Better Mixin AP configuration (#423)

* [SPON-15] Apply Mixin AP config for all projects.

* Revert "[SPON-15] Apply Mixin AP config for all projects."

This reverts commit 93576e83b1221949d551b6307938f7dd6dc8fbbe.

* use setter & getter

* fix broken test introduced in 54d6ef7896

* initial commit for mixin extension

* refactor getConfiguration

* apply mixin extension

* [SPON-15] allow across project AP config

* [SPON-15] revert some changes

* [SPON-15] refactor codes

* [SPON-15] fix bugs

* [SPON-15] bring back cross-project apconfig

* [SPON-15] bug fix: move add default sourceSet earlier

* [SPON-15] fix style

* [SPON-15] refactor MixinAPExtension

* add test

* update test

* [SPON-15] fix test

* Update MixinAnnotationProcessorExtension.java

* [SPON-15] fix test

* fix deprecated gradle API

* [SPON-15] refactor ApInvoker

* [SPON-15] refactor ApInvoker

* allow change refmap name in sourceSet bases

* add new condition on test

* [SPON-15] fix wrong suffix

* Revert "[SPON-15] fix wrong suffix"

This reverts commit 98910392d91c26cd0454cca8cfc03c4e3d417fd6.

* fix mixinjson suffix

* use stream instead of collection for mixin json name

* change name for function

* use correct auto-refmap

* fix file name

* add with action

* add test

* refactor some codes

* refactor code

* update test

* fix checkstyle

* better error message

* fix checkstyle

* remove corss project option

* allow mixin inside loom

* remove project0

I should remove all project0. If I forget one please tell me.

* move `mixin` inside `loom`

* fix spotless

* merge attempt

* fix checkstyle

* seperate api & impl

* add experimental annotation for API

* use API

* Fix indentation

Co-authored-by: Juuxel <6596629+Juuxel@users.noreply.github.com>

* fix typo

Co-authored-by: Juuxel <6596629+Juuxel@users.noreply.github.com>

* fix typo

Co-authored-by: Juuxel <6596629+Juuxel@users.noreply.github.com>

* better javadoc

Co-authored-by: Juuxel <6596629+Juuxel@users.noreply.github.com>

src/main/java/net/fabricmc/loom/LoomGradleExtension.java

@@ -44,6 +44,7 @@ import net.fabricmc.loom.configuration.providers.mappings.MappingsProviderImpl;
 import net.fabricmc.loom.configuration.providers.minecraft.MinecraftMappedProvider;
 import net.fabricmc.loom.extension.LoomFiles;
 import net.fabricmc.loom.extension.LoomGradleExtensionImpl;
+import net.fabricmc.loom.extension.MixinApExtension;
 
 public interface LoomGradleExtension extends LoomGradleExtensionAPI {
 	static LoomGradleExtension get(Project project) {
@@ -102,4 +103,6 @@ public interface LoomGradleExtension extends LoomGradleExtensionAPI {
 		// TODO reimplement a way to change this, was never really supported api anyway
 		return String.format("https://maven.fabricmc.net/net/fabricmc/intermediary/%1$s/intermediary-%1$s-v2.jar", minecraftVersion);
 	}
+
+	MixinApExtension getMixinApExtension();
 }

src/main/java/net/fabricmc/loom/api/LoomGradleExtensionAPI.java

@@ -31,6 +31,7 @@ import org.gradle.api.Action;
 import org.gradle.api.NamedDomainObjectContainer;
 import org.gradle.api.artifacts.Dependency;
 import org.gradle.api.file.ConfigurableFileCollection;
+import org.jetbrains.annotations.ApiStatus;
 
 import net.fabricmc.loom.api.decompilers.LoomDecompiler;
 import net.fabricmc.loom.configuration.ide.RunConfigSettings;
@@ -81,6 +82,9 @@ public interface LoomGradleExtensionAPI {
 
 	NamedDomainObjectContainer<RunConfigSettings> getRunConfigs();
 
+	@ApiStatus.Experimental
+	void mixin(Action<MixinApExtensionAPI> action);
+
 	void setCustomManifest(String customManifest);
 
 	String getCustomManifest();

src/main/java/net/fabricmc/loom/api/MixinApExtensionAPI.java

@@ -0,0 +1,92 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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.api;
+
+import org.gradle.api.Action;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+import org.jetbrains.annotations.ApiStatus;
+
+@ApiStatus.Experimental
+public interface MixinApExtensionAPI {
+	/**
+	 * Apply Mixin AP to sourceSet.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name. By default this will
+	 *                      be {@link net.fabricmc.loom.LoomGradleExtension#getRefmapName()}
+	 * @param action used for filter the mixin json files. By default this will be all files
+	 *                  with name {@code *.mixins.json} that is inside the {@code resources} folder
+	 *                  of {@code sourceSet}.
+	 */
+	void add(SourceSet sourceSet, String refmapName, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name.
+	 */
+	void add(SourceSet sourceSet, String refmapName);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 * @param action used for filter the mixin json files.
+	 */
+	void add(SourceSet sourceSet, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 */
+	void add(SourceSet sourceSet);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name.
+	 * @param action used for filter the mixin json files.
+	 */
+	void add(String sourceSetName, String refmapName, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name.
+	 */
+	void add(String sourceSetName, String refmapName);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 * @param action used for filter the mixin json files.
+	 */
+	void add(String sourceSetName, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 */
+	void add(String sourceSetName);
+}

src/main/java/net/fabricmc/loom/build/MixinRefmapHelper.java

@@ -25,71 +25,47 @@
 package net.fabricmc.loom.build;
 
 import java.io.File;
-import java.io.IOException;
-import java.io.InputStreamReader;
 import java.nio.file.Path;
-import java.util.HashSet;
-import java.util.Set;
+import java.util.Objects;
+import java.util.stream.Stream;
 import java.util.zip.ZipEntry;
 
 import com.google.gson.JsonObject;
+import org.gradle.api.Project;
 import org.zeroturnaround.zip.ZipUtil;
 import org.zeroturnaround.zip.transform.StringZipEntryTransformer;
 import org.zeroturnaround.zip.transform.ZipEntryTransformerEntry;
 
+import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.LoomGradlePlugin;
+import net.fabricmc.loom.extension.MixinApExtension;
 
 public final class MixinRefmapHelper {
 	private MixinRefmapHelper() { }
 
-	public static boolean addRefmapName(String filename, Path outputPath) {
+	public static boolean addRefmapName(Project project, Path outputPath) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
 		File output = outputPath.toFile();
-		Set<String> mixinFilenames = findMixins(output, true);
 
-		if (mixinFilenames.size() > 0) {
-			return ZipUtil.transformEntries(output, mixinFilenames.stream().map((f) -> new ZipEntryTransformerEntry(f, new StringZipEntryTransformer("UTF-8") {
+		return mixin.getMixinSourceSetsStream().map(sourceSet -> {
+			MixinApExtension.MixinInformationContainer container = Objects.requireNonNull(
+					MixinApExtension.getMixinInformationContainer(sourceSet)
+			);
+			Stream<String> mixinJsonNames = container.getMixinJsonNames();
+			String refmapName = container.getRefmapName();
+
+			return ZipUtil.transformEntries(output, mixinJsonNames.map(f -> new ZipEntryTransformerEntry(f, new StringZipEntryTransformer("UTF-8") {
 				@Override
-				protected String transform(ZipEntry zipEntry, String input) throws IOException {
+				protected String transform(ZipEntry zipEntry, String input) {
 					JsonObject json = LoomGradlePlugin.GSON.fromJson(input, JsonObject.class);
 
 					if (!json.has("refmap")) {
-						json.addProperty("refmap", filename);
+						json.addProperty("refmap", refmapName);
 					}
 
 					return LoomGradlePlugin.GSON.toJson(json);
 				}
 			})).toArray(ZipEntryTransformerEntry[]::new));
-		} else {
-			return false;
-		}
-	}
-
-	private static Set<String> findMixins(File output, boolean onlyWithoutRefmap) {
-		// first, identify all of the mixin files
-		Set<String> mixinFilename = new HashSet<>();
-		// TODO: this is a lovely hack
-		ZipUtil.iterate(output, (stream, entry) -> {
-			if (!entry.isDirectory() && entry.getName().endsWith(".json") && !entry.getName().contains("/") && !entry.getName().contains("\\")) {
-				// JSON file in root directory
-				try (InputStreamReader inputStreamReader = new InputStreamReader(stream)) {
-					JsonObject json = LoomGradlePlugin.GSON.fromJson(inputStreamReader, JsonObject.class);
-
-					if (json != null) {
-						boolean hasMixins = json.has("mixins") && json.get("mixins").isJsonArray();
-						boolean hasClient = json.has("client") && json.get("client").isJsonArray();
-						boolean hasServer = json.has("server") && json.get("server").isJsonArray();
-
-						if (json.has("package") && (hasMixins || hasClient || hasServer)) {
-							if (!onlyWithoutRefmap || !json.has("refmap") || !json.has("minVersion")) {
-								mixinFilename.add(entry.getName());
-							}
-						}
-					}
-				} catch (Exception ignored) {
-					// ...
-				}
-			}
-		});
-		return mixinFilename;
+		}).reduce(false, Boolean::logicalOr);
 	}
 }

src/main/java/net/fabricmc/loom/build/mixin/AnnotationProcessorInvoker.java

@@ -29,16 +29,17 @@ import java.io.IOException;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
-import java.util.stream.Stream;
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.stream.Collectors;
 
 import org.gradle.api.Project;
 import org.gradle.api.Task;
 import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.artifacts.ConfigurationContainer;
-import org.gradle.api.plugins.JavaPluginConvention;
 import org.gradle.api.tasks.SourceSet;
-import org.gradle.api.tasks.TaskCollection;
 
+import net.fabricmc.loom.extension.MixinApExtension;
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.util.Constants;
 
@@ -48,37 +49,46 @@ import net.fabricmc.loom.util.Constants;
  * See Java and Kapt implementations for a more deep understanding of the things passed by the children.
  */
 public abstract class AnnotationProcessorInvoker<T extends Task> {
+	public static final String JAVA = "java";
+	public static final String SCALA = "scala";
+
 	protected final Project project;
-	private final Collection<Configuration> annotationProcessorConfigurations;
-	protected final TaskCollection<T> invokerTasks;
+	protected final Map<SourceSet, T> invokerTasks;
+	private final Collection<Configuration> apConfigurations;
 
 	protected AnnotationProcessorInvoker(Project project,
-										Collection<Configuration> annotationProcessorConfigurations,
-										TaskCollection<T> invokerTasks) {
+										Collection<Configuration> apConfigurations,
+										Map<SourceSet, T> invokerTasks) {
 		this.project = project;
-		this.annotationProcessorConfigurations = annotationProcessorConfigurations;
+		this.apConfigurations = apConfigurations;
 		this.invokerTasks = invokerTasks;
 	}
 
+	protected static Collection<Configuration> getApConfigurations(Project project, Function<String, String> getApConfigNameFunc) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getApConfigurationsStream(getApConfigNameFunc).collect(Collectors.toList());
+	}
+
 	protected abstract void passArgument(T compileTask, String key, String value);
 
-	protected abstract File getDestinationDir(T task);
+	protected abstract File getRefmapDestinationDir(T task);
 
-	protected final String getRefmapDestination(T task, LoomGradleExtension extension) throws IOException {
-		return new File(getDestinationDir(task), extension.getRefmapName()).getCanonicalPath();
+	protected final String getRefmapDestination(T task, String refmapName) throws IOException {
+		return new File(getRefmapDestinationDir(task), refmapName).getCanonicalPath();
 	}
 
-	private void passMixinArguments(T task) {
+	private void passMixinArguments(T task, SourceSet sourceSet) {
 		try {
-			LoomGradleExtension extension = LoomGradleExtension.get(project);
+			LoomGradleExtension loom = LoomGradleExtension.get(project);
+			String refmapName = Objects.requireNonNull(MixinApExtension.getMixinInformationContainer(sourceSet)).getRefmapName();
 			Map<String, String> args = new HashMap<>() {{
-					put(Constants.MixinArguments.IN_MAP_FILE_NAMED_INTERMEDIARY, extension.getMappingsProvider().tinyMappings.getCanonicalPath());
-					put(Constants.MixinArguments.OUT_MAP_FILE_NAMED_INTERMEDIARY, extension.getNextMixinMappings().getCanonicalPath());
-					put(Constants.MixinArguments.OUT_REFMAP_FILE, getRefmapDestination(task, extension));
+					put(Constants.MixinArguments.IN_MAP_FILE_NAMED_INTERMEDIARY, loom.getMappingsProvider().tinyMappings.getCanonicalPath());
+					put(Constants.MixinArguments.OUT_MAP_FILE_NAMED_INTERMEDIARY, loom.getNextMixinMappings().getCanonicalPath());
+					put(Constants.MixinArguments.OUT_REFMAP_FILE, getRefmapDestination(task, refmapName));
 					put(Constants.MixinArguments.DEFAULT_OBFUSCATION_ENV, "named:intermediary");
 				}};
 
-			project.getLogger().debug("Outputting refmap to dir: " + getDestinationDir(task) + " for compile task: " + task);
+			project.getLogger().debug("Outputting refmap to dir: " + getRefmapDestinationDir(task) + " for compile task: " + task);
 			args.forEach((k, v) -> passArgument(task, k, v));
 		} catch (IOException e) {
 			project.getLogger().error("Could not configure mixin annotation processors", e);
@@ -90,7 +100,7 @@ public abstract class AnnotationProcessorInvoker<T extends Task> {
 		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		if (!extension.ideSync()) {
-			for (Configuration processorConfig : annotationProcessorConfigurations) {
+			for (Configuration processorConfig : apConfigurations) {
 				project.getLogger().info("Adding mixin to classpath of AP config: " + processorConfig.getName());
 				// Pass named MC classpath to mixin AP classpath
 				processorConfig.extendsFrom(
@@ -105,14 +115,8 @@ public abstract class AnnotationProcessorInvoker<T extends Task> {
 			}
 		}
 
-		for (T task : invokerTasks) {
-			passMixinArguments(task);
+		for (Map.Entry<SourceSet, T> entry : invokerTasks.entrySet()) {
+			passMixinArguments(entry.getValue(), entry.getKey());
 		}
 	}
-
-	static Stream<SourceSet> getNonTestSourceSets(Project project) {
-		return project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets()
-						.stream()
-						.filter(sourceSet -> !sourceSet.getName().equals("test"));
-	}
 }

src/main/java/net/fabricmc/loom/build/mixin/JavaApInvoker.java

@@ -25,17 +25,30 @@
 package net.fabricmc.loom.build.mixin;
 
 import java.io.File;
-import java.util.List;
+import java.util.Map;
+import java.util.Objects;
 import java.util.stream.Collectors;
 
 import org.gradle.api.Project;
-import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.plugins.JavaPlugin;
+import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.compile.JavaCompile;
 
+import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.extension.MixinApExtension;
+
 public class JavaApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	public JavaApInvoker(Project project) {
-		super(project, getConfigurations(project), project.getTasks().withType(JavaCompile.class));
+		super(
+				project,
+				AnnotationProcessorInvoker.getApConfigurations(project, JavaApInvoker::getAptConfigurationName),
+				getInvokerTasks(project));
+	}
+
+	private static Map<SourceSet, JavaCompile> getInvokerTasks(Project project) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getInvokerTasksStream(AnnotationProcessorInvoker.JAVA)
+				.collect(Collectors.toMap(Map.Entry::getKey, entry -> Objects.requireNonNull((JavaCompile) entry.getValue())));
 	}
 
 	@Override
@@ -44,18 +57,10 @@ public class JavaApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	}
 
 	@Override
-	protected File getDestinationDir(JavaCompile task) {
+	protected File getRefmapDestinationDir(JavaCompile task) {
 		return task.getDestinationDir();
 	}
 
-	private static List<Configuration> getConfigurations(Project project) {
-		// java plugin generates an AP configuration for every source set based off of the getAptConfigurationName method.
-		return AnnotationProcessorInvoker.getNonTestSourceSets(project)
-						.map(sourceSet -> project.getConfigurations()
-										.getByName(getAptConfigurationName(sourceSet.getName()))
-						).collect(Collectors.toList());
-	}
-
 	private static String getAptConfigurationName(String sourceSet) {
 		// This is documented by the gradle 4.6 release notes https://docs.gradle.org/4.6/release-notes.html#potential-breaking-changes
 		return sourceSet.equals("main") ? JavaPlugin.ANNOTATION_PROCESSOR_CONFIGURATION_NAME : sourceSet + "AnnotationProcessor";

src/main/java/net/fabricmc/loom/build/mixin/KaptApInvoker.java

@@ -29,18 +29,18 @@ import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
-import java.util.List;
+import java.util.Map;
+import java.util.Objects;
 import java.util.stream.Collectors;
 
 import kotlin.Unit;
 import org.gradle.api.Project;
-import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.compile.JavaCompile;
-import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.gradle.plugin.KaptExtension;
 
 import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.extension.MixinApExtension;
 
 public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	private final KaptExtension kaptExtension = project.getExtensions().getByType(KaptExtension.class);
@@ -48,7 +48,10 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	private final File dummyRefmapDirectory;
 
 	public KaptApInvoker(Project project) {
-		super(project, getConfigurations(project), project.getTasks().withType(JavaCompile.class));
+		super(
+				project,
+				AnnotationProcessorInvoker.getApConfigurations(project, KaptApInvoker::getKaptConfigurationName),
+				getInvokerTasks(project));
 
 		try {
 			dummyRefmapDirectory = Files.createTempDirectory("temp_refmap").toFile();
@@ -62,18 +65,26 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 		kaptExtension.setIncludeCompileClasspath(false);
 	}
 
+	private static Map<SourceSet, JavaCompile> getInvokerTasks(Project project) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getInvokerTasksStream(AnnotationProcessorInvoker.JAVA)
+				.collect(Collectors.toMap(Map.Entry::getKey, entry -> Objects.requireNonNull((JavaCompile) entry.getValue())));
+	}
+
 	@Override
 	public void configureMixin() {
 		super.configureMixin();
 
-		for (JavaCompile task : invokerTasks) {
+		for (Map.Entry<SourceSet, JavaCompile> entry : invokerTasks.entrySet()) {
 			// Kapt only allows specifying javac args to all annotation processors at once. So we need to specify some dummy
 			// target location for the refmap and then move it to the correct place for each sourceset
+			JavaCompile task = entry.getValue();
+			SourceSet sourceSet = entry.getKey();
 			task.doLast(t -> {
 				try {
-					LoomGradleExtension extension = LoomGradleExtension.get(project);
-					Path src = Paths.get(getRefmapDestination(task, extension));
-					Path dest = Paths.get(task.getDestinationDir().toString(), extension.getRefmapName());
+					String refmapName = Objects.requireNonNull(MixinApExtension.getMixinInformationContainer(sourceSet)).getRefmapName();
+					Path src = Paths.get(getRefmapDestination(task, refmapName));
+					Path dest = Paths.get(task.getDestinationDir().toString(), refmapName);
 
 					// Possible that no mixin annotations exist
 					if (Files.exists(src)) {
@@ -87,15 +98,6 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 		}
 	}
 
-	@NotNull
-	private static List<Configuration> getConfigurations(Project project) {
-		// Kapt generates an AP configuration for every source set based off of the getKaptConfigurationName method.
-		return AnnotationProcessorInvoker.getNonTestSourceSets(project)
-						.map(sourceSet -> project.getConfigurations()
-										.getByName(getKaptConfigurationName(sourceSet.getName()))
-						).collect(Collectors.toList());
-	}
-
 	// Pulled out from the internal class: https://github.com/JetBrains/kotlin/blob/33a0ec9b4f40f3d6f1f96b2db504ade4c2fafe03/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/kapt/Kapt3KotlinGradleSubplugin.kt#L92
 	private static String getKaptConfigurationName(String sourceSetName) {
 		if (!sourceSetName.equals(SourceSet.MAIN_SOURCE_SET_NAME)) {
@@ -116,7 +118,7 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	}
 
 	@Override
-	protected File getDestinationDir(JavaCompile task) {
+	protected File getRefmapDestinationDir(JavaCompile task) {
 		return dummyRefmapDirectory;
 	}
 }

src/main/java/net/fabricmc/loom/build/mixin/ScalaApInvoker.java

@@ -25,17 +25,31 @@
 package net.fabricmc.loom.build.mixin;
 
 import java.io.File;
+import java.util.Map;
+import java.util.Objects;
+import java.util.stream.Collectors;
 
 import com.google.common.collect.ImmutableList;
 import org.gradle.api.Project;
+import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.scala.ScalaCompile;
 
+import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.extension.MixinApExtension;
+
 public class ScalaApInvoker extends AnnotationProcessorInvoker<ScalaCompile> {
 	public ScalaApInvoker(Project project) {
-		super(project,
-						// Scala just uses the java AP configuration afaik. This of course assumes the java AP also gets configured.
-						ImmutableList.of(),
-						project.getTasks().withType(ScalaCompile.class));
+		super(
+				project,
+				// Scala just uses the java AP configuration afaik. This of course assumes the java AP also gets configured.
+				ImmutableList.of(),
+				getInvokerTasks(project));
+	}
+
+	private static Map<SourceSet, ScalaCompile> getInvokerTasks(Project project) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getInvokerTasksStream(AnnotationProcessorInvoker.SCALA)
+				.collect(Collectors.toMap(Map.Entry::getKey, entry -> Objects.requireNonNull((ScalaCompile) entry.getValue())));
 	}
 
 	@Override
@@ -44,7 +58,7 @@ public class ScalaApInvoker extends AnnotationProcessorInvoker<ScalaCompile> {
 	}
 
 	@Override
-	protected File getDestinationDir(ScalaCompile task) {
+	protected File getRefmapDestinationDir(ScalaCompile task) {
 		return task.getDestinationDir();
 	}
 }

src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java

@@ -33,6 +33,7 @@ import org.gradle.api.tasks.compile.JavaCompile;
 import org.gradle.api.tasks.javadoc.Javadoc;
 import org.gradle.jvm.tasks.Jar;
 
+import net.fabricmc.loom.extension.MixinApExtension;
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.build.mixin.JavaApInvoker;
 import net.fabricmc.loom.build.mixin.KaptApInvoker;
@@ -143,6 +144,9 @@ public final class CompileConfiguration {
 			System.setProperty("log4j.skipJansi", "true");
 
 			project.getLogger().info("Configuring compiler arguments for Java");
+			MixinApExtension mixinApExtension = LoomGradleExtension.get(project).getMixinApExtension();
+			mixinApExtension.init();
+
 			new JavaApInvoker(project).configureMixin();
 
 			if (project.getPluginManager().hasPlugin("scala")) {

src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionApiImpl.java

@@ -36,6 +36,7 @@ import org.gradle.api.artifacts.Dependency;
 import org.gradle.api.file.ConfigurableFileCollection;
 import org.gradle.api.plugins.BasePluginConvention;
 
+import net.fabricmc.loom.api.MixinApExtensionAPI;
 import net.fabricmc.loom.api.decompilers.LoomDecompiler;
 import net.fabricmc.loom.api.LoomGradleExtensionAPI;
 import net.fabricmc.loom.configuration.ide.RunConfigSettings;
@@ -159,6 +160,11 @@ public abstract class LoomGradleExtensionApiImpl implements LoomGradleExtensionA
 		return remapMod;
 	}
 
+	@Override
+	public void mixin(Action<MixinApExtensionAPI> action) {
+		action.execute(getMixinApExtension());
+	}
+
 	@Override
 	public void setCustomManifest(String customManifest) {
 		Objects.requireNonNull(customManifest, "Custom manifest cannot be null");
@@ -174,6 +180,8 @@ public abstract class LoomGradleExtensionApiImpl implements LoomGradleExtensionA
 
 	protected abstract LoomFiles getFiles();
 
+	protected abstract MixinApExtension getMixinApExtension();
+
 	// This is here to ensure that LoomGradleExtensionApiImpl compiles without any unimplemented methods
 	private final class EnsureCompile extends LoomGradleExtensionApiImpl {
 		private EnsureCompile() {
@@ -190,5 +198,10 @@ public abstract class LoomGradleExtensionApiImpl implements LoomGradleExtensionA
 		protected LoomFiles getFiles() {
 			throw new RuntimeException("Yeah... something is really wrong");
 		}
+
+		@Override
+		protected MixinApExtension getMixinApExtension() {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
 	}
 }

src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionImpl.java

@@ -47,6 +47,7 @@ import net.fabricmc.loom.configuration.processors.JarProcessorManager;
 
 public class LoomGradleExtensionImpl extends LoomGradleExtensionApiImpl implements LoomGradleExtension {
 	private final Project project;
+	private final MixinApExtension mixinApExtension;
 	private final LoomFiles loomFiles;
 	private final ConfigurableFileCollection unmappedMods;
 
@@ -62,6 +63,7 @@ public class LoomGradleExtensionImpl extends LoomGradleExtensionApiImpl implemen
 	public LoomGradleExtensionImpl(Project project, LoomFiles files) {
 		super(project, files);
 		this.project = project;
+		this.mixinApExtension = new MixinApExtensionImpl(project);
 		this.loomFiles = files;
 		this.unmappedMods = project.files();
 	}
@@ -160,4 +162,9 @@ public class LoomGradleExtensionImpl extends LoomGradleExtensionApiImpl implemen
 
 		return provider;
 	}
+
+	@Override
+	public MixinApExtension getMixinApExtension() {
+		return this.mixinApExtension;
+	}
 }

src/main/java/net/fabricmc/loom/extension/MixinApExtension.java

@@ -0,0 +1,126 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2016-2017 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.extension;
+
+import java.util.Collection;
+import java.util.Map;
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+import org.gradle.api.InvalidUserDataException;
+import org.gradle.api.Task;
+import org.gradle.api.artifacts.Configuration;
+import org.gradle.api.plugins.ExtraPropertiesExtension;
+import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import net.fabricmc.loom.api.MixinApExtensionAPI;
+
+/**
+ * A gradle extension to configure mixin annotation processor.
+ */
+@ApiStatus.Experimental
+public interface MixinApExtension extends MixinApExtensionAPI {
+	String MIXIN_INFORMATION_CONTAINER = "mixin";
+
+	/**
+	 * An information container stores necessary information
+	 * for configuring the mixin annotation processor. It's stored
+	 * in [SourceSet].ext.mixin.
+	 */
+	final class MixinInformationContainer {
+		private final SourceSet sourceSet;
+		private final String refmapName;
+		private Stream<String> mixinJsonNames;
+
+		final PatternSet mixinJsonPattern;
+
+		public MixinInformationContainer(@NotNull SourceSet sourceSet,
+										@NotNull String refmapName,
+										@NotNull PatternSet mixinJsonPattern) {
+			this.sourceSet = sourceSet;
+			this.refmapName = refmapName;
+			this.mixinJsonPattern = mixinJsonPattern;
+		}
+
+		void setMixinJsonNames(@NotNull Stream<String> mixinJsonNames) {
+			if (this.mixinJsonNames == null) {
+				this.mixinJsonNames = mixinJsonNames;
+			}
+		}
+
+		@NotNull
+		public Stream<String> getMixinJsonNames() {
+			return Objects.requireNonNull(mixinJsonNames);
+		}
+
+		@NotNull
+		public SourceSet getSourceSet() {
+			return sourceSet;
+		}
+
+		@NotNull
+		public String getRefmapName() {
+			return refmapName;
+		}
+	}
+
+	@Nullable
+	static MixinInformationContainer getMixinInformationContainer(SourceSet sourceSet) {
+		ExtraPropertiesExtension extra = sourceSet.getExtensions().getExtraProperties();
+		return extra.has(MIXIN_INFORMATION_CONTAINER) ? (MixinInformationContainer) extra.get(MIXIN_INFORMATION_CONTAINER) : null;
+	}
+
+	static void setMixinInformationContainer(SourceSet sourceSet, MixinInformationContainer container) {
+		ExtraPropertiesExtension extra = sourceSet.getExtensions().getExtraProperties();
+
+		if (extra.has(MIXIN_INFORMATION_CONTAINER)) {
+			throw new InvalidUserDataException("The sourceSet " + sourceSet.getName()
+					+ " has been configured for mixin annotation processor multiple times");
+		}
+
+		extra.set(MIXIN_INFORMATION_CONTAINER, container);
+	}
+
+	@NotNull
+	Stream<SourceSet> getMixinSourceSetsStream();
+
+	@NotNull
+	Stream<Configuration> getApConfigurationsStream(Function<String, String> getApConfigNameFunc);
+
+	@NotNull
+	Stream<Map.Entry<SourceSet, Task>> getInvokerTasksStream(String compileTaskLanguage);
+
+	@NotNull
+	@Input
+	Collection<SourceSet> getMixinSourceSets();
+
+	void init();
+}

src/main/java/net/fabricmc/loom/extension/MixinApExtensionApiImpl.java

@@ -0,0 +1,110 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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.extension;
+
+import org.gradle.api.Action;
+import org.gradle.api.InvalidUserDataException;
+import org.gradle.api.Project;
+import org.gradle.api.plugins.JavaPluginConvention;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+
+import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.api.MixinApExtensionAPI;
+
+public abstract class MixinApExtensionApiImpl implements MixinApExtensionAPI {
+	protected abstract Project getProject();
+	protected abstract PatternSet add0(SourceSet sourceSet, String refmapName);
+
+	@Override
+	public void add(SourceSet sourceSet, String refmapName, Action<PatternSet> action) {
+		PatternSet pattern = add0(sourceSet, refmapName);
+		action.execute(pattern);
+	}
+
+	@Override
+	public void add(SourceSet sourceSet, String refmapName) {
+		add(sourceSet, refmapName, x -> { });
+	}
+
+	@Override
+	public void add(String sourceSetName, String refmapName, Action<PatternSet> action) {
+		// try to find sourceSet with name sourceSetName in this project
+		SourceSet sourceSet = getProject().getConvention().getPlugin(JavaPluginConvention.class)
+				.getSourceSets().findByName(sourceSetName);
+
+		if (sourceSet == null) {
+			throw new InvalidUserDataException("No sourceSet " + sourceSetName + " was found");
+		}
+
+		PatternSet pattern = add0(sourceSet, refmapName);
+		action.execute(pattern);
+	}
+
+	@Override
+	public void add(String sourceSetName, String refmapName) {
+		add(sourceSetName, refmapName, x -> { });
+	}
+
+	@Override
+	public void add(SourceSet sourceSet, Action<PatternSet> action) {
+		LoomGradleExtension extension = LoomGradleExtension.get(getProject());
+		add(sourceSet, extension.getRefmapName(), action);
+	}
+
+	@Override
+	public void add(SourceSet sourceSet) {
+		add(sourceSet, x -> { });
+	}
+
+	@Override
+	public void add(String sourceSetName, Action<PatternSet> action) {
+		LoomGradleExtension extension = LoomGradleExtension.get(getProject());
+		add(sourceSetName, extension.getRefmapName(), action);
+	}
+
+	@Override
+	public void add(String sourceSetName) {
+		add(sourceSetName, x -> { });
+	}
+
+	// This is here to ensure that LoomGradleExtensionApiImpl compiles without any unimplemented methods
+	private final class EnsureCompile extends MixinApExtensionApiImpl {
+		private EnsureCompile() {
+			super();
+			throw new RuntimeException();
+		}
+
+		@Override
+		protected Project getProject() {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
+
+		@Override
+		protected PatternSet add0(SourceSet sourceSet, String refmapName) {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
+	}
+}

src/main/java/net/fabricmc/loom/extension/MixinApExtensionImpl.java

@@ -0,0 +1,125 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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.extension;
+
+import java.io.File;
+import java.util.AbstractMap;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.gradle.api.Project;
+import org.gradle.api.Task;
+import org.gradle.api.UnknownTaskException;
+import org.gradle.api.artifacts.Configuration;
+import org.gradle.api.plugins.JavaPluginConvention;
+import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+import org.jetbrains.annotations.NotNull;
+
+public class MixinApExtensionImpl extends MixinApExtensionApiImpl implements MixinApExtension {
+	private boolean isDefault;
+	private final Project project;
+
+	public MixinApExtensionImpl(Project project) {
+		this.isDefault = true;
+		this.project = project;
+	}
+
+	@Override
+	public Project getProject() {
+		return this.project;
+	}
+
+	@Override
+	protected PatternSet add0(SourceSet sourceSet, String refmapName) {
+		PatternSet pattern = new PatternSet().setIncludes(Collections.singletonList("*.mixins.json"));
+		MixinApExtension.setMixinInformationContainer(sourceSet, new MixinApExtension.MixinInformationContainer(sourceSet, refmapName, pattern));
+
+		isDefault = false;
+
+		return pattern;
+	}
+
+	@Override
+	@NotNull
+	public Stream<SourceSet> getMixinSourceSetsStream() {
+		return project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets().stream()
+				.filter(sourceSet -> {
+					MixinApExtension.MixinInformationContainer container = MixinApExtension.getMixinInformationContainer(sourceSet);
+
+					if (container != null) {
+						PatternSet pattern = container.mixinJsonPattern;
+						Stream<String> mixinJsonNames = sourceSet.getResources()
+								.matching(pattern).getFiles().stream().map(File::getName);
+						container.setMixinJsonNames(mixinJsonNames);
+						return true;
+					}
+
+					return false;
+				});
+	}
+
+	@Override
+	@NotNull
+	public Stream<Configuration> getApConfigurationsStream(Function<String, String> getApConfigNameFunc) {
+		return getMixinSourceSetsStream()
+				.map(sourceSet -> project.getConfigurations().getByName(getApConfigNameFunc.apply(sourceSet.getName())));
+	}
+
+	@Override
+	@NotNull
+	public Stream<Map.Entry<SourceSet, Task>> getInvokerTasksStream(String compileTaskLanguage) {
+		return getMixinSourceSetsStream()
+				.flatMap(sourceSet -> {
+					try {
+						Task task = project.getTasks().getByName(sourceSet.getCompileTaskName(compileTaskLanguage));
+						return Stream.of(new AbstractMap.SimpleEntry<>(sourceSet, task));
+					} catch (UnknownTaskException ignored) {
+						return Stream.empty();
+					}
+				});
+	}
+
+	@Override
+	@NotNull
+	@Input
+	public Collection<SourceSet> getMixinSourceSets() {
+		return getMixinSourceSetsStream().collect(Collectors.toList());
+	}
+
+	@Override
+	public void init() {
+		if (isDefault) {
+			project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets().forEach(this::add);
+		}
+
+		isDefault = false;
+	}
+}

src/main/java/net/fabricmc/loom/task/RemapJarTask.java

@@ -170,7 +170,7 @@ public class RemapJarTask extends Jar {
 						throw new RuntimeException("Failed to remap " + input + " to " + output + " - file missing!");
 					}
 
-					if (MixinRefmapHelper.addRefmapName(extension.getRefmapName(), output)) {
+					if (MixinRefmapHelper.addRefmapName(project, output)) {
 						project.getLogger().debug("Transformed mixin reference maps in output JAR!");
 					}