[PATCH evolve-ext] topic: centralize compatibility logic between hg versions into compat module

[FUJIWARA Katsunori]

# HG changeset patch
# User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
# Date 1505050914 -32400
#      Sun Sep 10 22:41:54 2017 +0900
# Node ID 3412cce8dbb22a937e72939a5d726c0949715983
# Parent  23c9600607e7ea3c6d95cddc5ad134cab4f7d7fe
# Available At https://foozy@bitbucket.org/foozy/hgext-evolve
#              hg pull https://foozy@bitbucket.org/foozy/hgext-evolve -r 3412cce8dbb2
# EXP-Topic topic-hg-version-portability
topic: centralize compatibility logic between hg versions into compat module

This patch can delay loading obsutil and obsolete modules until they
are actually used at "hg topics" or so, if demandimport of Mercurial
is enabled.

diff --git a/hgext3rd/topic/__init__.py b/hgext3rd/topic/__init__.py
--- a/hgext3rd/topic/__init__.py
+++ b/hgext3rd/topic/__init__.py
@@ -79,6 +79,7 @@ from mercurial import (
 )
 
 from . import (
+    compat,
     constants,
     revset as topicrevset,
     destination,
@@ -727,16 +728,6 @@ def _showlasttouched(repo, fm, opts):
             fm.plain('\n')
     fm.end()
 
-getmarkers = None
-try:
-    from mercurial import obsutil
-    getmarkers = getattr(obsutil, 'getmarkers', None)
-except ImportError:
-    pass
-
-if getmarkers is None:
-    getmarkers = obsolete.getmarkers
-
 def _getlasttouched(repo, topics):
     """
     Calculates the last time a topic was used. Returns a dictionary of seconds
@@ -758,7 +749,7 @@ def _getlasttouched(repo, topics):
                 maxtime = rt
             # looking on the markers also to get more information and accurate
             # last touch time.
-            obsmarkers = getmarkers(repo, [repo[revs].node()])
+            obsmarkers = compat.getmarkers(repo, [repo[revs].node()])
             for marker in obsmarkers:
                 rt = marker.date()
                 if rt[0] > maxtime[0]:
diff --git a/hgext3rd/topic/compat.py b/hgext3rd/topic/compat.py
new file mode 100644
--- /dev/null
+++ b/hgext3rd/topic/compat.py
@@ -0,0 +1,24 @@
+# Copyright 2017 FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""
+Compatibility module
+"""
+from __future__ import absolute_import
+
+from mercurial import obsolete
+
+getmarkers = None
+successorssets = None
+try:
+    from mercurial import obsutil
+    getmarkers = getattr(obsutil, 'getmarkers', None)
+    successorssets = getattr(obsutil, 'successorssets', None)
+except ImportError:
+    pass
+
+if getmarkers is None:
+    getmarkers = obsolete.getmarkers
+if successorssets is None:
+    successorssets = obsolete.successorssets
diff --git a/hgext3rd/topic/evolvebits.py b/hgext3rd/topic/evolvebits.py
--- a/hgext3rd/topic/evolvebits.py
+++ b/hgext3rd/topic/evolvebits.py
@@ -1,15 +1,6 @@
 import collections
-from mercurial import obsolete
 
-successorssets = None
-try:
-    from mercurial import obsutil
-    successorssets = getattr(obsutil, 'successorssets', None)
-except ImportError:
-    pass
-
-if successorssets is None:
-    successorssets = obsolete.successorssets
+from . import compat
 
 # Copied from evolve 081605c2e9b6
 
@@ -82,14 +73,14 @@ def _singlesuccessor(repo, p):
         return p.rev()
     obs = repo[p]
     ui = repo.ui
-    newer = successorssets(repo, obs.node())
+    newer = compat.successorssets(repo, obs.node())
     # search of a parent which is not killed
     while not newer:
         ui.debug("stabilize target %s is plain dead,"
                  " trying to stabilize on its parent\n" %
                  obs)
         obs = obs.parents()[0]
-        newer = successorssets(repo, obs.node())
+        newer = compat.successorssets(repo, obs.node())
     if len(newer) > 1 or len(newer[0]) > 1:
         raise MultipleSuccessorsError(newer)