Use exclusiveContent for our maven

This is a little nasty as we need to include ForgeGradle's repo too, but
should still help a bit!

buildSrc/src/main/kotlin/cc-tweaked.forge.gradle.kts

@@ -10,8 +10,9 @@ import cc.tweaked.gradle.IdeaRunConfigurations
 import cc.tweaked.gradle.MinecraftConfigurations
 
 plugins {
-    id("cc-tweaked.java-convention")
     id("net.minecraftforge.gradle")
+    // We must apply java-convention after Forge, as we need the fg extension to be present.
+    id("cc-tweaked.java-convention")
     id("org.parchmentmc.librarian.forgegradle")
 }
 

buildSrc/src/main/kotlin/cc-tweaked.java-convention.gradle.kts

@@ -37,9 +37,25 @@ java {
 
 repositories {
     mavenCentral()
-    maven("https://squiddev.cc/maven") {
+
+    val mainMaven = maven("https://squiddev.cc/maven") {
         name = "SquidDev"
         content {
+            // Until https://github.com/SpongePowered/Mixin/pull/593 is merged
+            includeModule("org.spongepowered", "mixin")
+        }
+    }
+
+    exclusiveContent {
+        forRepositories(mainMaven)
+
+        // Include the ForgeGradle repository if present. This requires that ForgeGradle is already present, which we
+        // enforce in our Forge overlay.
+        val fg =
+            project.extensions.findByType(net.minecraftforge.gradle.userdev.DependencyManagementExtension::class.java)
+        if (fg != null) forRepositories(fg.repository)
+
+        filter {
             includeGroup("org.squiddev")
             includeGroup("cc.tweaked")
             // Things we mirror
@@ -49,8 +65,6 @@ repositories {
             includeGroup("me.shedaniel.cloth")
             includeGroup("mezz.jei")
             includeModule("com.terraformersmc", "modmenu")
-            // Until https://github.com/SpongePowered/Mixin/pull/593 is merged
-            includeModule("org.spongepowered", "mixin")
         }
     }
 }

buildSrc/src/main/kotlin/net/minecraftforge/gradle/common/util/runs/RunConfigSetup.kt

@@ -56,12 +56,13 @@ internal fun setRunConfigInternal(project: Project, spec: JavaExecSpec, config:
     for ((k, v) in config.lazyTokens) lazyTokens[k] = v
     lazyTokens.compute(
         "source_roots",
-        { key: String, sourceRoots: Supplier<String>? ->
+        { _, sourceRoots ->
             Supplier<String> {
                 val modClasses = RunConfigGenerator.mapModClassesToGradle(project, config)
-                (if (sourceRoots != null) Stream.concat<String>(
-                    sourceRoots.get().split(File.pathSeparator).stream(), modClasses,
-                ) else modClasses).distinct().collect(Collectors.joining(File.pathSeparator))
+                (when (sourceRoots) {
+                    null -> modClasses
+                    else -> Stream.concat<String>(sourceRoots.get().split(File.pathSeparator).stream(), modClasses)
+                }).distinct().collect(Collectors.joining(File.pathSeparator))
             }
         },
     )