Re: git index: how does it work?

Shaun Cutts [off-list ref] writes:

Are renames being tracked by the index, and is there a more basic
interface than "status" to query about them?

No.  Index, nor git in general, never records renames.  git records
contents, not content changes.  The index records a state, so does the
tree object pointed at by the HEAD commit.

When you ask for "status", git will notice that you have lost a file, and
added a new one, between these two states, by comparing them.  The
contents of these lost files and added files are then compared, and ones
with similar contents are paired up.

That way, you do not have to use "git mv A B" to "rename" A to B.  You can
just as well "mv A B; git rm A; git add B", and get the same outcome,
exactly because git does not record renames.

Instead, we track them by deducing that you renamed from the result.

The tree-vs-index comparison "git status" does to figure all this out is
"git diff-index -M --cached HEAD".

As it should be obvious from the above description,

	git diff-index -M --cached HEAD -- A

is *NOT* the way for you to ask about "possible renames of A".  You need
to run the diff for the whole tree without path limitation so that you can
pair deletions and creations up in order to deduce renames.