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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Initial setup.

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  $ hg init repo

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  $ cd repo

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  $ touch thefile

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  $ hg ci -A -m 'Initial commit.'

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  adding thefile

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Create a tag.

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  $ hg tag branchortag

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Create a branch with the same name as the tag.

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  $ hg branch branchortag

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  marked working directory as branch branchortag

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  (branches are permanent and global, did you want a bookmark?)

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  $ hg ci -m 'Create a branch with the same name as a tag.'

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This is what we have:

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  $ hg log

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  changeset:   2:10519b3f489a

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  branch:      branchortag

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  tag:         tip

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Create a branch with the same name as a tag.

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  changeset:   1:2635c45ca99b

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Added tag branchortag for changeset f57387372b5d

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  changeset:   0:f57387372b5d

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  tag:         branchortag

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Initial commit.

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Update to the tag:

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  $ hg up 'tag(branchortag)'

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

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  $ hg parents

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  changeset:   0:f57387372b5d

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  tag:         branchortag

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Initial commit.

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Updating to the branch:

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  $ hg up 'branch(branchortag)'

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

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  $ hg parents

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  changeset:   2:10519b3f489a

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  branch:      branchortag

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  tag:         tip

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  user:        test

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  date:        Thu Jan 01 00:00:00 1970 +0000

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  summary:     Create a branch with the same name as a tag.

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  $ cd ..