scmutil: introduce filecache The idea is being able to associate a file with a property, and watch that file stat info for modifications when we decide it's important for it to be up-to-date. Once it changes, we recreate the object. On filesystems that can't uniquely identify a file, we always recreate. As a consequence, localrepo.invalidate() will become much less expensive in the case where nothing changed on-disk.

basic:

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fakeuncacheable:

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