Respond to PR feedback

- Throws if the SERVICE layer was not built instead of using a default layer
- Extracts the discoverer service type constants to a new shared class and
  adds the ImmediateWindowProvider to this list.

loader/src/main/java/net/neoforged/fml/loading/ClasspathTransformerDiscoverer.java

@@ -41,8 +41,9 @@ public static List<Path> allExcluded() {
 
     private void scan(final Path gameDirectory) {
         try {
-            locateTransformers("META-INF/services/cpw.mods.modlauncher.api.ITransformationService");
-            locateTransformers("META-INF/services/net.neoforged.neoforgespi.locating.IModLocator");
+            for (final String serviceClass : TransformerDiscovererConstants.SERVICES) {
+                locateTransformers("META-INF/services/" + serviceClass);
+            }
         } catch (IOException e) {
             LogManager.getLogger().error("Error during discovery of transform services from the classpath", e);
         }

loader/src/main/java/net/neoforged/fml/loading/ImmediateWindowHandler.java

@@ -36,7 +36,7 @@ public static void load(final String launchTarget, final String[] arguments) {
             LOGGER.info("Loading ImmediateWindowProvider {}", providername);
             final var layer = Launcher.INSTANCE.findLayerManager()
                     .flatMap(manager -> manager.getLayer(Layer.SERVICE))
-                    .orElse(ImmediateWindowHandler.class.getModule().getLayer()); // This will likely be the BOOT layer, but is a sensible fallback.
+                    .orElseThrow(() -> new IllegalStateException("Couldn't find SERVICE layer to load immediate window handler"));
             final var maybeProvider = ServiceLoader.load(layer, ImmediateWindowProvider.class)
                     .stream()
                     .map(ServiceLoader.Provider::get)

loader/src/main/java/net/neoforged/fml/loading/ModDirTransformerDiscoverer.java

@@ -22,15 +22,9 @@
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Set;
 
 public class ModDirTransformerDiscoverer implements ITransformerDiscoveryService {
     private static final Logger LOGGER = LogUtils.getLogger();
-    private static final Set<String> SERVICES = Set.of(
-        "cpw.mods.modlauncher.api.ITransformationService",
-        "net.neoforged.neoforgespi.locating.IModLocator",
-        "net.neoforged.neoforgespi.locating.IDependencyLocator"
-    );
     private UncheckedIOException alreadyFailed;
 
     @Override
@@ -102,6 +96,6 @@ private static boolean shouldLoadInServiceLayer(Path path) {
         JarMetadata metadata = JarMetadata.from(new JarContentsBuilder().paths(path).build());
         return metadata.providers().stream()
             .map(SecureJar.Provider::serviceName)
-            .anyMatch(SERVICES::contains);
+            .anyMatch(TransformerDiscovererConstants.SERVICES::contains);
     }
 }

loader/src/main/java/net/neoforged/fml/loading/TransformerDiscovererConstants.java

@@ -0,0 +1,26 @@
+package net.neoforged.fml.loading;
+
+
+import cpw.mods.modlauncher.api.IModuleLayerManager.Layer;
+import cpw.mods.modlauncher.serviceapi.ITransformerDiscoveryService;
+
+import java.util.Set;
+
+/**
+ * Defines a class containing constants which implementations of {@link ITransformerDiscoveryService}
+ * may use.
+ */
+public class TransformerDiscovererConstants {
+    private TransformerDiscovererConstants() { }
+
+    /**
+     * Defines the set of FML service types which should be loaded on the
+     * {@link Layer#SERVICE} module layer.
+     */
+    public static final Set<String> SERVICES = Set.of(
+        "cpw.mods.modlauncher.api.ITransformationService",
+        "net.neoforged.neoforgespi.locating.IModLocator",
+        "net.neoforged.neoforgespi.locating.IDependencyLocator",
+        "net.neoforged.fml.loading.ImmediateWindowProvider"
+    );
+}