wireprotov2: define and implement "filesdata" command Previously, the only way to access file revision data was the "filedata" command. This command is useful to have. But, it only allowed resolving revision data for a single file. This meant that clients needed to send 1 command for each tracked path they were seeking data on. Furthermore, those commands would need to enumerate the exact file nodes they wanted data for. This approach meant that clients were sending a lot of data to remotes in order to request file data. e.g. if there were 1M file revisions, we'd need at least 20,000,000 bytes just to encode file nodes! Many clients on the internet don't have that kind of upload capacity. In order to limit the amount of data that clients must send, we'll need more efficient ways to request repository data. This commit defines and implements a new "filesdata" command. This command allows the retrieval of data for multiple files by specifying changeset revisions and optional file patterns. The command figures out what file revisions are "relevant" and sends them in bulk. The logic around choosing which file revisions to send in the case of haveparents not being set is overly simple and will over-send files. We will need more smarts here eventually. (Specifically, the client will need to tell the server which revisions it knows about.) This work is deferred until a later time. Differential Revision: https://phab.mercurial-scm.org/D4981

wireprotov2: extract file object emission to own function An upcoming commit will introduce another caller. Differential Revision: https://phab.mercurial-scm.org/D4980

wireprotov2: change how revisions are specified to changesetdata Right now, we have a handful of arguments for specifying the revisions whose data should be returned. Defining how all these arguments interact when various combinations are present is difficult. This commit establishes a new, generic mechanism for specifying revisions. Instead of a hodgepodge of arguments defining things, we have a list of dicts that specify revision selectors. The final set of revisions is a union of all these selectors. We implement support for specifying revisions based on: * An explicit list of changeset revisions * An explicit list of changeset revisions plus ancestry depth * A DAG range between changeset roots and heads If you squint hard enough, this problem has already been solved by revsets. But I'm reluctant to expose revsets to the wire protocol because that would require servers to implement a revset parser. Plus there are security and performance implications: the set of revision selectors needs to be narrowly and specifically tailored for what is appropriate to be executing on a server. Perhaps there would be a way for us to express the "parse tree" of a revset query, for example. I'm not sure. We can explore this space another time. For now, the new mechanism should bring sufficient flexibility while remaining relatively simple. The selector "types" are prefixed with "changeset" because I plan to add manifest and file-flavored selectors as well. This will enable us to e.g. select file revisions based on a range of changeset revisions. Differential Revision: https://phab.mercurial-scm.org/D4979

wireprotov2: stop sending phase updates for base revisions This feature is broken and doesn't work properly in all scenarios. e.g. if we have the following DAGs: client server D draft C draft C draft B draft B public A public A public The current code would only send the phase data for C. The client wouldn't see that B moved from draft to public. This feature will be restored in a future commit. For now, it is making refactoring of how revisions are specified in the wire protocol a bit difficult... Differential Revision: https://phab.mercurial-scm.org/D4978

debugcommands: support wrapping long lines If a line within a block is indented more than the line that came before, we automatically concatenate it with the previous line. This allows us to pretty format data. This will make tests easier to read. At some point we may just want to evaluate entire blocks as Python code or something, as even with this change, things aren't perfect, as we can't e.g. have formatting like: foo eval:[ True ] But this is strictly better than before, where we couldn't wrap long lines. Differential Revision: https://phab.mercurial-scm.org/D4977

exchangev2: honor server advertised manifestdata recommended batch size Let's plug the client up to the server-advertised recommended batch size for manifestdata requests. Differential Revision: https://phab.mercurial-scm.org/D4976

wireprotov2: advertise recommended batch size for requests Currently, exchangev2 hardcodes the batch size for how many revisions to fetch per command request. A single value is not appropriate for every repository because some repositories may have a drastically different "shape" from other repositories. e.g. a repo with lots of small files may benefit from larger batch sizes than a repo with lots of large files. And depending on caching used by the server, the server may wish to control the number of commands (to e.g. mitigate overhead of following content redirects). This commit teaches wireprotov2 commands to declare extra metadata which is advertised as part of the command descriptor. The manifestdata command has been taught to advertise a recommended batch size for requests. Differential Revision: https://phab.mercurial-scm.org/D4975