unionrepo: read-only operations on a union of two localrepos unionrepo is just like bundlerepo without bundles. The implementation is very similar to bundlerepo, but I don't see any obvious way to generalize it. Some most obvious use cases for this would be log and diff across local repos, as a kind of preview of pulls, for instance: $ hg -R union:repo1+repo2 heads $ hg -R union:repo1+repo2 log -r REPO1REV -r REPO2REV $ hg -R union:repo1+repo2 log -r '::REPO1REV-::REPO2REV' $ hg -R union:repo1+repo2 log -r 'ancestor(REPO1REV,REPO2REV)' $ hg -R union:repo1+repo2 diff -r REPO1REV -r REPO2REV This is going to be used in RhodeCode, and Bitbucket already uses something similar. Having a core implementation would be beneficial.