DataFixerUpper VS DecompilerMC

You don't need to load a world in every version and in fact this is not recommended because later versions fix various bugs with converting older worlds and with the exception of Beta 1.3 (Alpha to Region*) and release 1.2 (Region to Anvil*) only chunks you've loaded will be converted (since 1.13 there is an "optimize world" feature which can force a full conversion and is recommended mainly to avoid lag due to the game converting chunks on the fly; modern versions change data formats so often Mojang created an entire "data fixer" library and data versioning so it can tell exactly what version a file was last saved in and update it properly, anything without a version tag is assumed to be pre-1.9, which barely changed aside from Alpha-Region-Anvil).

No need to guess, we know pretty much exactly what this is referring to, because it was performance changes in one of the open-source components, DataFixerUpper. The code is open to the public, and you can look at the changes yourself if you want to. It's somewhat technical but I'll try to explain.

Read it and weep! https://github.com/Mojang/DataFixerUpper

java and generics mentioned in the same headline and noone's linked the funny library yet, smh

And I work on Minecraft.

DataFixerUpper, particularly codecs

You can write a library for profunctor optics, something that is usually used in functional languages like Haskell, in Java, but that doesn't mean it's convenient or even practical to use.

Honestly the way I learned is just downloading the code (https://github.com/hube12/DecompilerMC or https://github.com/QuiltMC/quilt-mappings are probably the best ways right now) and poking around until I found what I was looking for.

I have no clue how item shadowing in 1.18 is possible but if you want to have a look at the source code you could try MCP Reborn which even allows you to modify the code and run it easily, though not all variables are deobfuscated. You can also use the official obfuscation mappings to manually decompile Minecraft (wiki article or use DecompilerMC to automate that task (with this method afaik nothing is obfuscated but there is no function to run the code. It would probably be quite easy to port the gradle tasks from MCP reborn or create your own but I’m not a Java dev so I’m not sure)

this tool for code with mojang mappings(no parameter names): https://github.com/hube12/DecompilerMC

You can use DecompilerMC to decompile the latest versions and MCP to decompile older versions. Minecraft's code is definitely a giant mess of spaghetti, although maybe not as bad as it used to be.

If you do wanna look at mc code though, you can use DecompilerMC, or just download the fabric example mod and run the genSources gradle task

If you do wanna deobfuscate and decompile it tho, look into yarn or DecompilerMC

2) Use this, it uses mojang mappings https://github.com/hube12/DecompilerMC 3) Use mcp-reborn (mcpconfig) which use modcoderpack mappings https://github.com/Hexeption/MCP-Reborn