Avoiding conflicts

• Develop on feature branches!
• Conflicts can be avoided if you think and talk with your colleagues before committing.
• Monolithic entangled spaghetti-code maximizes risk of conflicts.
• Modular programming minimizes risk of conflicts.
• Resolve conflicts early.
• If a branch affects code that is likely to be modified by others, the branch should:
  • be short-lived and/or merge often to the main development line.
  • merge the main development line often to stay up-to-date.

Develop on feature branches

• Keeps bugs away from the main development line.
• Divide and conquer: do not create a branch for “everything”.
• The more you do on one branch the longer it will take until you can reintegrate it, and vice versa

When is a good moment to merge?

• Feature branches merge to master typically once (at the end of their lifetime).
• But there may be good reasons for merging branches to master more often (release branch).
• For modular projects with write-protected master and code review and very high discipline:
  • You typically should not merge master except the occasional git cherry-pick.
• For entangled projects where most of the development happens directly on master:
  • It is good to merge master to your topic branch often to stay in sync with main development line.
  • Merge conflicts should be resolved early.

How to test combinations of features?

• I develop feature-a, my colleague develops feature-b.
• Both are not ready yet to go into the main line.
• How can we test their combination?
• Do not cross-merge feature branches.
• Reason: if feature-a becomes ready, it cannot be integrated to the main line because it is then diluted with feature-b.
• Test combinations on integration branches.
• Integration branches only receive merges, we do not “work” on them.
• Same holds for testing combinations with the main line.
• The main line should ideally be an integration branch.

Encountering a bug while working on a feature branch

Common situation:

• While working on your feature branch you discover a defect or bug that has nothing to do with your new feature.
• You are a responsible developer and you do not want to leave this defect.
• You decide to fix this defect right on your new branch “while at it”.
• This is probably a bad idea - why?

• Reasoning
  • If you fix it on your branch other people might not see it.
  • You may want to merge it to master but you cannot since your new feature is not ready yet.
  • Perhaps somebody else will fix it on master in a different way and then it will conflict with your new feature.
  • Before you commit a change, think: “who needs this change?”.
  • Based on the answer select the appropriate branch.
  • Develop separate features on separate branches and be very strict and disciplined with this.
• Better solution
  • Fix it on master, so other developers can see it.
  • More specifically, fix it on a hotfix-X branch and merge it to master.
  • Than merge it to your development/topic branch.

• Developing separate features on separate branches minimizes conflicts.
• It makes branches shorter-lived, which again minimizes conflicts.

Wrong branch - what now?

Help! I made a commit to the “wrong” branch and it is a public branch and I was told I should not edit public commits, what now?

Solution: git cherry-pick the commit to the “right” branch:

Rewinding the local master branch

You made few commits to the local master branch. You then realize that it broke some tests but you have no time now to fix them. So you wish you had committed them to an experimental branch instead.

What now?

You want to move last three commits to a separate branch.

First make sure that your working directory and staging area are empty.

Then create a new branch (e.g. feature):

Now reset master back three commits:

$ git checkout master
$ git branch feature   # create feature branch but stay on master
$ git reset --hard c2  # on master

Another job well done. However, this should not be done if the commits have already been shared with others.

How do we correct public commits?

• Not with git reset because we do not want to change the history for commits that others depend on.
• We use git revert which creates new commits that revert changes.
• git revert does not modify past commits.

Exercises

In the following exercises you will practice cherry-picking commits, testing combinations of features, and rewinding the master branch.

Let’s continue with “recipe” directory from the previous episode:

$ git graph

*   13792bc (HEAD -> master) Merge branch 'dislike-cilantro'
|\  
| * b542667 reduce the amount of cilantro
* | 5a35ac6 we try with more cilantro
|/  
*   f0272c2 (origin/master, origin/HEAD) Merge branch 'less-salt'
|\  
| * 89d5730 (origin/less-salt) reduce amount of salt
* |   0e6c5b1 Merge branch 'experiment'
|\ \  
| * | d4d360e (origin/experiment) maybe little bit less cilantro
| * | b859fe2 let us try with some cilantro
| |/  
* | b100795 draft a README.md file
|/  
* 78d6661 enjoy your dish!
* 8094aee add half an onion
* 4c02218 adding ingredients and instructions

And create a dev branch:

$ git branch
  dev
* master

Exercise 1: Cherry-picking commits

We will fix a “bug” on the dev branch, and then cherry-pick it to master.

• First checkout the dev branch.
• Then replace “salt” with “onion” in the last line of the ingredients file (fixing the bug).
• Realize that you committed to the wrong branch.
• Switch to the master branch, and cherry-pick the bugfix from the dev branch.
• Inspect the result with git graph.

Exercise 2: Testing combinations of features

Use the same repository as in the previous exercise.

• Create two new branches from the master branch.
• In each, add a new ingredient to ingredients.txt.
• Create a new branch integration from one of the new branches.
• Merge the other branch into the integration branch. Resolve conflicts if needed.
• Inspect the result with git graph.

Exercise 3: Rewinding the local master branch

• Make a couple of commits on the master branch.
• Realize that these commits should have been on a new branch feature.
• Create a new branch feature, and rewind the master branch.
• Inspect the result with git graph.