Fix StackOverflowError on resolving recursive types by collapsing cha…

…ins of type bounds (#1075)

* Fixes StackOverflowError on resolving recursive types.

See Issue JodaOrg#440, Issue JodaOrg#603, tests.

* fix 'codacy' coding style warnings

* added copyright header

gson/src/main/java/com/google/gson/internal/$Gson$Types.java

@@ -75,7 +75,13 @@ public static GenericArrayType arrayOf(Type componentType) {
    * this returns {@code ?}, which is shorthand for {@code ? 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);
   }
 
   /**
@@ -84,7 +90,13 @@ public static WildcardType subtypeOf(Type bound) {
    * 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);
   }
 
   /**

gson/src/test/java/com/google/gson/internal/bind/RecursiveTypesResolveTest.java

@@ -0,0 +1,89 @@
+/*
+ * 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.google.gson.internal.bind;
+
+import com.google.gson.Gson;
+import com.google.gson.TypeAdapter;
+import com.google.gson.internal.$Gson$Types;
+import junit.framework.TestCase;
+
+import java.io.PrintStream;
+import java.lang.ref.WeakReference;
+
+/**
+ * Test fixes for infinite recursion on {@link $Gson$Types#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;'
+ */
+public class RecursiveTypesResolveTest extends TestCase {
+
+  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.
+   */
+  public void testRecursiveResolveSimple() {
+    TypeAdapter<Foo1> adapter = new Gson().getAdapter(Foo1.class);
+    assertNotNull(adapter);
+  }
+
+  //
+  // Real-world samples, found in Issues #603 and #440.
+  //
+  public void testIssue603PrintStream() {
+    TypeAdapter<PrintStream> adapter = new Gson().getAdapter(PrintStream.class);
+    assertNotNull(adapter);
+  }
+
+  public void testIssue440WeakReference() throws Exception {
+    TypeAdapter<WeakReference> adapter = new Gson().getAdapter(WeakReference.class);
+    assertNotNull(adapter);
+  }
+
+  //
+  // Tests belows check the behaviour of the methods changed for the fix
+  //
+
+  public void testDoubleSupertype() {
+    assertEquals($Gson$Types.supertypeOf(Number.class),
+            $Gson$Types.supertypeOf($Gson$Types.supertypeOf(Number.class)));
+  }
+
+  public void testDoubleSubtype() {
+    assertEquals($Gson$Types.subtypeOf(Number.class),
+            $Gson$Types.subtypeOf($Gson$Types.subtypeOf(Number.class)));
+  }
+
+  public void testSuperSubtype() {
+    assertEquals($Gson$Types.subtypeOf(Object.class),
+            $Gson$Types.supertypeOf($Gson$Types.subtypeOf(Number.class)));
+  }
+
+  public void testSubSupertype() {
+    assertEquals($Gson$Types.subtypeOf(Object.class),
+            $Gson$Types.subtypeOf($Gson$Types.supertypeOf(Number.class)));
+  }
+}