--- a/lib/python/mozilla_buildtools/test/test_util_hg.py
+++ b/lib/python/mozilla_buildtools/test/test_util_hg.py
@@ -1049,31 +1049,16 @@ class TestHg(unittest.TestCase):
         mercurial(self.repodir, self.wc, shareBase=shareBase, mirrors=[mirror])
 
         # Since we used the mirror, we should be missing a commit
         self.assertNotEquals(getRevisions(self.repodir), getRevisions(self.wc))
         self.assertNotEquals(
             getRevisions(self.repodir), getRevisions(sharerepo))
         self.assertEquals(getRevisions(mirror), getRevisions(self.wc))
 
-    def testMercurialByRevWithShareAndMirror(self):
-        # First create the mirror
-        mirror = os.path.join(self.tmpdir, 'repo2')
-        clone(self.repodir, mirror)
-
-        shareBase = os.path.join(self.tmpdir, 'share')
-        sharerepo = os.path.join(shareBase, self.repodir.lstrip("/"))
-        os.mkdir(shareBase)
-        mercurial(self.repodir, self.wc, shareBase=shareBase, mirrors=[
-                  mirror], clone_by_rev=True, revision=self.revisions[-1])
-
-        # We should only have the one revision
-        self.assertEquals(getRevisions(sharerepo), self.revisions[-1:])
-        self.assertEquals(getRevisions(self.wc), self.revisions[-1:])
-
     def testMercurialSkipPull(self):
         # Clone once into our working copy
         mercurial(self.repodir, self.wc)
 
         # The second clone should avoid calling pull()
         with patch('util.hg.pull') as patched_pull:
             mercurial(self.repodir, self.wc, revision=self.revisions[-1])
             self.assertEquals(patched_pull.call_count, 0)

--- a/lib/python/util/hg.py
+++ b/lib/python/util/hg.py
@@ -477,16 +477,51 @@ def mercurial(repo, dest, branch=None, r
     dest = os.path.abspath(dest)
     if shareBase is DefaultShareBase:
         shareBase = os.environ.get("HG_SHARE_BASE_DIR", None)
 
     log.info("Reporting hg version in use")
     cmd = ['hg', '-q', 'version']
     run_cmd(cmd, cwd='.')
 
+    # New code path: if a share base directory is specified, use the
+    # robustcheckout extension/command for doing everything.
+    if shareBase and update_dest and (revision or branch):
+        robustcheckout_ext = get_hg_ext('robustcheckout.py')
+        cmd = [
+            'hg',
+            '--config', 'extensions.robustcheckout=%s' % robustcheckout_ext,
+            'robustcheckout', repo, dest,
+            '--sharebase', shareBase,
+        ]
+        if revision:
+            cmd.extend(['--revision', revision])
+        elif branch:
+            cmd.extend(['--branch', branch])
+
+        if autoPurge:
+            cmd.append('--purge')
+
+        # We only take the first mirror because that's all robustcheckout can
+        # take.
+        if mirrors:
+            cmd.extend(['--upstream', mirrors[0]])
+
+        try:
+            out = get_output(cmd, include_stderr=True)
+            for line in out.splitlines():
+                m = re.match('^updated to ([a-f0-9]{40})$', line)
+                if m:
+                    return m.group(1)
+
+            raise HgUtilError('unable to find updated to revision')
+        except subprocess.CalledProcessError as e:
+            log.info('OUTPUT: %s' % e.output)
+            raise
+
     if shareBase:
         # Check that 'hg share' works
         try:
             log.info("Checking if share extension works")
             output = get_hg_output(['help', 'share'], dont_log=True)
             if 'no commands defined' in output:
                 # Share extension is enabled, but not functional
                 log.info("Disabling sharing since share extension doesn't seem to work (1)")