Bazel vs SCons: What are the differences?

Introduction

In the world of software development, build systems play a crucial role in automating the process of converting source code into executable software. Two popular build systems used in the industry are Bazel and SCons. While they both serve the same purpose, there are key differences between them that make each suitable for different use cases.

1. Language Support: Bazel focuses on providing extensive language support, including but not limited to Java, C++, Python, and Go. On the other hand, SCons offers a more limited set of programming languages, with support for C, C++, and Python out of the box. However, SCons can be extended to support additional languages with custom builders.

2. Dependency Handling: Bazel's dependency management is based on a concept called "build graphs" which allows for efficient and parallel building of only the necessary dependencies. It uses a fine-grained analysis of the code to determine the minimal set of dependencies needed for a particular build. In contrast, SCons follows a more simplistic approach where the dependencies are explicitly defined and managed by the user.

3. Scalability and Performance: Bazel is known for its high scalability and performance, particularly in large codebases. It can handle builds with thousands of targets and millions of lines of code efficiently by leveraging distributed caching and parallelism. SCons, while being a reliable build system, might struggle with large codebases, leading to slower build times.

4. Build Configuration: Bazel adopts a declarative configuration approach, where the build rules and dependencies are defined in a separate build file using a domain-specific language called Starlark. This allows for a clear separation between the build logic and the source code. On the other hand, SCons uses a more imperative configuration approach, where build rules and dependencies are defined within the build scripts themselves, making the build configuration tightly coupled with the source code.

5. Build System Ecosystem: Bazel has gained popularity among large-scale software projects and is actively supported by Google, which develops it. It has a growing ecosystem and community support, along with an extensive set of build rules and tools. SCons, while being a mature build system, may have a smaller ecosystem in comparison, and the availability of specific tools or rules might vary depending on the language or framework being used.

6. Platform Compatibility: Bazel supports various platforms, including Linux, macOS, and Windows, making it suitable for cross-platform development. SCons also offers cross-platform compatibility, but it may require additional configuration or customization, depending on the target platform and the specific dependencies.

In summary, Bazel provides extensive language support, efficient dependency handling, high scalability, declarative build configuration, a growing ecosystem, and excellent cross-platform compatibility. On the other hand, SCons offers a more limited set of language support, user-managed dependency handling, reliable performance, imperative build configuration, and platform compatibility. The choice between Bazel and SCons depends on the specific requirements and characteristics of the software project at hand.