shelve: use matcher to restrict prefetch to just the modified files Shelve currently operates by: - make a temp commit - identify all the bases necessary to shelve, put them in the bundle - use exportfile to export the temp commit to the bundle ('file' here means "export to this fd", not "export this file") - remove the temp commit exportfile calls prefetchfiles, and prefetchfiles uses a matcher to restrict what files it's going to prefetch; if it's not provided, it's alwaysmatcher. This means that `hg shelve` in a remotefilelog repo can possibly download the file contents of everything in the repository, even when it doesn't need to. It luckily is restricted to the narrowspec (if there is one), but this is still a lot of downloading that's just unnecessary, especially if there's a "smart" VCS-aware filesystem involved. exportfile is called with exactly one revision to emit, so we're just restricting it to prefetching the files from that revision. The base revisions having separate files should not be a concern since they're handled already; example: commit 10 is draft and modifies foo/a.txt and foo/b.txt commit 11 is draft and modifies foo/a.txt my working directory that I'm shelving modifies foo/b.txt By the time we get to exportfile, commit 10 and 11 are already handled, so the matcher only specifying foo/b.txt does not cause any problems. I verified this by doing an `hg unbundle` on the bundle that shelve produces, and getting the full contents of those commits back out, instead of just the files that were modified in the shelve. Differential Revision: https://phab.mercurial-scm.org/D5268