Abstract:

This instructional webinar provides a comprehensive tutorial on using the Bazel build system for C++ development, focusing on achieving scalable, reliable, and hermetic builds. The video guides viewers through setting up a new C++ project, explaining why Bazel is often a superior choice over traditional tools like CMake or Makefiles. Key topics include managing external dependencies hermetically using the Bazel Central Registry, integrating with IDEs and editors like VS Code via clangd and a compilation database, and performing cross-compilation. The tutorial demonstrates how to build a Linux/ARM64 binary from a macOS host by configuring platforms and using a sysroot for headers and libraries. It also covers packaging the resulting application into a minimal OCI container for deployment and using advanced features like transitions for efficient multi-platform builds. Finally, it touches on developer productivity tools for linting and automatic build file generation.

Building C++ with Bazel: A Guide to Scalable and Hermetic Builds

• 3:19 Why Bazel for C++?: Beyond supporting large-scale, multi-language monorepos, Bazel is presented as a superior build tool for C++ in its own right compared to CMake or Makefiles. Its key advantages are hermeticity (reproducible builds) and robust toolchain management, which prevents builds from depending on locally installed system libraries and compilers.
• 10:27 Initial Project Setup: The tutorial begins by creating a new C++ project using the aspect init command. A simple "Hello World" C application is created, demonstrating the basic cc_binary rule. The presenter shows how to use bazel aquery to inspect the exact compiler commands Bazel will run, illustrating how Bazel abstracts away complex command-line flags from the developer.
• 26:20 Hermetic Dependency Management: The video demonstrates how to correctly manage external dependencies by adding the libmagic library from the Bazel Central Registry (BCR). This approach avoids version skew and portability issues associated with linking against system-installed libraries. It also covers managing runtime data dependencies required by the library.
• 36:40 Editor and IDE Integration: A critical step for developer experience is shown: integrating Bazel with a language server (clangd). By running a tool to generate a compile_commands.json file, the editor gains full awareness of the hermetic build environment, enabling features like go-to-definition, autocompletion, and accurate in-line error reporting.
• 43:51 Cross-Compilation using Platforms and Sysroots: The webinar showcases one of Bazel's most powerful features: cross-compilation. It explains the concepts of host, execution, and target platforms. A practical demonstration shows how to compile a C++ application for a linux/arm64 target while on a macOS host by configuring a sysroot, which provides all the necessary headers and libraries for the target architecture, ensuring a fully hermetic build.
• 49:34 Packaging Applications into OCI Containers: After cross-compiling the binary, the video demonstrates how to package it for deployment using rules_oci. This allows for the creation of a minimal, production-ready container image (e.g., Docker) directly from the build system.
• 54:04 Multi-Platform Builds with Transitions: The tutorial introduces "transitions," an advanced Bazel feature that allows a build target to change its configuration (like the target platform) without requiring a command-line flag. This enables building for multiple platforms (e.g., amd64 and arm64) in a single bazel build command, which is ideal for creating multi-architecture container images.
• 57:44 Developer Tooling for Linting and Generation: The video briefly covers additional productivity tools. It demonstrates bazel lint (an Aspect CLI command) to run clang-tidy for code analysis and mentions using Gazelle with custom extensions to automatically generate and maintain C++ BUILD files, reducing boilerplate.