When creating the proxy instance using the set of interfaces derived from the 'interfaceType', remove all super types of the interfaces that are in the set. That is to avoid IllegalArgumentException if any of the super types are sealed.

RELNOTES=n/a
PiperOrigin-RevId: 782100677

Author: java-team-github-bot

android/guava-testlib/src/com/google/common/testing/DummyProxy.java

@@ -29,6 +29,7 @@
 import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
+import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.Set;
 import org.jspecify.annotations.NullMarked;
@@ -50,7 +51,22 @@ abstract class DummyProxy {
    */
   final <T> T newProxy(TypeToken<T> interfaceType) {
     Set<Class<?>> interfaceClasses = new LinkedHashSet<>();
-    interfaceClasses.addAll(interfaceType.getTypes().interfaces().rawTypes());
+    Set<Class<? super T>> allInterfaceClasses = interfaceType.getTypes().interfaces().rawTypes();
+    for (Class<? super T> itf : allInterfaceClasses) {
+      Iterator<Class<?>> iterator = interfaceClasses.iterator();
+      boolean addToSet = true;
+      while (iterator.hasNext()) {
+        Class<?> current = iterator.next();
+        if (current == itf || itf.isAssignableFrom(current)) {
+          // Skip any super interface of the ones that are already included.
+          addToSet = false;
+          break;
+        }
+      }
+      if (addToSet) {
+        interfaceClasses.add(itf);
+      }
+    }
     // Make the proxy serializable to work with SerializableTester
     interfaceClasses.add(Serializable.class);
     Object dummy =

guava-testlib/src/com/google/common/testing/DummyProxy.java

@@ -29,6 +29,7 @@
 import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
+import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.Set;
 import org.jspecify.annotations.NullMarked;
@@ -50,7 +51,22 @@ abstract class DummyProxy {
    */
   final <T> T newProxy(TypeToken<T> interfaceType) {
     Set<Class<?>> interfaceClasses = new LinkedHashSet<>();
-    interfaceClasses.addAll(interfaceType.getTypes().interfaces().rawTypes());
+    Set<Class<? super T>> allInterfaceClasses = interfaceType.getTypes().interfaces().rawTypes();
+    for (Class<? super T> itf : allInterfaceClasses) {
+      Iterator<Class<?>> iterator = interfaceClasses.iterator();
+      boolean addToSet = true;
+      while (iterator.hasNext()) {
+        Class<?> current = iterator.next();
+        if (current == itf || itf.isAssignableFrom(current)) {
+          // Skip any super interface of the ones that are already included.
+          addToSet = false;
+          break;
+        }
+      }
+      if (addToSet) {
+        interfaceClasses.add(itf);
+      }
+    }
     // Make the proxy serializable to work with SerializableTester
     interfaceClasses.add(Serializable.class);
     Object dummy =