How should you create a patch for an older tag in source control?

Question

Let's say I released a version of my software about a year ago and tagged it at 2.3 in Git.

So I keep adding features and fixing bugs and before you know it, the software is now at version 3.0. But now I have a bug on version 2.3 of the software and the person that needs it fixed is not ready to upgrade to version 3.0.

As far as Git is concerned what would be that best way to manage applying a patch to 2.3 and creating version 2.3.1 of the software without changing the history of the Git repo.

For instance, I can't checkout version 2.3, apply the patch and then tag it at 2.3.1 and push it up since that would create a new head.

How do developers typically manage supporting older versions of their software?

Edit

Okay, so I followed @AnoE advise and now my workflow is as follows for patching previous versions. Advice is welcome.

git checkout v2.3.0
// Make code changes
git add -A
git commit -m "Fixed a bug in old app"
// Do something to verify the changes work on a different environment
git checkout -b v2_3_1
git tag -a v2.3.1 -m "Fixed small bug."
git push origin v2_3_1
git push --tags

The reason I had to create a branch is because the tag wouldn't show up on Kiln, our repo hosting solution. I don't know if other providers like Bitbucket or Github will show a tag without a branch associated or if this is just a side effect of how Git stores things. The tag showed up locally when I ran git tag -l but it wasn't visible through the web UI. After I pushed up the branch and tag I just deleted the branch and it showed up properly from the Web UI.

git push --delete v2_3_1

If anyone has an explanation as to why something like this would happen, it would be appreciated.

Answer 1

Checking out version 2.3, applying the patch, tagging it 2.3.1 is exactly what you are going to do.

Creating a new head (rather, a new branch) is not a problem whatsoever, it's what git was made for. Note that "HEAD" has no structural meaning in git, it only stands out because it is the one commit that is active in your current working directory. Git only cares about commits, structurally, and you can have as many "top-level" commits as you like.

So:

git checkout 2.3    # gives you a "detached HEAD" 
git checkout -b dev_2.3    # a new branch, more for convenience
...modify files...
git add ... ; git commit ...
git tag 2.3.1
git branch -D dev_2.3     # get rid of it if you have a feeling that you won't be comming back soon

Keep in mind that both branches and tags are nothing special at all in git. They are simply sticky notes pointing to commits. Making a (maybe temporary) branch in this manner is just a bit more convenient since you can easily switch to/from it if the backport you are doing involves a bit more than one quick commit.