Branching (revision control)

Branching, in revision control and software configuration management, is the duplication of an object under revision control (such as a source code file or a directory tree) so that modifications can happen in parallel along both branches.

Branches are also known as trees, streams or codelines. The originating branch is sometimes called the parent branch, the upstream branch (or simply upstream, especially if the branches are maintained by different organizations or individuals), or the backing stream. Child branches are branches that have a parent; a branch without a parent is referred to as the trunk or the mainline.

In some distributed revision control systems, such as Darcs, there is no distinction made between repositories and branches; in these systems, fetching a copy of a repository is equivalent to branching.

Branching also generally implies the ability to later merge or integrate changes back onto the parent branch. Often the changes are merged back to the trunk, even if this is not the parent branch. A branch not intended to be merged (e.g. because it has been relicensed under an incompatible license by a third party, or it attempts to serve a different purpose) is usually called a fork.

Branches allow for parts of software to be developed in parallel. Large projects require many roles to be filled, including developers, build managers, and quality assurance personnel. Further, multiple releases on different operating system platforms may have to be maintained. Branches allow contributors to isolate changes without destabilizing the codebase, for example, fixes for bugs, new features, and versions integration. These changes may be later merged (resynchronized) after testing.

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