Are you planning to explore the source code for a specific purpose, or do you have any questions about Stardew Valley or game development in general?
Here's a high-level report on the Stardew Valley source code: stardew source code
https://github.com/ConcernedApe/StardewValley Are you planning to explore the source code
Barone has openly discussed certain “hacks” that became permanent: stardew source code