Add task to check for duplicate names

(cherry picked from commit c9756f7dcb)

build.gradle

@@ -101,6 +101,7 @@ import net.fabricmc.filament.task.mappingio.CompleteMappingsTask
 import net.fabricmc.filament.task.mappingio.ConvertMappingsTask
 import net.fabricmc.filament.task.mappingio.FormatMappingsTask
 import net.fabricmc.filament.task.mappingio.MergeMappingsTask
+import net.fabricmc.filament.task.mappingio.CheckMappingsTask
 import net.fabricmc.mappingio.format.MappingFormat
 import net.fabricmc.nameproposal.MappingNameCompleter
 import org.gradle.work.DisableCachingByDefault
@@ -551,6 +552,11 @@ javadocLint {
 	mappingDirectory = file("mappings")
 }
 
+def checkDuplicates = tasks.register("checkDuplicateNames", CheckMappingsTask) {
+	input = mergeV2.outputFile
+}
+
+check.dependsOn checkDuplicates
 check.dependsOn javadocLint
 
 publishing {

filament/src/main/java/net/fabricmc/filament/task/mappingio/CheckMappingsTask.java

@@ -0,0 +1,63 @@
+package net.fabricmc.filament.task.mappingio;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.gradle.api.tasks.TaskAction;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import net.fabricmc.filament.task.base.FilamentTask;
+import net.fabricmc.filament.task.base.WithFileInput;
+import net.fabricmc.mappingio.MappingReader;
+import net.fabricmc.mappingio.tree.MappingTree;
+import net.fabricmc.mappingio.tree.MemoryMappingTree;
+
+public abstract class CheckMappingsTask extends FilamentTask implements WithFileInput {
+	private static final Logger LOGGER = LoggerFactory.getLogger(CheckMappingsTask.class);
+
+	@TaskAction
+	public final void run() throws IOException {
+		Path path = getInput().get().getAsFile().toPath();
+		MemoryMappingTree tree = new MemoryMappingTree();
+		MappingReader.read(path, tree);
+
+		int minNamespaceId = tree.getMinNamespaceId();
+		int maxNamespaceId = tree.getMaxNamespaceId();
+
+		List<String> duplicates = new ArrayList<>();
+
+		for (MappingTree.ClassMapping classMapping : tree.getClasses()) {
+			method: for (MappingTree.MethodMapping method : classMapping.getMethods()) {
+				Set<String> names = new HashSet<>();
+				for (int id = minNamespaceId; id < maxNamespaceId; id++) {
+					String name = method.getName(id);
+
+					if (name == null) {
+						break method;
+					}
+
+					names.add(name);
+				}
+
+				if (names.size() == 1 && method.getSrcName().startsWith("method_")) {
+					duplicates.add(classMapping.getSrcName() + "." + method.getSrcName());
+				}
+			}
+		}
+
+		if (duplicates.isEmpty()) {
+			return;
+		}
+
+		for (String duplicate : duplicates) {
+			LOGGER.error("Method {} has the same name in all namespaces", duplicate);
+		}
+
+		throw new RuntimeException("Duplicate mappings detected");
+	}
+}