Motivation

I recently activated my heavens-arena repository to be my public notebook of source codes.

I had previously created two separate repositories for my self learning of Conan package manager and PlantUML. [By the way, I have given tech talks on these two topics internally in my corporate world at the Smart Coffee Break—of which, I’m also an organizer.] I decided to consolidate those repositories into this new single notebook.

Merging git repositories

Simply copy-pasting the files from one repository to another is no fun. If I did that, I would have no reason to write this blog. I wanted to properly merge those two repositories into the new one, including their respective commit histories. I’m not sure if this is more amusing or amazing: I could do this seemingly complex task easily without referring any documentation or StackExchange/reddit forums, or any technical blogs.

One of the most useful things for a git user to know is what a git commit actually is, which I most certainly do. [I will separately write a post later that will explain a git commit in a simple manner, that would make it very easy to follow various git commands.] For now, here are the steps to merge a git repository into another, using my above-mentioned conan repository as example.

  • Checkout destination branch in destination repository: Checkout the branch in the destination repository where the commits from the other (source) repository should be merged.

    In my current case, the destination repository is heavens-arena, where I created a new branch conan.

    C:\WORK\dragondive\heavens-arena (zero -> origin)
λ git checkout -b conan

  • Add the other repository as a remote: git generally has pointer to a single remote repository (usually named origin), but one can configure additional remote repositories.

    In my case, the other repository is conan_learning, which I added as a second remote:

    C:\WORK\dragondive\heavens-arena (conan)
λ git remote add conan https://github.com/dragondive/conan_learning.git

    • (Optional) Verify remotes information:

      C:\WORK\dragondive\heavens-arena (conan)
λ git remote --verbose
conan   https://github.com/dragondive/conan_learning.git (fetch)
conan   https://github.com/dragondive/conan_learning.git (push)
origin  https://github.com/dragondive/heavens-arena.git (fetch)
origin  https://github.com/dragondive/heavens-arena.git (push)

  • Fetch from other remote: This will bring the commits from the other remote into the “local scope”.

    C:\WORK\dragondive\heavens-arena (conan)
λ git fetch -p conan
remote: Enumerating objects: 227, done.
remote: Counting objects: 100% (227/227), done.
remote: Compressing objects: 100% (154/154), done.
remote: Total 227 (delta 68), reused 223 (delta 64), pack-reused 0
Receiving objects: 100% (227/227), 899.79 KiB | 1.60 MiB/s, done.
Resolving deltas: 100% (68/68), done.
From https://github.com/dragondive/conan_learning
 * [new branch]      master     -> conan/master

  • List the commits from the other remote: This enables cherry-picking the commits to the current branch in the next step.

    C:\WORK\dragondive\heavens-arena (conan)                                               
λ git log --oneline conan/master                                                       
e152634 (conan/master) added doxyfile for plantuml demo                                
82ccd56 minor fix to CMakeLists.txt                                                    
514fb75 enhanced conan_gtest example to include boost library                          
83f84f6 Added README.md with links to blog entries                                     
b343514 Added blog "Profiles, build_requires and cross-building"                       
01eb4cb Moved example source codes into sources directory                              
92b7c4d Added blog "Working with non-Conan packages"                                   
05d9170 Added example for cross-building from Linux to Windows                         
ae233a3 Added Conan profile files                                                      
d99d61b Added example for creating Conan package from non-Conan packages               
6e2d432 Made a few small improvements                                                  
869f34a Added blog "Publishing conan package to artifactory"                           
4659c3f Added blog "Creating and testing a conan package"                              
9b5a364 Added conanfile.py to create the package                                       
5e57c52 Added blog "Setting up Google Test with Conan package manager"                 
ea0aa94 Added blog "Getting Started with Conan"                                        
38f5b3c Added conan_gtest simple example

  • cherry-pick the required commits: The required commits can now be cherry-picked to the current branch.

    There are several ways to do this:

    • Specify a range of commits: In my case, this is the most suitable approach as I want to cherry-pick all the commits. From the above git log output, I specified the first and last commit as below:

      C:\WORK\dragondive\heavens-arena (conan)
λ git cherry-pick 38f5b3c..e152634

    • Interactive rebase “hack”: For more complex choice of commits, one could “hack” an interactive rebase and then in the text file that opens up, specify the list and order of commits to be cherry-picked. [I may write about this approach separately in another post.]

    Any merge conflicts that occur during the cherry-picking should be resolved, in the usual manner as with any rebase operations.

  • Push the new branch to the destination remote: After the successful cherry-pick operation, the commits from the other remote are now available on the new branch in the destination repository, and can be pushed to remote as usual.

    C:\WORK\dragondive\heavens-arena (conan)
λ git push origin conan

Similarly, I merged the PlantUML repository onto another branch in heavens-arena. The two branches are now available as below:

Note that the history is not lost on the destination branch as the commit includes information about the original author and time:

C:\WORK\dragondive\heavens-arena (plantuml -> origin)
λ git log -1 --pretty="fuller"
commit 8ebaeaaac6ceb9fcaacd0eb3a70a3d6cb80284d6 (HEAD -> plantuml, origin/plantuml)
Author:     Aravind Pai <dragondive@outlook.in>
AuthorDate: Thu Oct 21 15:06:57 2021 +0530
Commit:     Aravind Pai <dragondive@outlook.in>
CommitDate: Sat Mar 18 19:16:50 2023 +0530

  bugfix: added video for integration markdown