Add assignment1 draft
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Alex Hirsch
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[*.{hpp,cpp,h,c}]
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assignment1/README.md
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# Assignment 1 (draft)
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*due on 18 November 2020*
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In this first assignment you are tasked to create a very basic version control system (VCS) similar to [Git](https://git-scm.com/) or [Mercurial](https://www.mercurial-scm.org/).
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For this assignment you are *not* allowed to work in teams.
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You are not allowed to use code from other people participating in this course.
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Always state the origin of non-original code and ideas.
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It is recommend to be familiar Git to understand the intensions behind the following commands.
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## `lit`
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All functionality of your VCS is bundled into one executable named `lit`.
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Similar to `git`, it provides multiple *sub-commands* like `checkout` and `status`.
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These sub-commands are always provided as first argument to `lit` and explained below.
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### `lit help`
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Displays a concise usage information.
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Each sub-command is listed and described briefly.
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### `lit init`
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To initialize a repository run `lit init` inside some directory.
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This directory is now the root of the repository.
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Additionally, the VCS creates a new folder `.lit` containing all internal data.
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All files of the directory are tracked.
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There is no need to explicitly add them as you'd do with Git.
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### `lit status`
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Lists all files that have been added, removed, or modified, with respect to the currently checked out commit.
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Keep the output concise, similar to `git status --short`.
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### `lit commit`
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Creates a new commit containing *all* changes.
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In contrast to Git, there is no staging area.
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A commit is comprised of a unique identifier, the identifier of the previous commit, a timestamp, a message, and the recorded changes.
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The message is provided to the `commit` sub-command as additional argument.
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As unique identifier use a counter (starting from 0) and prefix the value with `r` (for revision).
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```
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$ lit commit 'Commit message goes here'
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Commit: r42
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Date: Mon Sep 28 23:27:53 CEST 2020
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```
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### `lit show`
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This sub-command is used to inspect the given commit.
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If no commit is specified, display the currently checked out one.
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```
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$ lit show r42
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Commit: r42
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Date: Mon Sep 28 23:27:53 CEST 2020
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Commit message goes here
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--- a/Assets/Generic/Logic/Utils/Math.cs
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+++ b/Assets/Generic/Logic/Utils/Math.cs
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@@ -1,5 +1,10 @@
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using UnityEngine;
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+static class Vector2Extensions
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+{
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+ public static Vector3 AsVector3(this Vector2 v) => new Vector3(v.x, v.y);
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+}
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+
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static class Vector3Extensions
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{
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public static Vector2 AsVector2(this Vector3 v) => new Vector2(v.x, v.y);
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```
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### `lit checkout`
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This resets the state of all files to the given commit's state.
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All un-commited changes are dropped upon checkout.
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If no commit is specified, reset the current state to the currently checked out commit.
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You can add new branches by first checking out a previous commit, and then creating a new commit.
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### `lit merge`
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This command initiates a merge with the currently checked out commit and the specified commit.
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A merge is only initiated if there are no un-commited changes.
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Auto-merging files that have been touched in both branches is not supported.
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If a file has been modified in both branches, the whole file is treated as a conflict.
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If a conflict is encountered, stop the merge process and provide the respective files of the other branch as well as the common base.
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```
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$ lit merge r1
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Merge conflict(s) detected:
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- robot.c
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$ ls
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robot.c # currently checked out version.
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robot.c.r1 # version of the other branch
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robot.c.r0 # common base of both branches
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# Manually resolving the merge conflict:
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$ vimdiff robot.c robot.c.r1 robot.c.r0
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# Cleanup
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$ rm robot.c.r1 robot.c.r0
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$ lit commit
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```
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To complete the merge after manually resolving a conflict, invoke the `commit` sub-command.
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To abort the merge, use `checkout`.
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### `lit log`
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Displays a graph of all commits, one line per commit.
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The currently checked out commit is highlighted.
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You don't have to follow the exact format of this example:
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```
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$ lit log
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o─┐ < r3 "Merge r2 with r1"
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│ o r2 "Add chocolate egg dispenser"
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o │ r1 "Add coin operated self destruct feature"
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o─┘ r0 "First Commit"
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```
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## Implementation
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You are only allowed to use:
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- C++ standard library (C++17 standard)
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- C standard library (as fallback)
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- POSIX standard library
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- `diff` / `patch` command
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You must use CMake as build system.
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Use [ClangFormat](https://clang.llvm.org/docs/ClangFormat.html) to automatically format your code using the provided `.clang-format` configuration.
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There is probably a plugin for your text editor / IDE to automate this process.
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Your VCS must store the differences (as reported by `diff -u`).
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Storing a full copy of the repository's files for each commit is not allowed.
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You don't need to track empty folders, yet files located in sub-directories.
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You may assume that only one instance of your VCS operators on a repository at any point in time.
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Hence, you don't need to add some form of locking mechanism to prevent concurrent access.
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The executable does not depend on any additional resources (except for `diff` and `patch`).
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You may assume that `diff` and `patch` are present and available via `PATH`.
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**Hint:** It may be a good idea to create a dedicated class for invoking shell commands like `diff` and `patch`.
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Simply using `system(3)` may not give you enough control over the process as you also need to interactive with `stdin` / `stdout`.
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Consider using `popen(3)` and getting some inspiration from [Go's `exec` package](https://golang.org/pkg/os/exec/) or [Python's `subprocess` module](https://docs.python.org/3/library/subprocess.html).
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## Testing
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Along with this specification a rudimentary test script [`lit-test`](lit-test) is provided, have a look at it.
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It assumes that the `lit` executable is in your path.
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Remember that you can use `bash -x` to debug the test script.
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You are encouraged to setup some more test cases for your implementation.
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## Evaluation (9 points)
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- (3) Can create new commits and checkout old ones (no branches)
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- (2) Can create new branches and switch between branches
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- (1) Can inspect a commit using `lit show`
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- (1) Can merge two branches (no conflict)
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- (1) Can merge two branches (with conflict)
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- (1) Can display a graph with all commits and their relationships
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## Submission
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TBD
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181
assignment1/lit-test
Executable file
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assignment1/lit-test
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#!/bin/bash
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set -euo pipefail
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readonly TEST_DIR=$(mktemp --tmpdir --directory lit-test.XXXXXX)
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echo "== Using $TEST_DIR"
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pushd "$TEST_DIR"
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echo "== Initializing repository"
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lit init
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echo "== Creating the first commit"
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cat >file1 <<-EOF
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This is the first line of the first file. 🚀
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This is the second line of the first file.
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EOF
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# Let's check the status. Should look something like this:
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# Changes:
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# Add file1
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lit status
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# We expect the first commit to be identified as r0.
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lit commit "Add file1"
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echo "== Creating more commits"
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echo >>file1 "A third line is added to the first file."
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# Let's check the status again, just to be sure.
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lit status
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# This one would be r1.
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lit commit "Extend file1"
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echo >>file1 "A forth line is added."
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# This should be r2.
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lit commit "Extend file1 even further"
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echo "== Displaying graph"
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# o < r2 Extend file1 even further
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# o r1 Extend file1
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# o r0 Add file1
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lit log
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echo "== Switching to r0"
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lit checkout r0
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# Checking the file content.
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diff -s file1 - <<-EOF
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This is the first line of the first file. 🚀
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This is the second line of the first file.
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EOF
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echo "== Switching back to r2"
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lit checkout r2
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# Checking the file content again.
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diff -s file1 - <<-EOF
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This is the first line of the first file. 🚀
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This is the second line of the first file.
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A third line is added to the first file.
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A forth line is added.
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EOF
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echo "== Adding and discarding changes"
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echo >>file1 "This fifth line should be gone in an instant."
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lit checkout
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# Let's confirm.
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diff -s file1 - <<-EOF
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This is the first line of the first file. 🚀
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This is the second line of the first file.
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A third line is added to the first file.
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A forth line is added.
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EOF
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echo "== Creating another branch"
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lit checkout r0
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mkdir subfolder
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cat >subfolder/file2 <<-EOF
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This is the first line of the second file.
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And another line in the second file.
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EOF
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# This should be r3.
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lit commit "Add file2"
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# o < r3 Add file2
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# │ o r2 Extend file1 even further
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# │ o r1 Extend file1
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# o─┘ r0 Add file1
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lit log
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echo "== Going back"
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lit checkout r2
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# file2 should be gone.
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test ! -f subfolder/file2
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echo "== Merging (no conflict)"
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# This creates a merge commit r4.
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lit merge r3
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# file2 should now be present.
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diff -s subfolder/file2 <<-EOF
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This is the first line of the second file.
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And another line in the second file.
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EOF
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# o─┐ < r4 Merge r3 into r2
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# │ o r3 Add file2
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# o │ r2 Extend file1 even further
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# o │ r1 Extend file1
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# o─┘ r0 Add file1
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lit log
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echo "== Setting up a conflict"
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echo >>file1 "Fifth line ontop of r4."
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lit commit "Extend file1 one way" # r5
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lit checkout r3
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echo >>file1 "Third line ontop of r3."
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lit commit "Extend file1 another way" # r6
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# o < r6 Extend file1 another way
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# o │ r5 Extend file1 one way
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# o─┤ r4 Merge r3 into r2
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# │ o r3 Add file2
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# o │ r2 Extend file1 even further
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# o │ r1 Extend file1
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# o─┘ r0 Add file1
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lit log
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# Going back and merging.
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lit checkout r5
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lit merge r6 || true
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# Let's check all file versions:
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# Current commit
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diff -s file1 - <<-EOF
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This is the first line of the first file. 🚀
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This is the second line of the first file.
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A third line is added to the first file.
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A forth line is added.
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Fifth line ontop of r4.
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EOF
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# other breanch
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diff -s file1.r6 - <<-EOF
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This is the first line of the first file. 🚀
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This is the second line of the first file.
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Third line ontop of r3.
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EOF
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# common base
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diff -s file1.r3 - <<-EOF
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This is the first line of the first file. 🚀
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This is the second line of the first file.
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EOF
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# To resolve the conflict, we simply take the version of the current commit.
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rm file1.r6 file1.r3
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lit commit # r7
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# o─┐ < r7 Merge r6 into r5
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# │ o r6 Extend file1 another way
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# o │ r5 Extend file1 one way
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# o─┤ r4 Merge r3 into r2
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# │ o r3 Add file2
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# o │ r2 Extend file1 even further
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# o │ r1 Extend file1
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# o─┘ r0 Add file1
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lit log
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echo "== Cleanup"
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popd
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rm -r "$TEST_DIR"
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