The client was developed with MCP 910 and OptiFine 1.8 HD U H6, using Eclipse 2023-09 (4.29.0).
The uploaded files are only the custom packages for the client.
I've done crucial changes to some critical main game files (like Minecraft.java), so you need to DOWNLOAD the modified 1.8 MCP (mod coder pack) to debug the client. Obviously I can't just upload the whole pack to GitHub, since it's almost a gigabyte.
When the download is completed, just open Eclipse, and enter the ..\moonlight-client\eclipse path. Then you're ready to run & debug.