Bazel is a powerful build and test tool similar to Make, Maven, and Gradle. It uses a human-readable, high-level build language. Bazel supports projects in multiple languages and builds outputs for multiple platforms. Bazel supports large codebases across multiple repositories and large numbers of users, enabling a highly scalable build process.

One of Bazel's core strengths is its ability to support multiple build environments using different compilers. For example, Bazel can build projects using gcc, clang on Unix-like platforms, and MSVC on Windows. This versatility ensures that Bazel can be used in varied development ecosystems seamlessly.

Configuring Bazel to Use Different Compilers

Bazel automates the selection of compilers based on the environment and the configuration settings in the BUILD files. To explicitly specify a different compiler, modifications in the .bazelrc file or flags on the command line need to be set. Below are examples for switching compilers in Bazel.

Using GCC:

To use gcc explicitly, you can set the CC environment variable:

export CC=/usr/bin/gcc
bazel build //my:project

Alternatively, you can use a Bazel build flag:

bazel build //my:project --action_env=CC=/usr/bin/gcc

Using Clang:

Similarly, to configure Bazel to use clang, you can set:

export CC=/usr/bin/clang
bazel build //my:project

Or, using a build flag:

bazel build //my:project --action_env=CC=/usr/bin/clang

Using MSVC on Windows:

Configuring Bazel to use MSVC is slightly more complex because of the need to set up the build environment that MSVC expects. This setup is commonly done using a bazelrc file that configures the environment and toolchain flags:

set BAZEL_VC=C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC
set BAZEL_VC_FULL_VERSION=14.28.29333
bazel build //my:project

Technical Details and Considerations

Bazel uses a sandboxing technique to ensure that the build does not inadvertently depend on undeclared inputs. This isolation helps in maintaining the correctness of the build process, especially when switching compilers. Here are the general steps Bazel performs during a build:

1. Analysis Phase: Bazel determines which targets need to be built and in what order, based on dependencies declared in BUILD files.
2. Execution Phase: Bazel builds the targets using the specific compiler and flags set in the configuration, ensuring each action is executed in its own sandbox.

When compiling with a different compiler, it is essential to manage dependencies and toolchain configurations correctly. For instance, if C++ code is compiled with gcc and clang, ensure that all dependencies (like libraries) are compatible and tested against both compilers.

Summary Table

Conclusion

Using Bazel with different compilers enhances the flexibility and portability of software projects. By configuring Bazel appropriately, developers can ensure that their projects are buildable and testable in diverse environments, leading to more robust and reliable software. Proper configuration and management of compilers and toolchains are essential to leverage the full potential of Bazel in multi-compiler environments.