Error `Expected initialization of constant` when initializing a const vec2[] in the shader global scope

Question

I have this defined outside of any functions in a shader.
I get the error Expected initialization of constant

const vec2 rels[4] = {
    vec2(-1.0, 0.0),
    vec2(1.0, 0.0),
    vec2(0.0, -1.0),
    vec2(0.0, 1.0)
};  

But in the godot documentation I can see it shows initializing an array of vec2 in a function scope and a const array of scalars in the global scope.
Is it possible that initializing an array of vec2 in the global scope is not supported?