Native provider loading

- Native provider classes load from the provider jars before the plugin class loader
- Another plugin bundling VolmLib natives no longer supplies Iris native capabilities on Spigot
- Tests cover provider jar classes taking precedence over the plugin loader

core/src/main/java/art/arcane/iris/platform/bootstrap/NativeRuntimeLibraries.java

@@ -65,8 +65,7 @@ public final class NativeRuntimeLibraries {
     public URLClassLoader openProviderLoader(Path downloads) {
         try {
             List<URL> urls = providerUrls(downloads, NativeRuntimeLibraries.class.getClassLoader());
-            URLClassLoader loader = new URLClassLoader("Iris native providers", urls.toArray(URL[]::new),
-                    NativeAdapters.class.getClassLoader());
+            URLClassLoader loader = providerLoader(urls.toArray(URL[]::new), NativeAdapters.class.getClassLoader());
             NativeAdapters.registerProviderLoader(loader);
             return loader;
         } catch (IOException exception) {
@@ -74,6 +73,10 @@ public final class NativeRuntimeLibraries {
         }
     }
 
+    static URLClassLoader providerLoader(URL[] urls, ClassLoader parent) {
+        return new ProviderClassLoader(urls, parent);
+    }
+
     List<URL> providerUrls(Path downloads, ClassLoader resources) throws IOException {
         List<URL> urls = new ArrayList<>(providers.size());
         for (Provider provider : providers) {
@@ -123,4 +126,28 @@ public final class NativeRuntimeLibraries {
 
     private record Provider(String module, String version, String sha256) {
     }
+
+    private static final class ProviderClassLoader extends URLClassLoader {
+        private ProviderClassLoader(URL[] urls, ClassLoader parent) {
+            super("Iris native providers", urls, parent);
+        }
+
+        @Override
+        protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+            synchronized (getClassLoadingLock(name)) {
+                Class<?> loaded = findLoadedClass(name);
+                if (loaded == null) {
+                    try {
+                        loaded = findClass(name);
+                    } catch (ClassNotFoundException absent) {
+                        return super.loadClass(name, resolve);
+                    }
+                }
+                if (resolve) {
+                    resolveClass(loaded);
+                }
+                return loaded;
+            }
+        }
+    }
 }

core/src/test/java/art/arcane/iris/platform/bootstrap/NativeRuntimeLibrariesTest.java

@@ -3,6 +3,8 @@ package art.arcane.iris.platform.bootstrap;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
+import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.Opcodes;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -25,6 +27,7 @@ import java.util.stream.Stream;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
@@ -41,6 +44,20 @@ public class NativeRuntimeLibrariesTest {
         assertThrows(IllegalStateException.class, () -> NativeRuntimeLibraries.from(fixture.manifest(), "26.2.0"));
     }
 
+    @Test
+    public void providerClassesLoadFromTheProviderJarBeforeThePluginLoader() throws Exception {
+        String implementation = "art/arcane/volmlib/nativelib/v26_2_R1/Probe";
+        String api = "art/arcane/volmlib/nativelib/Api";
+        Path plugin = classJar("plugin.jar", implementation, api);
+        Path provider = classJar("provider.jar", implementation);
+        try (URLClassLoader parent = new URLClassLoader(new URL[]{plugin.toUri().toURL()}, null);
+             URLClassLoader loader = NativeRuntimeLibraries.providerLoader(new URL[]{provider.toUri().toURL()}, parent)) {
+            assertSame(loader, loader.loadClass(implementation.replace('/', '.')).getClassLoader());
+            assertSame(parent, loader.loadClass(api.replace('/', '.')).getClassLoader());
+            assertSame(String.class, loader.loadClass("java.lang.String"));
+        }
+    }
+
     @Test
     public void rejectsMinecraftVersionsWithoutProvider() throws Exception {
         EmbeddedFixture fixture = embeddedFixture();
@@ -156,6 +173,21 @@ public class NativeRuntimeLibrariesTest {
         return new EmbeddedFixture(properties, resources);
     }
 
+    private Path classJar(String name, String... classes) throws IOException {
+        Path jar = temporary.newFolder().toPath().resolve(name);
+        try (JarOutputStream output = new JarOutputStream(Files.newOutputStream(jar))) {
+            for (String type : classes) {
+                ClassWriter writer = new ClassWriter(0);
+                writer.visit(Opcodes.V17, Opcodes.ACC_PUBLIC, type, null, "java/lang/Object", null);
+                writer.visitEnd();
+                output.putNextEntry(new JarEntry(type + ".class"));
+                output.write(writer.toByteArray());
+                output.closeEntry();
+            }
+        }
+        return jar;
+    }
+
     private static void assertNoFailedExtract(Path downloads) throws IOException {
         try (Stream<Path> files = Files.walk(downloads)) {
             assertFalse(files.anyMatch(path -> Files.isRegularFile(path)