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2.3-branches_merging.qmd
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2.3-branches_merging.qmd
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---
title: "Intro to `git`"
subtitle: "Block 2.3: Branches & Merging"
---
# Alternate Realities: <br> `git branches` {background-color="black" background-opacity="0.7" background-image="images/backgrounds/suganth-V1YEEItoOTE-unsplash.jpg"}
::: attribution
Background: https://unsplash.com/photos/V1YEEItoOTE
:::
## What are git branches? 🌳
- Branches allow you to have different versions of your code within the same repository next to each other
- You can switch back and forth between branches
- In the end you can merge your changes back into your `main` branch
:::{.callout-note}
The default branch used to be called `master`, this was more-or-less recently changed to `main`, but not all repositories have changed yet.
:::
## What are git branches? 🌲 {background-color="#5cbcfc"}
## Creating new branches
- There are two ways to create new branches
- `git checkout -b my-branch` ✅
- Create a new branch and immediately check it out
- `git branch my-branch` ❌
- Create a new branch, but **don't** check it out
```bash
git checkout -b my-branch
# Switched to a new branch 'my-branch'
```
## Working on branches
- So far you have always been working on a single branch: `main`
- Nothing changes when working with multiple branches, you just have to keep an eye on your current branch
```bash
git status
# On branch my-branch
# nothing to commit, working tree clean
```
## Switching branches
You can switch branches with `git checkout` (as we've already done earlier)
```bash
git checkout my-branch
```
:::{.callout-tip}
There's no more `-b` when the branch already exists
:::
:::{.callout-note}
You can also use `git switch my-branch`, but this command is still experimental right now and may change.
:::
## Bringig it all together: Merging
- You can combine two different branches by merging them with each other
- `git merge my-branch`
- You will merge the branch that you name in the command *into* the one you are currently on
- In most cases you will want to be on the `main` branch when using `git merge` (but not always!)
- Merging will create a new "merge" commit
## Bringig it all together: Merging
:::{.callout-note}
Only branches with a shared history can be merged, but this should (almost) always be the case.
:::
## Visual Example of Merging {background-color="#5cbcfc"}
# Demo: [learngitbranching.js.org](https://learngitbranching.js.org/?NODEMO?) {background-color="black" background-opacity="0.7" background-image="images/backgrounds/berlin-demo-govid-loAFGkJxYzgxu3NKnZ.gif"}
::: attribution
Background: https://giphy.com/gifs/berlin-demo-govid-loAFGkJxYzgxu3NKnZ
:::
## Practical: Branches and merging {background-color="black"}
1. Go back to your Terminal in `git-exercise`
2. Create a new branch called `new-feature`
- Make sure to also checkout that branch, you can check whether you're on it with `git status`
3. Add a commit on that new branch
4. Go back to `main`
6. Merge the `new-feature` branch into `main`
7. Repeat all the above steps (with a different branch name & commit) using a GUI
# The Ugly Side of `git`: Merge Conflicts {background-color="black" background-opacity="0.5" background-image="images/backgrounds/git-merge-cFkiFMDg3iFoI.gif"}
## What are Merge Conflicts?
- `git` is very smart in the way it combines changes from two branches
- **But** there's not always a clear solution
- If git doesn't know how to merge the two branches, we get a *merge conflict*
- Merge conflicts have to be manually resolved (by us)
## How to Get a Merge Conflict 🧨
And how to avoid it.
- Merge conflcits occur when there are edits to the same file (and at the same location) on two different branches
- If you merge your branches / edits before making more changes, you can avoid conflicts
## Merge Conflicts: Illustration (1)
## Merge Conflicts: Illustration (2)
## Merge Conflicts: Illustration (3)
## Resolving Merge Conflicts
- To resolve a merge conflict, we will have to pick one of the two versions
- Once a solution is picked for every conflict you can commit the solution and the merge continues / finishes
- Picking a solution is easiest to do by using GUI tools
- Both Sourcetree and VSCode have great UIs for this
# DEMO: Resolving merge conflicts in VS Code and SourceTree
# *Practical:* Creating & Resolving a Merge Conflict {background-color="black"}
## Practical: Setup {background-color="black"}
1. Create a new file called `guessing_conflict.txt`
2. Write the "Question" with the letters A to D into the file, with empty lines in between e.g.
```text
Question A
Question B
Question C
Question D
```
## Practical: Setup {background-color="black"}
3. Create a new branch called `guesses` and check it out
- Double check whether you checked out the correct branch with `git status`
4. We're done with the preparations
## Practical: Guessing Game {background-color="black"}
Write your guess below the line with the matching letter.
a) How many liters of Beer have been drunken at the Oktoberfest in Munich in 2019? 🍻
b) How many people live in Karlsruhe? (Exactly) 🏘️
c) What percentage of Americans asked in a survey in 2017, indicated that they believe in Astrology? 🌟
d) What percentage (same sample as C), indicated that they believe in psychics? 🔮
## Practical: Guessing Game Answers {background-color="black"}
5. Check out the `main` branch again
6. Write down the actual answers below the letters in the now empty file again
```text
Question A 🍻 Liters of beer [^1]
7,850,200
Question B 🏘️ People in Karlsruhe
313,092
Question C 🌟 % believing in Astrology [^2]
29%
Question D 🔮 % believing in Psychics [^2]
41%
```
[^1]: https://opendata.muenchen.de/tr/dataset/oktoberfest
[^2]: https://www.pewresearch.org/fact-tank/2018/10/01/new-age-beliefs-common-among-both-religious-and-nonreligious-americans/
https://opendata.muenchen.de/tr/dataset/oktoberfest
## Practical: The Actual Conflcit {background-color="black"}
7. Use `git merge` to merge the `guesses` branch into your `main` branch
8. Explore the files in the resulting merge conflict
9. Resolve the merge conflict
## 🎉 Bonus Practical: *learngitbranching* {background-color="black"}
1. Go to https://learngitbranching.js.org/
2. Finish Lessons 1, 2 and 3 on the website
## 🎉 Bonus: Rebasing - The Alternative to Merging
- You can also combine two branches by rebasing them (instead of merging)
- When rebasing, all extra commits on your current branch will be moved to the target branch
- This alters the affected commits ‼️
- Leads to a single history
- Use with caution
```bash
# You call git rebase e.g. on the feature branch
git checkout feature
```
::: attribution
More Info: <https://www.atlassian.com/git/tutorials/merging-vs-rebasing>
:::
## 🎉 Rebasing: The Alternative to Merging {background-color="#5cbcfc"}
:::: {.columns}
::: {.column .fragment width="50%"}
Merging
{width=65%}
:::
::: {.column .fragment width="50%"}
Rebasing
{width=65%}
:::
::::
## *End of Block* 🎉 {background-color="black" background-opacity="0.4" background-image="images/backgrounds/dolomites.jpg"}
:::{.r-fit-text}
Any Questions?
:::
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