tests/test-debug-revlog-stats.t

revlog: add a C implementation of `headrevsdiff`

Python implementation of `headrevsdiff` can be very slow in the worst
case compared with the `heads` computation it replaces, since the
latter is done in C.

Even the average case of this Python implementation is still
noticeable in the profiles.

This patch makes the computation much much faster by doing it in C.

Force revlog max inline value to be smaller than default

  $ mkdir $TESTTMP/ext
  $ cat << EOF > $TESTTMP/ext/small_inline.py
  > from mercurial import revlog
  > revlog._maxinline = 8
  > EOF

  $ cat << EOF >> $HGRCPATH
  > [extensions]
  > small_inline=$TESTTMP/ext/small_inline.py
  > EOF

  $ hg init repo
  $ cd repo

Try on an empty repository

  $ hg debug-revlog-stats
  rev-count   data-size inl type      target 

  $ mkdir folder
  $ touch a b folder/c folder/d
  $ hg commit -Aqm 0
  $ echo "text" > a
  $ hg rm b
  $ echo "longer string" > folder/d
  $ hg commit -Aqm 1

Differences in data size observed with pure is due to different compression
algorithms

  $ hg debug-revlog-stats
  rev-count   data-size inl type      target 
          2         138 no  changelog  (no-pure !)
          2         137 no  changelog  (pure !)
          2         177 no  manifest   (no-pure !)
          2         168 no  manifest   (pure !)
          2           6 yes file      a
          1           0 yes file      b
          1           0 yes file      folder/c
          2          15 no  file      folder/d

Test 'changelog' command argument

  $ hg debug-revlog-stats -c
  rev-count   data-size inl type      target 
          2         138 no  changelog  (no-pure !)
          2         137 no  changelog  (pure !)

Test 'manifest' command argument

  $ hg debug-revlog-stats -m
  rev-count   data-size inl type      target 
          2         177 no  manifest   (no-pure !)
          2         168 no  manifest   (pure !)

Test 'file' command argument

  $ hg debug-revlog-stats -f
  rev-count   data-size inl type      target 
          2           6 yes file      a
          1           0 yes file      b
          1           0 yes file      folder/c
          2          15 no  file      folder/d

Test multiple command arguments

  $ hg debug-revlog-stats -cm
  rev-count   data-size inl type      target 
          2         138 no  changelog  (no-pure !)
          2         137 no  changelog  (pure !)
          2         177 no  manifest   (no-pure !)
          2         168 no  manifest   (pure !)