git-merge

Git Merge

Types of Merge

• Fast-Forward Merge (If branches are not Diverged)
• 3-way Merge (If branches are Diverged)

If we want to merge branch2 into branch1

# First Switch to the branch you want to merge INTO
git switch branch1
git merge branch2

# Merge with No-Fast-Forward Option
git merge --no-ff branch2

When we have Merge Conflicts

• If there is a Merge Conflict, We'll be shown a CONFLICT message by Git.
• In-order to merge changes, We'll open mergetool of our choice.
• We'll Accept the changes either Current, Incoming or Both.
• Do not Introduce any extra code while we are solving Conflicts in a Merge Operation.
• When we are done accepting those changes we'll stage those files using git add command
• We'll commit those changes using git commit

While merge Operation, we usually don't provide a Commit Message with git commit command because if we don't provide a Commit Message, Git will open a default text editor for a Commit Message with a predefined Merge Commit Message to commit the Merge.

# To Abort Merge Operation
git merge --abort

Undo Faulty Merge Commit

If we haven't shared our code with anyone else then we can use git reset and delete the Current Faulty Merge Commit and Create a new Correct Merge Commit from old bases.

# Reset to the tip of Merge Commit
git reset --hard commitId/HEAD~x

If we have shared our code with someone then we would not like to rewrite the Commit History in a complicated way. So here we'll use git revert to create a new Merge Commit which will resolve Faulty Merge Commit's code.

# Revert to i-th parent of Merge Commit
git revert -m parentIndex commitId/HEAD~x

If we merged feature branch INTO main branch then 1st Parent of the Merge Commit will be the main branch.

Squash & Merge

Let's say we are working on bugfix branch and after resolving the Bug, its time to merge that branch into main branch. Now, we want to merge those branches but We also don't wanna keep commits of bugfix branch in our History. So, We can create a commit that Combines all the changes made throughout bugfix branch and then just attach that Commit to main branch.

Combining those multiple commits into a Single Commit is Called Squashing.

# Switch to branch1
git switch branch1
# Squash Changes
git merge --squash branch2

These Squashed changes will be staged and we'll have to create a Commit Manually.

After performing Squash & Merge, we still won't be able to see it in Merged Branches list...

git branch --merged

So, It is highly suggested that we Delete Squash & Merge branches Just after we make a Successful Merge.

Rebase & Merge

Suppose We have 3 commits on branch feature and after that we made a commit on Branch main. Now, If we want to perform Fast-Forward merge only between these 2 branches then Right now it seems impossible, because branch main already has another commit; So the branches are already diverged. Unless if we Change the base of branch feature to the Tip of branch main. To do that we can perform a Rebase Operation on Branch feature which will change the Base of branch feature and then we can apply Fast-Forward Merge to it.

# Switch to Branch - Feature
git switch feature

# Perform Rebase operation on feature to change the Base to the tip of branch main
git rebase main
# Resolve conflicts if any

# Switch back to Branch - Main
git switch main

# Perform Fast-Forward Merge
git merge feature  # OR
git merge --ff-only feature

During the Rebase Operation...

# Abort Rebase Operation
git rebase --abort

# Accept current Commit and Continue Rebase Operation
git rebase --continue

# Skip current Commit and Continue Rebase Operation
git rebase --skip