Re: master^ is not a local branch -- huh?!?

Ron Garret <ron1@flownet.com> writes:

I think it would be helpful to point out one issue that may hurt you (and anybody who thinks "git update --tree" without --index is a good idea).

Keeping the index and HEAD in sync but matching the work tree files to that of a different commit has one major downside. To git, a work tree file that does not exist in the index is a yet-to-be-added-untracked file (that is how and why "rm --cached file" works, for example). It won't participate in the diff output (other than being treated as "no such file in the work tree version").

Suppose that you used to have a path in older revision, but not in the current revision. You remove everything from the work tree and replace it with the files in the older revision, and you do not touch HEAD nor index. "git diff -R" appears to show "what changed since that older version and the latest", because it compares what is in the index relative to what is in the work tree. Nice.

Not quite. Since the index does not know that path you recently removed, you won't see that path. If you run "git ls-files" for a list of files known to git, it wouldn't be shown either.

Your original "git checkout master^" is a valid and probably the optimal way to get a checkout of a older revision (which you could feed to your running Lisp interpreter, in addition to being able to run "less" and "make" on them). Exactly because the index is updated to that of the older version, you won't lose the sight of the path that you removed in a later version, and you can review the change with "git diff -R master".

I think this is an XY problem that comes from your wanting to use "git diff" (compare work tree with index) instead of "git diff $commit", and that was because you wanted to use "HEAD" as a name of a commit. If you used a branch name you originally came from, none of this desire to "keep index intact" or "keep HEAD intact" would have been necessary.

But this is all tangent; I think you now know more about git to improve your IDE integration, without fighting with git but instead taking advantage of it.