[PATCH 5 of 5 RFC] lfs: control tracked file selection via a tracked file

[Jun Wu]

Excerpts from Matt Harbison's message of 2018-01-14 23:58:52 -0500:
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> 
> Jun previously expressed concern about efficiency when scaling to large repos,
> so I tried avoiding 'repo[None]'.  (localrepo.commit() gets repo[None] already,

Is repo[None] slow? I thought it's an O(1) operation and '.hglfs' in wctx is
like os.path.exists test.

FWIW I added a similar behavior reading config in working copy [1] for the
"dirsync" extension (which is a hacky temporary solution).

Given the fact .hgignore uses working copy version, and whether to use lfs
or not feels similar to what .hgignore does, I think the working copy
version might be a simple and more flexible choice. But I don't feel strong.

Greg has a proposal checking in a .hgrc. I think that is a more general
purposed solution for these kinds of stuffs. Since we now have configitems,
maybe it's doable by carefully whitelisting configs.

[1]: https://bitbucket.org/facebook/hg-experimental/commits/de0cc94acd

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