As an option, error messages should be displayed to help shaderpack developers (and end-users) diagnose and solve errors. Optifine has a similar feature to this, which leads shaderpack developers to use it during development rather than IRIS. Since IRIS gives worlds better performance than Optifine and is gathering a ton of support, modern shaderpacks should be designed for IRIS.

(Screenshot from Optifine)

Got it, thanks so much!