Fork with updated version: https://github.com/neon-age/shader-graph-nodes

Issue

This asset still uses CodeFunctionNode API, which was made internal in 2018.2.,
Instead of it, Unity forces us to manually update ALL our nodes to sub-graphs, which is super clumsy and is not as robust.
We can't do any custom UI or methods selection using it.

Solution

Instead of rewriting every node to sub-graphs, we'll just access forbidden API again, by using AsmRef:
https://docs.unity.cn/2019.4/Documentation/Manual/class-AssemblyDefinitionReferenceImporter.html

Which only required:

• Unity 2019.4 or higher.
• Adding AsmReference to main folder with definition to Unity.ShaderGraph.Editor.
  This will include and compile all our custom nodes inside ShaderGraph assembly, giving us access to internal API's.
• Changing node classes to be internal to avoid accessibility compile errors.

The CodeFunctionNode API hasn't changed a bit since Unity 2018.2 and works in newer versions up to 2021.2!