THIS IS AN ALTERNATIVE, NOT A FORK!

This mod can:

Download and install Cleanroom automatically if you are running MMC-based launchers
Download and launch Cleanroom if you are using other launchers

Difference compare to official one:

A config option to use local Cleanroom mmc pack, which allow the installation of action builds
Allow modpacks to ship default config Cleanroom version and args
Proxy config for mmc zip & libraries downloading
Maven mirror. Only useful for players in certain regions though
Custom library path, allow reusing libraries with existing launchers

Highlight Features for Pack Makers

You can ship a custom default Cleanroom mmcpack with your pack, which won't be updated but can be updated easily
You can ship a JRE with your pack (by filling relative path), so your players don't need to install new Java themselves
You can ship all libraries in your pack, which will means instant one-clicked relaunch

About Java 8u51

Official launcher ships with outdated Java 8u51 (released 2015), which doesn't contain certificates of later Let's Encrypt (used by Cleanroom maven) and Azure (used by libraries.minecraft.net).

The mod will add those certs into JVM if old java detected. In fact, I added whole keystore from latest Java.

But there's another bug in 8u51 that will cause deadlock in multi-thread downloading. Updating your JVM is always the best solution.

About bundled libraries & files

Apache Httpcomponents 5: Shadowed to use multi-thread download.
java-utils: Created by CleanroomMC, used to detect installed JVMs.
MigLayout: Used to provide a decent GUI layout.
sslcontext-kickstart: Used to import keystore.
cacerts.jks: Keystore copied from latest Temurin JRE 8.0.462+8.
mmcpack.zip: Latest Cleanroom 0.3.13-alpha mmc zip. Can be verified by comparing checksum to the release one.

If you want to…

Update Cleanroom version: remove mmcpack.zip and mmcpack/ folder in relauncher/, then launch the game.
Rollback to Forge: Disable the mod if you are using regular launcher, change game version, lwjgl version and Forge version back to regular in MMC instance setting if you are using that.

Note

By MMC-based launchers, I mean MultiMC, PolyMC and PrismLauncher.

You need to install a Java 21 to use this!

This is a client only mod! For server, please download installer jar from Cleanroom repository.

If anything gone wrong, remove cleanroom_relauncher.cfg config file and try again!

FAQ:

Q: What is Cleanroom?
A: Cleanroom is a 1.12.2 Forge fork, providing newer toolchain, new APIs and 99% compatibility. Our plan is to make 1.12.2 up-to-date with latest toolchain while adding more feature to Forge & vanilla, so we don't need to care about higher versions' X point release * Y Mod API headache.
Q: How to install Cleanroom?
A: Please follow the instructions in README.
Q: Can I include this in my Forge modpack? Will it crash my Forge pack?
A: Yes, you can, and it is safe! This mod won't be loaded or crash anything in a Forge environment.
Q: Java version?
A: 21 or 22. We are planning to support development using latest LTS version Java and running with latest Java.
Q: Current state?
A: Cleanroom have reached well usability, small packs like Tekkit 2 could be run out-of-box with Fugue, while larger pack like e2ee and Mystics Monstrosity is working after some tweaks. But we are lacking manpower, please join our Discord if you are willing to help.

Cleanroom relauncher unofficial