crossroad

crossroad is a Gradle plugin for generating headers that are the intersection of two or more input jars: the headers only contain classes, methods, and fields accessible in every input jar, under the same name & with the same types.

For the time being, crossroad only emits "header jars" - method bodies do not contain any code.

The intended use-case is for writing software against the common subset of several, radically-different versions of a dependency:

• Simply dumping both versions in the same subproject won't have the intended effect.
• You can use one subproject for each version, but if the dependencies are similar, it requires a lot of cut-and-pasting code.
• You can write code against the lower version, and have another subproject include its source-code together with the higher version on the compile classpath, but the only way to tell if you're using something removed in the update is "try compiling and see if it fails", which is not ideal. (This also confuses the hell out of IDEs.)

When the dependencies are merged: you statically know what exists in all versions, and are statically prevented from compiling code that doesn't use things extant in all versions.

Usage

Apply the plugin...

buildscript {
	repositories {
		mavenCentral()
		maven { url "https://repo.sleeping.town/" }
	}
	dependencies {
		classpath "agency.highlysuspect:crossroad:0.3"
	}
}

apply plugin: "java"
apply plugin: "agency.highlysuspect.crossroad"

This makes a crossroad.merge function available in your scripts, which you can use as such:

def hybridGson = crossroad.merge(
	"com.google.code.gson:gson:2.10.1",
	"com.google.code.gson:gson:1.7.2"
);

dependencies {
	compileOnly files(hybridGson);
	//Now, only the common subset of GSON 1 and 2 is available in my IDE.
	//Yes this is a contrived example
}

//Or like this, it doesn't matter:
dependencies {
	compileOnly files(crossroad.merge("...", "...", "..."));
}

• You can pass Paths, Files, dependencies with one artifact, and strings (they will be resolved to maven dependencies).
• merge returns a Path. If you'd like a dependency, convert it to one with project.files.
• merge accepts a variable number of arguments.

Usage with minivan

Apply both plugins...

buildscript {
	repositories {
		maven { url = "https://maven.fabricmc.net/"}
		maven { url = "https://repo.sleeping.town/" }
		gradlePluginPortal()
	}
	dependencies {
		classpath "agency.highlysuspect:minivan:0.2"
		classpath "agency.highlysuspect:crossroad:0.3"
	}
}

apply plugin: "java"
apply plugin: "agency.highlysuspect.minivan"
apply plugin: "agency.highlysuspect.crossroad"

The process is as follows:

• Set up an instance of Minecraft using minivan's manual API: minivan.getMinecraft("1.19.4")
• Access the raw Minecraft jar using the .minecraft property
• Pass them to crossroad
• Add the merged jar to the project

We then add the oldest version's Maven .dependencies as well - I guess we could try to match up the Maven deps and merge them with crossroad as well, but in practice it's not really an issue, the third-party libraries have 100000% less churn than vanilla Minecraft and modders rarely use them anyway (other than google gson).

dependencies {
	def a = minivan.getMinecraft("1.16.5")
	def b = minivan.getMinecraft("1.18.2")
	def c = minivan.getMinecraft("1.19.2")
	def d = minivan.getMinecraft("1.19.4")
	
	compileOnly project.files(crossroad.merge(a.minecraft, b.minecraft, c.minecraft, d.minecraft))
	a.dependencies.each { compileOnly it }
}

A complete Minecraft example, including a dependency on a MC-independent "core" module, is available in Apathy's codebase.