Allow enabling extensions from the classpath via CLI args (#127)

* Allow enabling extensions from the classpath via CLI args

* Change from arbitrary args to --ext(ension)=name arg

* Add MixinExtension$CLIProvider

* System.err

src/main/java/net/fabricmc/tinyremapper/Main.java

@@ -29,14 +29,16 @@
 import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
+import java.util.ServiceLoader;
 import java.util.Set;
 import java.util.regex.Pattern;
 
 import net.fabricmc.tinyremapper.TinyRemapper.LinkedMethodPropagation;
-import net.fabricmc.tinyremapper.extension.mixin.MixinExtension;
 
 public class Main {
 	public static void main(String[] rawArgs) {
@@ -60,7 +62,12 @@ public static void main(String[] rawArgs) {
 		boolean inferNameFromSameLvIndex = false;
 		NonClassCopyMode ncCopyMode = NonClassCopyMode.FIX_META_INF;
 		int threads = -1;
-		boolean enableMixin = false;
+
+		Map<String, TinyRemapper.CLIExtensionProvider> providerMap = new HashMap<>();
+		List<TinyRemapper.Extension> providedExtensions = new ArrayList<>();
+		ServiceLoader<TinyRemapper.CLIExtensionProvider> cliProviderLoader =
+				ServiceLoader.load(TinyRemapper.CLIExtensionProvider.class);
+		cliProviderLoader.iterator().forEachRemaining(provider -> providerMap.put(provider.name(), provider));
 
 		for (String arg : rawArgs) {
 			if (arg.startsWith("--")) {
@@ -143,7 +150,11 @@ public static void main(String[] rawArgs) {
 
 					break;
 				case "mixin":
-					enableMixin = true;
+					handleExtension(providerMap, "mixin", providedExtensions);
+					break;
+				case "ext":
+				case "extension":
+					handleExtension(providerMap, arg.substring(valueSepPos + 1), providedExtensions);
 					break;
 				default:
 					System.out.println("invalid argument: "+arg+".");
@@ -255,8 +266,8 @@ public static void main(String[] rawArgs) {
 				.inferNameFromSameLvIndex(inferNameFromSameLvIndex)
 				.threads(threads);
 
-		if (enableMixin) {
-			builder = builder.extension(new MixinExtension());
+		for (TinyRemapper.Extension ext : providedExtensions) {
+			ext.attach(builder);
 		}
 
 		TinyRemapper remapper = builder.build();
@@ -276,4 +287,19 @@ public static void main(String[] rawArgs) {
 
 		System.out.printf("Finished after %.2f ms.\n", (System.nanoTime() - startTime) / 1e6);
 	}
+
+	private static void handleExtension(Map<String, TinyRemapper.CLIExtensionProvider> providerMap, String extName, List<TinyRemapper.Extension> providedExtensions) {
+		TinyRemapper.CLIExtensionProvider provider = providerMap.get(extName);
+
+		if (provider == null) {
+			System.err.println("No such extension: " + extName);
+			System.exit(1);
+		}
+
+		TinyRemapper.Extension extension = provider.provideExtension();
+
+		if (extension != null) {
+			providedExtensions.add(extension);
+		}
+	}
 }

src/main/java/net/fabricmc/tinyremapper/TinyRemapper.java

@@ -258,6 +258,13 @@ public interface Extension {
 		void attach(TinyRemapper.Builder builder);
 	}
 
+	public interface CLIExtensionProvider {
+		String name();
+
+		// nullable return
+		Extension provideExtension();
+	}
+
 	public interface AnalyzeVisitorProvider {
 		/**
 		 * @deprecated use {@link #insertAnalyzeVisitor(boolean, int, String, ClassVisitor, InputTag[])} instead

src/main/java/net/fabricmc/tinyremapper/extension/mixin/MixinExtension.java

@@ -57,6 +57,18 @@ public class MixinExtension implements TinyRemapper.Extension {
 	private final Set<AnnotationTarget> targets;
 	private final /* @Nullable */ Predicate<InputTag> inputTagFilter;
 
+	public static final class CLIProvider implements TinyRemapper.CLIExtensionProvider {
+		@Override
+		public String name() {
+			return "mixin";
+		}
+
+		@Override
+		public TinyRemapper.Extension provideExtension() {
+			return new MixinExtension();
+		}
+	}
+
 	public enum AnnotationTarget {
 		/**
 		 * The string literal in mixin annotation. E.g. Mixin, Invoker, Accessor, Inject,

src/main/resources/META-INF/services/net.fabricmc.tinyremapper.TinyRemapper$CLIExtensionProvider

@@ -0,0 +1 @@
+net.fabricmc.tinyremapper.extension.mixin.MixinExtension$CLIProvider