repository: define new interface for running commands Today, the peer interface exposes methods for each command that can be executed. In addition, there is an iterbatch() API that allows commands to be issued in batches and provides an iterator over the results. This is a glorified wrapper around the "batch" wire command. Wire protocol version 2 supports nicer things (such as batching any command and out-of-order replies). It will require a more flexible API for executing commands. This commit introduces a new peer interface for making command requests. In the new world, you can't simply call a method on the peer to execute a command: you need to obtain an object to be used for executing commands. That object can be used to issue a single command or it can batch multiple requests. In the case of full duplex peers, the command may even be sent out over the wire immediately. There are no per-command methods. Instead, there is a generic method to call a command. The implementation can then perform domain specific processing for specific commands. This includes passing data via a specially named argument. Arguments are also passed as a dictionary instead of using **kwargs. While **kwargs is nicer to use, we've historically gotten into trouble using it because there will inevitably be a conflict between the name of an argument to a wire protocol command and an argument we want to pass into a function. Instead of a command returning a value, it returns a future which will resolve to a value. This opens the door for out-of-order response handling and concurrent response handling in the version 2 protocol. Differential Revision: https://phab.mercurial-scm.org/D3267

pycompat: export a handle on concurrent.futures On Python 3, we use the built-in version in the standard library. Else we use our vendored backport. Differential Revision: https://phab.mercurial-scm.org/D3266

setup: add packages for concurrent.futures We conceivably don't need to distribute this package on Python 3 since we will use the version in the standard library. However, we want installs to be usable of multiple versions of Python. So it is best to always have it. Differential Revision: https://phab.mercurial-scm.org/D3265