Varying in shader is not working

[SirPigeonz]

Ubuntu - Godot version: 3.0 master
nvidia GeForce GTX 570

Issue description:

Varying variables are not working in shader lang.
When I try to use it, mesh that has assigned current shader becomes big white something :D

Steps to reproduce:
Try:

varying vec4 meh;

void vertex() {
	meh = vec4(0);
}