Bazel vs Pants: What are the differences?

Introduction

Bazel and Pants are both build systems that provide tools and workflows for managing software builds. While they have similarities, there are key differences that set them apart.

1. Build File Language: Bazel uses Starlark, a Python-like configuration language, for writing build files, while Pants primarily uses a declarative BUILD language, which is more concise and easier to read and write.

2. Build Execution: Bazel has a distributed caching feature that enables efficient reusability of build artifacts across different machines and builds, making it ideal for large-scale projects. On the other hand, Pants focuses more on incremental builds and maximizing parallelism within a single machine, making it suitable for smaller and medium-scale projects.

3. Build Graph: Bazel represents the build graph as a directed acyclic graph (DAG), which allows for fine-grained control over build dependencies and enables efficient parallelization. Pants, on the other hand, represents the build graph as a target hierarchy, which provides high-level visibility but can be less optimal for some complex dependency scenarios.

4. Ecosystem: Bazel has a mature and extensive ecosystem with support for various programming languages and frameworks, including C++, Java, and Python. It also has a large community and a well-documented set of rules and tools. Pants, while also supporting multiple languages, has a smaller ecosystem and a more focused community primarily around Python projects.

5. Configuration and Extensibility: Bazel allows users to extend its functionality through custom rules and provides a flexible and extensible configuration system. Pants, on the other hand, focuses on simplicity and convention-over-configuration, aiming to minimize the need for customization by providing a set of sensible defaults.

6. Tooling and Integration: Bazel integrates well with popular development tools and IDEs, such as Visual Studio Code and IntelliJ, providing features like code navigation, autocompletion, and integrated test runners. While Pants also has some tooling support, it may not be as extensive or seamless as Bazel's integration.

In summary, Bazel and Pants differ in their build file languages, build execution strategies, representation of build graphs, ecosystem support, configuration approach, and tooling/integration capabilities.