Branches

About branches

Branches let you develop features, fix bugs, or safely experiment with new ideas in a contained area of your repository.

You always create a branch from an existing branch. Typically, you might create a new branch from the default branch of your repository. You can then work on this new branch in isolation from changes that other people are making to the repository.

A branch you create to build a feature is commonly called a feature branch or topic branch. See Managing branches within your repository.

You can also use a branch to publish a GitHub Pages site. See GitHub Pages とは.

You must have write access to a repository to create a branch, open a pull request, or delete and restore branches in a pull request. See GitHubに対するアクセス許可.

About the default branch

GitHub にコンテンツがあるリポジトリを作成すると、GitHub により、1 つのブランチを持つリポジトリが作成されます。リポジトリ内のこの最初のブランチがデフォルトブランチです。 The default branch is the branch that GitHub displays when anyone visits your repository. The default branch is also the initial branch that Git checks out locally when someone clones the repository. 異なるブランチを指定しないかぎり、リポジトリ内のデフォルトブランチが新しいPull Requestやコードコミットのベースブランチになります。

By default, GitHub names the default branch main in any new repository.

既存のリポジトリのデフォルトブランチを変更できます。詳しくは、「デフォルトブランチを変更する」をご覧ください。

新しいリポジトリのためのデフォルトブランチの名前を設定できます。詳細については、「リポジトリのデフォルトブランチ名を管理する」、「組織のリポジトリのデフォルトブランチ名を管理する」、「Enterprise でリポジトリ管理ポリシーを適用する」を参照してください。

Working with protected branches

Protected branches help maintainers enforce rules on important branches. A protected branch can block force pushes or deletion, require status checks, require reviews, require code owner approval, or require signed commits before changes can merge.

These protections help teams keep important branches stable and make expectations clear before a pull request is merged. To see whether your pull request can be merged, check the merge box at the bottom of the pull request's Conversation tab. See 保護されたブランチについて.

メモ

If you're a repository administrator, you can merge pull requests on branches with branch protections enabled even if the pull request does not meet the requirements, unless branch protections have been set to "Include administrators."

Comparing branches in pull requests

A pull request compares the proposed changes on the head branch with the base branch. When you create your pull request, you can change the base branch that you're comparing your changes against. The Files changed tab shows what would change if the pull request merged.

Diff views help reviewers understand the changes without reading every commit. You can view a unified diff, split diff, rich diff, or source diff; ignore whitespace changes; or filter files to focus on the most relevant changes.

Diffs may not display if a pull request exceeds repository diff limits or if a file is hidden by a rule in the repository's .gitattributes file. See リポジトリの制限 and GitHubでの変更されたファイルの表示方法のカスタマイズ.

Three-dot and two-dot Git diff comparisons

The git diff command supports two comparison methods. Pull requests on GitHub show a three-dot diff.

Method	Command	What it compares
Three-dot	`git diff A...B`	The most recent common commit of both branches (merge base) and the most recent version of the topic branch.
Two-dot	`git diff A..B`	The most recent state of the base branch (for example, `main`) and the most recent version of the topic branch.

A two-dot diff compares two Git committish references, such as SHAs or OIDs (Object IDs), directly with each other. On GitHub, the Git committish references in a two-dot diff comparison must be pushed to the same repository or its forks.

See Git diff options from the Pro Git book site.

About three-dot comparison on GitHub

Because the three-dot comparison uses the merge base, it focuses on "what a pull request introduces."

When you use a two-dot comparison, the diff changes when the base branch is updated, even if you haven't made any changes to the topic branch. A two-dot comparison also focuses on the base branch, which can make the changes introduced by the topic branch harder to understand.

In contrast, a three-dot comparison keeps showing the changes introduced by the topic branch since the branches diverged.

Merging often

To avoid confusion, merge the base branch (for example, main) into your topic branch frequently. When you merge the base branch, the diffs shown by two-dot and three-dot comparisons are the same. We recommend merging a pull request as soon as possible. This encourages contributors to make pull requests smaller, which we recommend in general.

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