What is source code management?

As software projects and products grow, their associated source code might turn complex and unwieldy. SCM helps transform that complexity and unwieldiness into a more manageable system, leading to agility and scalability.

Source code management consists of these key features:

• Repository

• Version control

• Branching

• Commits

• Merging

A repository, also called a repo, houses a project’s source code and other related artifacts, such as build scripts, configuration files, database scripts, documentation, integration tests and unit tests. Think of repos as organized storage spaces or warehouses for software products.

This shared, centralized repository can be hosted on prem or in the cloud. Private repos are typically used for closed source or proprietary software, while open-source software employs public repos.

Software development teams can choose between two primary repository architectures:

• Monorepo: A monorepo holds multiple projects within a single repository. It generally applies to tightly coupled components.

• Polyrepo: Polyrepos keep projects in their own separate repositories. This architecture is commonly used for loosely coupled components, such as microservices.

Version control allows teams to keep a history of the codebase. It tracks various versions of source code files and artifacts so modifications can be traced and won’t be lost permanently. Developers can compare current source code with its version history, reverting to previous versions as necessary and helping with debugging. This version history can also form the basis of release notes, which are published alongside software launches or updates.

A branch is a separate copy of the source code repository that can be checked out and cloned to a developer’s local environment. A repo can be forked into different branches, and changes can be made to a branch without affecting the central repository. With branching, team members can tackle different parts of the codebase simultaneously, facilitating parallel development.

A main branch acts as the “trunk” from which all branches originate and merge back into. It contains the latest stable version or production-ready release of code.

Software engineering teams can adopt a branching strategy that fits their needs. For instance, they can create a dedicated branch for each new feature and another branch just for bug fixes, or follow a stacked workflow that branches off from previous changes so code changes build on top of each other.

A commit records a set of changes to the source code and repository history. As a best practice, atomic commits represent a single logical change that addresses only one specific task, passes all required tests and compiles or builds without failing, leaving the codebase in a valid state. Commits must be accompanied by clear and meaningful commit messages that describe what changed and why.

Merging refers to incorporating reviewed and approved code changes from one branch into the main branch. Most modifications can be automatically merged. In cases where a conflict occurs, such as when two separate changes impact the same lines of code, merging will need to be done manually to resolve conflicts.

Source code management and version control are often used interchangeably but reflect different purposes.

Version control makes up only one part of source code management. It focuses on tracking and managing version history, giving it a small scope.

Meanwhile, source code management includes version control but also involves workflows and how code is organized. It’s broader in scope, touching on different phases of the software development lifecycle (SDLC).

Source code management is vital to most phases of the software development lifecycle. SCM promotes proper handling of code as it flows throughout the SDLC.

This stage entails outlining a project’s design, which also includes choosing a repo architecture and setting it up. Teams map out a preliminary structure for the repository based on the software components, features or milestones defined in the design document or requirements specification document. Prototyping can help teams understand and visualize how the project’s source code and supporting files will be stored and organized.

The development phase is when branches are established. Developers write and commit code then create pull requests to flag their suggested changes for code review. Reviewers assess the changes before merging them to maintain code quality.

SCM works together with continuous integration (CI), the first part of the CI/CD pipeline and one of the hallmarks of the DevOps methodology. When source code is pushed to the repo, CI servers such as CircleCI, GitHub Actions, GitLab CI/CD and Jenkins trigger the build process, automating code compilation and packaging. CI tools run automated testing to make sure changes don’t break the codebase and identify any issues before they propagate to production.

Source code management integrates with continuous delivery (CD), which picks up where CI leaves off. SCM tools help ensure that only stable and valid source code versions are deployed, while CD tools automate the delivery of deployable code changes after they’ve passed automated testing.

Through continuous deployment, successfully validated changes are automatically deployed to production. In case a deployment fails, all these systems (SCM, CI/CD and continuous deployment) team up to seamlessly roll back to a previous stable version.

SCM facilitates smoother cycles for future releases. It’s integral to managing codebases as they evolve with bug fixes, enhancements, new features, patches, performance optimizations, refactoring and other updates.

Software engineering teams can gain these advantages from SCM systems:

• Access control and auditing

• Codebase backups

• Code quality improvements

• Efficient collaboration

• Swift software releases

Source code management can restrict access to a repository, making sure only authenticated and authorized users are allowed to make changes. This helps protect an organization’s IP and proves especially valuable for sectors like finance and healthcare, where safeguarding sensitive data remains crucial.

These systems also assist with auditing. SCM retains a complete version history of all code changes, producing a clear audit trail. This aids developers in understanding what was changed and why (through commit messages), who implemented them and when they were applied, making debugging easier and quicker.

Some SCM tools and version control systems offer functionality for backing up repos. This provides a way to restore codebases in the event of critical failures or sudden disruptions, saving teams from having to start from scratch.

Source code management streamlines code quality enhancements. Pull requests act as checkpoints, making sure commits get approved before merging to main. SCM systems can also work with linters to check for formatting or stylistic issues, static code analysis tools to pinpoint logical flaws and syntax errors, and CI tools to conduct security scanning and make sure code modifications pass tests.

With source code management, multiple developers can contribute to software projects. They don’t need to wait on one another to finish before starting their own task. All their changes are merged together in the end, with any conflicting edits resolved.

Distributed teams spread across different locations can build on each other’s work without fear of overwriting their modifications. Members can share changes with each other through pull requests, while peer reviews cultivate passing on knowledge and feedback.

Through SCM, each team member can work separately yet concurrently. And since source code management seamlessly integrates with CI/CD pipelines, delivery cycles become faster. Development teams can rapidly respond to production issues and release patches sooner.

One of the earliest iterations of SCM tools was the Source Code Control System (SCCS) developed by Bell Labs computer programmer Marc Rochkind in the 1970s. SCCS enforced a strict locking mechanism, allowing only one person at a time to modify a file, with revisions stored as full copies. Its successor, Revision Control System (RCS), improved upon SCCS, keeping a file’s latest version but storing only the differences between older versions.

In the 1980s, Concurrent Versions System (CVS) emerged. It was built on top of RCS and followed a client-server repo model that introduced concurrency and merging.

Subversion (SVN) came about in the early 2000s with the aim of being a “better CVS.” It retained much of the functionalities of CVS but added features such as atomic commits and versioned directories. Officially known as Apache Subversion, it’s currently maintained as an open-source project by the Apache Software Foundation and continues to be widely used.

The mid-2000s saw the rise of decentralized version control systems. Linux creator Linus Torvalds spearheaded the development of Git, an open-source distributed version control system originally built for the Linux kernel. Instead of storing files and their modifications, Git saves snapshots of a project’s state over time. It can be used on its own by running Git commands on the command line, but it also has a rich ecosystem of tools, including GUIs and IDE integrations.

Git serves as the foundation for some of today’s most popular source code management tools, including Bitbucket, GitHub and GitLab. But with AI agents now generating vast amounts of code, some companies are rethinking SCM. For instance, Cursor’s Origin dubs itself as the “git forge for the agentic era,” while Zed’s DeltaDB links code changes to the agent conversation that produced it. Similarly, GitLab is working on what it calls “next-generation source code management” for fleets of coding agents.