Bazel build tool

Bazel is a powerful and fast build tool created by Google. It is designed to handle large-scale codebases across multiple languages and platforms. Bazel can build and test software quickly and reliably, offering advanced features such as incremental builds, remote builds, and dependency management. Here's a comprehensive overview of Bazel and its key features:

Key Features of Bazel

1. Language Agnostic:

   • Bazel supports multiple programming languages including Java, C++, Python, Go, and more.
   • It uses specific build rules for each language to handle compilation, packaging, and testing.

2. Fast and Incremental Builds:

   • Bazel performs incremental builds by only rebuilding the parts of the codebase that have changed.
   • This reduces build times significantly, especially for large projects.

3. Reproducible Builds:

   • Bazel ensures that builds are hermetic, meaning they are isolated from the environment and produce the same output given the same input.
   • This is achieved through sandboxing and strict dependency management.

4. Scalability:

   • Bazel is designed to scale with large codebases and large teams.
   • It can handle complex build graphs with thousands of build targets and dependencies.

5. Remote Build Execution:

   • Bazel can offload build and test actions to remote servers, distributing the workload and speeding up the build process.
   • This is especially useful for large projects with heavy computational requirements.

6. Extensibility:

   • Bazel is highly extensible, allowing custom build rules and macros to be defined.
   • Users can write their own rules in Starlark, a subset of Python used for Bazel configuration.

7. Dependency Management:

   • Bazel manages dependencies explicitly, ensuring that builds are reproducible and dependencies are tracked accurately.
   • External dependencies are specified in the WORKSPACE file.

Core Components of Bazel

1. WORKSPACE File:

   • Defines the root of the project and specifies external dependencies.
   • Each Bazel project has a WORKSPACE file at its root directory.

2. BUILD Files:

   • Contain build rules and targets for the project.
   • Each directory with source code usually has a BUILD file defining how to build the code in that directory.

3. Build Targets:

   • A build target is a unit of code or data that Bazel can build, such as a library, binary, or test.
   • Targets are specified in BUILD files using rules like java_library, cc_binary, etc.

4. Rules:

   • Rules define how to build different types of targets.
   • Bazel has built-in rules for many languages, and users can define custom rules using Starlark.

Example of a Bazel Project

WORKSPACE File

The WORKSPACE file sets up external dependencies and repositories:

workspace(name = "my_project")

# Load rules for Java
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "rules_java",
    urls = ["https://github.com/bazelbuild/rules_java/releases/download/4.0.0/rules_java-4.0.0.tar.gz"],
    sha256 = "e8aa167a5918f6b567e5b2a416e1a9a0c0a0d2eb6aaebfede7cf2db577a6d0a8",
)

load("@rules_java//java:repositories.bzl", "rules_java_dependencies", "rules_java_toolchains")

rules_java_dependencies()
rules_java_toolchains()

BUILD File

A BUILD file defines build targets and their dependencies:

# Example for a Java project

load("@rules_java//java:defs.bzl", "java_library", "java_binary")

java_library(
    name = "my_library",
    srcs = glob(["src/main/java/com/example/**/*.java"]),
    deps = [
        "@maven//:guava",
    ],
)

java_binary(
    name = "my_app",
    srcs = glob(["src/main/java/com/example/app/**/*.java"]),
    main_class = "com.example.app.Main",
    deps = [
        ":my_library",
    ],
)

Building and Testing

To build the project, you use Bazel commands:

# Build the binary target
bazel build //:my_app

# Run the binary
bazel run //:my_app

# Test the project
bazel test //:my_app_tests

Advantages of Using Bazel

1. Speed:

   • Incremental builds and parallel execution significantly reduce build times.

2. Reliability:

   • Hermetic builds ensure consistency and reproducibility.

3. Scalability:

   • Handles large codebases and complex dependency graphs efficiently.

4. Extensibility:

   • Custom rules and macros allow Bazel to be tailored to specific project needs.

5. Cross-Platform:

   • Bazel supports building and testing across different operating systems and architectures.