What happens in Git to a tag when you amend the commit that was tagged?

I have committed a few source files to my git repository and tagged it a开发者_如何学Pythons a new version of my software. But I saw a mistake I had just made and used the "amend" feature to commit the corrected files.

Now, I see that the tag was not transferred to the new commit (the one made with the "amend" feature). But I can also see that the tag still exists...

I would like to know what happened to the tag. Is this behavior a bug? Is the tag linked to a commit which doesn't exist anymore ?

I know I can force the creation of the same tag on the new commit, but I believe there should be a better way (like a command line parameter on the commit using "amend").

This is by design. Git tracks commits, tags, blobs and trees as SHA-1 hashes of their contents. They are simply pointers to the objects. The object that the tag points to is still there. This is the version of the commit before you amended it. Just delete the tag and create it again. Ensure that you let others that are using the repository know what you did if they started anything from that commit.

To get a good background of how git works, take a look at Scott Chacon's Rails Conference talk about git on gitcasts.com. Also, read the short book on git: progit.org/book.