Merge branch 'dev/0.11' into exp/0.12

src/main/java/net/fabricmc/loom/api/mappings/layered/MappingsNamespace.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2016-2021 FabricMC
+ * Copyright (c) 2016-2022 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
@@ -26,6 +26,8 @@ package net.fabricmc.loom.api.mappings.layered;
 
 import java.util.Locale;
 
+import org.jetbrains.annotations.Nullable;
+
 /**
  * The standard namespaces used by loom.
  */
@@ -49,6 +51,21 @@ public enum MappingsNamespace {
 	 */
 	NAMED;
 
+	/**
+	 * Gets a {@code MappingsNamespace} from a namespace string.
+	 *
+	 * @param namespace the name of the namespace as a lowercase string
+	 * @return the {@code MappingsNamespace}, or null if not found
+	 */
+	public static @Nullable MappingsNamespace of(String namespace) {
+		return switch (namespace) {
+		case "official" -> OFFICIAL;
+		case "intermediary" -> INTERMEDIARY;
+		case "named" -> NAMED;
+		default -> null;
+		};
+	}
+
 	@Override
 	public String toString() {
 		return name().toLowerCase(Locale.ROOT);

src/main/java/net/fabricmc/loom/api/mappings/layered/spec/FileMappingsSpecBuilder.java

@@ -0,0 +1,101 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021-2022 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.mappings.layered.spec;
+
+import org.jetbrains.annotations.ApiStatus;
+
+import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
+
+/**
+ * A builder for a file mappings layer.
+ * This layer type supports any mapping type that mapping-io can read.
+ */
+@ApiStatus.Experimental
+public interface FileMappingsSpecBuilder {
+	/**
+	 * Sets the mapping path inside a zip or jar.
+	 * This will have no effect if the file of this mapping spec
+	 * is not a zip.
+	 *
+	 * <p>Path components within the path should be separated with {@code /}.
+	 *
+	 * <p>The default mapping path is {@code mappings/mappings.tiny}, matching regular mapping dependency jars
+	 * such as Yarn's.
+	 *
+	 * @param mappingPath the mapping path, or null if a bare file
+	 * @return this builder
+	 */
+	FileMappingsSpecBuilder mappingPath(String mappingPath);
+
+	/**
+	 * Sets the fallback namespaces. They will be used
+	 * if the mapping format itself doesn't provide namespaces with names
+	 * (e.g. Enigma mappings).
+	 *
+	 * <p>The default fallback namespaces are {@code intermediary} as the source namespace
+	 * and {@code named} as the target namespace as in Yarn.
+	 *
+	 * @param sourceNamespace the fallback source namespace
+	 * @param targetNamespace the fallback target namespace
+	 * @return this builder
+	 */
+	FileMappingsSpecBuilder fallbackNamespaces(String sourceNamespace, String targetNamespace);
+
+	/**
+	 * Marks that the file contains Enigma mappings.
+	 * Because they are stored in a directory, the format cannot be auto-detected.
+	 *
+	 * @return this builder
+	 */
+	FileMappingsSpecBuilder enigmaMappings();
+
+	/**
+	 * Sets the merge namespace of this mappings spec.
+	 *
+	 * <p>The merge namespace is the namespace that is used to match up this layer's
+	 * names to the rest of the mappings. For example, Yarn mappings should be merged through
+	 * the intermediary names.
+	 *
+	 * <p>The default merge namespace is {@link MappingsNamespace#INTERMEDIARY}.
+	 *
+	 * @param namespace the new merge namespace
+	 * @return this builder
+	 */
+	FileMappingsSpecBuilder mergeNamespace(MappingsNamespace namespace);
+
+	/**
+	 * Sets the merge namespace of this mappings spec.
+	 *
+	 * <p>The merge namespace is the namespace that is used to match up this layer's
+	 * names to the rest of the mappings. For example, Yarn mappings should be merged through
+	 * the intermediary names.
+	 *
+	 * <p>The default merge namespace is {@code intermediary}.
+	 *
+	 * @param namespace the new merge namespace
+	 * @return this builder
+	 */
+	FileMappingsSpecBuilder mergeNamespace(String namespace);
+}

src/main/java/net/fabricmc/loom/api/mappings/layered/spec/FileSpec.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2021 FabricMC
+ * Copyright (c) 2021-2022 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
@@ -50,9 +50,10 @@ public interface FileSpec {
 	 * <p>The parameter will be evaluated like this:
 	 * <ul>
 	 * <li>{@link File}, {@link Path} and {@link FileSystemLocation} will be resolved as local files</li>
-	 * <li>{@link Provider} (including {@link org.gradle.api.provider.Property} will recursively be resolved as its current value</li>
+	 * <li>{@link Provider} (including {@link org.gradle.api.provider.Property}) will recursively be resolved as its current value</li>
 	 * <li>{@link CharSequence} (including {@link String} and {@link groovy.lang.GString}) will be resolved as Maven dependencies</li>
 	 * <li>{@link Dependency} will be resolved as any dependency</li>
+	 * <li>{@code FileSpec} will just return the spec itself</li>
 	 * </ul>
 	 *
 	 * @param o the file notation
@@ -73,6 +74,8 @@ public interface FileSpec {
 			return createFromFile(p);
 		} else if (o instanceof FileSystemLocation l) {
 			return createFromFile(l);
+		} else if (o instanceof FileSpec s) {
+			return s;
 		}
 
 		throw new UnsupportedOperationException("Cannot create FileSpec from object of type:" + o.getClass().getCanonicalName());

src/main/java/net/fabricmc/loom/api/mappings/layered/spec/LayeredMappingSpecBuilder.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2021 FabricMC
+ * Copyright (c) 2021-2022 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
@@ -77,4 +77,40 @@ public interface LayeredMappingSpecBuilder {
 	 */
 	@ApiStatus.Experimental
 	LayeredMappingSpecBuilder signatureFix(Object object);
+
+	/**
+	 * Add a layer that uses a mappings file or directory.
+	 *
+	 * @param file the file notation for a {@link FileSpec}
+	 * @return this builder
+	 * @see FileMappingsSpecBuilder
+	 */
+	@ApiStatus.Experimental
+	default LayeredMappingSpecBuilder mappings(Object file) {
+		return mappings(file, builder -> { });
+	}
+
+	/**
+	 * Configure and add a layer that uses a mappings file or directory.
+	 *
+	 * @param file    the file notation for a {@link FileSpec}
+	 * @param closure the configuration action
+	 * @return this builder
+	 * @see FileMappingsSpecBuilder
+	 */
+	@ApiStatus.Experimental
+	default LayeredMappingSpecBuilder mappings(Object file, @DelegatesTo(value = FileMappingsSpecBuilder.class, strategy = Closure.DELEGATE_FIRST) Closure<?> closure) {
+		return mappings(file, new ClosureAction<>(closure));
+	}
+
+	/**
+	 * Configure and add a layer that uses a mappings file or directory.
+	 *
+	 * @param file   the file notation for a {@link FileSpec}
+	 * @param action the configuration action
+	 * @return this builder
+	 * @see FileMappingsSpecBuilder
+	 */
+	@ApiStatus.Experimental
+	LayeredMappingSpecBuilder mappings(Object file, Action<? super FileMappingsSpecBuilder> action);
 }

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

@@ -24,11 +24,14 @@
 
 package net.fabricmc.loom.configuration.ide.idea;
 
+import java.util.ArrayList;
 import java.util.List;
 
+import org.gradle.StartParameter;
+import org.gradle.TaskExecutionRequest;
 import org.gradle.api.Project;
 import org.gradle.api.tasks.TaskProvider;
-import org.gradle.execution.taskgraph.TaskExecutionGraphInternal;
+import org.gradle.internal.DefaultTaskExecutionRequest;
 
 import net.fabricmc.loom.task.LoomTasks;
 
@@ -42,8 +45,10 @@ public class IdeaConfiguration {
 			return;
 		}
 
-		// Run the idea sync task, is this exposed via the api?
-		final TaskExecutionGraphInternal taskGraph = (TaskExecutionGraphInternal) project.getGradle().getTaskGraph();
-		taskGraph.whenReady(taskExecutionGraph -> taskGraph.addEntryTasks(List.of(ideaSyncTask.get())));
+		final StartParameter startParameter = project.getGradle().getStartParameter();
+		final List<TaskExecutionRequest> taskRequests = new ArrayList<>(startParameter.getTaskRequests());
+
+		taskRequests.add(new DefaultTaskExecutionRequest(List.of("ideaSyncTask")));
+		startParameter.setTaskRequests(taskRequests);
 	}
 }

src/main/java/net/fabricmc/loom/configuration/providers/mappings/LayeredMappingSpecBuilderImpl.java

@@ -30,12 +30,14 @@ import java.util.List;
 
 import org.gradle.api.Action;
 
+import net.fabricmc.loom.api.mappings.layered.spec.FileMappingsSpecBuilder;
 import net.fabricmc.loom.api.mappings.layered.spec.FileSpec;
 import net.fabricmc.loom.api.mappings.layered.spec.LayeredMappingSpecBuilder;
 import net.fabricmc.loom.api.mappings.layered.spec.MappingsSpec;
 import net.fabricmc.loom.api.mappings.layered.spec.MojangMappingsSpecBuilder;
 import net.fabricmc.loom.api.mappings.layered.spec.ParchmentMappingsSpecBuilder;
 import net.fabricmc.loom.configuration.providers.mappings.extras.signatures.SignatureFixesSpec;
+import net.fabricmc.loom.configuration.providers.mappings.file.FileMappingsSpecBuilderImpl;
 import net.fabricmc.loom.configuration.providers.mappings.intermediary.IntermediaryMappingsSpec;
 import net.fabricmc.loom.configuration.providers.mappings.mojmap.MojangMappingsSpecBuilderImpl;
 import net.fabricmc.loom.configuration.providers.mappings.parchment.ParchmentMappingsSpecBuilderImpl;
@@ -68,6 +70,13 @@ public class LayeredMappingSpecBuilderImpl implements LayeredMappingSpecBuilder
 		return addLayer(new SignatureFixesSpec(FileSpec.create(object)));
 	}
 
+	@Override
+	public LayeredMappingSpecBuilder mappings(Object file, Action<? super FileMappingsSpecBuilder> action) {
+		FileMappingsSpecBuilderImpl builder = FileMappingsSpecBuilderImpl.builder(FileSpec.create(file));
+		action.execute(builder);
+		return addLayer(builder.build());
+	}
+
 	public LayeredMappingSpec build() {
 		List<MappingsSpec<?>> builtLayers = new LinkedList<>();
 		// Intermediary is always the base layer

src/main/java/net/fabricmc/loom/configuration/providers/mappings/file/FileMappingsLayer.java

@@ -0,0 +1,85 @@
+/*
+ * 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.configuration.providers.mappings.file;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.Map;
+
+import net.fabricmc.loom.api.mappings.layered.MappingLayer;
+import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
+import net.fabricmc.loom.configuration.providers.mappings.intermediary.IntermediaryMappingLayer;
+import net.fabricmc.loom.util.FileSystemUtil;
+import net.fabricmc.loom.util.ZipUtils;
+import net.fabricmc.mappingio.MappingReader;
+import net.fabricmc.mappingio.MappingUtil;
+import net.fabricmc.mappingio.MappingVisitor;
+import net.fabricmc.mappingio.adapter.MappingNsRenamer;
+import net.fabricmc.mappingio.adapter.MappingSourceNsSwitch;
+import net.fabricmc.mappingio.format.MappingFormat;
+
+public record FileMappingsLayer(
+		Path path, String mappingPath,
+		String fallbackSourceNamespace, String fallbackTargetNamespace,
+		boolean enigma, // Enigma cannot be automatically detected since it's stored in a directory.
+		String mergeNamespace
+) implements MappingLayer {
+	@Override
+	public void visit(MappingVisitor mappingVisitor) throws IOException {
+		// Bare file
+		if (!ZipUtils.isZip(path)) {
+			visit(path, mappingVisitor);
+		} else {
+			try (FileSystemUtil.Delegate fileSystem = FileSystemUtil.getJarFileSystem(path)) {
+				visit(fileSystem.get().getPath(mappingPath), mappingVisitor);
+			}
+		}
+	}
+
+	private void visit(Path path, MappingVisitor mappingVisitor) throws IOException {
+		MappingSourceNsSwitch nsSwitch = new MappingSourceNsSwitch(mappingVisitor, mergeNamespace.toString());
+
+		// Replace the default fallback namespaces with
+		// our fallback namespaces if potentially needed.
+		Map<String, String> fallbackNamespaceReplacements = Map.of(
+				MappingUtil.NS_SOURCE_FALLBACK, fallbackSourceNamespace,
+				MappingUtil.NS_TARGET_FALLBACK, fallbackTargetNamespace
+		);
+		MappingNsRenamer renamer = new MappingNsRenamer(nsSwitch, fallbackNamespaceReplacements);
+
+		MappingReader.read(path, enigma ? MappingFormat.ENIGMA : null, renamer);
+	}
+
+	@Override
+	public MappingsNamespace getSourceNamespace() {
+		return MappingsNamespace.of(mergeNamespace);
+	}
+
+	@Override
+	public List<Class<? extends MappingLayer>> dependsOn() {
+		return List.of(IntermediaryMappingLayer.class);
+	}
+}

src/main/java/net/fabricmc/loom/configuration/providers/mappings/file/FileMappingsSpec.java

@@ -0,0 +1,41 @@
+/*
+ * 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.configuration.providers.mappings.file;
+
+import net.fabricmc.loom.api.mappings.layered.MappingContext;
+import net.fabricmc.loom.api.mappings.layered.spec.FileSpec;
+import net.fabricmc.loom.api.mappings.layered.spec.MappingsSpec;
+
+public record FileMappingsSpec(
+		FileSpec fileSpec, String mappingPath,
+		String fallbackSourceNamespace, String fallbackTargetNamespace,
+		boolean enigma,
+		String mergeNamespace
+) implements MappingsSpec<FileMappingsLayer> {
+	@Override
+	public FileMappingsLayer createLayer(MappingContext context) {
+		return new FileMappingsLayer(fileSpec.get(context), mappingPath, fallbackSourceNamespace, fallbackTargetNamespace, enigma, mergeNamespace);
+	}
+}

src/main/java/net/fabricmc/loom/configuration/providers/mappings/file/FileMappingsSpecBuilderImpl.java

@@ -0,0 +1,94 @@
+/*
+ * 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.configuration.providers.mappings.file;
+
+import java.util.Objects;
+
+import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
+import net.fabricmc.loom.api.mappings.layered.spec.FileMappingsSpecBuilder;
+import net.fabricmc.loom.api.mappings.layered.spec.FileSpec;
+
+public class FileMappingsSpecBuilderImpl implements FileMappingsSpecBuilder {
+	/**
+	 * The mapping path of regular mapping dependencies.
+	 */
+	private static final String DEFAULT_MAPPING_PATH = "mappings/mappings.tiny";
+
+	private final FileSpec fileSpec;
+	private String mappingPath = DEFAULT_MAPPING_PATH;
+	private String fallbackSourceNamespace = MappingsNamespace.INTERMEDIARY.toString();
+	private String fallbackTargetNamespace = MappingsNamespace.NAMED.toString();
+	private boolean enigma = false;
+	private String mergeNamespace = MappingsNamespace.INTERMEDIARY.toString();
+
+	private FileMappingsSpecBuilderImpl(FileSpec fileSpec) {
+		this.fileSpec = fileSpec;
+	}
+
+	public static FileMappingsSpecBuilderImpl builder(FileSpec fileSpec) {
+		return new FileMappingsSpecBuilderImpl(fileSpec);
+	}
+
+	@Override
+	public FileMappingsSpecBuilderImpl mappingPath(String mappingPath) {
+		this.mappingPath = Objects.requireNonNull(mappingPath, "mapping path cannot be null");
+		return this;
+	}
+
+	@Override
+	public FileMappingsSpecBuilderImpl fallbackNamespaces(String sourceNamespace, String targetNamespace) {
+		fallbackSourceNamespace = Objects.requireNonNull(sourceNamespace, "fallback source namespace cannot be null");
+		fallbackTargetNamespace = Objects.requireNonNull(targetNamespace, "fallback target namespace cannot be null");
+		return this;
+	}
+
+	@Override
+	public FileMappingsSpecBuilderImpl enigmaMappings() {
+		enigma = true;
+		return this;
+	}
+
+	@Override
+	public FileMappingsSpecBuilderImpl mergeNamespace(MappingsNamespace namespace) {
+		mergeNamespace = Objects.requireNonNull(namespace, "merge namespace cannot be null").toString();
+		return this;
+	}
+
+	@Override
+	public FileMappingsSpecBuilderImpl mergeNamespace(String namespace) {
+		Objects.requireNonNull(namespace, "merge namespace cannot be null");
+
+		if (MappingsNamespace.of(namespace) == null) {
+			throw new IllegalArgumentException("Namespace '" + namespace + "' is unsupported! It must be either 'official', 'intermediary' or 'named'.");
+		}
+
+		mergeNamespace = namespace;
+		return this;
+	}
+
+	public FileMappingsSpec build() {
+		return new FileMappingsSpec(fileSpec, mappingPath, fallbackSourceNamespace, fallbackTargetNamespace, enigma, mergeNamespace);
+	}
+}

src/main/java/net/fabricmc/loom/util/ZipUtils.java

@@ -25,6 +25,7 @@
 package net.fabricmc.loom.util;
 
 import java.io.ByteArrayInputStream;
+import java.io.DataInputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.UncheckedIOException;
@@ -47,6 +48,22 @@ import org.jetbrains.annotations.Nullable;
 import net.fabricmc.loom.LoomGradlePlugin;
 
 public class ZipUtils {
+	public static boolean isZip(Path zip) throws IOException {
+		if (Files.notExists(zip)) {
+			throw new NoSuchFileException("Cannot check if '" + zip + "' is a zip because it doesn't exist!");
+		}
+
+		if (Files.isRegularFile(zip)) {
+			try (DataInputStream in = new DataInputStream(Files.newInputStream(zip))) {
+				int header = in.readInt();
+				// See https://en.wikipedia.org/wiki/List_of_file_signatures
+				return header == 0x504B0304 || header == 0x504B0506 || header == 0x504B0708;
+			}
+		} else {
+			return false;
+		}
+	}
+
 	public static boolean contains(Path zip, String path) {
 		try (FileSystemUtil.Delegate fs = FileSystemUtil.getJarFileSystem(zip, false)) {
 			Path fsPath = fs.get().getPath(path);