Write a minimal GLSL test exposing bug in setting a varying inside if statement

[Oletus]

This type of vertex shader code failed to render a vertical gradient, which is why the current code generates different shaders for vertical and non-vertical gradients:

if (abs(uCoords0.x - uCoords1.x) < 0.001) {
varying = vertical gradient formula;
} else {
gradient code
varying = result;
}

Figure out if this really was a bug in WebGL / NVIDIA driver v311 stack or some misunderstanding, and see if it reproes elsewhere.