FMJv2 will be a breaking change to FMJv1 with several incompatible changes.
Forge uses a TOML file, mods.toml, instead of JSON. Forge mod metadata file is very small, and all features except update check URL exist in FMJv1. Update checking should NOT be included in FMJv2, as that is beyond the scope of Fabric API/Loader. Mod Menu might be able to implement it.
Therefore, no feature from Forge metadata is worth bringing over.
If you share this list, please use this link instead: https://lambdaurora.dev/optifine_alternatives
It may still be only a redirection link, but it will have a better web display of the list soon. And the list being on GitHub/GitHub pages improves load times.
The gist version of this list will stop being updated.
This primer is licensed under CC0, do whatever you want.
BUT do note that this can be updated, so leave a link here so readers can see the updated information themselves.
1.13 and 1.14 are lumped together in this doc, you're on your own if you just want to go to 1.13 and not 1.14, for some reason.
1.15 stuff: https://gist.github.com/williewillus/30d7e3f775fe93c503bddf054ef3f93e
ResourceLocation now throw on non-snake-case names instead of silently lowercasing for you, so you probably should go and change all those string constants now. More precisely, domains must only contain alphanumeric lowercase, underscore (_), dash (-), or dot (.). Paths have the same restrictions, but can also contain forward slashes (/).
If you are familiar with Java's generics, and are coming to Rust, you might be lead to assume that its generics are working the same way.
However, due to the different type systems, and different implementation details, there are quite a few differences between generic code in both languages.
This document tries to give a short summary about those differences: