GLSL Debugging Trick: Version Control
Small mistakes could be time-consuming to find out in GLSL shaders. But found a good way to figure out:
If the shader is not working after some change, check the code change in version control tools, compare line by line change, from which figure out what change broke the shader.
In this example, I deleted the left parenthesis, then the shader broke. But figured out immediately with the help of version control comparison: