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Git LFS & Bisect

Goal

  • In this project you will learn:
    • How to use git-LFS. For that we will add a website to our versioning.
    • How to use git bisect.

Task 1 - Git LFS

First we need to create a new repository.

  • Create a new folder called website in VSCode.

  • Navigate into the new folder and make a repository out of it with git init.

  • Now we need a website. On https://freehtml5.co/ you can find many templates for websites. Just search for a template you like.

  • Click on the download button and copy the download URL with a right click and a click on copy link url.

  • Download the template as a zip-file with:
curl --output website.zip <URL>
  • Extract the zip file with:
unzip website.zip
  • Remove the website.zip.

Task 2

Now we have all files we need in our repository and as a next step we want to commit these files. Nevertheless we also want all binary files to be deposited with git LFS. The first step is to tell git that we are going to use LFS in this repository:

git lfs install

Now we need to tell git what binary files we want to manage with LFS. This is possible to configure with any file extension as follow:

git lfs track "-.<file-extension>"

Important: don't forget the quotation marks. Which file extensions we need to track is depending on the template that was downloaded earlier. The results of the track commands can be reviewed in the file .gitattributes. Now we can commit our changes:

  • Commit the website.

Task 3

We will now push our repository to the Gitlab server. On the server you will find a project with the name git-lfs. On the landing page of the project you are instructed on how to push an already existing repository to this project.

  • Push the repository.

Note the output on the command line regarding the processing of the LFS files. On the Gitlab project page you can see those LFS files as well. These are also marked as LFS managed there. If someone else, with installed git lfs, will check out this repository in the future, everything will setup and work out of the box.

Task 4 - Bisect preperations

Search in Gitlab for the project git-bisect and clone it.

Solution (Click on the arrow if you are stuck)
  • Search in Gitlab in the left upper corner Menu->Projects for the project git-bisect. If you don't find the project directly here, you can find it under Your projects.
  • Copy the link from Clone with HTTPS.
  • Switch back to the terminal of the VSCode instance and ensure that the current working directory is /root/workspace. Therefore move upwards from previous repositories with cd .. or alternatively switch directly into the directory with: cd /root/workspace.
  • Clone the project with the command git clone {URL}.

Task 5 - Manual bisect

A fellow developer is asking you for help. He noticed that something is broken on his branch but cannot find the commit that started this change. All you know is the following:

  • On main it is working.
  • On his branch 'bisect_manual' it doesn't work.
  • The branch 'bisect_manual' is 50 commits ahead of main.

For simplicity the branch only contains a file named test.txt. It contains either 'Here is my good code...' or 'Here is my bad code...'. Your task is to find the commit that introduced the change from 'good' to 'bad'.

  • Start by switching to the branch 'bisect_manual'.
  • Take a look at the file test.txt (cat test.txt).
  • Begin the search with git bisect start.
  • Mark the known last good commit git bisect good <id> and the current bad commit with git bisect bad <id>.
Solution (Click on the arrow if you are stuck)
  • To start the bisect process, run the following commands: 
    git bisect start
git bisect good main
git bisect bad HEAD

  • Git checks out a commit in between main and HEAD. Check if that commit is good or bad with cat test.txt and mark the commit accordingly with git bisect good or git bisect bad.

  • Repeat the process until you receive the commit which broke your code.

Once finished, inspect the changes of the commit you found and stop the bisect process.

Solution (Click on the arrow if you are stuck)
  • Verify the changes in the commit with git show <id>.
  • End the bisect process with git bisect reset.

Task 6 - Automated bisect

Did you find it tedious to check every commit by hand?

Bisect comes with a 'run' option that helps you automate the process. This can come in handy if you want to find a commit in a bigger part of your project history. This time the branch has 50.000 commits. In addition to the test.txt, there is also a check_commit.sh script. Its purpose is to distinguish between good and bad commits.

  • Start by switching to the branch bisect_auto.
  • Take a look at the branch.
  • Take a look at the script.
  • Begin the search with git bisect start
  • After you tagged a good and a bad commit, try git bisect run ....
Solution (Click on the arrow if you are stuck)
  • To start the bisect process, run the following commands: 
    git bisect start
git bisect good main
git bisect bad HEAD
  • To start the automation with the script run: 
    git bisect run ./check_commit.sh