WebGSL doesn't share anything with the C++14 based Metal Shading Language.

https://gpuweb.github.io/gpuweb/wgsl.html

Actually it even seems to have a Rust flavour to it.

    fn main() -> void {
        gl_FragColor = vec4<f32>(0.4, 0.4, 0.8, 1.0);
    }