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257 lines
11 KiB
Markdown
---
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title: Project management 2. Git continued
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marp: true
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paginate: true
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theme: buutti
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---
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<!-- headingDivider: 3 -->
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<!-- class: invert -->
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# Project management 2. Git continued
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## Branches
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* A Git repository can have multiple ***branches***
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* By default, a Git repository has only one branch
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* named either `master` or `main`
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* Using multiple branches makes it possible to work on new features step by step in their own ***feature branches***
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* Meanwhile, the `master` branch is kept clean and in a working state
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* Only when the feature is completed, the branch is merged into the `master` branch!
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### Active branch
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* Even though your local repository can have multiple branches, only one of them is *active* at a given time
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* `git status` tells you firsthand which branch you are on: `On branch master`
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## `git branch` & `git checkout`
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* You can create a new branch with `git branch <branchName>`
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* The new branch is not empty: it contains a copy of the code of the branch you executed this command in
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* ***Note:*** `git branch <branchName>` does not make the branch active!
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* To make the branch active, a.k.a "move" to the branch:
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* `git checkout <branchName>`.
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* For example, to move back to master use `git checkout master`
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### Local vs. remote branches
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* `git branch <branchName>` only creates a local branch
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* When you try to push changes from a new local branch, Git nags you that a matching remote branch doesn't yet exist
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* Git tells you how to create the remote branch:
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* `git push --set-upstream origin <newBranch>`
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* Afterwards, `git push` pushes the changes to the matching remote branch
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### Extra branch commands
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* Handy command: `git checkout -b <branchName>`
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* It's a shorthand for `git branch <branchName>` + `git checkout <branchName>`
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* Get a list of local branches with `git branch`
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* ...and all branches (incl. the remote ones) with `git branch -a`
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* Delete a local branch with `git branch -d <branchName>`
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* Remote branch can be deleted in the GitHub/etc website
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* ...or with `git push origin -d <branchName>`
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* ***Note:*** If deleted remote branches still show up in `git branch -a`, you can use the command `git remote prune origin` to remove them from the list.
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## `git merge`
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* So you've been working on a feature branch. What next?
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* When the feature is done (and all the broken things fixed), you want to apply your changes back to `master`
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* For this, we use `git merge <branchToMerge>`
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* It applies changes from `<branchToMerge>` to the ***current active branch***
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* `master` branch is usually (and should be) protected, so we can't merge our new code to `master` directly
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* Instead, we do the *inverse*.
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## Merging with a pull request
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1) Make sure you have the newest version of the `master` branch:
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* Checkout `master` branch
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* Pull changes from GitHub/etc
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* Checkout the feature branch
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* Merge the contents of `master` to `featureBranch` with `git merge master`
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2) Then, create a ***pull request*** on GitHub/etc (In GitLab, it's called ***merge request***!)
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* This creates a formal process for merging your *remote* feature branch to remote `master`
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* This adds a layer of protection to the `master` branch: no direct merging!
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---
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* UI of a new pull request (*Pull requests > New pull request*) can be confusing...
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* *base* is the branch you're merging, *compare* is the branch you're merging into!
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### If automatic merge fails...
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1) Pull remote changes to your local `master`.
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* ***Pro tip:*** If you're on your feature branch, you can do this quickly without changing branches with
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```git fetch origin master:master```
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2) Merge changes from `master` to your local feature branch.
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3) Fix the ensuing ***conflicts*** (see [next section](#3-conflicts))
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4) Push your new local branch to GitHub/etc
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## Extra: Merging without a pull request
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<!-- _class: "extra invert" -->
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1) First, checkout the `master` branch with `git checkout master`
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2) Then, do a `git pull` so you have the newest version of the `master` branch
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* Someone else might have done changes to it while you were working on your feature!
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3) Then, merge `<featureBranch>` to `master` with `git merge <featureBranch>`
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* Fix conflicts
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## Exercise 1. Pushing onwards
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<!--_class: "exercise invert" -->
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Continue the exercise from [Git Basics](1-git-basics) or create a new repository for these exercises.
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* Create a new branch (with a name `new-feature`, for instance) in your local repository.
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* Checkout the branch, make some changes to `GitTest.md` there, and push the changes to GitHub.
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* Then, merge the changes from your `new-feature` branch to `master` branch by using
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a) pull request in GitHub
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b) `git merge` from command line
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## GitLens
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* To make the Git workflow easier, install the GitLens extension to VS code
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* It helps in managing conflicts, comparing branches or commits
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* Install it from the Extensions panel (access with ***CTRL+SHIFT+X***)
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* Adds many new views to the source control tab:
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* Commits
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* Repositories
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* File History
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* Line History
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* Branches
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* Remotes
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* etc...
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# 3. Conflicts
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## Conflicts
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* Sometimes two people have made changes in the same lines of code!
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* This leads to a conflict.
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* Let's assume we're trying to merge changes from featureBranch to master.
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* If a conflict happens, the merge does not conclude automatically. Instead, we need to ***fix all the conflicts*** by hand and then ***conclude the merge*** with some commands.
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* Conflicting lines of code are framed by some `<<<<<<< garbage ======= symbols >>>>>>>` we don't yet understand
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* Before we can conclude the merge, we need to get rid of the garbage.
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### Said garbage
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```c#
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<<<<<<< HEAD:Player.cs
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if (Input.anyKey) {
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return true;
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}
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=======
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if (Input.anyKey)
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return true;
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>>>>>>> featureBranch:Player.cs
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```
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* ***Current change*** is between `<<<<<<<` and `=======`: old code in `master`
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* ***Incoming change*** is between `>>>>>>>` and `=======`: new code from `featureBranch`
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* Use your text editor to choose which (or some combination of both) you want to preserve
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### VS Code tools
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* VS Code gives us tools to make conflict resolution a quick process
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* Click which lines of code you want to preserve:
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* ***Accept Current Change*** (old code is preserved, new code removed)
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* ***Accept Incoming Change*** (new code is preserved, old code removed)
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* ***Accept Both Changes*** (both are preserved)
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## After resolving the conflict
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* After resolving conflicting files, use `git add <filename>` to add them to the commit
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* Then use `git commit` to apply changes (without a message! no `-m`)
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* Close the automatically opened `COMMITMSG` file. This should finish the merge.
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* Then just `git push` to apply changes in the remote repository
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<!-- _footer: "If VS code is not configured properly as Git's text editor, and you encounter an error, run `git config core.editor code --wait`" -->
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## Exercise 2. Fixing conflicts
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<!--_class: "exercise invert" -->
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* Create a new branch in your local repository, but do not checkout it just yet.
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* First, we simulate your teammate's changes by making changes to the `master` branch directly: On the `master` branch, make some changes to `GitTest.md`, and **add & commit**.
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* Then, checkout the new feature branch.
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* Then, make some other changes to GitTest.md to the same line as before, **add & commit**.
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* Then, merge the changes from the `master` branch to your feature branch by using `git merge`
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* Fix the ensuing conflicts, add & commit & push.
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* Now you can create a pull request to merge your changes to the master branch.
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## Git workflow 3: Undoing
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* Git doesn't have a general "undo" command
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* If you make a mistake, it is very case-specific what you need to do to fix it
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* See [undo options here](https://docs.gitlab.com/ee/topics/git/numerous_undo_possibilities_in_git/)
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* Also, [ohshitgit.com](https://ohshitgit.com/)
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## `git log` & `git checkout <hashcode>`
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* Use `git log` to see the commit history
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* Or `git log --oneline` for a more concise version
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* Press ***Q*** to quit the log view.
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* The newest changes are seen on top
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* On the left side of the commit message you see the ***hashcode*** of the commit
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* Use `git checkout <hashcode>` to "time travel" into the commit
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* ***Note:*** If you have GitLens, check the Commits view in the Source control tab to see the commit history.
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## Revert one file to a previous state
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* Sometimes you want to revert just one file to its previous state
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* For that, you need to figure out the commit hash of the state you want to return to
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* Find that out in one of the following methods:
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* `git log --oneline`
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* VS Code: *Source control > File history*
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* GitHub: check commits
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* Then, run
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* `git checkout <commit-hash> -- <filename>`
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## Collaboration in Unity
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* ***The zeroth rule:*** Make sure that everyone on team uses the same Unity and package versions.
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* ***The first rule:*** Don't ever work on the same thing simultaneously.
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* ***The second rule:*** When you do break rule #1, make necessary changes in communication so you won't break it again.
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* Be sure to communicate about ***scene ownership***
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* Scenes are not code files, so you can't easily merge changes if two people have worked on them
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* Thus, the ***Scene Owner*** will be the only person on the team who should be working on a certain scene
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* If a scene needs GameObject contributions from others, they can create prefabs that the Scene Owners then add to their scene
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## Exercise 3. Branching team effort
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<!--_class: "exercise invert" -->
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* Work as a group for this assignment.
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* Continue Exercise 2 from [Git basics](1-git-basics).
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* Every group member creates an individual branch from the master, and makes some changes to the `GitTest.md` file.
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* Add new files as well, at least one per group member.
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* Do not tell other group members what you're going to change! :D
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* Then, merge the changes back to the master branch. Fix ensuing conflicts, if any appear.
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## Reading
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* [Pro Git book](https://git-scm.com/book/en/v2)
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* [Oh shit Git](https://ohshitgit.com/)
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* [Undo possibilities](https://docs.gitlab.com/ee/topics/git/numerous_undo_possibilities_in_git/)
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## Very extra: `git rebase`
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<!-- _class: "extra invert" -->
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* `git merge` creates a new commit for the merge process
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* Sometimes that's undesirable, so an alternative is to use `git rebase`
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* Unlike merge, rebase applies changes from the rebased branch ***one commit at a time***
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* Whenever there's a conflict:
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1) After fixing the conflict, add the conflicting file with `git add <filename>`
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2) Then continue the rebase process with `git rebase --continue`
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3) If you want to disregard a conflicting commit, use `git rebase --skip`
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4) If you get cold feet, you can cancel the rebase with `git rebase --abort`
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* ***Note:*** A good link for [understanding rebase](https://borbware.github.io/unity-basics-course/project-management/2-git-continued-slides.html)
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## Very very extra: Git submodules
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<!-- _class: "extra invert" -->
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* To add external code to your project from someone else's repository, Git has a neat system called *submodules*
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* To add a submodule to your project, use `git submodule add <submodule-url> <folder>`
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* To remove a submodule, use `git rm <path-to-submodule>`
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* If you clone a project with submodules, you need to run `git submodule update --init --recursive` once.
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* ***Note:*** If you don't want submodules to appear in the Source control tab of VS Code, go to settings and disable the *Git: Detect Submodules* setting. |