Ensure that there are no duplicate files across projects. (#4301)

* Ensure that there are no duplicate files across projects.

* Depend on check

build.gradle

@@ -753,19 +753,42 @@ dependencies {
 	}
 }
 
-remapJar {
-	afterEvaluate {
-		subprojects.each {
-			if (it.name in devOnlyModules || metaProjects.contains(it.name)) {
-				return
-			}
+configurations {
+	nestedJars {
+		transitive = false
+	}
+}
 
-			// Include the signed or none signed jar from the sub project.
-			nestedJars.from project("${it.path}").tasks.getByName("signRemapJar")
+dependencies {
+	subprojects.each {
+		if (it.name in devOnlyModules || metaProjects.contains(it.name)) {
+			return
 		}
+
+		nestedJars project("${it.path}")
+	}
+}
+
+remapJar {
+	nestedJars.from configurations.nestedJars
+}
+
+// Attempt to create a single jar with all files from all nested jars, this will fail if there are duplicate files.
+tasks.register("checkNoDuplicateFiles", Zip) {
+	inputs.files configurations.nestedJars
+	destinationDirectory = layout.buildDirectory.dir("test")
+
+	from {
+		configurations.nestedJars.files.collect { zipTree(it) }
 	}
+
+	// We expect these files to be duplicated, so exclude them.
+	exclude 'META-INF/**'
+	exclude 'fabric.mod.json'
 }
 
+check.dependsOn "checkNoDuplicateFiles"
+
 publishMods {
 	file = signRemapJar.output
 	changelog = providers.environmentVariable("CHANGELOG").getOrElse("No changelog provided")