[PATCH 2 of 7 shelve-ext v5] shelve: add a function to check whether obs-based shelve is enabled

[Kostia Balytskyi]

# HG changeset patch
# User Kostia Balytskyi <ikostia at fb.com>
# Date 1490790691 25200
#      Wed Mar 29 05:31:31 2017 -0700
# Node ID 0aa864184c9d78c11d18980cf0faa10828445ff5
# Parent  b5d6e501621808f330e46295d09526a5d1e9064a
shelve: add a function to check whether obs-based shelve is enabled

A central place to check whether code should use traditional or
obsolescense-based shelve behavior.

diff --git a/hgext/shelve.py b/hgext/shelve.py
--- a/hgext/shelve.py
+++ b/hgext/shelve.py
@@ -41,6 +41,7 @@ from mercurial import (
     mdiff,
     merge,
     node as nodemod,
+    obsolete,
     patch,
     phases,
     repair,
@@ -72,6 +73,18 @@ patchextension = 'patch'
 # generic user for all shelve operations
 shelveuser = 'shelve at localhost'
 
+def isobsshelve(repo, ui):
+    """Check whether obsolescense-based shelve is enabled"""
+    obsshelve = ui.configbool('experimental', 'obsshelve')
+    if not obsshelve:
+        return False
+    if not obsolete.isenabled(repo, obsolete.createmarkersopt):
+        w = _('ignoring experimental.obsshelve because createmarkers option '
+              'is disabled')
+        ui.warn(w)
+        return False
+    return True
+
 class shelvedfile(object):
     """Helper for the file storing a single shelve