Migrating to Git and GitHub

Solve merge and rebase conflicts

Imagine that there are two branches and you want to merge them, there are two main ways to do it:

• Merge: It creates a new commit with two parents, the last commit of each branch. All conflicts between the branches are resolved in that commit (See more information in git-merge Manual Page).
• Rebase: It re-apply all the commits of one of the branches next to the last commit from the other (See more information in git-rebase Manual Page).

The idea of this document is to illustrate both process from the beginning to the end.

Scenario

Initial state

Suppose that we have a repository with only one file with the follow content:

    Merge Demo
    ================

    This is a demo file created to demonstrate how to resolve conflicts with git.

    Line 2

    Line 3

    Line 4

Branch A state before merge

We have a branch-a with 3 commits, one for each change, the content of last version of the file before merge in this branch is:

    Merge Demo
    ================
    
    This is a demo file created to demonstrate how to resolve conflicts with git.
    
    Change 1 (from branch-a)
    
    Line 2
    
    Change 3 (from branch-a)
    
    Line 3
    
    Change 2 (from branch-a)
    
    Line 4

Branch B state before merge

We have a branch-b with 3 commits, one for each change, the content of last version of the file before merge in this branch is:

    Merge Demo
    ================
    
    This is a demo file created to demonstrate how to resolve conflicts with git.
    
    Change 2 (from branch-b)
    
    Line 2
    
    Change 3 (from branch-b)
    
    Line 3
    
    Change 1 (from branch-b)
    
    Line 4

Desired state

Suppose that we expect the follow content after the merge:

    Merge Demo
    ================
    
    This is a demo file created to demonstrate how to resolve conflicts with git.
    
    Change 2
    
    Line 2
    
    Change 3
    
    Line 3
    
    Change 2
    
    Line 4

Merge process

We want to merge branch-a into branch-b.

$ git checkout branch-b
$ git merge branch-a

But there are conflicts. So we will edit it with notepad (you can also use your favorite merge tool, I like p4merge)

Notice that the conflicts are all together, and are fixed in only one step.

When the result file is done, we commit the modified file, creating a merge commit with two parents.

$ git add demo-file.md
$ git commit -m 'Merge branch-a'

Rebase process

To demonstrate Rebase, I will reset the state as before to merge. And then start to rebase branch-b on branch-a.

$ git checkout branch-b
$ git rebase branch-a

It shows a conflict between branch-a and the first commit of branch-b

When it is fixed (with notepad in this case), we apply the changes and continue with rebase process.

$ git notepad demo-file.md
$ git add demo-file.md
$ git rebase --continue

In this case there are conflicts between the result of previous state and the second commit of branch-b.

And conflicts with the third commit. When all branch-b commits are applied on top of branch-a, the rebase finish.

You can download this repository with all the commits, branches and tags from https://github.com/MakingSense/resolve-conflicts-demo.git