The non-cached version asks the question:
show me the differences between HEAD and the currently checked out
- tree - index contents _and_ files that aren't up-to-date
+ tree - index contents _and_ files that aren't up to date
which is obviously a very useful question too, since that tells you what
you *could* commit. Again, the output matches the 'git diff-tree -r'
torvalds@ppc970:~/v2.6/linux> git diff-index --abbrev HEAD
:100644 100664 7476bb... 000000... kernel/sched.c
-i.e., it shows that the tree has changed, and that `kernel/sched.c` has is
-not up-to-date and may contain new stuff. The all-zero sha1 means that to
+i.e., it shows that the tree has changed, and that `kernel/sched.c` is
+not up to date and may contain new stuff. The all-zero sha1 means that to
get the real diff, you need to look at the object in the working directory
directly rather than do an object-to-object diff.