Port Gson Types recursion fix for subtypeOf/supertypeOf

From google/gson@a300148

First step in resolving #338

moshi/src/main/java/com/squareup/moshi/Types.java

@@ -139,15 +139,27 @@ public static GenericArrayType arrayOf(Type componentType) {
    * ? extends Object}.
    */
   public static WildcardType subtypeOf(Type bound) {
-    return new WildcardTypeImpl(new Type[] { bound }, EMPTY_TYPE_ARRAY);
+    Type[] upperBounds;
+    if (bound instanceof WildcardType) {
+      upperBounds = ((WildcardType) bound).getUpperBounds();
+    } else {
+      upperBounds = new Type[] { bound };
+    }
+    return new WildcardTypeImpl(upperBounds, EMPTY_TYPE_ARRAY);
   }
 
   /**
    * Returns a type that represents an unknown supertype of {@code bound}. For example, if {@code
    * bound} is {@code String.class}, this returns {@code ? super String}.
    */
   public static WildcardType supertypeOf(Type bound) {
-    return new WildcardTypeImpl(new Type[] { Object.class }, new Type[] { bound });
+    Type[] lowerBounds;
+    if (bound instanceof WildcardType) {
+      lowerBounds = ((WildcardType) bound).getLowerBounds();
+    } else {
+      lowerBounds = new Type[] { bound };
+    }
+    return new WildcardTypeImpl(new Type[] { Object.class }, lowerBounds);
   }
 
   public static Class<?> getRawType(Type type) {

moshi/src/test/java/com/squareup/moshi/internal/RecursiveTypesResolveTest.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) 2017 Gson Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.squareup.moshi.internal;
+
+import com.squareup.moshi.JsonAdapter;
+import com.squareup.moshi.Moshi;
+import com.squareup.moshi.Types;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+/**
+ * Test fixes for infinite recursion on {@link Util#resolve(java.lang.reflect.Type, Class,
+ * java.lang.reflect.Type)}, described at <a href="https://github.com/google/gson/issues/440">Issue #440</a>
+ * and similar issues.
+ * <p>
+ * These tests originally caused {@link StackOverflowError} because of infinite recursion on attempts to
+ * resolve generics on types, with an intermediate types like 'Foo2&lt;? extends ? super ? extends ... ? extends A&gt;'
+ * <p>
+ * Adapted from https://github.com/google/gson/commit/a300148003e3a067875b1444e8268b6e0f0e0e02 in
+ * service of https://github.com/square/moshi/issues/338.
+ */
+public final class RecursiveTypesResolveTest {
+
+  private static class Foo1<A> {
+    public Foo2<? extends A> foo2;
+  }
+
+  private static class Foo2<B> {
+    public Foo1<? super B> foo1;
+  }
+
+  /**
+   * Test simplest case of recursion.
+   */
+  @Test public void testRecursiveResolveSimple() {
+    JsonAdapter<Foo1> adapter = new Moshi.Builder().build().adapter(Foo1.class);
+    assertNotNull(adapter);
+  }
+
+  //
+  // Tests belows check the behaviour of the methods changed for the fix
+  //
+
+  @Test public void testDoubleSupertype() {
+    assertEquals(Types.supertypeOf(Number.class),
+            Types.supertypeOf(Types.supertypeOf(Number.class)));
+  }
+
+  @Test public void testDoubleSubtype() {
+    assertEquals(Types.subtypeOf(Number.class),
+            Types.subtypeOf(Types.subtypeOf(Number.class)));
+  }
+
+  @Test public void testSuperSubtype() {
+    assertEquals(Types.subtypeOf(Object.class),
+            Types.supertypeOf(Types.subtypeOf(Number.class)));
+  }
+
+  @Test public void testSubSupertype() {
+    assertEquals(Types.subtypeOf(Object.class),
+            Types.subtypeOf(Types.supertypeOf(Number.class)));
+  }
+}