Gen sources config caching support

src/main/java/net/fabricmc/loom/configuration/decompile/DecompileConfiguration.java

@@ -30,6 +30,7 @@
 import org.gradle.api.artifacts.ConfigurationContainer;
 
 import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
 import net.fabricmc.loom.configuration.providers.mappings.MappingConfiguration;
 import net.fabricmc.loom.configuration.providers.minecraft.MinecraftJar;
 import net.fabricmc.loom.configuration.providers.minecraft.mapped.MappedMinecraftProvider;
@@ -63,5 +64,6 @@ protected final void configureUnpick(GenerateSourcesTask task, File unpickOutput
 		task.getUnpickConstantJar().setFrom(configurations.getByName(Constants.Configurations.MAPPING_CONSTANTS));
 		task.getUnpickClasspath().setFrom(configurations.getByName(Constants.Configurations.MINECRAFT_COMPILE_LIBRARIES));
 		task.getUnpickClasspath().from(configurations.getByName(Constants.Configurations.MOD_COMPILE_CLASSPATH_MAPPED));
+		extension.getMinecraftJars(MappingsNamespace.NAMED).forEach(task.getUnpickClasspath()::from);
 	}
 }

src/main/java/net/fabricmc/loom/configuration/decompile/SingleJarDecompileConfiguration.java

@@ -58,7 +58,7 @@ public final void afterEvaluation() {
 			// Decompiler will be passed to the constructor of GenerateSourcesTask
 			project.getTasks().register(taskName, GenerateSourcesTask.class, options).configure(task -> {
 				task.getInputJarName().set(minecraftJar.getName());
-				task.getOutputJar().fileValue(GenerateSourcesTask.getJarFileWithSuffix("-sources.jar", minecraftJar.getPath()));
+				task.getSourcesOutputJar().fileValue(GenerateSourcesTask.getJarFileWithSuffix("-sources.jar", minecraftJar.getPath()));
 
 				task.dependsOn(project.getTasks().named("validateAccessWidener"));
 				task.setDescription("Decompile minecraft using %s.".formatted(decompilerName));

src/main/java/net/fabricmc/loom/configuration/decompile/SplitDecompileConfiguration.java

@@ -55,7 +55,7 @@ public void afterEvaluation() {
 
 		final TaskProvider<Task> commonDecompileTask = createDecompileTasks("Common", task -> {
 			task.getInputJarName().set(commonJar.getName());
-			task.getOutputJar().fileValue(GenerateSourcesTask.getJarFileWithSuffix("-sources.jar", commonJar.getPath()));
+			task.getSourcesOutputJar().fileValue(GenerateSourcesTask.getJarFileWithSuffix("-sources.jar", commonJar.getPath()));
 
 			if (mappingConfiguration.hasUnpickDefinitions()) {
 				File unpickJar = new File(extension.getMappingConfiguration().mappingsWorkingDir().toFile(), "minecraft-common-unpicked.jar");
@@ -65,7 +65,7 @@ public void afterEvaluation() {
 
 		final TaskProvider<Task> clientOnlyDecompileTask = createDecompileTasks("ClientOnly", task -> {
 			task.getInputJarName().set(clientOnlyJar.getName());
-			task.getOutputJar().fileValue(GenerateSourcesTask.getJarFileWithSuffix("-sources.jar", clientOnlyJar.getPath()));
+			task.getSourcesOutputJar().fileValue(GenerateSourcesTask.getJarFileWithSuffix("-sources.jar", clientOnlyJar.getPath()));
 
 			if (mappingConfiguration.hasUnpickDefinitions()) {
 				File unpickJar = new File(extension.getMappingConfiguration().mappingsWorkingDir().toFile(), "minecraft-clientonly-unpicked.jar");

src/main/java/net/fabricmc/loom/configuration/providers/minecraft/mapped/AbstractMappedMinecraftProvider.java

@@ -28,6 +28,7 @@
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
@@ -76,11 +77,18 @@ public List<MinecraftJar.Type> getDependencyTypes() {
 
 	public List<MinecraftJar> provide(ProvideContext context) throws Exception {
 		final List<RemappedJars> remappedJars = getRemappedJars();
-		assert !remappedJars.isEmpty();
+		final List<MinecraftJar> minecraftJars = remappedJars.stream()
+				.map(RemappedJars::outputJar)
+				.toList();
 
-		if (!areOutputsValid(remappedJars) || context.refreshOutputs()) {
+		if (remappedJars.isEmpty()) {
+			throw new IllegalStateException("No remapped jars provided");
+		}
+
+		if (!areOutputsValid(remappedJars) || context.refreshOutputs() || !hasBackupJars(minecraftJars)) {
 			try {
 				remapInputs(remappedJars, context.configContext());
+				createBackupJars(minecraftJars);
 			} catch (Throwable t) {
 				cleanOutputs(remappedJars);
 
@@ -99,9 +107,29 @@ public List<MinecraftJar> provide(ProvideContext context) throws Exception {
 			}
 		}
 
-		return remappedJars.stream()
-				.map(RemappedJars::outputJar)
-				.toList();
+		return minecraftJars;
+	}
+
+	// Create two copies of the remapped jar, the backup jar is used as the input of genSources
+	public static Path getBackupJarPath(MinecraftJar minecraftJar) {
+		final Path outputJarPath = minecraftJar.getPath();
+		return outputJarPath.resolveSibling(outputJarPath.getFileName() + ".backup");
+	}
+
+	protected boolean hasBackupJars(List<MinecraftJar> minecraftJars) {
+		for (MinecraftJar minecraftJar : minecraftJars) {
+			if (!Files.exists(getBackupJarPath(minecraftJar))) {
+				return false;
+			}
+		}
+
+		return true;
+	}
+
+	protected void createBackupJars(List<MinecraftJar> minecraftJars) throws IOException {
+		for (MinecraftJar minecraftJar : minecraftJars) {
+			Files.copy(minecraftJar.getPath(), getBackupJarPath(minecraftJar), StandardCopyOption.REPLACE_EXISTING);
+		}
 	}
 
 	public record ProvideContext(boolean applyDependencies, boolean refreshOutputs, ConfigContext configContext) {
@@ -234,6 +262,7 @@ public static void configureSplitRemapper(RemappedJars remappedJars, TinyRemappe
 	private void cleanOutputs(List<RemappedJars> remappedJars) throws IOException {
 		for (RemappedJars remappedJar : remappedJars) {
 			Files.deleteIfExists(remappedJar.outputJarPath());
+			Files.deleteIfExists(getBackupJarPath(remappedJar.outputJar()));
 		}
 	}
 

src/main/java/net/fabricmc/loom/configuration/providers/minecraft/mapped/ProcessedNamedMinecraftProvider.java

@@ -58,17 +58,20 @@ public ProcessedNamedMinecraftProvider(P parentMinecraftProvide, MinecraftJarPro
 
 	@Override
 	public List<MinecraftJar> provide(ProvideContext context) throws Exception {
+		final List<MinecraftJar> parentMinecraftJars = parentMinecraftProvider.getMinecraftJars();
+		final Map<MinecraftJar, MinecraftJar> minecraftJarOutputMap = parentMinecraftJars.stream()
+				.collect(Collectors.toMap(Function.identity(), this::getProcessedJar));
+		final List<MinecraftJar> minecraftJars = List.copyOf(minecraftJarOutputMap.values());
+
 		parentMinecraftProvider.provide(context.withApplyDependencies(false));
 
-		boolean requiresProcessing = context.refreshOutputs() || parentMinecraftProvider.getMinecraftJars().stream()
+		boolean requiresProcessing = context.refreshOutputs() || !hasBackupJars(minecraftJars) || parentMinecraftJars.stream()
 				.map(this::getProcessedPath)
 				.anyMatch(jarProcessorManager::requiresProcessingJar);
 
-		final Map<MinecraftJar, MinecraftJar> minecraftJarOutputMap = parentMinecraftProvider.getMinecraftJars().stream()
-				.collect(Collectors.toMap(Function.identity(), this::getProcessedJar));
-
 		if (requiresProcessing) {
 			processJars(minecraftJarOutputMap, context.configContext());
+			createBackupJars(minecraftJars);
 		}
 
 		if (context.applyDependencies()) {