chgserver: invalidate the server if extensions fail to load

Previously, if extensions fail to load, chg server will just keep working
without those extensions. It will print a warning message but only if a new
server starts.

This patch invalidates the server if any extension failed to load, but still
serve the client (hopefully just) once. It will help chg pass some test cases
of test-bad-extension.t.

hgext/chgserver.py

@@ -451,7 +451,10 b' class chgcmdserver(commandserver.server)'
         if newhash.mtimehash != self.hashstate.mtimehash:
             addr = _hashaddress(self.baseaddress, self.hashstate.confighash)
             insts.append('unlink %s' % addr)
-            insts.append('reconnect')
+            # mtimehash is empty if one or more extensions fail to load.
+            # to be compatible with hg, still serve the client this time.
+            if self.hashstate.mtimehash:
+                insts.append('reconnect')
         if newhash.confighash != self.hashstate.confighash:
             addr = _hashaddress(self.baseaddress, newhash.confighash)
             insts.append('redirect %s' % addr)
@@ -636,6 +639,7 b' class AutoExitMixIn: # use old-style to'
 class chgunixservice(commandserver.unixservice):
     def init(self):
         self._inithashstate()
+        self._checkextensions()
         class cls(AutoExitMixIn, SocketServer.ForkingMixIn,
                   SocketServer.UnixStreamServer):
             ui = self.ui
@@ -656,6 +660,15 b' class chgunixservice(commandserver.unixs'
         self.hashstate = hashstate.fromui(self.ui)
         self.address = _hashaddress(self.address, self.hashstate.confighash)
 
+    def _checkextensions(self):
+        if not self.hashstate:
+            return
+        if extensions.notloaded():
+            # one or more extensions failed to load. mtimehash becomes
+            # meaningless because we do not know the paths of those extensions.
+            # set mtimehash to an illegal hash value to invalidate the server.
+            self.hashstate.mtimehash = ''
+
     def _createsymlink(self):
         if self.baseaddress == self.address:
             return