --config hooks.commit="sh ../issue3344.sh" tag tag
  pushing to $TESTTMP/repo-tag-target (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 2 files

automatically merge resolvable tag conflicts (i.e. tags that differ in rank)
create two clones with some different tags as well as some common tags
check that we can merge tags that differ in rank

  $ hg init repo-automatic-tag-merge
  $ cd repo-automatic-tag-merge
  $ echo c0 > f0
  $ hg ci -A -m0
  adding f0
  $ hg tag tbase
  $ hg up -qr '.^'
  $ hg log -r 'wdir()' -T "{latesttagdistance}\n"
  1
  $ hg up -q
  $ hg log -r 'wdir()' -T "{latesttagdistance}\n"
  2
  $ cd ..
  $ hg clone repo-automatic-tag-merge repo-automatic-tag-merge-clone
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd repo-automatic-tag-merge-clone
  $ echo c1 > f1
  $ hg ci -A -m1
  adding f1
  $ hg tag t1 t2 t3
  $ hg tag --remove t2
  $ hg tag t5
  $ echo c2 > f2
  $ hg ci -A -m2
  adding f2
  $ hg tag -f t3

  $ cd ../repo-automatic-tag-merge
  $ echo c3 > f3
  $ hg ci -A -m3
  adding f3
  $ hg tag -f t4 t5 t6

  $ hg up -q '.^'
  $ hg log -r 'wdir()' -T "{changessincelatesttag} changes since {latesttag}\n"
  1 changes since t4:t5:t6
  $ hg log -r '.' -T "{changessincelatesttag} changes since {latesttag}\n"
  0 changes since t4:t5:t6
  $ echo c5 > f3
  $ hg log -r 'wdir()' -T "{changessincelatesttag} changes since {latesttag}\n"
  1 changes since t4:t5:t6
  $ hg up -qC

  $ hg tag --remove t5
  $ echo c4 > f4
  $ hg log -r '.' -T "{changessincelatesttag} changes since {latesttag}\n"
  2 changes since t4:t6
  $ hg log -r '.' -T "{latesttag % '{latesttag}\n'}"
  t4
  t6
  $ hg log -r '.' -T "{latesttag('t4') % 'T: {tag}, C: {changes}, D: {distance}\n'}"
  T: t4, C: 2, D: 2
  $ hg log -r '.' -T "{latesttag('re:\d') % 'T: {tag}, C: {changes}, D: {distance}\n'}"
  T: t4, C: 2, D: 2
  T: t6, C: 2, D: 2
  $ hg log -r . -T '{join(latesttag(), "*")}\n'
  t4*t6
  $ hg ci -A -m4
  adding f4
  $ hg log -r 'wdir()' -T "{changessincelatesttag} changes since {latesttag}\n"
  4 changes since t4:t6
  $ hg tag t2
  $ hg tag -f t6

  $ cd ../repo-automatic-tag-merge-clone
  $ hg pull
  pulling from $TESTTMP/repo-automatic-tag-merge (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 6 changesets with 6 changes to 3 files (+1 heads)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg merge --tool internal:tagmerge
  merging .hgtags
  2 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg status
  M .hgtags
  M f3
  M f4
  $ hg resolve -l
  R .hgtags
  $ cat .hgtags
  9aa4e1292a27a248f8d07339bed9931d54907be7 t4
  9aa4e1292a27a248f8d07339bed9931d54907be7 t6
  9aa4e1292a27a248f8d07339bed9931d54907be7 t6
  09af2ce14077a94effef208b49a718f4836d4338 t6
  6cee5c8f3e5b4ae1a3996d2f6489c3e08eb5aea7 tbase
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t1
  929bca7b18d067cbf3844c3896319a940059d748 t2
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
  0000000000000000000000000000000000000000 t2
  875517b4806a848f942811a315a5bce30804ae85 t5
  9aa4e1292a27a248f8d07339bed9931d54907be7 t5
  9aa4e1292a27a248f8d07339bed9931d54907be7 t5
  0000000000000000000000000000000000000000 t5
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
  79505d5360b07e3e79d1052e347e73c02b8afa5b t3

check that the merge tried to minimize the diff with the first merge parent

  $ hg diff --git -r 'p1()' .hgtags
  diff --git a/.hgtags b/.hgtags
  --- a/.hgtags
  +++ b/.hgtags
  @@ -1,9 +1,17 @@
  +9aa4e1292a27a248f8d07339bed9931d54907be7 t4
  +9aa4e1292a27a248f8d07339bed9931d54907be7 t6
  +9aa4e1292a27a248f8d07339bed9931d54907be7 t6
  +09af2ce14077a94effef208b49a718f4836d4338 t6
   6cee5c8f3e5b4ae1a3996d2f6489c3e08eb5aea7 tbase
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t1
  +929bca7b18d067cbf3844c3896319a940059d748 t2
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
   0000000000000000000000000000000000000000 t2
   875517b4806a848f942811a315a5bce30804ae85 t5
  +9aa4e1292a27a248f8d07339bed9931d54907be7 t5
  +9aa4e1292a27a248f8d07339bed9931d54907be7 t5
  +0000000000000000000000000000000000000000 t5
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
   79505d5360b07e3e79d1052e347e73c02b8afa5b t3

detect merge tag conflicts

  $ hg update -C -r tip
  3 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ hg tag t7
  $ hg update -C -r 'first(sort(head()))'
  3 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ printf "%s %s\n" `hg log -r . --template "{node} t7"` >> .hgtags
  $ hg commit -m "manually add conflicting t7 tag"
  $ hg merge --tool internal:tagmerge
  merging .hgtags
  automatic .hgtags merge failed
  the following 1 tags are in conflict: t7
  automatic tag merging of .hgtags failed! (use 'hg resolve --tool :merge' or another merge tool of your choice)
  2 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
  [1]
  $ hg resolve -l
  U .hgtags
  $ cat .hgtags
  6cee5c8f3e5b4ae1a3996d2f6489c3e08eb5aea7 tbase
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t1
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
  0000000000000000000000000000000000000000 t2
  875517b4806a848f942811a315a5bce30804ae85 t5
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
  79505d5360b07e3e79d1052e347e73c02b8afa5b t3
  ea918d56be86a4afc5a95312e8b6750e1428d9d2 t7

  $ cd ..

handle the loss of tags

  $ hg clone repo-automatic-tag-merge-clone repo-merge-lost-tags
  updating to branch default
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd repo-merge-lost-tags
  $ echo c5 > f5
  $ hg ci -A -m5
  adding f5
  $ hg tag -f t7
  $ hg update -r 'p1(t7)'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ printf '' > .hgtags
  $ hg commit -m 'delete all tags'
  created new head
  $ hg log -r 'max(t7::)'
  changeset:   17:ffe462b50880
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag t7 for changeset fd3a9e394ce3
  
  $ hg update -r 'max(t7::)'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge -r tip --tool internal:tagmerge
  merging .hgtags
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg resolve -l
  R .hgtags
  $ cat .hgtags
  6cee5c8f3e5b4ae1a3996d2f6489c3e08eb5aea7 tbase
  0000000000000000000000000000000000000000 tbase
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t1
  0000000000000000000000000000000000000000 t1
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
  0000000000000000000000000000000000000000 t2
  875517b4806a848f942811a315a5bce30804ae85 t5
  0000000000000000000000000000000000000000 t5
  4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
  79505d5360b07e3e79d1052e347e73c02b8afa5b t3
  0000000000000000000000000000000000000000 t3
  ea918d56be86a4afc5a95312e8b6750e1428d9d2 t7
  0000000000000000000000000000000000000000 t7
  ea918d56be86a4afc5a95312e8b6750e1428d9d2 t7
  fd3a9e394ce3afb354a496323bf68ac1755a30de t7

also check that we minimize the diff with the 1st merge parent

  $ hg diff --git -r 'p1()' .hgtags
  diff --git a/.hgtags b/.hgtags
  --- a/.hgtags
  +++ b/.hgtags
  @@ -1,12 +1,17 @@
   6cee5c8f3e5b4ae1a3996d2f6489c3e08eb5aea7 tbase
  +0000000000000000000000000000000000000000 tbase
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t1
  +0000000000000000000000000000000000000000 t1
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t2
   0000000000000000000000000000000000000000 t2
   875517b4806a848f942811a315a5bce30804ae85 t5
  +0000000000000000000000000000000000000000 t5
   4f3e9b90005b68b4d8a3f4355cedc302a8364f5c t3
   79505d5360b07e3e79d1052e347e73c02b8afa5b t3
  +0000000000000000000000000000000000000000 t3
   ea918d56be86a4afc5a95312e8b6750e1428d9d2 t7
  +0000000000000000000000000000000000000000 t7
   ea918d56be86a4afc5a95312e8b6750e1428d9d2 t7
   fd3a9e394ce3afb354a496323bf68ac1755a30de t7