Bazel Blog

Bazel on Windows -- a year in retrospect

Bazel on Windows is no longer experimental. We think Bazel on Windows is now stable and usable enough to qualify for the Beta status we have given Bazel on other platforms.

Over the last year, we put a lot of work into improving Bazel's Windows support:

  • Bazel no longer depends on the MSYS runtime. This means Bazel is now a native Windows binary and we no longer link it to the MSYS DLLs. Bazel still needs Bash (MSYS or Git Bash) and the GNU binutils (binaries under /usr/bin) if your dependency graph includes genrule or sh_* rules (similarly to requiring python.exe to build py_* rules), but you can use any MSYS version and flavour you like, including Git Bash.
  • Bazel can now build Android applications. If you use native android_* rules, Bazel on Windows can now build and deploy Android applications.
  • Bazel is easier to set up. You now (typically) no longer need to set the following environment variables:
    • BAZEL_SH and BAZEL_PYTHON -- Bazel attempts to autodetect your Bash and Python installation paths.
    • JAVA_HOME -- we release Bazel with an embedded JDK. (We also release binaries without an embedded JDK if you want to use a different one.)
  • Visual C++ is the default C++ compiler. We no longer use GCC by default, though Bazel still supports it.
  • Bazel integrates better with the Visual C++ compiler. Bazel no longer dispatches to a helper script to run the compiler; instead Bazel now has a CROSSTOOL definition for Visual C++ and drives the compiler directly. This means Bazel creates fewer processes to run the compiler. By removing the script, we have eliminated one more point of failure.
  • Bazel creates native launchers. Bazel builds native Windows executables from java_binary, sh_binary, and py_binary rules. Unlike the .cmd files that Bazel used to build for these rules, the new .exe files no longer dispatch to a shell script to launch the xx_binaries, resulting in faster launch times. (If you see errors, you can use the --[no]windows_exe_launcher flag to fall back to the old behavior; if you do, please file a bug. We'd like to remove this flag and only support the new behavior.)

Coming soon

We are also working on bringing the following to Bazel on Windows:

  • Android Studio integration. We'll ensure Bazel works with Android Studio on Windows the same way it does on Linux and macOS. See issue #3888.
  • Dynamic C++ Linking. Bazel will support building and linking to DLLs on Windows. See issue #3311.
  • Skylark rule migration guide. We'll publish tutorials on writing Skylark rules that work not just on Linux and macOS, but also on Windows. See issue #3889.

Looking ahead, we aim to maintain feature parity between Windows and other platforms. We aim to maximize portability between host systems, so you get the same fast, correct builds on your developer OS of choice. If you run into any problems, please don't hesitate to file a bug.

By László Csomor