tests/test-state-extension.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.

Test extension of unfinished states support.
  $ mkdir chainify
  $ cd chainify
  $ cat >> chainify.py <<EOF
  > from mercurial import cmdutil, error, extensions, exthelper, node, scmutil, state
  > from hgext import rebase
  > 
  > eh = exthelper.exthelper()
  > 
  > extsetup = eh.finalextsetup
  > cmdtable = eh.cmdtable
  > 
  > # Rebase calls addunfinished in uisetup, so we have to call it in extsetup.
  > # Ideally there'd by an 'extensions.afteruisetup()' just like
  > # 'extensions.afterloaded()' to allow nesting multiple commands.
  > @eh.extsetup
  > def _extsetup(ui):
  >     state.addunfinished(
  >         b'chainify',
  >         b'chainify.state',
  >         continueflag=True,
  >         childopnames=[b'rebase'])
  > 
  > def _node(repo, arg):
  >     return node.hex(scmutil.revsingle(repo, arg).node())
  > 
  > @eh.command(
  >     b'chainify',
  >     [(b'r', b'revs', [], b'revs to chain', b'REV'),
  >      (b'', b'continue', False, b'continue op')],
  >     b'chainify [-r REV] +',
  >     inferrepo=True)
  > def chainify(ui, repo, **opts):
  >     """Rebases r1, r2, r3, etc. into a chain."""
  >     with repo.wlock(), repo.lock():
  >         cmdstate = state.cmdstate(repo, b'chainify.state')
  >         if opts['continue']:
  >             if not cmdstate.exists():
  >                 raise error.Abort(b'no chainify in progress')
  >         else:
  >             cmdutil.checkunfinished(repo)
  >             data = {
  >                 b'tip': _node(repo, opts['revs'][0]),
  >                 b'revs': b','.join(_node(repo, r) for r in opts['revs'][1:]),
  >             }
  >             cmdstate.save(1, data)
  > 
  >         data = cmdstate.read()
  >         while data[b'revs']:
  >             tip = data[b'tip']
  >             revs = data[b'revs'].split(b',')
  >             with state.delegating(repo, b'chainify', b'rebase'):
  >                 ui.status(b'rebasing %s onto %s\n' % (revs[0][:12], tip[:12]))
  >                 if state.ischildunfinished(repo, b'chainify', b'rebase'):
  >                     rc = state.continuechild(ui, repo, b'chainify', b'rebase')
  >                 else:
  >                     rc = rebase.rebase(ui, repo, rev=[revs[0]], dest=tip)
  >                 if rc and rc != 0:
  >                     raise error.Abort(b'rebase failed (rc: %d)' % rc)
  >             data[b'tip'] = _node(repo, b'tip')
  >             data[b'revs'] = b','.join(revs[1:])
  >             cmdstate.save(1, data)
  >         cmdstate.delete()
  >         ui.status(b'done chainifying\n')
  > EOF

  $ chainifypath=`pwd`/chainify.py
  $ echo '[extensions]' >> $HGRCPATH
  $ echo "chainify = $chainifypath" >> $HGRCPATH
  $ echo "rebase =" >> $HGRCPATH

  $ cd $TESTTMP
  $ hg init a
  $ cd a
  $ echo base > base.txt
  $ hg commit -Aqm 'base commit'
  $ echo foo > file1
  $ hg commit -Aqm 'add file'
  $ hg co -q ".^"
  $ echo bar > file2
  $ hg commit -Aqm 'add other file'
  $ hg co -q ".^"
  $ echo foo2 > file1
  $ hg commit -Aqm 'add conflicting file'
  $ hg co -q ".^"
  $ hg log --graph --template '{rev} {files}'
  o  3 file1
  |
  | o  2 file2
  |/
  | o  1 file1
  |/
  @  0 base.txt
  
  $ hg chainify -r 8430cfdf77c2 -r f8596309dff8 -r a858b338b3e9
  rebasing f8596309dff8 onto 8430cfdf77c2
  rebasing 2:f8596309dff8 "add other file"
  saved backup bundle to $TESTTMP/* (glob)
  rebasing a858b338b3e9 onto 83c722183a8e
  rebasing 2:a858b338b3e9 "add conflicting file"
  merging file1
  warning: conflicts while merging file1! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see 'hg resolve', then 'hg chainify --continue')
  [240]
  $ hg status --config commands.status.verbose=True
  M file1
  ? file1.orig
  # The repository is in an unfinished *chainify* state.
  
  # Unresolved merge conflicts:
  # 
  #     file1
  # 
  # To mark files as resolved:  hg resolve --mark FILE
  
  # To continue:    hg chainify --continue
  # To abort:       hg chainify --abort
  
  $ echo foo3 > file1
  $ hg resolve --mark file1
  (no more unresolved files)
  continue: hg chainify --continue
  $ hg chainify --continue
  rebasing a858b338b3e9 onto 83c722183a8e
  rebasing 2:a858b338b3e9 "add conflicting file"
  saved backup bundle to $TESTTMP/* (glob)
  done chainifying
  $ hg log --graph --template '{rev} {files}'
  o  3 file1
  |
  o  2 file2
  |
  o  1 file1
  |
  @  0 base.txt