Abstract:

This video provides a beginner-friendly introduction to Bazel, a build system designed for large-scale monorepos. Using IntelliJ IDEA with the Bazel plugin, the tutorial demystifies Bazel's core concepts by creating a simple project and progressively adding complexity. It covers fundamental terminology, including modules, repositories, packages, and targets. The video demonstrates the modern module-based dependency management system (bzlmod), showing how to declare project dependencies, fetch external libraries like JUnit from Maven using module extensions, and add support for new languages like Kotlin. A key focus is on practical project configuration through MODULE.bazel and BUILD.bazel files. Finally, it introduces the concept of project view files (.bazelproject) as a powerful tool for improving developer experience in large monorepos by scoping the IDE to only relevant code.

Getting Started with Bazel: A Practical Guide

• 00:00:04 Introduction to Bazel: Bazel is a build system optimized for very large codebases (monorepos). This tutorial aims to explain its fundamental concepts using IntelliJ IDEA and the official Bazel plugin.
• 00:02:24 Core Tooling and Reproducibility: The setup uses Bazelisk, a launcher that automatically downloads the correct Bazel version specified in the .bazelversion file. This ensures that all developers use the same version, leading to reproducible builds.
• 00:02:53 Key Concepts: Repositories and Modules:
  • Repository: A collection of source files used in a build. The main project is the "main repository," and external dependencies (like tools or libraries) are brought in as other repositories.
  • Module: A versioned unit for dependency management in Bazel's modern system, called bzlmod. Modules are defined in the MODULE.bazel file.
• 00:05:53 Managing External Dependencies: The video demonstrates fetching external JVM libraries from Maven. This is done by using a "module extension" (maven.install) from the rules_jvm_external module to define a new repository containing libraries like JUnit. The use_repo command makes this repository's contents available for use.
• 00:07:45 Key Concepts: Packages and Targets:
  • Package: A directory containing a BUILD.bazel file. It acts as a unit of visibility and organization for code.
  • Rule: A function (e.g., java_binary, java_test) that tells Bazel how to perform actions, such as compiling code.
  • Target: The output artifact defined by a rule within a BUILD file. It's the primary thing Bazel builds or tests.
• 00:09:51 Declaring Dependencies: The deps attribute in a rule specifies its dependencies. The tutorial shows how to link to a target in another local package (//app/src/main/java:main) and a target from an external repository (@test_deps//:junit_junit).
• 01:11:45 Fetching Library Sources: To enable "go to definition" and view source code for external libraries in the IDE, you can add the fetch_sources = True parameter to the maven.install configuration in MODULE.bazel.
• 01:13:35 Adding Support for a New Language: To build Kotlin code, you first add the rules_kotlin module as a dependency in MODULE.bazel. Then, you use the appropriate rule (e.g., kt_jvm_library) in the BUILD.bazel file to compile the Kotlin source files.
• 01:15:43 Improving Monorepo Workflow with Project Views: For large monorepos, .bazelproject view files allow developers to configure the IntelliJ plugin to only load and display specific directories and targets. This significantly improves IDE performance and reduces clutter by hiding irrelevant parts of the codebase.