tests/test-merge-revert2.t

branches: avoid unnecessary changectx.branch() calls

This requires reading from the changelog, which can be costly over NFS.

Note that this does not totally remove reading from the changelog; we
still do that when calling changectx.closesbranch(). That call will be
removed in a later patch.

Running hg branches on the PyPy repo (with 996) over a busy NFS server,
before this change:

$ time hg --profile branches > /dev/null
   CallCount    Recursive     Total(s)    Inline(s) module:lineno(function)
        2042            0      2.2827      2.2827   <open>
        2036            0      0.9840      0.9840   <method 'close' of 'file' objects>
        2036            0      0.0464      0.0464   <method 'read' of 'file' objects>
        5233            0      0.1985      0.0453   mercurial.repoview:161(changelog)
       10462            0      0.0791      0.0314       mercurial.changelog:133(tip)
        5233            0      0.0388      0.0176       mercurial.localrepo:26(__get__)
       10462            0      0.0250      0.0126       <len>
        5233            0      0.0059      0.0039       mercurial.repoview:112(filterrevs)
       10462            0      0.0029      0.0029       <hash>
        2034            0      0.0444      0.0444   <method 'seek' of 'file' objects>
        5340            0      0.0390      0.0390   mercurial.revlog:296(rev)
        2582            0      0.0371      0.0371   <zlib.decompress>
        3155            0      0.1963      0.0366   mercurial.context:202(__init__)
        3155            0      0.1238      0.0306       mercurial.repoview:161(changelog)
        3155            0      0.0261      0.0080       mercurial.changelog:183(rev)
        9465            0      0.0061      0.0061       <isinstance>
        1096            0      0.0023      0.0023       <binascii.unhexlify>
        4251            0      0.0014      0.0014       <len>
        2059            0      3.7341      0.0332   mercurial.changelog:270(read)
        2059            0      3.6304      0.0307       mercurial.revlog:907(revision)
        2057            0      0.0262      0.0137       mercurial.changelog:28(decodeextra)
        4118            0      0.0094      0.0094       <method 'split' of 'str' objects>
        4118            0      0.0270      0.0048       mercurial.encoding:61(tolocal)
        2059            0      0.0040      0.0040       <method 'index' of 'str' objects>
       10462            0      0.0791      0.0314   mercurial.changelog:133(tip)
       10462            0      0.0289      0.0207       mercurial.changelog:190(node)
       10462            0      0.0188      0.0091       <len>
       52433        20932      0.0478      0.0310   <len>
       20932            0      0.0221      0.0168       mercurial.revlog:262(__len__)
        2059            0      3.6304      0.0307   mercurial.revlog:907(revision)

real    0m4.361s
user    0m0.986s
sys     0m0.237s

After this change:

$ time hg --profile branches > /dev/null
   CallCount    Recursive     Total(s)    Inline(s) module:lineno(function)
        1069            0      1.1098      1.1098   <open>
        1063            0      0.4865      0.4865   <method 'close' of 'file' objects>
        4122            0      0.1811      0.0404   mercurial.repoview:161(changelog)
        8240            0      0.0712      0.0272       mercurial.changelog:133(tip)
        4122            0      0.0378      0.0177       mercurial.localrepo:26(__get__)
        8240            0      0.0221      0.0115       <len>
        4122            0      0.0057      0.0033       mercurial.repoview:112(filterrevs)
        8240            0      0.0025      0.0025       <hash>
        3029            0      0.1979      0.0371   mercurial.context:202(__init__)
        3029            0      0.1278      0.0310       mercurial.repoview:161(changelog)
        3029            0      0.0230      0.0081       mercurial.changelog:183(rev)
        9087            0      0.0061      0.0061       <isinstance>
        1096            0      0.0026      0.0026       <binascii.unhexlify>
        4125            0      0.0014      0.0014       <len>
        4229            0      0.0337      0.0337   mercurial.revlog:296(rev)
        1061            0      0.0296      0.0296   <method 'seek' of 'file' objects>
        1063            0      0.0292      0.0292   <method 'read' of 'file' objects>
        8240            0      0.0712      0.0272   mercurial.changelog:133(tip)
        8240            0      0.0271      0.0196       mercurial.changelog:190(node)
        8240            0      0.0169      0.0083       <len>
       40476        16488      0.0422      0.0271   <len>
       16488            0      0.0193      0.0152       mercurial.revlog:262(__len__)
        1342            0      0.0241      0.0241   <zlib.decompress>
        9445            0      0.0336      0.0224   mercurial.changelog:190(node)
        9445            0      0.0112      0.0112       mercurial.revlog:317(node)
        1074            0      1.9102      0.0224   mercurial.changelog:270(read)
        1074            0      1.8397      0.0202       mercurial.revlog:907(revision)
        1073            0      0.0187      0.0099       mercurial.changelog:28(decodeextra)
        2148            0      0.0061      0.0061       <method 'split' of 'str' objects>
        2148            0      0.0184      0.0034       mercurial.encoding:61(tolocal)

real    0m2.402s
user    0m0.735s
sys     0m0.177s

  $ hg init

  $ echo "added file1" > file1
  $ echo "another line of text" >> file1
  $ echo "added file2" > file2
  $ hg add file1 file2
  $ hg commit -m "added file1 and file2"

  $ echo "changed file1" >> file1
  $ hg commit -m "changed file1"

  $ hg -q log
  1:dfab7f3c2efb
  0:c3fa057dd86f
  $ hg id
  dfab7f3c2efb tip

  $ hg update -C 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg id
  c3fa057dd86f

  $ echo "changed file1" >> file1
  $ hg id
  c3fa057dd86f+

  $ hg revert --no-backup --all
  reverting file1
  $ hg diff
  $ hg status
  $ hg id
  c3fa057dd86f

  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg diff
  $ hg status
  $ hg id
  dfab7f3c2efb tip

  $ hg update -C 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo "changed file1 different" >> file1

  $ hg update
  merging file1
  warning: conflicts during merge.
  merging file1 incomplete! (edit conflicts, then use 'hg resolve --mark')
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]

  $ hg diff --nodates
  diff -r dfab7f3c2efb file1
  --- a/file1
  +++ b/file1
  @@ -1,3 +1,7 @@
   added file1
   another line of text
  +<<<<<<< local
  +changed file1 different
  +=======
   changed file1
  +>>>>>>> other

  $ hg status
  M file1
  ? file1.orig
  $ hg id
  dfab7f3c2efb+ tip

  $ hg revert --no-backup --all
  reverting file1
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  dfab7f3c2efb tip

  $ hg revert -r tip --no-backup --all
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  dfab7f3c2efb tip

  $ hg update -C
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  dfab7f3c2efb tip