fabric.mod.json generation task (#1345)

* fabric.mod.json DSL.

* A start on generating FMJs

* More work

* The rest

* Task works

* Javadoc and cleanup

* Fixes

src/main/java/net/fabricmc/loom/task/FabricModJsonV1Task.java

@@ -0,0 +1,115 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2025 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.task;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import javax.inject.Inject;
+
+import org.gradle.api.Action;
+import org.gradle.api.file.RegularFileProperty;
+import org.gradle.api.model.ObjectFactory;
+import org.gradle.api.provider.Property;
+import org.gradle.api.tasks.Nested;
+import org.gradle.api.tasks.OutputFile;
+import org.gradle.api.tasks.TaskAction;
+import org.gradle.workers.WorkAction;
+import org.gradle.workers.WorkParameters;
+import org.gradle.workers.WorkQueue;
+import org.gradle.workers.WorkerExecutor;
+
+import net.fabricmc.loom.api.fmj.FabricModJsonV1Spec;
+import net.fabricmc.loom.util.fmj.gen.FabricModJsonV1Generator;
+
+/**
+ * A task that generates a {@code fabric.mod.json} file using the configured {@link FabricModJsonV1Spec} specification.
+ */
+public abstract class FabricModJsonV1Task extends AbstractLoomTask {
+	/**
+	 * The fabric.mod.json spec.
+	 */
+	@Nested
+	public abstract Property<FabricModJsonV1Spec> getJson();
+
+	/**
+	 * The output file to write the generated fabric.mod.json to.
+	 */
+	@OutputFile
+	public abstract RegularFileProperty getOutputFile();
+
+	@Inject
+	protected abstract WorkerExecutor getWorkerExecutor();
+
+	@Inject
+	protected abstract ObjectFactory getObjectFactory();
+
+	public FabricModJsonV1Task() {
+		getJson().set(getObjectFactory().newInstance(FabricModJsonV1Spec.class));
+	}
+
+	/**
+	 * Configure the fabric.mod.json spec.
+	 *
+	 * @param action A {@link Action} that configures the spec.
+	 */
+	public void json(Action<FabricModJsonV1Spec> action) {
+		action.execute(getJson().get());
+	}
+
+	@TaskAction
+	public void run() {
+		final WorkQueue workQueue = getWorkerExecutor().noIsolation();
+
+		workQueue.submit(FabricModJsonV1WorkAction.class, params -> {
+			params.getSpec().set(getJson());
+			params.getOutputFile().set(getOutputFile());
+		});
+	}
+
+	public interface FabricModJsonV1WorkParameters extends WorkParameters {
+		Property<FabricModJsonV1Spec> getSpec();
+
+		RegularFileProperty getOutputFile();
+	}
+
+	public abstract static class FabricModJsonV1WorkAction implements WorkAction<FabricModJsonV1WorkParameters> {
+		@Override
+		public void execute() {
+			FabricModJsonV1Spec spec = getParameters().getSpec().get();
+			Path outputPath = getParameters().getOutputFile().get().getAsFile().toPath();
+
+			String json = FabricModJsonV1Generator.INSTANCE.generate(spec);
+
+			try {
+				Files.writeString(outputPath, json);
+			} catch (IOException e) {
+				throw new UncheckedIOException("Failed to write fabric.mod.json", e);
+			}
+		}
+	}
+}