Show me a C/C++ project that doesn't need a build system.

My stuff for instance:

https://github.com/floooh/sokol

...inspired by:

https://github.com/nothings/stb

(here's how the sokol headers are integrated into a Zig project, note that there is only a build.zig which builds everything: https://github.com/floooh/kc85.zig)

But it's not so much about build systems, but requiring a separate compiler toolchain to build any C++ or ObjC dependencies (Rust needs this, Zig currently does not - unless that controversial proposal is implemented).

(also even complex C++ libraries can be wrapped in a build.zig, so you don't require a separate build system like cmake for the C++ dependencies)

I still don't see why this is a problem. Single-header dependencies are cute but blow up compile times, and most of the world needs CMake/Meson/Autotools anyways so there's not an added cost to using it for your own projects.

Similarly I don't really understand why you want one toolchain for a multi-language project. It's not that useful or convenient since it's going to need to be orchestrated with a buildsystem somehow.

Like with Rust, you probably only have a build.rs file. It invokes a separate (possibly multiple) toolchains. Or with CMake. A simple project has a single CMakeLists.txt that can invoke any number of toolchains. I don't see why zig can't do that with a build.zig file, or why it matters.

Did you try the stuff you are proposing? This is all a royal pita in real world projects which the Zig toolchain solved wonderfully.

(also it's a myth that STB style libs increase compile time, that's only true for typical C++ single header libs with inline methods and template code)