tests/test-issue5979.t

extdiff: refactor logic which does diff of patches

The current extdiff code is hard to understand on first look. Took me few hours
to grasp the code. Before adding more things, decided to do some refactoring.

Differential Revision: https://phab.mercurial-scm.org/D8686

  $ hg init r1
  $ cd r1
  $ hg ci --config ui.allowemptycommit=true -m c0
  $ hg ci --config ui.allowemptycommit=true -m c1
  $ hg ci --config ui.allowemptycommit=true -m c2
  $ hg co -q 0
  $ hg ci --config ui.allowemptycommit=true -m c3
  created new head
  $ hg co -q 3
  $ hg merge --quiet
  $ hg ci --config ui.allowemptycommit=true -m c4

  $ hg log -G -T'{desc}'
  @    c4
  |\
  | o  c3
  | |
  o |  c2
  | |
  o |  c1
  |/
  o  c0
  

  >>> from mercurial import hg
  >>> from mercurial import ui as uimod
  >>> repo = hg.repository(uimod.ui())
  >>> for anc in repo.changelog.ancestors([4], inclusive=True):
  ...   print(anc)
  4
  3
  2
  1
  0