docs(git): add note regarding retroactive git commits

Author: anthops

content/🧠 Knowledge/🛠️ Tools & Platforms/Version Control/git/Retroactive Commits.md

@@ -0,0 +1,64 @@
+---
+title: Retroactive Commits
+tags:
+  - git
+url: git-retroactive-commits
+---
+Imagine that you're working on a project you want to publish or share with others. You look at your commit history and realize you squashed commits a little too much. There are commits combining multiple unrelated changes, and you wish you could go back in time and break them down properly.
+
+Thankfully, Git allows you to do this. While it’s not exactly a quick task, using **interactive rebase** makes it possible to split old commits while preserving history, authorship, and dates — and avoids the risks and pitfalls of orphan branches or force-rebuilding your repo from scratch.
+## The Process
+>[!warning] Backup!  
+>Before making history changes, make a backup branch or clone the repo. If anything goes wrong, you’ll be glad you did.
+
+1. Figure out how far back you want to start adding retroactive commits in the past. Use `git log` and identify the **parent commit** of the one you want to start making commits from. For example, in the log below we want to start making commits from `d22135`, so we'd choose it's parent, `d22135^` 
+	```log
+	commit 514f026d7895f38e8526d255444169bcdef8aed2 (HEAD -> main, origin/main, origin/HEAD)
+	Author: Tony <[email protected]>
+	Date:   Fri Apr 25 08:28:00 2025 +0930
+	
+			style(quartz): set code indent tab-size to 2 and change margins on images after a paragraph
+
+		.
+		.
+		.
+	
+	commit d22135af0b6f4bb89e0fd9c21e44a2f3f6bb82d3
+	Author: Tony <[email protected]>
+	Date:   Tue Apr 8 16:41:00 2025 +0930
+	
+			docs(springboot): add note on java springboot project layout
+	```
+2. Start an interactive rebase using the parent commit:
+	```sh
+	git rebase -i d22135^
+	```
+3. In the editor that opens, find the commits you want to split into multiple and change `pick` to `edit` for those lines. For example:
+	```log
+	edit d22135a docs(springboot): add note on java springboot project layout
+	pick 162d6aa docs(licensing): add initial notes on software licensing
+	edit 791c39d docs: add lots of notes in one big commit
+	pick 514f026 style(quartz): set code indent tab-size to 2 and change margins on images after a paragraph
+	```
+4. When editing each commit, unstage everything in the commit (this keeps the changes in your working directory so you can manually commit each one):
+	```sh
+	git reset HEAD~
+	```
+5. Create smaller commits manually, making sure to manually specify the commit date to be somewhat consistent with the original commit you're splitting up. 
+   
+   Note the use of both `GIT_COMMITTER_DATE` and `--date`. Both are required if you want remote repositories like GitHub to show the correct commit dates in the repository:
+	```sh
+	git add some-file
+	GIT_COMMITTER_DATE="Fri, Apr 25 08:28:00 2025 +0930" git commit --date="Fri, Apr 25 08:28:00 2025 +0930" -m "feat: a more specific commit"
+
+	git add another-file
+	GIT_COMMITTER_DATE="Fri, Apr 25 08:47:00 2025 +0930" git commit --date="Fri, Apr 25 08:47:00 2025 +0930" -m "feat: another more specific commit"
+	```
+6. Continue the rebase until finished:
+	```sh
+	git rebase --continue
+	```
+7. Once you're done, force push the updated history:
+	```sh
+	git push --force-with-lease
+	```