Add Forge implementation data to MANIFEST.MF

src/main/java/net/fabricmc/loom/providers/ForgeProvider.java

@@ -32,7 +32,7 @@ import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.DependencyProvider;
 
 public class ForgeProvider extends DependencyProvider {
-	private String forgeVersion = "NO_VERSION";
+	private ForgeVersion version = new ForgeVersion(null);
 
 	public ForgeProvider(Project project) {
 		super(project);
@@ -40,17 +40,48 @@ public class ForgeProvider extends DependencyProvider {
 
 	@Override
 	public void provide(DependencyInfo dependency, Consumer<Runnable> postPopulationScheduler) throws Exception {
-		forgeVersion = dependency.getDependency().getVersion();
+		version = new ForgeVersion(dependency.getDependency().getVersion());
 		addDependency(dependency.getDepString() + ":userdev", Constants.Configurations.FORGE_USERDEV);
 		addDependency(dependency.getDepString() + ":installer", Constants.Configurations.FORGE_INSTALLER);
 	}
 
-	public String getForgeVersion() {
-		return forgeVersion;
+	public ForgeVersion getVersion() {
+		return version;
 	}
 
 	@Override
 	public String getTargetConfig() {
 		return Constants.Configurations.FORGE;
 	}
+
+	public static final class ForgeVersion {
+		private final String minecraftVersion;
+		private final String forgeVersion;
+
+		public ForgeVersion(String combined) {
+			if (combined == null) {
+				this.minecraftVersion = "NO_VERSION";
+				this.forgeVersion = "NO_VERSION";
+				return;
+			}
+
+			int hyphenIndex = combined.indexOf('-');
+
+			if (hyphenIndex != -1) {
+				this.minecraftVersion = combined.substring(0, hyphenIndex);
+				this.forgeVersion = combined.substring(hyphenIndex + 1);
+			} else {
+				this.minecraftVersion = "NO_VERSION";
+				this.forgeVersion = combined;
+			}
+		}
+
+		public String getMinecraftVersion() {
+			return minecraftVersion;
+		}
+
+		public String getForgeVersion() {
+			return forgeVersion;
+		}
+	}
 }

src/main/java/net/fabricmc/loom/providers/LaunchProvider.java

@@ -73,7 +73,7 @@ public class LaunchProvider extends DependencyProvider {
 					.argument("--fml.mcVersion")
 					.argument(getExtension().getMinecraftProvider().getMinecraftVersion())
 					.argument("--fml.forgeVersion")
-					.argument(getExtension().getForgeProvider().getForgeVersion())
+					.argument(getExtension().getForgeProvider().getVersion().getForgeVersion())
 
 					.argument("client", "--launchTarget")
 					.argument("client", "fmluserdevclient")

src/main/java/net/fabricmc/loom/providers/MinecraftMappedProvider.java

@@ -26,9 +26,15 @@ package net.fabricmc.loom.providers;
 
 import java.io.File;
 import java.io.IOException;
+import java.net.URI;
+import java.nio.file.FileSystem;
+import java.nio.file.FileSystems;
+import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
 import java.util.Map;
 import java.util.function.Consumer;
 
@@ -128,6 +134,25 @@ public class MinecraftMappedProvider extends DependencyProvider {
 			} finally {
 				remapper.finish();
 			}
+
+			if (getExtension().isForge()) {
+				getProject().getLogger().lifecycle(":adding forge manifest data");
+
+				try (FileSystem fs = FileSystems.newFileSystem(URI.create("jar:" + output.toUri()), ImmutableMap.of("create", false))) {
+					Path manifestPath = fs.getPath("META-INF", "MANIFEST.MF");
+					ForgeProvider.ForgeVersion version = getExtension().getForgeProvider().getVersion();
+					List<String> lines = new ArrayList<>(Files.readAllLines(manifestPath));
+
+					lines.add("");
+					lines.add("Name: net/minecraftforge/fml/javafmlmod/");
+					lines.add("Implementation-Version: " + version.getForgeVersion());
+					lines.add("");
+					lines.add("Name: net/minecraftforge/fml/mclanguageprovider/");
+					lines.add("Implementation-Version: " + version.getMinecraftVersion());
+
+					Files.write(manifestPath, lines);
+				}
+			}
 		}
 	}