Support mixins without refmaps in mod dependencies (#976)

* Support mixins without refmaps in mod dependencies

* Fix review concerns

* Add test for MixinDetector

* Change warning to a RuntimeException

* FabricAPITest: Test building without mixin AP

* Deal with Eclipse being stuck in the 2010s and not supporting basic Groovy syntax

* Auto-fix Groovy code format

* Fix FabricAPITest not running

* Fix code style

src/main/java/net/fabricmc/loom/configuration/mods/MixinDetector.java

@@ -0,0 +1,74 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2023 FabricMC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.configuration.mods;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+
+import net.fabricmc.loom.LoomGradlePlugin;
+import net.fabricmc.loom.util.FileSystemUtil;
+import net.fabricmc.loom.util.fmj.FabricModJson;
+import net.fabricmc.loom.util.fmj.FabricModJsonFactory;
+
+public final class MixinDetector {
+	public static boolean hasMixinsWithoutRefmap(Path modJar) throws IOException {
+		try (FileSystemUtil.Delegate fs = FileSystemUtil.getJarFileSystem(modJar)) {
+			final List<String> mixinConfigs = getMixinConfigs(modJar);
+
+			if (!mixinConfigs.isEmpty()) {
+				for (String mixinConfig : mixinConfigs) {
+					final Path configPath = fs.getPath(mixinConfig);
+					if (Files.notExists(configPath)) continue;
+
+					try (BufferedReader reader = Files.newBufferedReader(configPath)) {
+						final JsonObject json = LoomGradlePlugin.GSON.fromJson(reader, JsonObject.class);
+
+						if (!json.has("refmap")) {
+							// We found a mixin config with no refmap, exit the loop.
+							return true;
+						}
+					} catch (JsonParseException e) {
+						throw new RuntimeException("Could not parse mixin config %s from jar %s".formatted(mixinConfig, modJar.toAbsolutePath()), e);
+					}
+				}
+			}
+
+			return false;
+		}
+	}
+
+	private static List<String> getMixinConfigs(Path modJar) {
+		// Nullable because we don't care here if we can't read it.
+		// We can just assume there are no mixins.
+		final FabricModJson fabricModJson = FabricModJsonFactory.createFromZipNullable(modJar);
+		return fabricModJson != null ? fabricModJson.getMixinConfigurations() : List.of();
+	}
+}

src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java

@@ -32,9 +32,11 @@ import java.io.UncheckedIOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
 import java.util.jar.Manifest;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -61,6 +63,7 @@ import net.fabricmc.tinyremapper.InputTag;
 import net.fabricmc.tinyremapper.NonClassCopyMode;
 import net.fabricmc.tinyremapper.OutputConsumerPath;
 import net.fabricmc.tinyremapper.TinyRemapper;
+import net.fabricmc.tinyremapper.extension.mixin.MixinExtension;
 
 public class ModProcessor {
 	private static final String fromM = MappingsNamespace.INTERMEDIARY.toString();
@@ -146,6 +149,10 @@ public class ModProcessor {
 			builder.extension(kotlinRemapperClassloader.getTinyRemapperExtension());
 		}
 
+		final Set<InputTag> hasMixinsWithoutRefmaps = new HashSet<>();
+		// Configure the mixin extension to remap mixins from mod jars detected not to contain refmaps.
+		builder.extension(new MixinExtension(hasMixinsWithoutRefmaps::contains));
+
 		final TinyRemapper remapper = builder.build();
 
 		for (Path minecraftJar : extension.getMinecraftJars(MappingsNamespace.INTERMEDIARY)) {
@@ -173,6 +180,12 @@ public class ModProcessor {
 
 			project.getLogger().debug("Adding " + info.getInputFile() + " as a remap input");
 
+			// Note: this is done at a jar level, not at the level of an individual mixin config.
+			// If a mod has multiple mixin configs, it's assumed that either all or none of them have refmaps.
+			if (MixinDetector.hasMixinsWithoutRefmap(info.getInputFile())) {
+				hasMixinsWithoutRefmaps.add(tag);
+			}
+
 			remapper.readInputsAsync(tag, info.getInputFile());
 			tagMap.put(info, tag);