[Git Notes] Git push conflict resolution.

There is a remote repo named origin/main which is developped by Users A and B at present, A's local repo, local A and B 's local repo, local B, are both up-to-date with origin/main Then, A add 1 line: 1+1=2 B add 1 line: 1+1=2 then A push it first. when B push its own commit, what will happen?

• Initial Setup: User A and User B both have their local repositories up-to-date with origin/main. Each adds the same line ("1+1=2") in their respective local copies.

• Pushing Changes:

  • User A pushes their change to origin/main first.
  • User B attempts to push second but finds the remote has been updated by User A.

• Conflict and Resolution:

  • User B's push is rejected because their branch is behind the remote's state.
  • B pulls from the remote, and Git prompts for conflict resolution because both A and B modified the same line.

• Decision and Commit:

  • User B decides how to resolve the conflict (could include both users' changes, just one, or a new modification).
  • B commits the resolution and pushes to origin/main.

• Outcome:

  • Both the initial commit by B and the merge commit after resolving conflicts are pushed to origin/main.
  • The HEAD of the remote repository is now at B's merge commit, reflecting an integrated history of contributions from both users.

• General Git Conflict Guidance:

  • Conflicts typically occur when the same lines are edited.
  • Non-conflicting changes (different lines or files) usually merge automatically.
  • All committed changes by a user, including those resolved for conflicts, are pushed to the remote repository, ensuring a comprehensive update.

How to dicide the conflict?

1. Identify the Conflict

When you attempt to merge branches or pull updates from a remote repository that include conflicting changes, Git will stop the process and notify you of the conflict. Typically, the conflict message will tell you which files are conflicting.

2. Review the Conflict

Open the conflicting files in your favorite text editor or integrated development environment (IDE). Git marks the conflicts in the file so you can easily see which parts are at odds:

<<<<<<< HEAD

// Your changes

1+1=2

=======

// Incoming changes

1+1=3 >>>>>>> branch-a

• HEAD refers to your current branch.
• branch-a is the branch you are trying to merge into your branch.

3. Decide on the Changes

You need to decide how to integrate the changes from both sides. Consider the following:

• Functional Requirements: Which change aligns best with the project requirements or goals?
• Quality and Impact: Does one change introduce errors or regressions? Choose the one that maintains or improves quality.
• Team Input: In collaborative settings, discuss with the team or the developers involved. This can be crucial for deciding on changes that affect multiple aspects of the project.

4. Edit and Resolve the Conflict

Remove the conflict markers and edit the file to incorporate the decided changes. For example, if you choose to accept the incoming changes:

1+1=3

Or, you might integrate both ideas or modify them to fit the project needs better.

5. Mark the Conflict as Resolved

Once you’ve edited the files, save them, and then use the following Git commands to mark the conflicts as resolved:

git add <filename>

This command stages the resolved file(s). Do not use git commit yet if you are in the middle of a merge or rebase; the merge or rebase process often handles the commit.

6. Continue the Merge or Rebase

After resolving all conflicts and staging the changes, continue the merge or rebase:

• For a merge:

  git commit

  Git will likely have a pre-populated commit message indicating a merge conflict resolution.
• For a rebase:

  git rebase --continue

7. Test and Validate

After resolving the conflict and completing the merge or rebase, thoroughly test the changes to ensure that everything works as expected and that no new issues have been introduced.

8. Push ChangesFinally, push your changes to the remote repository to share the resolved conflict with your team:

git push origin <branch-name>

Deciding on how to resolve conflicts requires understanding the code, project requirements, and potentially communicating with your team to ensure that the best possible decision is made for the integrity and functionality of the application.

From User A's perspective, once User B has resolved any conflicts and pushed their merge commit back to the remote repository, the state of the repository will reflect a new commit that integrates both A's and B's changes. This merge commit essentially updates the repository to include all agreed-upon changes, and from A's point of view, it might look like their original commit has been "updated" or augmented with additional modifications or conflict resolutions brought in by B.

But what if B didn't make an initial commit, B add a line and then pull the remote repo which is updated to A's commit, what will happen?

If User B adds a line to their local repository but hasn't committed that change before pulling from the remote repository (which has been updated with User A's commit), the outcome will depend on whether B's uncommitted changes conflict with the changes in the remote repository. Here's how the process generally unfolds:

Scenario Breakdown:

1. Uncommitted Changes in B’s Working Directory:

   • User B edits a file and adds a line but does not commit these changes. These modifications remain in the working directory.

2. Pulling the Remote Changes:

   • When B pulls from the remote repository (which includes A's latest committed changes), a couple of scenarios can occur:

No Conflicts:

• Non-Conflicting Changes:
  • If the changes made by A do not conflict with the uncommitted changes in B's working directory (i.e., they are in different parts of the file or unrelated files), Git will attempt to automatically merge A’s changes into B’s local repository.
  • If the automatic merge is successful, B will see A's changes reflected in their local repository, and their uncommitted changes will still be present in the working directory.

With Conflicts:

• Conflicting Changes:
  • If A's changes conflict with B's uncommitted changes (e.g., both modified the same lines in the same file), Git will not complete the pull and will alert B that there are conflicts that prevent the merge.
  • B will then need to resolve these conflicts manually. This involves choosing between A's changes, B's changes, or combining them in some way. However, since B's changes are uncommitted, they need to be careful to manage their local modifications during conflict resolution.

Steps to Resolve and Continue:

1. Stash or Commit Local Changes (Optional but Recommended):

   • To avoid complications with uncommitted changes during a pull, B might choose to use git stash to save the changes temporarily before pulling. After pulling and updating their local repository, B can then git stash pop to reapply their uncommitted changes and handle any conflicts at that time.

2. Manual Conflict Resolution:

   • If conflicts occur and B has not stashed their changes, they will need to manually edit the files to resolve the conflicts, then proceed as usual by adding and committing the resolved files.

3. Commit and Continue:

   • Once B has resolved any conflicts (whether through stashing or direct editing), they should commit the resolved changes to ensure that their local repository is fully synchronized with the remote, including both A’s and their own contributions.

4. Push If Necessary:

   • After resolving conflicts and committing, B can push their changes to the remote repository if they need to share their modifications with the team.