Abstract:

This webinar provides an approachable introduction to using the Bazel build system for C++ development, targeting product developers who may be new to Bazel. The presenter argues that beyond its usual benefits for large-scale and multi-language projects, Bazel is an excellent choice for C++ simply because it offers superior tooling compared to alternatives like CMake and Makefiles. The session walks through setting up a project from scratch, compiling a simple application, and managing dependencies hermetically using the Bazel Central Registry. A significant focus is placed on achieving reproducible, cross-platform builds by leveraging toolchains and a sysroot to decouple the build from the host machine. The webinar also covers essential developer workflows, including IDE integration with clangd via a compilation database, packaging applications into OCI containers, linting with clang-tidy, and automating BUILD file generation with Gazelle.

A Developer's Guide to C++ with Bazel

• 1:33 Personas and Goals: The webinar is tailored for product developers (the "100 series" persona), aiming to make Bazel feel more approachable by focusing on typical C++ developer workflows.
• 3:19 Why Use Bazel for C++?: The speaker presents three primary reasons to choose Bazel for C++: managing large-scale codebases, handling projects with multiple languages, and as a superior alternative to tools like CMake and Makefiles, which can become unmaintainable.
• 4:52 Hermetic and Reproducible Builds: A core concept of Bazel is hermeticity, ensuring a build is reproducible by knowing all of its inputs. For C++, this is achieved by using specific toolchains (like a managed version of LLVM/Clang) and a sysroot, which provides necessary headers and libraries, decoupling the build from the host operating system.
• 10:27 Project Scaffolding: The presenter uses the aspect init command to create a new, clean C++ repository. This process automatically downloads and sets up necessary components like the LLVM toolchain.
• 19:52 Creating a "Hello World" Binary: The first practical example involves creating a simple hello.c file and a corresponding cc_binary rule in a BUILD file. This demonstrates the declarative nature of Bazel, where the user describes the source files rather than directly invoking the compiler.
• 26:41 Managing External Dependencies: The webinar demonstrates the correct, hermetic way to handle third-party libraries by adding them from the Bazel Central Registry (BCR). The example uses libmagic, which is statically linked into the application, ensuring that all developers and CI systems use the exact same version.
• 36:40 IDE Integration with clangd: To enable features like auto-completion and jump-to-definition in an editor, the presenter shows how to generate a "compilation database" (compile_commands.json). This file is created by running a tool that queries Bazel's build graph and tells the clangd language server where to find all necessary headers and dependencies.
• 43:51 Cross-Compilation for Different Platforms: A key strength of Bazel is its ability to cross-compile code. The webinar explains how to build a binary for a linux_aarch64 target while working on a macOS machine. This is made possible by using a sysroot that contains the headers and libraries for the Linux target.
• 49:46 Packaging Binaries into Containers: After cross-compiling the application, the presenter uses rules_oci to package the resulting binary into a minimal, distroless Docker container. This demonstrates a complete build-and-deploy workflow.
• 54:04 Using Transitions for Simplified Builds: Instead of manually passing a --platforms flag on the command line for cross-compilation, Bazel's "transitions" feature can be used. This allows a target in a BUILD file to declare that it and its dependencies should be built for a specific platform, simplifying the build command.
• 57:44 Linting and Code Quality: The Aspect CLI's lint command is used to run clang-tidy over the C++ source files. This allows for programmatic enforcement of code quality standards, consistent with the warnings a developer would see in their configured editor.
• 59:44 Automating BUILD File Generation: The webinar briefly introduces Gazelle, a tool that can automatically generate and update BUILD files by analyzing source code, tracking #include statements, and determining dependencies.