make sync update adjusted branch to hide/unhide

This completes initial support for --hide-missing, although the
assistant still needs to be updated and it perhaps needs to be sped up,
and maybe there needs to be a way for git-annex get to operate on
missing files. Opened some more todos for those things.

This commit was sponsored by Henrik Riomar.

doc/todo/assistant_support_hide-missing.mdwn

@@ -0,0 +1,11 @@
+While `git annex sync` supports branches set up by `git annex adjust
+--hide-missing`, the assisitant does not yet.
+
+This would invole:
+
+* The assistant also needs to scan the original branch when looking for
+  files to download.
+
+* The assistant ought to update the adjusted branch at some point after
+  downloads, but it's not clear when. Perhaps this will need to be deferred
+  until it can be done more cheaply, so it can do it after every file.

doc/todo/better_way_to_get_missing_files.mdwn

@@ -0,0 +1,34 @@
+Currently in a `git annex adjust --hide-missing` branch, the only way to
+get missing files is to run `git annex sync --content`, with appropriate preferred
+content settings or with `-C path` to get a specific path. This is kind of
+klunky for ad-hoc getting files.
+
+It would be possible to make `git annex get`, `git annex copy --from remote`, etc
+operate on hidden files. Some of the infrastructure is there; it may be as
+simple as using LsFiles.inRepoOrBranch instead of LsFiles.inRepo to seek
+the files.
+
+Two open questions:
+
+* Would it make more sense for this to be the default behavior when in the
+  adjusted branch, or for it to be an option, like "--branch=master"?
+
+  One advantage to the latter is that it would also be usable in bare
+  repos, or if you just for some reason want to get files present in some
+  other branch than the current one.
+
+  The former might be easier, but it could also be kind of surprising.
+  `git annex get .` would download tons of files, which `ls` doesn't
+  display.
+
+  Of course, both things could be supported too.
+
+* After getting the files, they'll still be hidden until the branch is
+  updated to include them. When should that happen?
+
+  The current method of re-running `git annex adjust --hide-missing` will
+  expose them, but the way that works is probably too slow to run after
+  every command. Even if it were fast, it would generate a lot of dangling
+  objects over time. So leave the update up to the user to run the command
+  when they want it? But then the user may get confused, why did it
+  download files and they didn't appear?

doc/todo/hide_missing_files.mdwn

@@ -25,3 +25,5 @@ Thanks for any advice! --[[anarcat]]
 > > cleaner, of course, if adjusted branches could do this. --[[anarcat]]
 
 Other discussions: [[forum/How_to_hide_broken_symlinks]], where the idea of using views to hide missing files is introduced and [[forum/How_do_I_hide_files_not_present_in_the_local_annex__63__]], where it is said that placeholders shouldn't be used in direct mode... --[[anarcat]]
+
+> [[done]]! --[[Joey]]

doc/todo/hide_missing_files/comment_4_e3bf8aaecc0f612873609c92814dcd12._comment

@@ -11,13 +11,4 @@ My implementation is not as fast as it could be; each update
 is a linear scan of the whole original branch and rebuild of the adjusted
 branch. But it all works so we'll defer speeding this up to later bug
 reports about it being too slow. ;)
-
-What still needs to be done:
-
-* `git annex sync` needs to update the adjusted branch.
-* The assistant also needs to scan the original branch when looking for
-  files to download.
-* The assistant ought to update the adjusted branch at some point after
-  downloads, but it's not clear when. Perhaps this will need to be deferred
-  until it can be done more cheaply, so it can do it after every file.
 """]]