ui: move request exit handlers to global state

Since the ui objects can be created with the 'load' class method, it
is possible to lose the exit handlers information from the old ui instance. For
example, running 'test-bad-extension.t' leads to this situation where chg
creates a new ui instance which does not copy the exit handlers from the
earlier ui instance. For exit handlers, which are special cases anyways, it
probably makes sense to have a global state of the handlers. This would ensure
that the exit handlers registered once are definitely executed at the end of
the request.

Test Plan:
Ran all the tests without '--chg' option. This also fixes the
'test-bad-extension.t' with the '--chg' option.

Differential Revision: https://phab.mercurial-scm.org/D1166

mercurial/ui.py

@@ -183,6 +183,9 b' def _catchterm(*args):'
 # retrieving configuration value.
 _unset = object()
 
+# _reqexithandlers: callbacks run at the end of a request
+_reqexithandlers = []
+
 class ui(object):
     def __init__(self, src=None):
         """Create a fresh new ui object if no src given
@@ -193,8 +196,6 b' class ui(object):'
         """
         # _buffers: used for temporary capture of output
         self._buffers = []
-        # _exithandlers: callbacks run at the end of a request
-        self._exithandlers = []
         # 3-tuple describing how each buffer in the stack behaves.
         # Values are (capture stderr, capture subprocesses, apply labels).
         self._bufferstates = []
@@ -220,7 +221,6 b' class ui(object):'
         self._styles = {}
 
         if src:
-            self._exithandlers = src._exithandlers
             self.fout = src.fout
             self.ferr = src.ferr
             self.fin = src.fin
@@ -1098,6 +1098,10 b' class ui(object):'
 
         return True
 
+    @property
+    def _exithandlers(self):
+        return _reqexithandlers
+
     def atexit(self, func, *args, **kwargs):
         '''register a function to run after dispatching a request