Outline shader without unshaded render_mode

I've been trying to get the outline shader to play nice with CanvasModulate+Light2D but cannot get it to work. In unshaded mode the sprite is always visible, in blend_mix or other modes it's all hidden. I cannot see what would need adapted to fit between the two modes, do you have any ideas?

https://github.com/steincodes/godot-shader-tutorials/blob/master/Shaders/outline.shader