ui: add a context manager for silencing the ui (pushbuffer+popbuffer) We often silence the ui by calling `ui.pushbuffer()` followed (a later in the code) by `ui.popbuffer()`. These places can be identified by the fact that they ignore the output returned from `ui.popbuffer()`. Let's create a context manager for these cases, to avoid repetition, and to avoid accidentally leaving the ui silent on exceptions. I deliberately called the new function `silent()` instead of `buffered()`, because it's just an implementation detail that it uses `pushbuffer()` and `popbuffer()`. We could later optimize it to not buffer the output. Differential Revision: https://phab.mercurial-scm.org/D10884

--- a/mercurial/ui.py	Fri Jun 18 14:17:43 2021 -0700
+++ b/mercurial/ui.py	Fri Jun 18 15:48:51 2021 -0700
@@ -1146,6 +1146,14 @@
         self._fmsg = f
         self._fmsgout, self._fmsgerr = _selectmsgdests(self)
 
+    @contextlib.contextmanager
+    def silent(self, error=False, subproc=False, labeled=False):
+        self.pushbuffer(error=error, subproc=subproc, labeled=labeled)
+        try:
+            yield
+        finally:
+            self.popbuffer()
+
     def pushbuffer(self, error=False, subproc=False, labeled=False):
         """install a buffer to capture standard output of the ui object