tests/test-relink.t

mdiff: speed up showfunc for large diffs

This addresses the following issues with showfunc:

- Silly usage of regular expressions.
- Doing str.rstrip() needlessly in an inner loop.
- Doing catastrophic backtracking when trying to find a function line.

Finding function text is now at worst O(n lines in the old file), and
at best close to O(n hunks).

Given a diff like this[1]:

 src/main/antlr3/uk/ac/cam/ch/wwmm/pregenerated/ChemicalChunker.g        |      4 +-
 src/main/java/uk/ac/cam/ch/wwmm/pregenerated/ChemicalChunkerLexer.java  |      2 +-
 src/main/java/uk/ac/cam/ch/wwmm/pregenerated/ChemicalChunkerParser.java |  29189 +++++----
 3 files changed, 14741 insertions(+), 14454 deletions(-)

[1]: https://bitbucket.org/wwmm/chemicaltagger/changeset/d2bfbaecd4fc/raw

Without this change, hg log --stat --config diff.showfunc=1 takes an
absurdly long time to complete:

   CallCount    Recursive    Total(ms)   Inline(ms) module:lineno(function)
       32813            0     80.3546     40.6086   mercurial.mdiff:160(yieldhunk)
   [phone]            0     25.7227     25.7227   +<method 'match' of '_sre.SRE_Pattern' objects>
   [phone]            0     14.0221     14.0221   +<method 'rstrip' of 'str' objects>
       +1809            0      0.0009      0.0009   +mercurial.mdiff:148(contextend)
       +1809            0      0.0003      0.0003   +<len>
    65062746            0     25.7227     25.7227   <method 'match' of '_sre.SRE_Pattern' objects>
    65062763            0     14.0221     14.0221   <method 'rstrip' of 'str' objects>
         543            0      0.1631      0.1631   <zlib.decompress>
           3            0      0.0505      0.0505   <mercurial.bdiff.blocks>
       31007            0     80.4564      0.0477   mercurial.mdiff:147(_unidiff)
      +32813            0     80.3546     40.6086   +mercurial.mdiff:160(yieldhunk)
          +3            0      0.0505      0.0505   +<mercurial.bdiff.blocks>
       +3618            0      0.0022      0.0022   +mercurial.mdiff:154(contextstart)
       +5427            0      0.0013      0.0013   +<len>
          +3            0      0.0001      0.0000   +re:188(compile)
           1            0     80.8381      0.0322   mercurial.patch:1777(diffstatdata)
     +107499            0      0.0235      0.0235   +<method 'startswith' of 'str' objects>
      +31014            0     80.7820      0.0071   +mercurial.util:1284(iterlines)
          +3            0      0.0000      0.0000   +<method 'search' of '_sre.SRE_Pattern' objects>
          +4            0      0.0000      0.0000   +mercurial.patch:1783(addresult)
          +3            0      0.0000      0.0000   +<method 'group' of '_sre.SRE_Match' objects>
           6            0      0.0444      0.0283   mercurial.mdiff:12(splitnewlines)
          +6            0      0.0160      0.0160   +<method 'split' of 'str' objects>
          32            0      0.0246      0.0246   <method 'update' of '_hashlib.HASH' objects>
          11            0      0.0236      0.0236   <method 'read' of 'file' objects>
Time: real 80.880 secs (user 80.200+0.000 sys 0.380+0.000)

With this change, it's almost as fast as not using showfunc at all:

   CallCount    Recursive    Total(ms)   Inline(ms) module:lineno(function)
         543            0      0.1699      0.1699   <zlib.decompress>
           3            0      0.0501      0.0501   <mercurial.bdiff.blocks>
       32813            0      0.0415      0.0348   mercurial.mdiff:161(yieldhunk)
      +70837            0      0.0058      0.0058   +<method 'isalnum' of 'str' objects>
       +1809            0      0.0006      0.0006   +mercurial.mdiff:148(contextend)
       +1809            0      0.0002      0.0002   +<len>
           1            0      0.4879      0.0310   mercurial.patch:1777(diffstatdata)
     +107499            0      0.0230      0.0230   +<method 'startswith' of 'str' objects>
      +31014            0      0.4335      0.0065   +mercurial.util:1284(iterlines)
          +3            0      0.0000      0.0000   +<method 'search' of '_sre.SRE_Pattern' objects>
          +4            0      0.0000      0.0000   +mercurial.patch:1783(addresult)
          +1            0      0.0004      0.0000   +re:188(compile)
          32            0      0.0293      0.0293   <method 'update' of '_hashlib.HASH' objects>
           6            0      0.0427      0.0279   mercurial.mdiff:12(splitnewlines)
          +6            0      0.0147      0.0147   +<method 'split' of 'str' objects>
       31007            0      0.1169      0.0235   mercurial.mdiff:147(_unidiff)
          +3            0      0.0501      0.0501   +<mercurial.bdiff.blocks>
      +32813            0      0.0415      0.0348   +mercurial.mdiff:161(yieldhunk)
       +3618            0      0.0012      0.0012   +mercurial.mdiff:154(contextstart)
       +5427            0      0.0006      0.0006   +<len>
      107597            0      0.0230      0.0230   <method 'startswith' of 'str' objects>
          16            0      0.0213      0.0213   <mercurial.mpatch.patches>
         194            0      0.0149      0.0149   <method 'split' of 'str' objects>
Time: real 0.530 secs (user 0.450+0.000 sys 0.070+0.000)

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "relink=" >> $HGRCPATH

  $ fix_path() {
  >     tr '\\' /
  > }

  $ cat > arelinked.py <<EOF
  > import sys, os
  > from mercurial import util
  > path1, path2 = sys.argv[1:3]
  > if util.samefile(path1, path2):
  >     print '%s == %s' % (path1, path2)
  > else:
  >     print '%s != %s' % (path1, path2)
  > EOF


create source repository

  $ hg init repo
  $ cd repo
  $ echo a > a
  $ echo b > b
  $ hg ci -Am addfile
  adding a
  adding b
  $ cat $TESTDIR/binfile.bin >> a
  $ cat $TESTDIR/binfile.bin >> b
  $ hg ci -Am changefiles

make another commit to create files larger than 1 KB to test
formatting of final byte count

  $ cat $TESTDIR/binfile.bin >> a
  $ cat $TESTDIR/binfile.bin >> b
  $ hg ci -m anotherchange

don't sit forever trying to double-lock the source repo

  $ hg relink .
  relinking $TESTTMP/repo/.hg/store to $TESTTMP/repo/.hg/store
  there is nothing to relink


Test files are read in binary mode

  $ python -c "file('.hg/store/data/dummy.i', 'wb').write('a\r\nb\n')"
  $ cd ..


clone and pull to break links

  $ hg clone --pull -r0 repo clone
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 2 changes to 2 files
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd clone
  $ hg pull -q
  $ echo b >> b
  $ hg ci -m changeb
  created new head
  $ python -c "file('.hg/store/data/dummy.i', 'wb').write('a\nb\r\n')"


relink

  $ hg relink --debug | fix_path
  relinking $TESTTMP/repo/.hg/store to $TESTTMP/clone/.hg/store
  tip has 2 files, estimated total number of files: 3
  collecting: 00changelog.i 1/3 files (33.33%)
  collecting: 00manifest.i 2/3 files (66.67%)
  collecting: a.i 3/3 files (100.00%)
  collecting: b.i 4/3 files (133.33%)
  collecting: dummy.i 5/3 files (166.67%)
  collected 5 candidate storage files
  not linkable: 00changelog.i
  not linkable: 00manifest.i
  pruning: data/a.i 3/5 files (60.00%)
  not linkable: data/b.i
  pruning: data/dummy.i 5/5 files (100.00%)
  pruned down to 2 probably relinkable files
  relinking: data/a.i 1/2 files (50.00%)
  not linkable: data/dummy.i
  relinked 1 files (1.37 KB reclaimed)
  $ cd ..


check hardlinks

  $ python arelinked.py repo/.hg/store/data/a.i clone/.hg/store/data/a.i
  repo/.hg/store/data/a.i == clone/.hg/store/data/a.i
  $ python arelinked.py repo/.hg/store/data/b.i clone/.hg/store/data/b.i
  repo/.hg/store/data/b.i != clone/.hg/store/data/b.i