tests/test-debug-revlog-stats.t

interfaces: add the optional `bdiff.xdiffblocks()` method

PyCharm flagged where this was called on the protocol class in `mdiff.py` in the
previous commit, but pytype completely missed it.  PyCharm is correct here, but
I'm committing this separately to highlight this potential problem- some of the
implementations don't implement _all_ of the methods the others do, and there's
not a great way to indicate on a protocol class that a method or attribute is
optional- that's kinda the opposite of what static typing is about.

Making the method an `Optional[Callable]` attribute works here, and keeps both
PyCharm and pytype happy, and the generated `mdiff.pyi` and `modules.pyi` look
reasonable.  We might be getting a little lucky, because the method isn't
invoked directly- it is returned from another method that selects which block
function to use.  Except since it is declared on the protocol class, every
module needs this attribute (in theory, but in practice this doesn't seem to be
checked), so the check for it on the module has to change from `hasattr()` to
`getattr(..., None)`.  We defer defining the optional attrs to the type checking
phase as an extra precaution- that way it isn't an attr with a `None` value at
runtime if someone is still using `hasattr()`.

As to why pytype missed this, I have no clue.  The generated `mdiff.pyi` even
has the global variable typed as `bdiff: intmod.BDiff`, so uses of it really
should comply with what is on the class, protocol class or not.

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 !)