bundle2-push: provide transaction to reply unbundler This patch series is intended to allow bundle2 push reply part handlers to make changes to the local repository; it has been developed in parallel with an extension that allows the server to rebase incoming changesets while applying them. This diff adds an experimental config option "bundle2.pushback" which provides a transaction to the reply unbundler during a push operation. This behavior is opt-in because of potential security issues: the response can contain any part type that has a handler defined, allowing the server to make arbitrary changes to the local repository.

bundle2.processbundle: let callers request default behavior This patch series is intended to allow bundle2 push reply part handlers to make changes to the local repository; it has been developed in parallel with an extension that allows the server to rebase incoming changesets while applying them. The default transaction getter for processbundle is a private function that raises an exception; this diff lets calling code pass None as the transaction getter to explicitly request this default behavior. The next diff will check a config option to determine whether to provide a transaction to the reply bundle processor. If one shouldn't be provided, the code needs a way to specify that the default behavior should be used.

push: elevate phase transaction to cover entire operation This patch series is intended to allow bundle2 push reply part handlers to make changes to the local repository; it has been developed in parallel with an extension that allows the server to rebase incoming changesets while applying them. Most pushes already open a transaction in order to sync phase information. This diff replaces that transaction with one that spans the entire push operation. This transaction will be used in a later patch to guard repository changes made during the reply handler.

pull: extract transaction logic into separate object This patch series is intended to allow bundle2 push reply part handlers to make changes to the local repository; it has been developed in parallel with an extension that allows the server to rebase incoming changesets while applying them. Aside from the transaction logic, the pulloperation class is used primarily as a logic-free data structure for storing state information. This diff extracts the transaction logic into its own class that can be shared with push operations.

record: don't honor format-changing diffopts (issue4459) record does support the whitespace options, so honor those. In upcoming patches we'll replace all the other uses.

patch.difffeatureopts: add a feature for format-changing diffopts Typically, callers that are interested in this set are also interested in the others. We still add it as a first-class flag for convenience.

patch.difffeatureopts: add a feature for whitespace diffopts These aren't exactly format-breaking features -- just ones for which patches applied to a repo will produce incorrect commits, In any case, some commands like record and annotate only care about this feature.

patch.difffeatureopts: add a feature for diff.git This deserves to be its own feature -- indeed, this is often the only feature several commands care about.