Отмена изменений

Отмена коммитов и изменений

In this section, we will discuss the available 'undo' Git strategies and commands. It is first important to note that Git does not have a traditional 'undo' system like those found in a word processing application. It will be beneficial to refrain from mapping Git operations to any traditional 'undo' mental model. Additionally, Git has its own nomenclature for 'undo' operations that it is best to leverage in a discussion. This nomenclature includes terms like reset, revert, checkout, clean, and more.

A fun metaphor is to think of Git as a timeline management utility. Commits are snapshots of a point in time or points of interest along the timeline of a project's history. Additionally, multiple timelines can be managed through the use of branches. When 'undoing' in Git, you are usually moving back in time, or to another timeline where mistakes didn't happen.

This tutorial provides all of the necessary skills to work with previous revisions of a software project. First, it shows you how to explore old commits, then it explains the difference between reverting public commits in the project history vs. resetting unpublished changes on your local machine.

Finding what is lost: Reviewing old commits

В основе любой системы управления версиями лежит идея хранения «безопасных» копий проекта, чтобы у разработчиков не возникало опасений безвозвратно испортить базу кода. Когда в проекте сохранена история коммитов, можно повторно оценивать и анализировать любые ранее выполненные коммиты. Один из лучших инструментов для просмотра истории репозитория Git — команда git log. В примере ниже мы используем команду git log для получения последних коммитов популярной графической библиотеки с открытым исходным кодом.

git log --oneline
e2f9a78fe Replaced FlyControls with OrbitControls
d35ce0178 Editor: Shortcuts panel Safari support.
9dbe8d0cf Editor: Sidebar.Controls to Sidebar.Settings.Shortcuts. Clean up.
05c5288fc Merge pull request #12612 from TyLindberg/editor-controls-panel
0d8b6e74b Merge pull request #12805 from harto/patch-1
23b20c22e Merge pull request #12801 from gam0022/improve-raymarching-example-v2
fe78029f1 Fix typo in documentation
7ce43c448 Merge pull request #12794 from WestLangley/dev-x
17452bb93 Merge pull request #12778 from OndrejSpanel/unitTestFixes
b5c1b5c70 Merge pull request #12799 from dhritzkiv/patch-21
1b48ff4d2 Updated builds.
88adbcdf6 WebVRManager: Clean up.
2720fbb08 Merge pull request #12803 from dmarcos/parentPoseObject
9ed629301 Check parent of poseObject instead of camera
219f3eb13 Update GLTFLoader.js
15f13bb3c Update GLTFLoader.js
6d9c22a3b Update uniforms only when onWindowResize
881b25b58 Update ProjectionMatrix on change aspect

Each commit has a unique SHA-1 identifying hash. These IDs are used to travel through the committed timeline and revisit commits. By default, git log will only show commits for the currently selected branch. It is entirely possible that the commit you're looking for is on another branch. You can view all commits across all branches by executing git log --branches=*. The command git branch is used to view and visit other branches. Invoking the command, git branch -a will return a list of all known branch names. One of these branch names can then be logged using git log <branch_name>.

When you have found a commit reference to the point in history you want to visit, you can utilize the git checkout command to visit that commit. Git checkout is an easy way to “load” any of these saved snapshots onto your development machine. During the normal course of development, the HEAD usually points to master or some other local branch, but when you check out a previous commit, HEAD no longer points to a branch—it points directly to a commit. This is called a “detached HEAD” state, and it can be visualized as the following:

Git Tutorial: Checking out a previous commit

Переход к старой версии файла не перемещает указатель HEAD. Он остается в той же ветке и в том же коммите, что позволяет избежать открепления указателя HEAD. После этого можно выполнить коммит старой версии файла в новый снимок состояния, как и в случае других изменений. Соответственно, такое использование команды git checkout применительно к файлу позволяет откатиться к прежней версии отдельного файла. Для получения дополнительной информации об этих двух режимах посетите страницу команды git checkout.

Просмотр старых версий

This example assumes that you’ve started developing a crazy experiment, but you’re not sure if you want to keep it or not. To help you decide, you want to take a look at the state of the project before you started your experiment. First, you’ll need to find the ID of the revision you want to see.

git log --oneline

Let’s say your project history looks something like the following:

b7119f2 Continue doing crazy things
872fa7e Try something crazy
a1e8fb5 Make some important changes to hello.txt
435b61d Create hello.txt
9773e52 Initial import

You can use git checkout to view the “Make some import changes to hello.txt” commit as follows:

git checkout a1e8fb5

This makes your working directory match the exact state of the a1e8fb5 commit. You can look at files, compile the project, run tests, and even edit files without worrying about losing the current state of the project. Nothing you do in here will be saved in your repository. To continue developing, you need to get back to the “current” state of your project:

git checkout master

Предположим, вы ведете разработку в главной ветке по умолчанию. При каждом возвращении в главную ветку можно использовать команду git revert или git reset для отмены нежелательных изменений.

Undoing a committed snapshot

Технически существует несколько стратегий отмены коммитов. В дальнейших примерах предполагается, что история коммитов выглядит следующим образом:

git log --oneline
872fa7e Try something crazy
a1e8fb5 Make some important changes to hello.txt
435b61d Create hello.txt
9773e52 Initial import

We will focus on undoing the 872fa7e Try something crazy commit. Maybe things got a little too crazy.

How to undo a commit with git checkout

С помощью команды git checkout мы можем перейти к предыдущему коммиту , a1e8fb5, и вернуть репозиторий в состояние, предшествовавшее этому безумному коммиту. Переход к отдельному коммиту переведет репозиторий в состояние открепленного указателя HEAD. Работа при этом перестает принадлежать какой-либо из веток. При открепленном указателе HEAD все новые коммиты будут оставаться без родителя, пока вы не вернете ветки в положенное состояние. «Сборщик мусора» в Git удаляет коммиты без родителя. Этот сервис работает с определенными интервалами и удаляет такие коммиты без возможности восстановления. Чтобы такие коммиты не были удалены «сборщиком мусора», перед их выполнением нужно убедиться, что мы работаем в ветке.

From the detached HEAD state, we can execute git checkout -b new_branch_without_crazy_commit. This will create a new branch named new_branch_without_crazy_commit and switch to that state. The repo is now on a new history timeline in which the 872fa7e commit no longer exists. At this point, we can continue work on this new branch in which the 872fa7e commit no longer exists and consider it 'undone'. Unfortunately, if you need the previous branch, maybe it was your master branch, this undo strategy is not appropriate. Let's look at some other 'undo' strategies. For more information and examples review our in-depth git checkout discussion.

How to undo a public commit with git revert

Предположим, мы вернулись к исходному примеру истории коммитов. Истории, в которую входит коммит 872fa7e. В этот раз попробуем отмену путем обратной операции. При исполнении команды git revert HEAD Git создаст новый коммит с операцией, обратной последнему коммиту. В текущую историю ветки будет добавлен новый коммит, и она будет выглядеть следующим образом:

git log --oneline
e2f9a78 Revert "Try something crazy"
872fa7e Try something crazy
a1e8fb5 Make some important changes to hello.txt
435b61d Create hello.txt
9773e52 Initial import

At this point, we have again technically 'undone' the 872fa7e commit. Although 872fa7e still exists in the history, the new e2f9a78 commit is an inverse of the changes in 872fa7e. Unlike our previous checkout strategy, we can continue using the same branch. This solution is a satisfactory undo. This is the ideal 'undo' method for working with public shared repositories. If you have requirements of keeping a curated and minimal Git history this strategy may not be satisfactory.

How to undo a commit with git reset

Рассмотрение этой стратегии отмены мы продолжим на нашем рабочем примере. Команда git reset — это расширяемая команда с разнообразными функциями и вариантами использования. Если мы выполним команду git reset --hard a1e8fb5, история коммитов будет сброшена до указанного коммита. Просмотр истории коммитов с помощью команды git log теперь будет выглядеть так:

git log --oneline
a1e8fb5 Make some important changes to hello.txt
435b61d Create hello.txt
9773e52 Initial import

The log output shows the e2f9a78 and 872fa7e commits no longer exist in the commit history. At this point, we can continue working and creating new commits as if the 'crazy' commits never happened. This method of undoing changes has the cleanest effect on history. Doing a reset is great for local changes however it adds complications when working with a shared remote repository. If we have a shared remote repository that has the 872fa7e commit pushed to it, and we try to git push a branch where we have reset the history, Git will catch this and throw an error. Git will assume that the branch being pushed is not up to date because of it's missing commits. In these scenarios, git revert should be the preferred undo method.

Undoing the last commit

In the previous section, we discussed different strategies for undoing commits. These strategies are all applicable to the most recent commit as well. In some cases though, you might not need to remove or reset the last commit. Maybe it was just made prematurely. In this case you can amend the most recent commit. Once you have made more changes in the working directory and staged them for commit by using git add, you can execute git commit --amend. This will have Git open the configured system editor and let you modify the last commit message. The new changes will be added to the amended commit.

Undoing uncommitted changes

Before changes are committed to the repository history, they live in the staging index and the working directory. You may need to undo changes within these two areas. The staging index and working directory are internal Git state management mechanisms. For more detailed information on how these two mechanisms operate, visit the git reset page which explores them in depth.

The working directory

The working directory is generally in sync with the local file system. To undo changes in the working directory you can edit files like you normally would using your favorite editor. Git has a couple utilities that help manage the working directory. There is the git clean command which is a convenience utility for undoing changes to the working directory. Additionally, git reset can be invoked with the --mixed or --hard options and will apply a reset to the working directory.

The staging index

The git add command is used to add changes to the staging index. Git reset is primarily used to undo the staging index changes. A --mixed reset will move any pending changes from the staging index back into the working directory.

Undoing public changes

When working on a team with remote repositories, extra consideration needs to be made when undoing changes. Git reset should generally be considered a 'local' undo method. A reset should be used when undoing changes to a private branch. This safely isolates the removal of commits from other branches that may be in use by other developers. Problems arise when a reset is executed on a shared branch and that branch is then pushed remotely with git push. Git will block the push in this scenario complaining that the branch being pushed is out of date from the remote branch as it is missing commits.

Предпочтительная команда для отмены общей истории коммитов — git revert. Команда revert безопаснее, чем reset, так как она не удаляет коммиты из общей истории. Команда revert сохраняет отменяемые вами коммиты и создает новый коммит с операцией, обратной последнему коммиту. Этот метод можно безопасно применять в общих распределенных рабочих средах, так как удаленный разработчик может выполнить пул ветки и получить новый коммит, который отменяет его нежелательный коммит.

Summary

We covered many high-level strategies for undoing things in Git. It's important to remember that there is more than one way to 'undo' in a Git project. Most of the discussion on this page touched on deeper topics that are more thoroughly explained on pages specific to the relevant Git commands. The most commonly used 'undo' tools are git checkout, git revert, and git reset. Some key points to remember are:

  • Обычно после коммита внесенные изменения отменить невозможно
  • Используйте git checkout для переходов и просмотра истории коммитов
  • git revert is the best tool for undoing shared public changes
  • git reset is best used for undoing local private changes

Помимо основных команд отмены, мы рассмотрели другие команды Git: git log для поиска потерянных коммитов, git clean для отмены изменений, не подтвержденных коммитами, и git add для изменения индексирования.

Each of these commands has its own in-depth documentation. To learn more about a specific command mentioned here, visit the corresponding links.