transaction: make names a private attribute This is used to report the transaction name in __repr__. It is very obviously an implementation detail and doesn't need to be exposed as part of the public interface. So mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4633

transaction: make map a private attribute This is used to track which files are modified. It is an implementation detail of current transactions and doesn't need to be exposed to the public interface. So mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4632

transaction: make report a private attribute This is a callable used for logging. It isn't used outside the transaction code. It doesn't need to be part of the public interface. Let's mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4631

transaction: make opener a private attribute The VFS instance is an implementation detail of the transaction and doesn't belong as part of the public interface. So mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4630

transaction: make after a private attribute This is another callable that is passed in at __init__ time. It doesn't need to be part of the public interface. Differential Revision: https://phab.mercurial-scm.org/D4629

transaction: make checkambigfiles a private attribute This holds instance state that is passed in at __init__ time. It doesn't need to be exposed as part of the public interface. Differential Revision: https://phab.mercurial-scm.org/D4628

transaction: make validator a private attribute This is similar to releasefn. It holds state that doesn't need to be exposed as part of the public interface. Differential Revision: https://phab.mercurial-scm.org/D4627

transaction: make releasefn a private attribute This is a handle on a callable that is called when the journal is closed. The value is specified at __init__ time. It doesn't need to be exposed on the public interface. So mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4626

transaction: make file a private attribute This holds a file handle for the journal file. This file handle should not be touched outside the journal class and doesn't belong on the public interface. Differential Revision: https://phab.mercurial-scm.org/D4625

transaction: make journal a private attribute This attribute tracks the name of the journal file. It is an implementation detail of the current transaction and therefore shouldn't be exposed as part of the interface. Let's mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4624

transaction: make undoname a private attribute This attribute tracks the file pattern to use for undo files. It is an implementation detail of the current transaction semantics and doesn't need to be part of the future transaction interface. So mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4623

transaction: make count and usages private attributes I want to formalize the interface for transactions. As part of doing that, let's take the opportunity to make some attributes non-public. "count" and "usages" track how many times the transaction has been opened/nested/closed/released. This is internal state and doesn't need to be part of the public API. Differential Revision: https://phab.mercurial-scm.org/D4622

narrow: don't send the changelog information when widening without ellipses When we widen anon-ellipses narrow copy, the server sends the changelog information of all the changesets. The code was copied from ellipses case and in ellipses cases, it's required to send the new changelog data. But in non-ellipses cases, we don't need to send the changelog data as we will have all the changesets locally. Before this patch, there was a overhead of ~8-10 mins on each widening call because of all the changelog information being pulled and being applied. After this patch, we no more pull the changelog information. So this patch can save ~5 mins on Mozilla repo on each widening and more on repos which have more changesets. When we apply an empty changelog from changegroup, there is a devel-warn. This patch kind of hacks to silence that devel-warn. Differential Revision: https://phab.mercurial-scm.org/D4639

changegroup: add functionality to skip adding changelog data to changegroup In narrow extension, when we have a non-ellipses narrow working copy and we extend it, we pull all the changelog data again and the client tries to reapply all that changelog data. While downloading millions of changeset data is still not very expensive but applying them on the client side is very expensive and takes ~10 minutes. These 10 minutes are added to every `hg tracked --addinclude <>` call and extending a narrow copy becomes very slow. This patch adds a new changelog argument to cgpacker.generate() fn. If the changelog argument is set to False, we won't yield the changelog data. We still have to iterate over the deltas returned by _generatechangelog() because that's a generator and builds the data for clstate variable which is required for calculating manifests and filelogs. Differential Revision: https://phab.mercurial-scm.org/D4638

tests: add debug output in test-narrow-widen-no-ellipsis.t This will help us in understanding the upcoming patches better. Differential Revision: https://phab.mercurial-scm.org/D4637

changegroup: improve the devel-warn to specify changelog was empty Right now, the develwarn says "applied empty changegroup" which is not correct because we can send a changegroup without changelog with just manifest and filelogs and it will still say the same. Let's fix this to say that we are applying empty changelog from changegroup. In future patches I am will be adding functionality to send a changegroup from the server without an empty changelog. Differential Revision: https://phab.mercurial-scm.org/D4636

zsh_completion: add -b/--branch and -B/--bookmark(s) flags properly _hg_branch_bmark_opts used to add these two flags, but had the same descriptions for the flags regardless of what command took them and didn't allow specifying flags more than once (no '*' at the start). Even more importantly, it assumed that -B was always expecting an argument (i.e. --bookmark=foo), but in case of incoming and outgoing it's not so (--bookmarks is self-sufficient). Differential Revision: https://phab.mercurial-scm.org/D4612

narrow: when writing treemanifests, skip inspecting directories outside narrow This provides significant speed benefits when narrow and treemanifests are in use, see the timing numbers below. Note that like previously, differences of <5% are considered noise. The below timing numbers are in the same style as previously (example: ee7ee0c516ca). 'before' is 9db85644, and does not include that example commit's improvements. diff --git: repo | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before ------+---+---+------------------------+-----------------------+------------ m-u | | | 1.327 s +- 0.051 s | 1.296 s +- 0.009 s | 97.7% m-u | | x | 1.310 s +- 0.020 s | 1.295 s +- 0.015 s | 98.9% m-u | x | | 1.295 s +- 0.018 s | 1.296 s +- 0.007 s | 100.1% m-u | x | x | 83.5 ms +- 0.8 ms | 84.1 ms +- 0.8 ms | 100.7% l-d-r | | | 205.1 ms +- 3.5 ms | 205.0 ms +- 3.8 ms | 100.0% l-d-r | | x | 194.2 ms +- 5.6 ms | 192.3 ms +- 4.3 ms | 99.0% l-d-r | x | | 99.1 ms +- 2.2 ms | 97.8 ms +- 0.9 ms | 98.7% l-d-r | x | x | 66.2 ms +- 1.0 ms | 67.2 ms +- 2.7 ms | 101.5% diff -c . --git: repo | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before ------+---+---+------------------------+-----------------------+------------ m-u | | | 233.9 ms +- 1.9 ms | 235.6 ms +- 5.1 ms | 100.7% m-u | | x | 151.4 ms +- 1.2 ms | 152.2 ms +- 2.0 ms | 100.5% m-u | x | | 234.8 ms +- 2.7 ms | 235.0 ms +- 2.7 ms | 100.1% m-u | x | x | 127.8 ms +- 2.1 ms | 126.0 ms +- 1.1 ms | 98.6% l-d-r | | | 82.5 ms +- 1.6 ms | 82.3 ms +- 2.0 ms | 99.8% l-d-r | | x | 3.742 s +- 0.017 s | 3.819 s +- 0.208 s | 102.1% l-d-r | x | | 84.4 ms +- 1.5 ms | 83.2 ms +- 1.0 ms | 98.6% l-d-r | x | x | 751.2 ms +- 5.0 ms | 755.8 ms +- 12.9 ms | 100.6% rebase -r . --keep -d .^^: repo | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before ------+---+---+------------------------+-----------------------+------------ m-u | | | 5.519 s +- 0.038 s | 5.526 s +- 0.057 s | 100.1% m-u | | x | 5.588 s +- 0.048 s | 5.607 s +- 0.061 s | 100.3% m-u | x | | 5.520 s +- 0.044 s | 5.546 s +- 0.059 s | 100.5% m-u | x | x | 586.6 ms +- 12.8 ms | 554.9 ms +- 21.2 ms | 94.6% <-- l-d-r | | | 629.8 ms +- 5.5 ms | 627.4 ms +- 6.6 ms | 99.6% l-d-r | | x | 6.165 s +- 0.058 s | 6.255 s +- 0.303 s | 101.5% l-d-r | x | | 270.2 ms +- 2.3 ms | 271.4 ms +- 2.7 ms | 100.4% l-d-r | x | x | 4.700 s +- 0.025 s | 1.651 s +- 0.016 s | 35.1% <-- status --change . --copies: repo | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before ------+---+---+------------------------+-----------------------+------------ m-u | | | 215.4 ms +- 2.3 ms | 216.5 ms +- 4.2 ms | 100.5% m-u | | x | 132.9 ms +- 1.2 ms | 132.0 ms +- 1.4 ms | 99.3% m-u | x | | 217.0 ms +- 1.9 ms | 215.4 ms +- 1.9 ms | 99.3% m-u | x | x | 108.6 ms +- 1.0 ms | 108.2 ms +- 1.5 ms | 99.6% l-d-r | | | 80.0 ms +- 1.3 ms | 80.5 ms +- 1.1 ms | 100.6% l-d-r | | x | 3.916 s +- 0.187 s | 3.966 s +- 0.236 s | 101.3% l-d-r | x | | 84.4 ms +- 3.1 ms | 83.9 ms +- 1.1 ms | 99.4% l-d-r | x | x | 758.0 ms +- 8.2 ms | 753.5 ms +- 5.0 ms | 99.4% status --copies: repo | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before ------+---+---+------------------------+-----------------------+------------ m-u | | | 1.905 s +- 0.025 s | 1.910 s +- 0.044 s | 100.3% m-u | | x | 1.892 s +- 0.009 s | 1.895 s +- 0.012 s | 100.2% m-u | x | | 1.891 s +- 0.012 s | 1.902 s +- 0.018 s | 100.6% m-u | x | x | 93.3 ms +- 0.9 ms | 93.4 ms +- 0.8 ms | 100.1% l-d-r | | | 570.7 ms +- 7.8 ms | 571.9 ms +- 18.5 ms | 100.2% l-d-r | | x | 561.5 ms +- 5.2 ms | 562.9 ms +- 6.1 ms | 100.2% l-d-r | x | | 171.7 ms +- 2.6 ms | 171.9 ms +- 1.2 ms | 100.1% l-d-r | x | x | 142.7 ms +- 2.0 ms | 140.3 ms +- 1.0 ms | 98.3% update $rev^; ~/src/hg/hg{hg}/hg update $rev: repo | N | T | before (mean +- stdev) | after (mean +- stdev) | % of before ------+---+---+------------------------+-----------------------+------------ m-u | | | 3.126 s +- 0.016 s | 3.128 s +- 0.015 s | 100.1% m-u | | x | 3.014 s +- 0.068 s | 3.008 s +- 0.031 s | 99.8% m-u | x | | 3.143 s +- 0.037 s | 3.184 s +- 0.086 s | 101.3% m-u | x | x | 308.0 ms +- 1.8 ms | 308.1 ms +- 5.7 ms | 100.0% l-d-r | | | 430.8 ms +- 4.5 ms | 436.4 ms +- 8.7 ms | 101.3% l-d-r | | x | 9.676 s +- 0.127 s | 9.945 s +- 0.272 s | 102.8% l-d-r | x | | 254.2 ms +- 3.3 ms | 255.7 ms +- 3.1 ms | 100.6% l-d-r | x | x | 1.571 s +- 0.030 s | 1.555 s +- 0.014 s | 99.0% Differential Revision: https://phab.mercurial-scm.org/D4606

tests: fix a couple of drawdag.py references Differential Revision: https://phab.mercurial-scm.org/D4635

py3: fix kwargs handling in hgext/fastannotate.py Differential Revision: https://phab.mercurial-scm.org/D4588

narrow: use diffmatcher to send only new filelogs in non-ellipses widening Before this patch, when we widen a non-ellipses narrow clone, we downloads all the filelogs matching the resulting new matcher. This is same as the ellipses case but can be improved because, we don't pull new csets in non-ellipses cases, we can only download the new added files instead of downloading all the files which matches the new matcher. So, we only download files which matches the new matcher but does not matches the old matcher. There exists a match.differencematcher() which is used here. This will lead to significant amount of speedup in extending a non-ellipses narrow copy on large repos because we will download and process only the new required filelogs. The tests changes demonstrate that we are downloading now less files. Thanks to Augie for pointing that functionality of differencematcher exists in core. Differential Revision: https://phab.mercurial-scm.org/D4614

py3: add missing b'' prefixes in couple of test files These were missed in the earlier patch and caught by Yuya. # skip-blame because just b'' prefix Differential Revision: https://phab.mercurial-scm.org/D4613

run-tests: convert the remaining os.system() call to Unicode I wasn't able to hit this path in 543a788eea2d, but I have now when I accidentally left off `--local`.

py3: partially fix pager spawning on Windows Previously, spinning up the pager crashed because the command and environment was in bytes. (See also 543a788eea2d.) Now it aborts with an invalid handle: $ HGMODULEPOLICY=py py -3 ../hg --traceback --config extensions.evolve=! Traceback (most recent call last): File "c:\Users\Matt\projects\hg\mercurial\ui.py", line 967, in _write self.fout.write(''.join(msgs)) File "c:\Users\Matt\projects\hg\mercurial\windows.py", line 173, in write self.fp.write(s[start:end]) OSError: [WinError 6] The handle is invalid During handling of the above exception, another exception occurred: Traceback (most recent call last): File "c:\Users\Matt\projects\hg\mercurial\scmutil.py", line 164, in callcatch return func() File "c:\Users\Matt\projects\hg\mercurial\dispatch.py", line 350, in _runcatchfunc return _dispatch(req) File "c:\Users\Matt\projects\hg\mercurial\dispatch.py", line 930, in _dispatch return commands.help_(ui, 'shortlist') File "c:\Users\Matt\projects\hg\mercurial\commands.py", line 2930, in help_ ui.write(formatted) File "c:\Users\Matt\projects\hg\mercurial\ui.py", line 948, in write self._writenobuf(*args, **opts) File "c:\Users\Matt\projects\hg\mercurial\ui.py", line 960, in _writenobuf self._write(*msgs, **opts) File "c:\Users\Matt\projects\hg\mercurial\ui.py", line 969, in _write raise error.StdioError(err) mercurial.error.StdioError: [Errno 9] The handle is invalid abort: The handle is invalid The interesting bit here is that the abort message is marked with ANSI color, but the OSError is not.

censor: rename loop variable to silence pyflakes warning hgext/censor.py:92: list comprehension redefines 'c' from line 88

py3: add b'' prefixes in tests/test-hgweb-no-request-uri.t # skip-blame because just b'' prefixes. Differential Revision: https://phab.mercurial-scm.org/D4611

py3: add b'' prefixes in tests/test-hgweb-no-path-info.t # skip-blame because just b'' prefixes Differential Revision: https://phab.mercurial-scm.org/D4610

py3: add b'' prefixes in tests/test-hgweb-non-interactive.t # skip-blame because just b'' prefix Differential Revision: https://phab.mercurial-scm.org/D4609

py3: use codecs.encode() to encode in rot-13 encoding The other occurence will need some more love as description is bytes by default and we need to decode it and then encode it. Differential Revision: https://phab.mercurial-scm.org/D4608

py3: add two passing tests to whitelist found by buildbot The buildbot found these two new passing tests on Python 3. Differential Revision: https://phab.mercurial-scm.org/D4607

phabricator: mark extension as experimental for now I don't want us to commit to this having a stable interface just yet. Differential Revision: https://phab.mercurial-scm.org/D4605

phabricator: fix templating bug by using hybriddict Differential Revision: https://phab.mercurial-scm.org/D4604

phabricator: add tests of templatekeyword Having tests is paying off: I found a bug and now it'll be easy to fix! Differential Revision: https://phab.mercurial-scm.org/D4603

phabricator: move extension from contrib to hgext It's well-enough tested now and widely enough used I think we should ship it. Differential Revision: https://phab.mercurial-scm.org/D4602

tests: add some basic tests of phabricator interactions This uses the vcr library to avoid hitting phabricator on every test execution. In order to generate new recordings (vcr calls them cassettes) just remove the appropriate json file, and the test will regenerate it. It's not my favorite way to test things, but it'll let us have test coverage on the phabricator extension that'll make it resilient to refactors in core and let us move it to hgext. In the future, it'd probably be better to have a docker container we can spin up for creating the vcr recordings, but for now this is enough better than nothing I'm going to declare victory. Coverage reports about 73% of the extension is now covered. Differential Revision: https://phab.mercurial-scm.org/D4601

phabricator: add support for using the vcr library to mock interactions I'll use this in an upcoming test. The decorator dancing in this is more complicated than I'd like, but it beats repeating all this code everywhere. Differential Revision: https://phab.mercurial-scm.org/D4600

keepalive: work around slight deficiency in vcr VCR's response type doesn't define the will_close attribute. Let's just have keepalive default to closing the socket if the will_close attribute is missing. Differential Revision: https://phab.mercurial-scm.org/D4599

hghave: add a checker for the vcr HTTP record/replay library I'm going to use this to write some tests of the phabricator extension. Differential Revision: https://phab.mercurial-scm.org/D4598

py3: allow run-tests.py to run on Windows This is now functional: HGMODULEPOLICY=py py -3 run-tests.py --local test-help.t --pure --view bcompare However, on this machine without a C compiler, it tries to load cext anyway, and blows up. I haven't looked into why, other than to see that it does set the environment variable. When the test exits though, I see it can't find killdaemons.py, get-with-headers.py, etc. I have no idea why these changes are needed, given that it runs on Linux. But os.system() is insisting that it take a str, and subprocess.Popen() blows up without str: Errored test-help.t: Traceback (most recent call last): File "run-tests.py", line 810, in run self.runTest() File "run-tests.py", line 858, in runTest ret, out = self._run(env) File "run-tests.py", line 1268, in _run exitcode, output = self._runcommand(cmd, env) File "run-tests.py", line 1141, in _runcommand env=env) File "C:\Program Files\Python37\lib\subprocess.py", line 756, in __init__ restore_signals, start_new_session) File "C:\Program Files\Python37\lib\subprocess.py", line 1100, in _execute_child args = list2cmdline(args) File "C:\Program Files\Python37\lib\subprocess.py", line 511, in list2cmdline needquote = (" " in arg) or ("\t" in arg) or not arg TypeError: argument of type 'int' is not iterable This is exactly how it crashes when trying to spin up a pager too. I left one instance of os.system() unchanged in _installhg(), because it doesn't get there.

py3: ensure run-tests environment is uniformly str subprocess.popen() was crashing, and when I printed out `env`, all of the keys and most of the values were str. Except these.

py3: ensure run-tests.osenvironb is actually bytes Windows doesn't have os.environb, so it was falling back to the Unicode form, and all of the accesses are trying to use bytes.

py3: fix str vs bytes in enough places to run `hg version` on Windows I don't have Visual Studio 2015 at home, but this now works with a handful of extensions (blackbox, extdiff, patchbomb, phabricator and rebase, but not evolve): $ HGMODULEPOLICY=py py -3 ../hg version Enabling the evolve extension causes the usual "failed to import ..." line, but then print this before the usual version output: ('commit', '[b'debugancestor', b'debugapplystreamclonebundle', ..., b'verify', b'version']') ... where the elided part seems to be every command and alias known.

windows: open registry keys using unicode names Python3 complained it must be str. While here, use a context manager to close the key- it wouldn't wrap at 80 characters the old way, and would have had to move anyway.

py3: byteify strings in pycompat These surfaced when disabling the source transformer to debug the problems in win32.py. ./contrib/byteify-strings.py found a couple false positives, so I marked them with r'' explicitly (in case I'm wrong). # skip-blame since this is just b'' and r'' prefixing

wireprotov2: let clients drive delta behavior Previously, the "manifestdata" and "filedata" commands assumed the receiver had all parent revisions for requested nodes. Unless the revision had no parents, they emitted a delta instead of a fulltext. This strategy isn't appropriate for shallow clones and for clients that only want to access fulltext revision data for a single node without fetching their parent revisions. This commit adds an "haveparents" argument to the "manifestdata" and "filedata" commands that controls delta generation behavior. Unless "haveparents" is set, the server assumes that the client doesn't have parent revisions unless they were previously sent as part of the current group of revisions. This change allows the fulltext revision data of any individual revision to be obtained. This will facilitate shallow clones and other data retrieval strategies that don't require all previous revisions of an entity to be fetched. Differential Revision: https://phab.mercurial-scm.org/D4492

exchangev2: fetch file revisions Now that the server has an API for fetching file data, we can call into it to fetch file revisions. The implementation is relatively straightforward: we examine the manifests that we fetched and find all new file revisions referenced by them. We build up a mapping from file path to file nodes to manifest node. (The mapping to first manifest node allows us to map back to first changelog node/revision, which is used for the linkrev.) Once that map is built up, we iterate over it in a deterministic manner and fetch and store file data. The code is very similar to manifest fetching. So similar that we could probably extract the common bits into a generic function. With file data retrieval implemented, `hg clone` and `hg pull` are effectively feature complete, at least as far as the completeness of data transfer for essential repository data (changesets, manifests, files, phases, and bookmarks). We're still missing support for obsolescence markers, the hgtags fnodes cache, and the branchmap cache. But these are non-essential for the moment (and will be implemented later). This is a good point to assess the state of exchangev2 in terms of performance. I ran a local `hg clone` for the mozilla-unified repository using both version 1 and version 2 of the wire protocols and exchange methods. This is effectively comparing the performance of the wire protocol overhead and "getbundle" versus domain-specific commands. Wire protocol version 2 doesn't have compression implemented yet. So I tested version 1 with `server.compressionengines=none` to remove compression overhead from the equation. server before: user 220.420+0.000 sys 14.420+0.000 after: user 321.980+0.000 sys 18.990+0.000 client before: real 561.650 secs (user 497.670+0.000 sys 28.160+0.000) after: real 1226.260 secs (user 944.240+0.000 sys 354.150+0.000) We have substantial regressions on both client and server. This is obviously not desirable. I'm aware of some reasons: * Lack of hgtagsfnodes transfer (contributes significant CPU to client). * Lack of branch cache transfer (contributes significant CPU to client). * Little to no profiling / optimization performed on wire protocol version 2 code. * There appears to be a memory leak on the client and that is likely causing swapping on my machine. * Using multiple threads on the client may be counter-productive because Python. * We're not compressing on the server. * We're tracking file nodes on the client via manifest diffing rather than using linkrev shortcuts on the server. I'm pretty confident that most of these issues are addressable. But even if we can't get wire protocol version 2 on performance parity with "getbundle," I still think it is important to have the set of low level data-specific retrieval commands that we have implemented so far. This is because the existence of such commands allows flexibility in how clients access server data. Differential Revision: https://phab.mercurial-scm.org/D4491

wireprotov2: define and implement "filedata" command Continuing our trend of implementing *data commands for retrieving information about specific repository data primitives, this commit implements a command for retrieving data about an individual tracked file. The command is very similar to "manifestdata." The only significant difference is that we have a standalone function for obtaining storage for a tracked file. This is to provide a monkeypatch point for extensions to implement path-based access control. With this API available, wire protocol version 2 now exposes all data primitives necessary to implement a full clone. Of course, since "filedata" can only resolve data for a single path at a time, clients would need to issue N commands to perform a full clone. On the Firefox repository, this would be ~461k commands. We'll likely need to implement a file data retrieval command that supports multiple paths. But that can be implemented later. Differential Revision: https://phab.mercurial-scm.org/D4490

exchangev2: fetch manifest revisions Now that the server has support for retrieving manifest data, we can implement the client bits to call it. We teach the changeset fetching code to capture the manifest revisions that are encountered on incoming changesets. We then feed this into a new function which filters out known manifests and then batches up manifest data requests to the server. This is different from the previous wire protocol in a few notable ways. First, the client fetches manifest data separately and explicitly. Before, we'd ask the server for data pertaining to some changesets (via a "getbundle" command) and manifests (and files) would be sent automatically. Providing an API for looking up just manifest data separately gives clients much more flexibility for manifest management. For example, a client may choose to only fetch manifest data on demand instead of prefetching it (i.e. partial clone). Second, we send N commands to the server for manifest retrieval instead of 1. This property has a few nice side-effects. One is that the deterministic nature of the requests lends itself to server-side caching. For example, say the remote has 50,000 manifests. If the server is configured to cache responses, each time a new commit arrives, you will have a cache miss and need to regenerate all outgoing data. But if you makes N requests requesting 10,000 manifests each, a new commit will still yield cache hits on the initial, unchanged manifest batches/requests. A derived benefit from these properties is that resumable clone is conceptually simpler to implement. When making a monolithic request for all of the repository data, recovering from an interrupted clone is hard because the server was in the driver's seat and was maintaining state about all the data that needed transferred. With the client driving fetching, the client can persist the set of unfetched entities and retry/resume a fetch if something goes wrong. Or we can fetch all data N changesets at a time and slowly build up a repository. This approach is drastically easier to implement when we have server APIs exposing low-level repository primitives (such as manifests and files). We don't yet support tree manifests. But it should be possible to implement that with the existing wire protocol command. Differential Revision: https://phab.mercurial-scm.org/D4489