adjust --hide-missing

* At long last there's a way to hide annexed files whose content
  is missing from the working tree: git-annex adjust --hide-missing
* When already in an adjusted branch, running git-annex adjust
  again will update the branch as needed. This is mostly
  useful with --hide-missing to hide/unhide files after their content
  has been dropped or received.

Still needs integration with sync and the assistant, and not as fast as it
could be, but already usable.

This commit was sponsored by Ethan Aubin.

doc/forum/How_do_I_hide_files_not_present_in_the_local_annex__63__/comment_5_1ed5e10e51078a0aa7e6968ef48687a3._comment

@@ -0,0 +1,10 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 5"""
+ date="2018-10-18T18:59:54Z"
+ content="""
+Good news everyone! `git annex adjust --hide-missing` sets up a branch
+where only files with content available are included. And once in such a
+branch, `git annex sync` updates it as necessary to reflect changes in
+content availability.
+"""]]

doc/forum/How_to_hide_broken_symlinks/comment_5_1ed5e10e51078a0aa7e6968ef48687a3._comment

@@ -0,0 +1,10 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 5"""
+ date="2018-10-18T18:59:54Z"
+ content="""
+Good news everyone! `git annex adjust --hide-missing` sets up a branch
+where only files with content available are included. And once in such a
+branch, `git annex sync` updates it as necessary to reflect changes in
+content availability.
+"""]]

doc/git-annex-adjust.mdwn

@@ -4,7 +4,7 @@ git-annex adjust - enter an adjusted branch
 
 # SYNOPSIS
 
-git annex adjust `--unlock|--fix`
+git annex adjust `--unlock|--fix|--hide-missing [--unlock|--fix]`
 
 # DESCRIPTION
 
@@ -20,9 +20,14 @@ While in the adjusted branch, you can use git-annex and git commands as
 usual. Any commits that you make will initially only be made to the
 adjusted branch. 
 
-To propagate changes from the adjusted branch back to the original branch,
+To propagate commits from the adjusted branch back to the original branch,
 and to other repositories, as well as to merge in changes from other
-repositories, use `git annex sync`.
+repositories, run `git annex sync`.
+
+Re-running this command with the same options
+while inside the adjusted branch will update the adjusted branch
+as necessary (eg for `--hide-missing`), and will also propagate commits
+back to the original branch.
 
 This command can only be used in a v6 git-annex repository.
 
@@ -40,6 +45,22 @@ This command can only be used in a v6 git-annex repository.
   unusual way that prevents the symlinks committed to git from pointing at
   the annex objects.
 
+* `--hide-missing`
+
+  Only include annexed files in the adjusted branch when their content
+  is present.
+
+  The adjusted branch is not immediately changed when content availability
+  changes, so if you `git annex drop` files, they will become broken
+  links in the usual way. And when files that were missing are copied into the
+  repository from elsewhere, they won't immediatly become visible in the
+  branch. 
+  
+  To update the adjusted branch to reflect changes to content availability, 
+  run `git annex adjust --hide-missing` again.
+
+  This option can be combined with --unlock or --fix.
+
 # SEE ALSO
 
 [[git-annex]](1)

doc/todo/hide_missing_files/comment_4_e3bf8aaecc0f612873609c92814dcd12._comment

@@ -0,0 +1,25 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 4"""
+ date="2018-10-18T19:27:43Z"
+ content="""
+I implemented `git annex adjust --hide-missing`.
+It can be run after any change to content availability to update
+the adjusted branch, hiding or unhiding files.
+
+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 --content` needs to scan the original branch, not the
+  adjusted branch, to find files to transfer.
+* `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.
+"""]]