Create dangling commit without checking out

Question

Is there a way to silently create a commit that is

• Not connected to the current branch
• Not checked out afterwards

like

A-B-C-D-E-F-G   # master
       \   \
        X   Y

Where X and Y are created without the user noticing.

The reasoning:

I am writing a lot of exploratory experiment-code and want to automatically commit the current state when running an experiment. These intermediate states should not end up in my Git history and I do not want to go through the mental overhead of committing before running all the time (or forgetting it every now and then).

The idea is to have a lot of dangling commits that will not be pushed to my remote and may be deleted by garbage collection. Each individual commit SHA1 will be annotated to my experiment results, enabling me to trace back what changes had what effect on the results.

Answer 1

You can use the git commit-tree command to create a dangling commit.

First, stage the files you want to commit, e.g., by doing git add file.

Next, create a tree from the index.

git write-tree

This will print a hash to stdout. That is the hash of the tree you want to commit. Let's say the hash is 12345678.

Now that you have a tree for the index, you can unstage the changes so you won't commit them "for real" by mistake. (git reset HEAD file.)

Finally, create a commit from that tree.

git commit-tree 12345678 -p HEAD -m "Description"

This creates a new commit and prints its hash to stdout. The commit's parent is HEAD and the comment is Description.

As a reminder, this is a dangling commit and therefore will be subject to GC.