toolchains_llvm

In my previous position, we accomplished this using a "dev docker" (which I covered generally in a previous post: https://blog.fahhem.com/2023/12/dev-onboarding-then-now/) that's based around a specific version of Ubuntu (20.04) so the glibc is tied to that. In another project, I used a hermetic C++ toolchain (you can use gcc with https://github.com/f0rmiga/gcc-toolchain/ or clang/llvm with https://github.com/bazel-contrib/toolchains_llvm) that pulled in its own (locked) version of glibc and lld, etc.

The biggest feature I want out of Starlark the language (not Bazel the build system) is to allow optional type annotations. They don’t have to do anything, they don’t have to specified, it just needs to be syntactically valid to put type annotations somewhere. If there were syntax for type annotations that tools like Bazel ignored, it would be possible for some enterprising soul who’s forced to use Bazel at work to throw up an initial prototype of a type checker and a language server for Starlark in Bazel. The language is not that complicated that a type checker couldn’t be written by a hobbiest. My biggest frustration when using Bazel is not even Bazel—it’s the fact that when I’m looking at code like this[1], everything comes from a single, unannotated `rctx` variable that has no type annotation. So when I’m trying to read the code, it’s

Yeah the cross-compilation thing is definitely a rough spot. I have one project that's able to work around it via extensive hacks with macros, but at some point I'll need to do it "the right way." Honestly if the docs had a canonical example of e.g. using unix_cc_toolchain_config (example: [0]) + Bootlin to compile for aarch64, it'd probably go a long way to making things understandable. Because say what you will about the old CROSSTOOL approach, at least there was a nice tutorial for it. [0] https://github.com/grailbio/bazel-toolchain/blob/f14a8a5de8f...

The trick is that to provide Bazel with a custom toolchain involves way more than just setting an environment variable, because Bazel wants to control installing and making available the compiler reliably (e.g., what if `emcc` is not present on the system where Bazel was invoked? Bazel solves that problem by fetching it and building it for that system) There are projects that provide drop-in support for custom toolchains (e.g., we use this project[0] in Sorbet to fetch and build a custom LLVM/Clang toolchain for every host we build on (rather than relying on the system toolchain). But I'm not aware of a project that has done that for Emscripten. Maybe it would be as easy as plucking out what we've done in our project into a project that others could depend on, but to quote a colleague: > Setting up a cc toolchain in Bazel is a unique sort

I wish Bazel was more explicit about things leaking in from outside the workspace, but you can always vendor the toolchain to be more hermetic. For example see https://github.com/grailbio/bazel-toolchain which sets up LLVM and Clang for you. https://github.com/bazelbuild/bazel/issues/4558

That's not exactly true, for example see https://github.com/grailbio/bazel-toolchain