pre-commit: Update metadata when committing changes to annexed files within a view.

So the user can now switch to a view and then move files around within it
to manage metadata. For example, moving a file into a new directory
when in the tags=* view adds a tag to it.

Implementation is fairly efficient. One diff-index, which is no more
expensive than the first stage of a git commit, followed by possibly
some cat-file --batch traffic to find the key (when deleting a file).
Very similar to what's done in direct mode when committing. And like
direct mode when updating the WC after a merge, it has to buffer the
diff-tree values in order to make 2 passes over them.

When not in a view, pre-commit now does one extra git symbolic-ref,
which is tiny overhead.

This commit was sponsored by Andrew Eskridge.

1 files changed, 7 insertions, 4 deletions

diff --git a/doc/git-annex.mdwn b/doc/git-annex.mdwn
index a5f73ac8e..cdd59ef9c 100644
--- a/doc/git-annex.mdwn
+++ b/doc/git-annex.mdwn
@@ -321,10 +321,12 @@ subdirectories).
   shown in the view.
   
   Multiple values for a metadata field can be specified, either by using
-  a glob (field="\*") or by listing each wanted value. 
+  a glob (field="\*") or by listing each wanted value. The resulting view
+  will put files in subdirectories according to the value of their fields.
   
-  When multiple field values match, the view branch will have a
-  subdirectory for each value.
+  Once within a view, you can make additional subdirectories, and
+  copy or move files into them. When you commit, the metadata will
+  be updated to correspond to your changes.
 
 * `vpop [N]`
 
@@ -801,7 +803,8 @@ subdirectories).
 
   Fixes up symlinks that are staged as part of a commit, to ensure they
   point to annexed content. Also handles injecting changes to unlocked
-  files into the annex.
+  files into the annex. When in a view, updates metadata to reflect changes
+  made to files in the view.
 
 * `lookupkey [file ...]`