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/revset.py	Fri Jun 18 14:17:43 2021 -0700
+++ b/mercurial/revset.py	Fri Jun 18 15:48:51 2021 -0700
@@ -1872,9 +1872,10 @@
             revs = [repo.lookup(rev) for rev in revs]
         other = hg.peer(repo, {}, dest)
         try:
-            repo.ui.pushbuffer()
-            outgoing = discovery.findcommonoutgoing(repo, other, onlyheads=revs)
-            repo.ui.popbuffer()
+            with repo.ui.silent():
+                outgoing = discovery.findcommonoutgoing(
+                    repo, other, onlyheads=revs
+                )
         finally:
             other.close()
         missing.update(outgoing.missing)