Fix loading package-info classes

src/main/java/cpw/mods/cl/ModuleClassLoader.java

@@ -172,7 +172,9 @@ private Class<?> readerToClass(final ModuleReader reader, final ModuleReference
         var modroot = this.resolvedRoots.get(ref.descriptor().name());
         ProtectionDomainHelper.tryDefinePackage(this, name, modroot.jar().getManifest(), t->modroot.jar().getManifest().getAttributes(t), this::definePackage); // Packages are dirctories, and can't be signed, so use raw attributes instead of signed.
         var cs = ProtectionDomainHelper.createCodeSource(toURL(ref.location()), modroot.jar().verifyAndGetSigners(cname, bytes));
-        return defineClass(name, bytes, 0, bytes.length, ProtectionDomainHelper.createProtectionDomain(cs, this));
+        var cls = defineClass(name, bytes, 0, bytes.length, ProtectionDomainHelper.createProtectionDomain(cs, this));
+        ProtectionDomainHelper.trySetPackageModule(cls.getPackage(), cls.getModule());
+        return cls;
     }
 
     protected byte[] maybeTransformClassBytes(final byte[] bytes, final String name, final String context) {

src/main/java/cpw/mods/cl/ProtectionDomainHelper.java

@@ -1,5 +1,7 @@
 package cpw.mods.cl;
 
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
 import java.net.URL;
 import java.security.*;
 import java.util.HashMap;
@@ -27,6 +29,34 @@ public static ProtectionDomain createProtectionDomain(CodeSource codeSource, Cla
         }
     }
 
+    private static final VarHandle PKG_MODULE_HANDLE;
+    static {
+        try {
+            // Obtain VarHandle for NamedPackage#module via trusted lookup
+            var trustedLookupField = MethodHandles.Lookup.class.getDeclaredField("IMPL_LOOKUP");
+            trustedLookupField.setAccessible(true);
+            MethodHandles.Lookup trustedLookup = (MethodHandles.Lookup) trustedLookupField.get(null);
+
+            Class<?> namedPackage = Class.forName("java.lang.NamedPackage");
+            PKG_MODULE_HANDLE = trustedLookup.findVarHandle(namedPackage, "module", Module.class);
+        } catch (Throwable t) {
+            throw new RuntimeException("Error finding package module handle", t);
+        }
+    }
+
+    static void trySetPackageModule(Package pkg, Module module) {
+        // Ensure named packages are bound to their module of origin
+        // Necessary for loading package-info classes
+        Module value = (Module) PKG_MODULE_HANDLE.get(pkg);
+        if (value == null || !value.isNamed()) {
+            try {
+                PKG_MODULE_HANDLE.set(pkg, module);
+            } catch (Throwable t) {
+                throw new RuntimeException("Error setting package module", t);
+            }
+        }
+    }
+
     static Package tryDefinePackage(final ClassLoader classLoader, String name, Manifest man, Function<String, Attributes> trustedEntries, Function<String[], Package> definePackage) throws IllegalArgumentException
     {
         final var pname = name.substring(0, name.lastIndexOf('.'));

src/test/java/cpw/mods/cl/test/TestPackageInfo.java

@@ -0,0 +1,22 @@
+package cpw.mods.cl.test;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.lang.annotation.Annotation;
+import java.util.Arrays;
+
+public class TestPackageInfo {
+
+    @Test
+    public void testPackageInfoAvailability() throws Exception {
+        // package-info classes can be loaded
+        TestjarUtil.withTestjar1Setup(cl -> {
+            String annotationType = "cpw.mods.cl.testjar1.TestAnnotation";
+            // Reference package through a class to ensure correct behavior of ModuleClassLoader#findClass(String,String)
+            Class<?> cls = Class.forName("cpw.mods.cl.testjar1.SomeClass", true, cl);
+            Annotation[] annotations = cls.getPackage().getDeclaredAnnotations();
+            Assertions.assertTrue(Arrays.stream(annotations).anyMatch(ann -> ann.annotationType().getName().equals(annotationType)), "Expected package to be annotated with " + annotationType);
+        });
+    }
+}

src/testjar1/java/cpw/mods/cl/testjar1/SomeClass.java

@@ -0,0 +1,7 @@
+package cpw.mods.cl.testjar1;
+
+/**
+ * Referenced by {@code TestClassLoader}.
+ */
+public class SomeClass {
+}

src/testjar1/java/cpw/mods/cl/testjar1/TestAnnotation.java

@@ -0,0 +1,11 @@
+package cpw.mods.cl.testjar1;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Target(ElementType.PACKAGE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface TestAnnotation {
+}

src/testjar1/java/cpw/mods/cl/testjar1/package-info.java

@@ -0,0 +1,3 @@
+@TestAnnotation
+package cpw.mods.cl.testjar1;
+