Add DSL to configure mod class path groups. (#608)

* Add basic mod settings.

* Cleanup and review feedback.

* Add idea output dir support.

* Eclipse and vscode + better tests.

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

@@ -84,6 +84,16 @@ public interface LoomGradleExtensionAPI {
 
 	void mixin(Action<MixinExtensionAPI> action);
 
+	/**
+	 * Optionally register and configure a {@link ModSettings} object. The name should match the modid.
+	 * This is generally only required when the mod spans across multiple classpath directories, such as when using split sourcesets.
+	 */
+	@ApiStatus.Experimental
+	void mods(Action<NamedDomainObjectContainer<ModSettings>> action);
+
+	@ApiStatus.Experimental
+	NamedDomainObjectContainer<ModSettings> getMods();
+
 	@ApiStatus.Experimental
 	// TODO: move this from LoomGradleExtensionAPI to LoomGradleExtension once getRefmapName & setRefmapName is removed.
 	MixinExtensionAPI getMixin();

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

@@ -0,0 +1,55 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2022 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 javax.inject.Inject;
+
+import org.gradle.api.Named;
+import org.gradle.api.provider.ListProperty;
+import org.gradle.api.tasks.SourceSet;
+import org.jetbrains.annotations.ApiStatus;
+
+/**
+ * A {@link Named} object for setting mod-related values. The {@linkplain Named#getName() name} should match the mod id.
+ */
+@ApiStatus.Experimental
+public abstract class ModSettings implements Named {
+	/**
+	 * List of classpath directories, used to populate the `fabric.classPathGroups` Fabric Loader system property.
+	 */
+	public abstract ListProperty<SourceSet> getModSourceSets();
+
+	@Inject
+	public ModSettings() {
+		getModSourceSets().finalizeValueOnRead();
+	}
+
+	/**
+	 * Mark a {@link SourceSet} output directories part of the named mod.
+	 */
+	public void sourceSet(SourceSet sourceSet) {
+		getModSourceSets().add(sourceSet);
+	}
+}

src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java

@@ -50,6 +50,7 @@ import org.w3c.dom.Node;
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.configuration.InstallerData;
 import net.fabricmc.loom.configuration.ide.idea.IdeaSyncTask;
+import net.fabricmc.loom.configuration.ide.idea.IdeaUtils;
 import net.fabricmc.loom.configuration.providers.BundleMetadata;
 import net.fabricmc.loom.util.Constants;
 
@@ -101,16 +102,6 @@ public class RunConfig {
 		return e;
 	}
 
-	private static String getIdeaModuleName(Project project, SourceSet srcs) {
-		String module = project.getName() + "." + srcs.getName();
-
-		while ((project = project.getParent()) != null) {
-			module = project.getName() + "." + module;
-		}
-
-		return module;
-	}
-
 	private static void populate(Project project, LoomGradleExtension extension, RunConfig runConfig, String environment) {
 		runConfig.configName += extension.isRootProject() ? "" : " (" + project.getPath() + ")";
 		runConfig.eclipseProjectName = project.getExtensions().getByType(EclipseModel.class).getProject().getName();
@@ -166,7 +157,7 @@ public class RunConfig {
 		RunConfig runConfig = new RunConfig();
 		runConfig.configName = configName;
 		populate(project, extension, runConfig, environment);
-		runConfig.ideaModuleName = getIdeaModuleName(project, sourceSet);
+		runConfig.ideaModuleName = IdeaUtils.getIdeaModuleName(project, sourceSet);
 		runConfig.runDirIdeaUrl = "file://$PROJECT_DIR$/" + runDir;
 		runConfig.runDir = runDir;
 		runConfig.sourceSet = sourceSet;

src/main/java/net/fabricmc/loom/configuration/ide/idea/IdeaUtils.java

@@ -26,6 +26,9 @@ package net.fabricmc.loom.configuration.ide.idea;
 
 import java.util.Objects;
 
+import org.gradle.api.Project;
+import org.gradle.api.tasks.SourceSet;
+
 public class IdeaUtils {
 	public static boolean isIdeaSync() {
 		return Boolean.parseBoolean(System.getProperty("idea.sync.active", "false"));
@@ -42,4 +45,14 @@ public class IdeaUtils {
 		final int minor = Integer.parseInt(split[1]);
 		return major > 2021 || (major == 2021 && minor >= 3);
 	}
+
+	public static String getIdeaModuleName(Project project, SourceSet srcs) {
+		String module = project.getName() + "." + srcs.getName();
+
+		while ((project = project.getParent()) != null) {
+			module = project.getName() + "." + module;
+		}
+
+		return module;
+	}
 }

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

@@ -39,6 +39,7 @@ import org.gradle.api.tasks.SourceSet;
 import net.fabricmc.loom.api.InterfaceInjectionExtensionAPI;
 import net.fabricmc.loom.api.LoomGradleExtensionAPI;
 import net.fabricmc.loom.api.MixinExtensionAPI;
+import net.fabricmc.loom.api.ModSettings;
 import net.fabricmc.loom.api.decompilers.DecompilerOptions;
 import net.fabricmc.loom.api.mappings.intermediate.IntermediateMappingsProvider;
 import net.fabricmc.loom.api.mappings.layered.spec.LayeredMappingSpecBuilder;
@@ -77,6 +78,7 @@ public abstract class LoomGradleExtensionApiImpl implements LoomGradleExtensionA
 
 	private final NamedDomainObjectContainer<RunConfigSettings> runConfigs;
 	private final NamedDomainObjectContainer<DecompilerOptions> decompilers;
+	private final NamedDomainObjectContainer<ModSettings> mods;
 
 	protected LoomGradleExtensionApiImpl(Project project, LoomFiles directories) {
 		this.jarProcessors = project.getObjects().listProperty(JarProcessor.class)
@@ -106,6 +108,7 @@ public abstract class LoomGradleExtensionApiImpl implements LoomGradleExtensionA
 		this.runConfigs = project.container(RunConfigSettings.class,
 				baseName -> new RunConfigSettings(project, baseName));
 		this.decompilers = project.getObjects().domainObjectContainer(DecompilerOptions.class);
+		this.mods = project.getObjects().domainObjectContainer(ModSettings.class);
 
 		this.minecraftJarConfiguration = project.getObjects().property(MinecraftJarConfiguration.class).convention(MinecraftJarConfiguration.MERGED);
 		this.minecraftJarConfiguration.finalizeValueOnRead();
@@ -282,6 +285,16 @@ public abstract class LoomGradleExtensionApiImpl implements LoomGradleExtensionA
 		return interfaceInjectionExtension;
 	}
 
+	@Override
+	public void mods(Action<NamedDomainObjectContainer<ModSettings>> action) {
+		action.execute(getMods());
+	}
+
+	@Override
+	public NamedDomainObjectContainer<ModSettings> getMods() {
+		return mods;
+	}
+
 	// This is here to ensure that LoomGradleExtensionApiImpl compiles without any unimplemented methods
 	private final class EnsureCompile extends LoomGradleExtensionApiImpl {
 		private EnsureCompile() {

src/main/java/net/fabricmc/loom/task/launch/GenerateDLIConfigTask.java

@@ -42,6 +42,7 @@ import org.gradle.api.tasks.TaskAction;
 import net.fabricmc.loom.configuration.providers.minecraft.MinecraftVersionMeta;
 import net.fabricmc.loom.configuration.providers.minecraft.mapped.MappedMinecraftProvider;
 import net.fabricmc.loom.task.AbstractLoomTask;
+import net.fabricmc.loom.util.gradle.SourceSetHelper;
 
 public abstract class GenerateDLIConfigTask extends AbstractLoomTask {
 	@TaskAction
@@ -74,6 +75,10 @@ public abstract class GenerateDLIConfigTask extends AbstractLoomTask {
 			launchConfig.property("fabric.gameJarPath", getGameJarPath("common"));
 		}
 
+		if (!getExtension().getMods().isEmpty()) {
+			launchConfig.property("fabric.classPathGroups", getClassPathGroups());
+		}
+
 		final boolean plainConsole = getProject().getGradle().getStartParameter().getConsoleOutput() == ConsoleOutput.Plain;
 		final boolean ansiSupportedIDE = new File(getProject().getRootDir(), ".vscode").exists()
 				|| new File(getProject().getRootDir(), ".idea").exists()
@@ -103,6 +108,19 @@ public abstract class GenerateDLIConfigTask extends AbstractLoomTask {
 		};
 	}
 
+	/**
+	 * See: https://github.com/FabricMC/fabric-loader/pull/585.
+	 */
+	private String getClassPathGroups() {
+		return getExtension().getMods().stream()
+				.map(modSettings ->
+						SourceSetHelper.getClasspath(modSettings, getProject()).stream()
+							.map(File::getAbsolutePath)
+							.collect(Collectors.joining(File.pathSeparator))
+				)
+				.collect(Collectors.joining(File.pathSeparator+File.pathSeparator));
+	}
+
 	public static class LaunchConfig {
 		private final Map<String, List<String>> values = new HashMap<>();
 

src/main/java/net/fabricmc/loom/util/gradle/SourceSetHelper.java

@@ -0,0 +1,167 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2022 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.util.gradle;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import javax.xml.xpath.XPath;
+import javax.xml.xpath.XPathExpressionException;
+import javax.xml.xpath.XPathFactory;
+
+import org.gradle.api.Project;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.SourceSetOutput;
+import org.intellij.lang.annotations.Language;
+import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.VisibleForTesting;
+import org.xml.sax.InputSource;
+
+import net.fabricmc.loom.api.ModSettings;
+import net.fabricmc.loom.configuration.ide.idea.IdeaUtils;
+
+public final class SourceSetHelper {
+	@VisibleForTesting
+	@Language("xpath")
+	public static final String IDEA_OUTPUT_XPATH = "/project/component[@name='ProjectRootManager']/output/@url";
+
+	private SourceSetHelper() {
+	}
+
+	public static List<File> getClasspath(ModSettings modSettings, Project project) {
+		return modSettings.getModSourceSets().get().stream()
+				.flatMap(sourceSet -> getClasspath(sourceSet, project).stream())
+				.toList();
+	}
+
+	public static List<File> getClasspath(SourceSet sourceSet, Project project) {
+		final List<File> classpath = getGradleClasspath(sourceSet);
+
+		classpath.addAll(getIdeaClasspath(sourceSet, project));
+		classpath.addAll(getEclipseClasspath(sourceSet, project));
+		classpath.addAll(getVscodeClasspath(sourceSet, project));
+
+		return classpath;
+	}
+
+	private static List<File> getGradleClasspath(SourceSet sourceSet) {
+		final SourceSetOutput output = sourceSet.getOutput();
+		final File resources = output.getResourcesDir();
+
+		final List<File> classpath = new ArrayList<>();
+
+		classpath.addAll(output.getClassesDirs().getFiles());
+
+		if (resources != null) {
+			classpath.add(resources);
+		}
+
+		return classpath;
+	}
+
+	@VisibleForTesting
+	public static List<File> getIdeaClasspath(SourceSet sourceSet, Project project) {
+		final File projectDir = project.getRootDir();
+		final File dotIdea = new File(projectDir, ".idea");
+
+		if (!dotIdea.exists()) {
+			return Collections.emptyList();
+		}
+
+		final File miscXml = new File(dotIdea, "misc.xml");
+
+		if (!miscXml.exists()) {
+			return Collections.emptyList();
+		}
+
+		String outputDirUrl = evaluateXpath(miscXml, IDEA_OUTPUT_XPATH);
+
+		if (outputDirUrl == null) {
+			return Collections.emptyList();
+		}
+
+		outputDirUrl = outputDirUrl.replace("$PROJECT_DIR$", projectDir.getAbsolutePath());
+		outputDirUrl = outputDirUrl.replaceAll("^file:", "");
+
+		final File productionDir = new File(outputDirUrl, "production");
+		final File outputDir = new File(productionDir, IdeaUtils.getIdeaModuleName(project, sourceSet));
+
+		return Collections.singletonList(outputDir);
+	}
+
+	@Nullable
+	private static String evaluateXpath(File file, @Language("xpath") String expression) {
+		final XPath xpath = XPathFactory.newInstance().newXPath();
+
+		try (FileInputStream fis = new FileInputStream(file)) {
+			return xpath.evaluate(expression, new InputSource(fis));
+		} catch (XPathExpressionException e) {
+			return null;
+		} catch (IOException e) {
+			throw new UncheckedIOException(e);
+		}
+	}
+
+	@VisibleForTesting
+	public static List<File> getEclipseClasspath(SourceSet sourceSet, Project project) {
+		// Somewhat of a guess, I'm unsure if this is correct for multi-project builds
+		final File projectDir = project.getProjectDir();
+		final File classpath = new File(projectDir, ".classpath");
+
+		if (!classpath.exists()) {
+			return Collections.emptyList();
+		}
+
+		return getBinDirClasspath(projectDir, sourceSet);
+	}
+
+	@VisibleForTesting
+	public static List<File> getVscodeClasspath(SourceSet sourceSet, Project project) {
+		// Somewhat of a guess, I'm unsure if this is correct for multi-project builds
+		final File projectDir = project.getProjectDir();
+		final File dotVscode = new File(projectDir, ".vscode");
+
+		if (!dotVscode.exists()) {
+			return Collections.emptyList();
+		}
+
+		return getBinDirClasspath(projectDir, sourceSet);
+	}
+
+	private static List<File> getBinDirClasspath(File projectDir, SourceSet sourceSet) {
+		final File binDir = new File(projectDir, "bin");
+
+		if (!binDir.exists()) {
+			return Collections.emptyList();
+		}
+
+		return Collections.singletonList(new File(binDir, sourceSet.getName()));
+	}
+}