docs: add args/returns docs for some cmdutil, context, and registrar functions When writing my first extension, I found it hard to figure out these functions. I figured documenting their inputs/outputs would help future authors who are new to the codebase. Differential Revision: https://phab.mercurial-scm.org/D1440

commands: add value for cmdtype argument for read only commands In the previous release we added an argument `cmdtype` to registrar.command() which is a enum and tells whether the command is read only, recoverable write or unrecoverable write command. This patch add the value of cmdtype argument for commands which are read only. Differential Revision: https://phab.mercurial-scm.org/D1468

error: add InMemoryMergeConflictsError We'll raise this exception in the merge code, and in-memory users like rebase can catch it and retry without IMM. Differential Revision: https://phab.mercurial-scm.org/D1210

lfs: generate a large file by using `python` instead of yes | head yes(1) on some systems (like gcc112) feels compelled to inform you of broken pipes, such as those triggered by head(1). This works around the problem portably.

setup: add hgext.lfs to list of Python packages This is needed for lfs to get installed. Probably could stand to go into an earlier patch, but I just want to get this stuff pushed.

test-lfs: add tests demonstrating the interaction with largefiles Obviously the original series needs to be accepted first, but there are concerns about how well these extensions will play together before proceeding. It looks like the answer is surprisingly well. There are some merge surprises (largefiles seems to combine the choice of "keep tracking as a large/normal file" with taking the content of the large/normal file) and some existing diff weirdness (largefiles diffs the standins, not the large file). Converting the repo to normal files seemlessly transitions to lfs on the fly. I didn't test going the other way, because I'm not sure why anyone would want to do that. I flagged the lack of a repo requirement after converting, because some of the unsubmitted changes I have add a requirement on commit, but this somehow misses the convert case. I flagged an issue where devel-warnings are emitted on convert, which is a separate issue.

test-lfs: cast the flags printed to an int On Windows, the flag values in the subsequent tests were printing with a 'L' suffix.

lfs: register config options I'm not sure at what point we can get rid of the deprecated options, but for the sake of making progress, they are registered too.

lfs: quiesce check-module-import warnings Specifically, 'symbol import follows non-symbol import: mercurial.i18n'

lfs: import the Facebook git-lfs client extension The purpose of this is the same as the built-in largefiles extension- to handle huge files outside of the normal storage system, generally to keep the amount of data cloned to a lower amount. There are several benefits of implementing the git-lfs protocol, instead of using the largefiles extension: - Bitbucket and Github support (and probably wider support in 3rd party hosting sites in general). [1][2] - The number of hg internals monkey patched are several orders of magnitude lower, so it will be easier to reason about and maintain. Future commands will likely just work, without requiring various wrappers. - The "standin" files are only written to the filelog, not the disk. That should avoid weird edge cases where the largefile and standin files get out of sync. [3] It also avoids the occasional printing of the "hidden" standin file in various messages. - Filesets like size() will work, even if the file isn't present. (It always says 41 bytes for largefiles, whether present or not.) The only place that I see where largefiles comes out on top is that it works with `hg serve` for simple sharing, without external infrastructure. Getting lfs-test-server working was a hassle, and took awhile to figure out. Maybe we can do something to make it work in the future. Long term, I expect that this will be highly preferred over largefiles. But if we are to recommend this to largefile users, there are some UI issues to bikeshed. Until they are resolved, I've marked this experimental, and am not putting a pointer to this in the largefiles help. The (non exhaustive) list of issues I've seen so far are: - It isn't sufficient to just enable the largefiles extension- you have to explicitly add a file with --large before it will pay attention to the configured sizes and patterns on future adds. The justification being that once you use it, you're stuck with it. I've seen people confused by this, and haven't liked it myself. But it's also saved me a few times. Should we do something like have a specific enabling config setting that must be set in the local repo config, so that enabling this extension in the user or system hgrc doesn't silently start storing lfs files? - The largefiles extension adds a repo requirement when the first largefile is committed, so that the extension must always be enabled in the future. This extension is not doing that, and since I only enabled it locally to avoid infecting other repos, I got a cryptic error about missing flag processors when I cloned. Is there no repo requirement due to shallow/narrow clone considerations (or other future advanced things)? - In the (small amount of) reading I've done about the git implementation, it seems that the files and sizes are stored in a tracked .gitattributes file. I think a tracked file for this would be extremely useful for consistency across developers, but this kind of touches on the tracked hgrc file proposal a few months back. - The git client can specify file patterns, not just sizes. - The largefiles extension has a cache directory in the local repo, but also a system wide one. We should probably implement a system wide cache too, so that multiple clones don't have to refetch the files from the server. - Jun mentioned other missing features, like SSH authentication, gc, etc. The code corresponds to c0492b73c7ef in hg-experimental. [4] The only tweaks are to load the extension in the tests with 'lfs=' instead of 'lfs=$TESTDIR/../hgext3rd/lfs', change the import in the *.py test to hgext (from hgext3rd), add the 'testedwith' declaration, and mark it experimental for now. The infinite-push, p4fastimport, and remotefilelog tests were left behind. The devel-warnings for unregistered config options are not corrected yet, nor are the import check warnings. [1] https://www.mercurial-scm.org/pipermail/mercurial/2017-November/050699.html [2] https://bitbucket.org/site/master/issues/3843/largefiles-support-bb-3903 [3] https://bz.mercurial-scm.org/show_bug.cgi?id=5738 [4] https://bitbucket.org/facebook/hg-experimental