Backed out changeset 9b8f326731ac Unfortunately, disabling the rust extensions means newer Mercurial versions no longer have the persistent-nodemap feature enabled. This means a Mercurial 5.8.1 on RPM-based Linux distributions will no longer be able to read repositories created by a Mercurial 5.8 on RPM-based Linux distributions. This violates the compatibility rules (see https://www.mercurial-scm.org/wiki/CompatibilityRules ). For this reason, I have to backout this change. I'll try to find another solution to the 'hg purge' crashes. Differential Revision: https://phab.mercurial-scm.org/D10918

copies: Keep changelog sidedata file open during copy tracing Instead of having a callback that opens and closes that file many times, a add and use a context manager method on the `revlog` class that keeps files open for its duration. Differential Revision: https://phab.mercurial-scm.org/D10888