Auto skip remap by default for Mojang-mapped NeoForge projects

src/main/java/net/fabricmc/loom/configuration/providers/forge/FieldMigratedMappingConfiguration.java

@@ -69,9 +69,15 @@ public final class FieldMigratedMappingConfiguration extends MappingConfiguratio
 	private Path rawTinyMappings;
 	private Path rawTinyMappingsWithSrg;
 	private Path rawTinyMappingsWithMojang;
+	private final boolean mojangMappedProject;
 
-	public FieldMigratedMappingConfiguration(String mappingsIdentifier, Path mappingsWorkingDir) {
+	public FieldMigratedMappingConfiguration(String mappingsIdentifier, Path mappingsWorkingDir, boolean mojangMappedProject) {
 		super(mappingsIdentifier, mappingsWorkingDir);
+		this.mojangMappedProject = mojangMappedProject;
+	}
+
+	public boolean isMojangMappedProject() {
+		return this.mojangMappedProject;
 	}
 
 	@Override

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

@@ -49,6 +49,8 @@
 import net.fabricmc.loom.api.mappings.layered.MappingLayer;
 import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
 import net.fabricmc.loom.configuration.providers.mappings.extras.unpick.UnpickLayer;
+import net.fabricmc.loom.configuration.providers.mappings.mojmap.MojangMappingsSpec;
+import net.fabricmc.loom.configuration.providers.mappings.parchment.ParchmentMappingsSpec;
 import net.fabricmc.loom.configuration.providers.mappings.utils.AddConstructorMappingVisitor;
 import net.fabricmc.loom.util.ZipUtils;
 import net.fabricmc.mappingio.adapter.MappingDstNsReorder;
@@ -186,4 +188,10 @@ public void because(String s) {
 	public FileCollection getFiles() {
 		return project.files(resolve());
 	}
+
+	public boolean isMojangMappings() {
+		return this.layeredMappingSpec.layers().stream()
+				.skip(1) // see LayeredMappingSpecBuilderImpl
+				.allMatch(spec -> spec instanceof MojangMappingsSpec || spec instanceof ParchmentMappingsSpec);
+	}
 }

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

@@ -144,7 +144,15 @@ public static MappingConfiguration create(Project project, SharedServiceManager
 		MappingConfiguration mappingConfiguration;
 
 		if (extension.isForgeLike()) {
-			mappingConfiguration = new FieldMigratedMappingConfiguration(mappingsIdentifier, workingDir);
+			final boolean mojmap;
+
+			if (dependency.getDependency() instanceof LayeredMappingsDependency layered) {
+				mojmap = layered.isMojangMappings();
+			} else {
+				mojmap = false;
+			}
+
+			mappingConfiguration = new FieldMigratedMappingConfiguration(mappingsIdentifier, workingDir, mojmap);
 		} else {
 			mappingConfiguration = new MappingConfiguration(mappingsIdentifier, workingDir);
 		}

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

@@ -65,6 +65,7 @@
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
 import net.fabricmc.loom.build.IntermediaryNamespaces;
+import net.fabricmc.loom.configuration.providers.forge.FieldMigratedMappingConfiguration;
 import net.fabricmc.loom.task.service.JarManifestService;
 import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.ZipReprocessorUtil;
@@ -111,6 +112,11 @@ public abstract class AbstractRemapJarTask extends Jar {
 	@ApiStatus.Internal
 	public abstract Property<String> getJarType();
 
+	@ApiStatus.Experimental
+	@Input
+	@Optional
+	public abstract Property<Boolean> getAutoSkipRemap();
+
 	private final Provider<JarManifestService> jarManifestServiceProvider;
 
 	@Inject
@@ -125,6 +131,20 @@ public AbstractRemapJarTask() {
 		usesService(jarManifestServiceProvider);
 	}
 
+	protected final <P extends AbstractRemapParams> void autoSkipRemap(LoomGradleExtension extension, P params) {
+		if (getAutoSkipRemap().getOrElse(true) && shouldSkipRemap(extension)) {
+			params.getSourceNamespace().set(getTargetNamespace());
+		}
+	}
+
+	private boolean shouldSkipRemap(LoomGradleExtension extension) {
+		return extension.isNeoForge()
+				&& extension.getMappingConfiguration() instanceof FieldMigratedMappingConfiguration c
+				&& c.isMojangMappedProject()
+				&& MappingsNamespace.of(this.getSourceNamespace().get()) == MappingsNamespace.NAMED
+				&& MappingsNamespace.of(this.getTargetNamespace().get()) == MappingsNamespace.MOJANG;
+	}
+
 	public final <P extends AbstractRemapParams> void submitWork(Class<? extends AbstractRemapAction<P>> workAction, Action<P> action) {
 		final WorkQueue workQueue = getWorkerExecutor().noIsolation();
 

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

@@ -201,6 +201,8 @@ public void run() {
 		final LoomGradleExtension extension = LoomGradleExtension.get(getProject());
 
 		submitWork(RemapAction.class, params -> {
+			autoSkipRemap(extension, params);
+
 			if (getAddNestedDependencies().get()) {
 				params.getNestedJars().from(getNestedJars());
 

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

@@ -40,6 +40,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.task.service.SourceRemapperService;
 import net.fabricmc.loom.util.service.BuildSharedServiceManager;
 import net.fabricmc.loom.util.service.UnsafeWorkQueueHelper;
@@ -58,7 +59,11 @@ public RemapSourcesJarTask() {
 
 	@TaskAction
 	public void run() {
+		final LoomGradleExtension extension = LoomGradleExtension.get(getProject());
+
 		submitWork(RemapSourcesAction.class, params -> {
+			autoSkipRemap(extension, params);
+
 			if (!params.namespacesMatch()) {
 				params.getSourcesRemapperServiceUuid().set(UnsafeWorkQueueHelper.create(SourceRemapperService.create(serviceManagerProvider.get().get(), this)));
 			}