Fix a class loading deadlock involving TypeAdapters. (#2740)

* Fix a class loading deadlock involving `TypeAdapters`.

Fixes #2739.

* Remove deprecation of internal fields.

The idea was to discourage people from using these, but they have been there for
a long time and the deprecation isn't going to have much effect. Meanwhile the
deprecation required `@SuppressWarnings`, which was annoying.

Also move `JsonElementTypeFactory.ADAPTER` back into `TypeAdapters` so there is
no further circular dependency between the two classes. I think it was harmless
but it's easy enough to avoid.

* Omit unnecessary type qualificiation.

gson/src/main/java/com/google/gson/Gson.java

@@ -26,9 +26,7 @@
 import com.google.gson.internal.bind.ArrayTypeAdapter;
 import com.google.gson.internal.bind.CollectionTypeAdapterFactory;
 import com.google.gson.internal.bind.DefaultDateTypeAdapter;
-import com.google.gson.internal.bind.EnumTypeAdapter;
 import com.google.gson.internal.bind.JsonAdapterAnnotationTypeAdapterFactory;
-import com.google.gson.internal.bind.JsonElementTypeAdapter;
 import com.google.gson.internal.bind.JsonTreeReader;
 import com.google.gson.internal.bind.JsonTreeWriter;
 import com.google.gson.internal.bind.MapTypeAdapterFactory;
@@ -325,7 +323,7 @@ public Gson() {
     List<TypeAdapterFactory> factories = new ArrayList<>();
 
     // built-in type adapters that cannot be overridden
-    factories.add(JsonElementTypeAdapter.FACTORY);
+    factories.add(TypeAdapters.JSON_ELEMENT_FACTORY);
     factories.add(ObjectTypeAdapter.getFactory(objectToNumberStrategy));
 
     // the excluder must precede all adapters that handle user-defined types
@@ -388,7 +386,7 @@ public Gson() {
     factories.add(new MapTypeAdapterFactory(constructorConstructor, complexMapKeySerialization));
     this.jsonAdapterFactory = new JsonAdapterAnnotationTypeAdapterFactory(constructorConstructor);
     factories.add(jsonAdapterFactory);
-    factories.add(EnumTypeAdapter.FACTORY);
+    factories.add(TypeAdapters.ENUM_FACTORY);
     factories.add(
         new ReflectiveTypeAdapterFactory(
             constructorConstructor,

gson/src/main/java/com/google/gson/internal/Streams.java

@@ -21,7 +21,7 @@
 import com.google.gson.JsonNull;
 import com.google.gson.JsonParseException;
 import com.google.gson.JsonSyntaxException;
-import com.google.gson.internal.bind.JsonElementTypeAdapter;
+import com.google.gson.internal.bind.TypeAdapters;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
 import com.google.gson.stream.JsonWriter;
@@ -43,7 +43,7 @@ public static JsonElement parse(JsonReader reader) throws JsonParseException {
     try {
       JsonToken unused = reader.peek();
       isEmpty = false;
-      return JsonElementTypeAdapter.ADAPTER.read(reader);
+      return TypeAdapters.JSON_ELEMENT.read(reader);
     } catch (EOFException e) {
       /*
        * For compatibility with JSON 1.5 and earlier, we return a JsonNull for
@@ -65,7 +65,7 @@ public static JsonElement parse(JsonReader reader) throws JsonParseException {
 
   /** Writes the JSON element to the writer, recursively. */
   public static void write(JsonElement element, JsonWriter writer) throws IOException {
-    JsonElementTypeAdapter.ADAPTER.write(writer, element);
+    TypeAdapters.JSON_ELEMENT.write(writer, element);
   }
 
   public static Writer writerForAppendable(Appendable appendable) {

gson/src/main/java/com/google/gson/internal/bind/EnumTypeAdapter.java

@@ -32,8 +32,8 @@
 import java.util.Map;
 
 /** Adapter for enum classes (but not for the base class {@code java.lang.Enum}). */
-public class EnumTypeAdapter<T extends Enum<T>> extends TypeAdapter<T> {
-  public static final TypeAdapterFactory FACTORY =
+class EnumTypeAdapter<T extends Enum<T>> extends TypeAdapter<T> {
+  static final TypeAdapterFactory FACTORY =
       new TypeAdapterFactory() {
         @Override
         public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {

gson/src/main/java/com/google/gson/internal/bind/JsonElementTypeAdapter.java

@@ -22,7 +22,6 @@
 import com.google.gson.JsonObject;
 import com.google.gson.JsonPrimitive;
 import com.google.gson.TypeAdapter;
-import com.google.gson.TypeAdapterFactory;
 import com.google.gson.internal.LazilyParsedNumber;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
@@ -33,11 +32,8 @@
 import java.util.Map;
 
 /** Adapter for {@link JsonElement} and subclasses. */
-public class JsonElementTypeAdapter extends TypeAdapter<JsonElement> {
-  public static final JsonElementTypeAdapter ADAPTER = new JsonElementTypeAdapter();
-
-  public static final TypeAdapterFactory FACTORY =
-      TypeAdapters.newTypeHierarchyFactory(JsonElement.class, ADAPTER);
+class JsonElementTypeAdapter extends TypeAdapter<JsonElement> {
+  static final JsonElementTypeAdapter ADAPTER = new JsonElementTypeAdapter();
 
   private JsonElementTypeAdapter() {}
 

gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java

@@ -806,40 +806,12 @@ public void write(JsonWriter out, Locale value) throws IOException {
 
   public static final TypeAdapterFactory LOCALE_FACTORY = newFactory(Locale.class, LOCALE);
 
-  /*
-   * The following adapter and factory fields have not been removed yet and are only deprecated
-   * for now because external projects might be using them, despite being part of Gson's internal
-   * implementation.
-   */
-
-  /**
-   * @deprecated {@code TypeAdapters} is an internal Gson class. To obtain the adapter for {@link
-   *     JsonElement} and subclasses use instead:
-   *     <pre>{@code
-   * TypeAdapter<JsonElement> adapter = gson.getAdapter(JsonElement.class);
-   * }</pre>
-   */
-  @Deprecated
   public static final TypeAdapter<JsonElement> JSON_ELEMENT = JsonElementTypeAdapter.ADAPTER;
 
-  /**
-   * @deprecated {@code TypeAdapters} is an internal Gson class. To obtain the adapter for {@link
-   *     JsonElement} and subclasses use instead:
-   *     <pre>{@code
-   * TypeAdapter<JsonElement> adapter = gson.getAdapter(JsonElement.class);
-   * }</pre>
-   */
-  @Deprecated
-  public static final TypeAdapterFactory JSON_ELEMENT_FACTORY = JsonElementTypeAdapter.FACTORY;
+  public static final TypeAdapterFactory JSON_ELEMENT_FACTORY =
+      newTypeHierarchyFactory(JsonElement.class, JSON_ELEMENT);
 
-  /**
-   * @deprecated {@code TypeAdapters} is an internal Gson class. To obtain the adapter for a
-   *     specific enum class use instead:
-   *     <pre>{@code
-   * TypeAdapter<MyEnum> adapter = gson.getAdapter(MyEnum.class);
-   * }</pre>
-   */
-  @Deprecated public static final TypeAdapterFactory ENUM_FACTORY = EnumTypeAdapter.FACTORY;
+  public static final TypeAdapterFactory ENUM_FACTORY = EnumTypeAdapter.FACTORY;
 
   @SuppressWarnings("TypeParameterNaming")
   public static <TT> TypeAdapterFactory newFactory(