tests/test-log-exthook.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

Test hg log changeset printer external hook
-------------------------------------------

  $ cat > $TESTTMP/logexthook.py <<EOF
  > from __future__ import absolute_import
  > import codecs
  > from mercurial import (
  >   commands,
  >   logcmdutil,
  >   repair,
  > )
  > def brot13(b):
  >     return codecs.encode(b.decode('utf8'), 'rot-13').encode('utf8')
  > def rot13description(self, ctx):
  >     description = ctx.description().strip().splitlines()[0]
  >     self.ui.write(b"%s:     %s\n" % (brot13(b"summary"),
  >                                      brot13(description)))
  > def reposetup(ui, repo):
  >     logcmdutil.changesetprinter._exthook = rot13description
  > EOF

Prepare the repository

  $ hg init empty
  $ cd empty
  $ touch ROOT
  $ hg commit -A -m "Root" ROOT

  $ touch a b c
  $ hg commit -A -m "Add A, B, C" a b c

Check the log

  $ hg log --config extensions.t=$TESTTMP/logexthook.py
  changeset:   1:70fc82b23320
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  fhzznel:     Nqq N, O, P
  summary:     Add A, B, C
  
  changeset:   0:b00443a54871
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  fhzznel:     Ebbg
  summary:     Root
  
Check that exthook is working with graph log too

  $ hg log -G --config extensions.t=$TESTTMP/logexthook.py
  @  changeset:   1:70fc82b23320
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  fhzznel:     Nqq N, O, P
  |  summary:     Add A, B, C
  |
  o  changeset:   0:b00443a54871
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     fhzznel:     Ebbg
     summary:     Root