Med Java

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====== A Practical Guide to Correcting Git Commits (Amend & Squash) ======

This guide explains how to modify or combine commits that have already been created. These are powerful tools for keeping your Git history clean and readable.

<note warning>
**WARNING:** These operations rewrite Git history. **Never** rewrite history on public or shared branches (e.g., //main//, //develop//, //master//) that other team members are using. These techniques are safe to use on your own private feature branches before they are merged.
</note>

---

===== 1. Editing the Last Commit's Message =====

This is the perfect tool when you've made a mistake in the message of your **most recent commit**.

==== When to Use It? ====
  * You made a typo in the commit message.
  * You forgot to add a ticket ID (e.g., JIRA-123).
  * You want to add a very small code change to the previous commit instead of creating a new one.

==== How to Do It (Command Line) ====

  - **Step 1: Amend the Commit Locally**
    Run the following command. This will open your default text editor to let you change the message.
<code bash>
git commit --amend
</code>
    Alternatively, to change the message directly from the command line without opening the editor:
<code bash>
git commit --amend -m "feat(auth): [JIRA-123] Add user login endpoint"
</code>

  - **Step 2: Push the Changes to the Server**
    Because you have changed a commit that already exists on the remote server, you must force the update. **Always** use the safer `--force-with-lease` option.
<code bash>
git push --force-with-lease origin <your-branch-name>
</code>
<note>
The <code>--force-with-lease</code> flag is safer than <code>--force</code> because it checks if another person has pushed new commits to the branch in the meantime. If they have, the push will fail, preventing you from accidentally overwriting their work.
</note>

---

===== 2. Combining Multiple Commits (Squash) =====

"Squashing" means to combine several smaller, sequential commits into a single, logical commit.

==== When to Use It? ====
  * You have made several small, incremental commits (e.g., "WIP", "Fix typo", "Add test") and want to present them as one coherent feature.
  * You want to clean up your branch's history before creating a Pull/Merge Request, making it easier for others to review.

==== How to Do It (Command Line) ====

We will use the **interactive rebase** command (<code>git rebase -i</code>).

  - **Step 1: Start the Interactive Rebase**
    If you want to combine the last **3** commits, run the following command:
<code bash>
git rebase -i HEAD~3
</code>
    (Replace `3` with the number of commits you want to work with).

  - **Step 2: Choose Your Actions**
    A text editor will open with a list of the commits you selected, with the oldest one first.
<file>
pick 1a2b3c4 feat: Add initial login form structure
pick 5d6e7f8 fix: Correct validation logic on login
pick 9g8h7i6 refactor: Clean up login service
</file>
    To combine them, keep the first commit with **<code>pick</code>** and change the action for all subsequent commits to **<code>squash</code>** (or the shorthand **<code>s</code>**).
<file>
pick 1a2b3c4 feat: Add initial login form structure
s 5d6e7f8 fix: Correct validation logic on login
s 9g8h7i6 refactor: Clean up login service
</file>
    Now, save and exit the editor.

  - **Step 3: Write the New, Combined Commit Message**
    Git will open another text editor, containing the messages from all the commits you are squashing. Delete the old text and write a single, clear message that describes the combined change.
<file>
feat(auth): [JIRA-123] Implement user login functionality

- Adds the HTML structure and styling for the login form.
- Implements client-side and server-side validation for user credentials.
- Refactors the authentication service for better clarity and performance.
</file>
    Save and exit the editor.

  - **Step 4: Push the Changes to the Server**
    Your local history has now been rewritten. Update the remote server using the safe force-push command:
<code bash>
git push --force-with-lease origin <your-branch-name>
</code>

==== How to Do It (TortoiseGit) ====
  * In the **Log Messages** window, right-click on the commit that comes **before** the ones you want to combine.
  * From the context menu, choose **<code>Rebase "<your-branch-name>" onto this...</code>**.
  * A "Rebase" window will appear. For each commit you want to combine (except the first one), change its action from "Pick" to **<code>Squash</code>**.
  * Click **Start Rebase**. You will then be prompted to edit the final commit message.
  * After the rebase is complete, **Push** your changes, making sure to check the **force** option (preferably one that mentions "with lease").