--- a/hgext/share.py	Wed Feb 15 11:49:12 2017 -0800
+++ b/hgext/share.py	Mon Feb 13 14:05:24 2017 +0100
@@ -65,10 +65,14 @@
 
 @command('share',
     [('U', 'noupdate', None, _('do not create a working directory')),
-     ('B', 'bookmarks', None, _('also share bookmarks'))],
+     ('B', 'bookmarks', None, _('also share bookmarks')),
+     ('', 'relative', None, _('point to source using a relative path '
+                              '(EXPERIMENTAL)')),
+    ],
     _('[-U] [-B] SOURCE [DEST]'),
     norepo=True)
-def share(ui, source, dest=None, noupdate=False, bookmarks=False):
+def share(ui, source, dest=None, noupdate=False, bookmarks=False,
+          relative=False):
     """create a new shared repository
 
     Initialize a new repository and working directory that shares its
@@ -87,7 +91,7 @@
     """
 
     return hg.share(ui, source, dest=dest, update=not noupdate,
-                    bookmarks=bookmarks)
+                    bookmarks=bookmarks, relative=relative)
 
 @command('unshare', [], '')
 def unshare(ui, repo):

--- a/mercurial/help/internals/requirements.txt	Wed Feb 15 11:49:12 2017 -0800
+++ b/mercurial/help/internals/requirements.txt	Mon Feb 13 14:05:24 2017 +0100
@@ -55,6 +55,17 @@
 
 The requirement was added in Mercurial 1.3 (released July 2009).
 
+relshared
+=========
+
+Derivative of ``shared``; the location of the store is relative to the
+store of this repository.
+
+This requirement is set when a repository is created via :hg:`share`
+using the ``--relative`` option.
+
+The requirement was added in Mercurial 4.2 (released May 2017).
+
 dotencode
 =========
 

--- a/mercurial/hg.py	Wed Feb 15 11:49:12 2017 -0800
+++ b/mercurial/hg.py	Mon Feb 13 14:05:24 2017 +0100
@@ -195,7 +195,8 @@
         return ''
     return os.path.basename(os.path.normpath(path))
 
-def share(ui, source, dest=None, update=True, bookmarks=True, defaultpath=None):
+def share(ui, source, dest=None, update=True, bookmarks=True, defaultpath=None,
+          relative=False):
     '''create a shared repository'''
 
     if not islocal(source):
@@ -235,7 +236,16 @@
         if inst.errno != errno.ENOENT:
             raise
 
-    requirements += 'shared\n'
+    if relative:
+        try:
+            sharedpath = os.path.relpath(sharedpath, destvfs.base)
+            requirements += 'relshared\n'
+        except IOError as e:
+            raise error.Abort(_('cannot calculate relative path'),
+                              hint=str(e))
+    else:
+        requirements += 'shared\n'
+
     destvfs.write('requires', requirements)
     destvfs.write('sharedpath', sharedpath)
 

--- a/mercurial/localrepo.py	Wed Feb 15 11:49:12 2017 -0800
+++ b/mercurial/localrepo.py	Mon Feb 13 14:05:24 2017 +0100
@@ -244,7 +244,7 @@
     supportedformats = set(('revlogv1', 'generaldelta', 'treemanifest',
                             'manifestv2'))
     _basesupported = supportedformats | set(('store', 'fncache', 'shared',
-                                             'dotencode'))
+                                             'relshared', 'dotencode'))
     openerreqs = set(('revlogv1', 'generaldelta', 'treemanifest', 'manifestv2'))
     filtername = None
 
@@ -325,8 +325,11 @@
 
         self.sharedpath = self.path
         try:
-            vfs = scmutil.vfs(self.vfs.read("sharedpath").rstrip('\n'),
-                              realpath=True)
+            sharedpath = self.vfs.read("sharedpath").rstrip('\n')
+            if 'relshared' in self.requirements:
+                sharedpath = self.vfs.join(sharedpath)
+            vfs = scmutil.vfs(sharedpath, realpath=True)
+
             s = vfs.base
             if not vfs.exists():
                 raise error.RepoError(

--- a/tests/test-share.t	Wed Feb 15 11:49:12 2017 -0800
+++ b/tests/test-share.t	Mon Feb 13 14:05:24 2017 +0100
@@ -358,6 +358,41 @@
      bm4                       5:92793bfc8cad
   $ cd ..
 
+test shared clones using relative paths work
+
+  $ mkdir thisdir
+  $ hg init thisdir/orig
+  $ hg share -U thisdir/orig thisdir/abs
+  $ hg share -U --relative thisdir/abs thisdir/rel
+  $ cat thisdir/rel/.hg/sharedpath
+  ../../orig/.hg (no-eol)
+  $ grep shared thisdir/*/.hg/requires
+  thisdir/abs/.hg/requires:shared
+  thisdir/rel/.hg/requires:shared
+  thisdir/rel/.hg/requires:relshared
+
+test that relative shared paths aren't relative to $PWD
+
+  $ cd thisdir
+  $ hg -R rel root
+  $TESTTMP/thisdir/rel
+  $ cd ..
+
+now test that relative paths really are relative, survive across
+renames and changes of PWD
+
+  $ hg -R thisdir/abs root
+  $TESTTMP/thisdir/abs
+  $ hg -R thisdir/rel root
+  $TESTTMP/thisdir/rel
+  $ mv thisdir thatdir
+  $ hg -R thatdir/abs root
+  abort: .hg/sharedpath points to nonexistent directory $TESTTMP/thisdir/orig/.hg!
+  [255]
+  $ hg -R thatdir/rel root
+  $TESTTMP/thatdir/rel
+  $ rm -r thatdir
+
 Explicitly kill daemons to let the test exit on Windows
 
   $ killdaemons.py