Output from git diff

Here is another diff output question. The updated documentation in diff-format.txt still claims that the output from the diff commands has this format:

:100644 100644 bcd1234... 0123456... M file0

This is true for "git diff --raw", but diff-tree and friends print full 40-char hashes.

I can get diff-tree to use abbreviated hashes with --abbrev, but how do I tell diff to stop abbreviating?

And what should the documentation really say?