fileset: add a lightweight file filtering language This patch was inspired by one that Jun Wu authored for the fb-experimental repo, to avoid using matcher for efficiency[1]. We want a way to specify what files will be converted to LFS at commit time. And per discussion, we also want to specify what files to skip, text diff, or merge in another config option. The current `lfs.threshold` config option could not satisfy complex needs. I'm putting it in a core package because Augie floated the idea of also using it for narrow and sparse. Yuya suggested farming out to fileset.parse(), which added support for more symbols. The only fileset element not supported here is 'negate'. (List isn't supported by filesets either.) I also changed the 'always' token to the 'all()' predicate for consistency, and introduced 'none()' to improve readability in a future tracked file based config. The extension operator was changed from '.' to '**', to match how recursive path globs are specified. Finally, I changed the path matcher from '/' to 'path:' at Yuya's suggestion, for consistency with matcher. Unfortunately, ':' is currently reserved in filesets, so this has to be quoted to be processed as a string instead of a symbol[2]. We should probably revisit that, because it's seriously ugly. But it's only used by an experimental extension, and I think using a file based config for LFS may drive some more tweaks, so I'm settling for this for now. I reserved all of the glob characters in fileset except '.' and '_' for the extension test because those are likely valid extension characters. Sample filter settings: all() # everything size(">20MB") # larger than 20MB !**.txt # except for .txt files **.zip | **.tar.gz | **.7z # some types of compressed files "path:bin" # files under "bin" in the project root [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-December/109387.html [2] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-January/109729.html

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Corrupt an hg repo with a pull started during an aborted commit

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Create two repos, so that one of them can pull from the other one.

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  $ hg init source

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  $ cd source

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  $ touch foo

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  $ hg add foo

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  $ hg ci -m 'add foo'

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  $ hg clone . ../corrupted

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  updating to branch default

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  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

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  $ echo >> foo

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  $ hg ci -m 'change foo'

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Add a hook to wait 5 seconds and then abort the commit

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  $ cd ../corrupted

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  $ echo "[hooks]" >> .hg/hgrc

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  $ echo 'pretxncommit = sh -c "sleep 5; exit 1"' >> .hg/hgrc

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start a commit...

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  $ touch bar

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  $ hg add bar

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  $ hg ci -m 'add bar' &

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... and start a pull while the commit is still running

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  $ sleep 1

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  $ hg pull ../source 2>/dev/null

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  pulling from ../source

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  transaction abort!

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  rollback completed

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  abort: pretxncommit hook exited with status 1

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  searching for changes

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  adding changesets

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  adding manifests

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  adding file changes

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  added 1 changesets with 1 changes to 1 files

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  new changesets 52998019f625

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  (run 'hg update' to get a working copy)

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see what happened

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  $ wait

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  $ hg verify

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  checking changesets

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  checking manifests

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  crosschecking files in changesets and manifests

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  checking files

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  1 files, 2 changesets, 2 total revisions

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  $ cd ..