If you want to contribute to Forge

Prerequisites: Eclipse {or IntelliJ} (3.7 or better is probably good), Git (any version, must be on system PATH))

1. Fork the MinecraftForge repository
2. Clone your repository
3. Run gradlew setup.
4. Find anywhere you want for your IDE workspace.
5. Import projects/Clean into your workspace
6. Import projects/Forge into your workspace

• Make sure you run and test your changes
• Run gradlew genPatches (in the Forge root) to generate patch files for Minecraft base classes
• Sign Contributor License Agreement
• Submit a pull request. Explain as much as you did

Tips

• Take your time. Make sure your code does what it's supposed to do and does it well. Your PR probably won't be accepted if it doesn't cover all the uses
• Indent your code properly, and follow the conventions (take a look at other classes and read the code before editing). Space instead of tabs, open braces on a new line, etc. ONLY IF IT IS A NEW CLASS NOT IF IT IS A PATCH TO A MINECRAFT CLASS. Here're the IDEs formatters available if you want it.
• To update your repo to latest code from the official repository:
  1. If it's the first time, add a remote for the official repo (git remote add upstream https://github.com/MinecraftForge/MinecraftForge)
  2. Get the updates (git fetch upstream), and make sure you're on master (git checkout 1.15.x)
  3. If you don't want to rewrite your history (e.g. others have cloned your repository), do a merge (git merge upstream/1.15.x). For keeping pull requests as clean as possible, do a rebase (git rebase upstream/1.15.x). Git may reject your push the first time after each rebase and you'll have to do git push -f origin master (or git push origin 1.15.x --force).

Conventions for coding patches for a Minecraft-class (.java.patch)

This section applies to the ClassName.java.patch section of your contributions. Whenever a new update of Minecraft is released, these patches are applied to the original code provided by Mojang. To increase compatibility please keep the following conventions:

While coding:

• Prevent to add extra spaces/line breaks, even when there are already existing ones in the code between statements. Below is an example that comes from net.minecraft.entity.item.EntityItem#attackEntityFrom(DamageSource, float):

//snip
this.setBeenAttacked();
this.health = (int)((float)this.health - p_70097_2_);

if (this.health <= 0)
{
    this.setDead();
}

return false;
//snip

Lets say we add an if-statement between this.setBeenAttacked(); and this.health = (int)((float)this.health - p_70097_2_);. It seems that if-statements get extra spaces/line breaks in the original code. However, when contributing to a java.patch-file you should always try to keep the changes as minimal as possible. So, don't do:

//snip
this.setBeenAttacked();
++
++  if(isCondition) return false;
++
this.health = (int)((float)this.health - p_70097_2_);

if (this.health <= 0)
{
    this.setDead();
}

return false;
//snip

But do:

//snip
this.setBeenAttacked();
++ if(isCondition) return false;
this.health = (int)((float)this.health - p_70097_2_);

if (this.health <= 0)
{
    this.setDead();
}

return false;
//snip

• In spirit of the previous point: prevent to add more lines than necessary. If you can reduce your statement to one single line, please do so. Example here is an if-statement that could be written as follows to improve readability:

if((float)this.field_70291_e - p_70097_2_ <= 0.0F)
{
    if(net.minecraftforge.common.ForgeHooks.onItemDeath(this, p_70097_1_))
    {
        return false;
    }
}

However, to keep changes to .java.patch-files as minimal as possible. Try to write that statement to one single line:

if((float)this.field_70291_e - p_70097_2_ <= 0.0F && net.minecraftforge.common.ForgeHooks.onItemDeath(this, p_70097_1_)) return false;

• Prevent using imports and try using full qualifications in the code. Using imports will generate extra lines in patch-files which can be prevented. Imports that are already in the file are not your concern. Example below:

//snip
import net.minecraft.otherimports
import net.minecraftforge.event.GenericEvent
import net.minecraftforge.otherimports
//snip
        if (isCondition) MinecraftForge.EVENT_BUS.post(new GenericEvent());
//snip

Instead try to code it as:

//snip
import net.minecraft.otherimports
import net.minecraftforge.otherimports
//snip
        if (isCondition) MinecraftForge.EVENT_BUS.post(new net.minecraftforge.event.GenericEvent());
//snip

Sidenote: The previous example can be improved further. As FML/Forge is trying to move away from imports try to use net.minecraftforge.common.MinecraftForge even when an existing import is already there. An even better way is to add a function in net.minecraftforge.event.EventFactory or net.minecraftforge.common.ForgeHooks and use the full qualification function names.

Before gradlew genPatches & Committing

Before committing, check if your IDE hasn't put in extra spaces/line breaks in the import section of your java-file. Eclipse tend to reorganize the imports to improve readability and will cause extra spaces/line breaks to appear in the .java.patch-files. Review your patches (ClassName.java.patch) and the diff-states of your uncommitted changes on these patches for extra ++'s or + +'s. This means an extra space/line break has been added. Keep in mind that the original .java.patch-file never add extra spaces/break lines in between imports.