Validate jar and fail if it was built with Loom 1.5 or later.

src/main/java/net/fabricmc/loom/configuration/mods/ModConfigurationRemapper.java

@@ -88,6 +88,12 @@ public static void supplyModConfigurations(Project project, String mappingsSuffi
 				final List<ModDependency> modDependencies = new ArrayList<>();
 
 				for (ArtifactRef artifact : resolveArtifacts(project, sourceConfig)) {
+					try {
+						ModUtils.validateJarManifest(artifact.path());
+					} catch (IOException e) {
+						throw new UncheckedIOException("Failed to read manifest from" + artifact.path(), e);
+					}
+
 					if (!ModUtils.shouldRemapMod(project.getLogger(), artifact.path(), extension.getPlatform().get(), sourceConfig.getName())) {
 						artifact.applyToConfiguration(project, targetConfig);
 						continue;

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

@@ -24,10 +24,14 @@
 
 package net.fabricmc.loom.util;
 
+import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.UncheckedIOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.jar.Attributes;
+import java.util.jar.Manifest;
 
 import com.google.gson.JsonObject;
 import org.gradle.api.logging.Logger;
@@ -71,4 +75,21 @@ public static boolean shouldRemapMod(Logger logger, Path input, ModPlatform plat
 
 		return false;
 	}
+
+	public static void validateJarManifest(Path path) throws IOException {
+		try (FileSystemUtil.Delegate fs = FileSystemUtil.getJarFileSystem(path)) {
+			final Path manifestPath = fs.get().getPath("META-INF/MANIFEST.MF");
+
+			if (Files.exists(manifestPath)) {
+				final var manifest = new Manifest(new ByteArrayInputStream(Files.readAllBytes(manifestPath)));
+				final Attributes mainAttributes = manifest.getMainAttributes();
+
+				// Check to see if the jar was built with a newer version of loom.
+				// This version of loom does not support the remap type value so throw an exception.
+				if (mainAttributes.getValue("Fabric-Loom-Mixin-Remap-Type") != null) {
+					throw new IllegalStateException("This version of loom does not support the mixin remap type value. Please update to the latest version of loom.");
+				}
+			}
+		}
+	}
 }