Update FactoryProvider2 to support Java 15.

The private constructor used in looking up method handles has changed to take an extra parameter. This change update the code to look for both constructor signatures.

PiperOrigin-RevId: 339124988

extensions/assistedinject/src/com/google/inject/assistedinject/FactoryProvider2.java

@@ -900,13 +900,26 @@ protected Object initialValue() {
       findMethodHandlesLookupCxtor();
 
   private static Constructor<MethodHandles.Lookup> findMethodHandlesLookupCxtor() {
-    try {
-      Constructor<MethodHandles.Lookup> cxtor =
-          MethodHandles.Lookup.class.getDeclaredConstructor(Class.class, int.class);
+    // Different JDK implementations have different constructors so look for a constructor that
+    // takes a class and an int first (openjdk-8, openjdk-11) and fallback to a constructor that
+    // takes two classes and an int (openjdk-15).
+    // TODO(b/171738889): Figure out a better way to handle this.
+    Constructor<MethodHandles.Lookup> cxtor = findMethodHandlesLookupCxtor(Class.class, int.class);
+    if (cxtor == null) {
+      cxtor = findMethodHandlesLookupCxtor(Class.class, Class.class, int.class);
+    }
+    if (cxtor != null) {
       cxtor.setAccessible(true);
-      return cxtor;
-    } catch (ReflectiveOperationException ignored) {
-      // Ignore, the code falls back to a less-precise check if we can't create method handles.
+    }
+    return cxtor;
+  }
+
+  private static Constructor<MethodHandles.Lookup> findMethodHandlesLookupCxtor(
+      Class<?>... parameterTypes) {
+    try {
+      return MethodHandles.Lookup.class.getDeclaredConstructor(parameterTypes);
+    } catch (NoSuchMethodException e) {
+      // Ignored if the constructor doesn't exist.
       return null;
     }
   }
@@ -919,7 +932,12 @@ private static MethodHandle createMethodHandle(Method method, Object proxy) {
     int allModes =
         Modifier.PRIVATE | Modifier.STATIC /* package */ | Modifier.PUBLIC | Modifier.PROTECTED;
     try {
-      MethodHandles.Lookup lookup = methodHandlesLookupCxtor.newInstance(declaringClass, allModes);
+      MethodHandles.Lookup lookup;
+      if (methodHandlesLookupCxtor.getParameterCount() == 2) {
+        lookup = methodHandlesLookupCxtor.newInstance(declaringClass, allModes);
+      } else {
+        lookup = methodHandlesLookupCxtor.newInstance(declaringClass, null, allModes);
+      }
       method.setAccessible(true);
       return lookup.unreflectSpecial(method, declaringClass).bindTo(proxy);
     } catch (ReflectiveOperationException roe) {