localrepo: cache types for filtered repos (issue5043) Python introduces a reference cycle on dynamically created types via __mro__, making them very easy to leak. See https://bugs.python.org/issue17950. Previously, repo.filtered() created a type on every invocation. Long-running processes (like `hg convert`) could call this function thousands of times, leading to a steady memory leak. Since we're Unable to stop the leak because this is a bug in Python, the next best thing is to contain it. This patch adds a cache of of the dynamically generated repoview/filter types on the localrepo object. Since we only generate each type once, we cap the amount of memory that can leak to something reasonable. After this change, `hg convert` no longer leaks memory on every revision. The process will likely grow memory usage over time due to e.g. larger manifests. But there are no leaks.

--- a/mercurial/statichttprepo.py	Tue Jul 11 02:10:04 2017 +0900
+++ b/mercurial/statichttprepo.py	Sat Jul 01 20:51:19 2017 -0700
@@ -165,6 +165,8 @@
         self.encodepats = None
         self.decodepats = None
         self._transref = None
+        # Cache of types representing filtered repos.
+        self._filteredrepotypes = {}
 
     def _restrictcapabilities(self, caps):
         caps = super(statichttprepository, self)._restrictcapabilities(caps)