Bazel is an open-source build and test tool developed by Google. It is designed to handle large-scale software projects with complex dependencies and is used to automate the building and testing of code.

 

Here are some key features and characteristics of Bazel:

1.    High Performance: Bazel is optimized for speed and can efficiently handle large codebases with many dependencies. It supports parallel execution and caching to minimize build times.

2.    Language Support: Bazel supports multiple programming languages, including Java, C++, Python, Go, and more. It allows for polyglot builds, where projects can have components written in different languages.

3.    Reproducible Builds: Bazel ensures that builds are reproducible by maintaining a consistent build environment. This means that given the same source code, dependencies, and environment, Bazel will produce the same build outputs.

4.    Scalability: Bazel is designed to scale with your project. It can handle projects with millions of lines of code and complex dependency graphs.

5.    Remote Execution and Caching: Bazel can distribute build and test tasks across multiple machines, leveraging remote execution and caching to further speed up the build process.

6.    Extensibility: Bazel is highly extensible, allowing users to define custom build rules and macros to fit their specific needs.

7.    Dependency Management: Bazel provides a robust mechanism for managing dependencies, ensuring that builds are correct and isolated from changes in the environment or other parts of the codebase.

 

Bazel is used by many large organizations, including Google, to manage their extensive codebases and complex build processes.

 

Bazel terms and basics explained

Workspace

The workspace is typically the directory where Bazel constructs your project's build files from your source code. It contains various source files in a nested hierarchical fashion. At the highest or root level of your workspace, your project might also have a dedicated WORKSPACE text file. It contains references to all the external dependencies your project requires to generate your builds. Precisely, the workspace is where your inputs are extracted and converted to outputs to generate the desired build file.

Packages

Packages are simply directories located below the top-level directory in a workspace. They contain your build files that may be named BUILD or BUILD.bazel , along with other related files and specified dependencies. One package may be nested in another since your source code is organized in a hierarchical fashion.

Targets

Everything inside your packages can be considered targets. It includes source files that developers of your team wrote and added to your project or generated files that Bazel constructs based on your build configurations. Other than files, targets often involve rules that govern the relationship between your input files and output files. In other words, target rules specify how Bazel is going to construct your build files, the intermediary steps it's going to take along with every executable operation it will need to perform. Your input files for target rules could be either source files or generated files. Although, your output files are always generated files, since it's an outcome of the build tool itself. You may specify your target rules to chain your inputs and outputs for consecutive build operations. For instance, you could use a generated file from a previous step as an input file for another step in the future.

Labels

The nomenclature of a target is known as a label. It's just a way to recognize different targets falling under a package and distinguishing them from other targets in the same or different packages.

Dependencies

When you build your specified targets, one or more target may depend on another for the build process. The latter is a dependency. To explain further, consider two targets Target1 and Target2. Let's say Target1 needs Target2 at build or execution time. We can express this relationship as a Directed Acyclic Graph that demonstrates how Target1 is dependent on `Target12 in this process. Bazel calls this a dependency graph and is used to differentiate between actual and declared dependencies.

 

Build Files

Earlier, we said that under a WORKSPACE every package contains its own BUILD file. Build files contain the program that enables Bazel to generate the desired builds for your project. It's evaluated using Starlark and contains a list of sequential statements that are executed by Bazel. The build files contain your declared rules, functions that execute these rules, and variables required in a simple syntax form.

We know that Bazel caches previous builds for speeding up the build process. Whenever your source files change, it is the BUILD file that Bazel references for understanding the underlying changes.

Commands

Bazel offers a set of commands that allow you to execute certain operations. The simplest command you can run is to check if Bazel is successfully installed in your system: $ bazel version