CONTRIBUTORS

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)

[This file is here for historical purposes, all recent contributors
should appear in the changelog directly]

Andrea Arcangeli <andrea at suse.de>
Thomas Arendsen Hein <thomas at intevation.de>
Goffredo Baroncelli <kreijack at libero.it>
Muli Ben-Yehuda <mulix at mulix.org>
Mikael Berthe <mikael at lilotux.net>
Benoit Boissinot <bboissin at gmail.com>
Brendan Cully <brendan at kublai.com>
Vincent Danjean <vdanjean.ml at free.fr>
Jake Edge <jake at edge2.net>
Michael Fetterman <michael.fetterman at intel.com>
Edouard Gomez <ed.gomez at free.fr>
Eric Hopper <hopper at omnifarious.org>
Alecs King <alecsk at gmail.com>
Volker Kleinfeld <Volker.Kleinfeld at gmx.de>
Vadim Lebedev <vadim at mbdsys.com>
Christopher Li <hg at chrisli.org>
Chris Mason <mason at suse.com>
Colin McMillen <mcmillen at cs.cmu.edu>
Wojciech Milkowski <wmilkowski at interia.pl>
Chad Netzer <chad.netzer at gmail.com>
Bryan O'Sullivan <bos at serpentine.com>
Vicent Seguí Pascual <vseguip at gmail.com>
Sean Perry <shaleh at speakeasy.net>
Nguyen Anh Quynh <aquynh at gmail.com>
Ollivier Robert <roberto at keltia.freenix.fr>
Alexander Schremmer <alex at alexanderweb.de>
Arun Sharma <arun at sharma-home.net>
Josef "Jeff" Sipek <jeffpc at optonline.net>
Kevin Smith <yarcs at qualitycode.com>
TK Soh <teekaysoh at yahoo.com>
Radoslaw Szkodzinski <astralstorm at gorzow.mm.pl>
Samuel Tardieu <sam at rfc1149.net>
K Thananchayan <thananck at yahoo.com>
Andrew Thompson <andrewkt at aktzero.com>
Michael S. Tsirkin <mst at mellanox.co.il>
Rafael Villar Burke <pachi at mmn-arquitectos.com>
Tristan Wibberley <tristan at wibberley.org>
Mark Williamson <mark.williamson at cl.cam.ac.uk>