changegroup: don't try to build changelog chunks if not required When we extend a narrow clone without ellipsis, we don't download changelog information because that's already present with the client. However we still try to build that chunk stream. Building that chunk stream involves calling a lookup function and store.emitrevisions() API. The lookup function is called len(cl) number of times. On large repositories, where len(cl) is in millions, calling that lookup function is not a good idea. Also it's not required to use the store.emitrevisons() API because we already have nodes present which we can use. This patch short-circuits state building logic if we are processing a non-ellipsis case and changelog is not required. This saves up ~20 seconds on our internal repo for a single extend call. Differential Revision: https://phab.mercurial-scm.org/D5733

revlog: make sure we never use sparserevlog without general delta (issue6056) We are getting user report where the delta code tries to use `sparse-revlog` logic on repository where `generaldelta` is disabled. This can't work so we ensure the two booleans have a consistent value. Creating this kind of repository is not expected to be possible the current bug report point at a clonebundle related bug that is still to be properly isolated (Yuya Nishihara seems to a have done it). Corrupting a repository to reproduce the issue is possible. A test using this method is included in this fix.

sparserevlog: document the config option This was overlooked when this graduated from experimental.