context: correct metadataonlyctx's parameter It's "originalctx", not "path" as Yuya pointed in [1]. [1]: www.mercurial-scm.org/pipermail/mercurial-devel/2016-December/091508.html

registrar: raise a programming error on duplicated registering Previous, registering different object with the same name would silently overwrite the first value with the second one. We now detect the situation and raise an error. No extension in test or core had the issues.