Parsing Map<Enum,Obj> - 501 (#1950)

* Added parsing support for enum that has overridden toString() method.

* Fix a tiny formatting problem

* Fixed formatting issue

Co-authored-by: Éamonn McManus <emcmanus@google.com>

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

@@ -775,6 +775,7 @@ public void write(JsonWriter out, Locale value) throws IOException {
 
   private static final class EnumTypeAdapter<T extends Enum<T>> extends TypeAdapter<T> {
     private final Map<String, T> nameToConstant = new HashMap<String, T>();
+    private final Map<String, T> stringToConstant = new HashMap<String, T>();
     private final Map<T, String> constantToName = new HashMap<T, String>();
 
     public EnumTypeAdapter(final Class<T> classOfT) {
@@ -801,6 +802,8 @@ public EnumTypeAdapter(final Class<T> classOfT) {
           @SuppressWarnings("unchecked")
           T constant = (T)(constantField.get(null));
           String name = constant.name();
+          String toStringVal = constant.toString();
+
           SerializedName annotation = constantField.getAnnotation(SerializedName.class);
           if (annotation != null) {
             name = annotation.value();
@@ -809,6 +812,7 @@ public EnumTypeAdapter(final Class<T> classOfT) {
             }
           }
           nameToConstant.put(name, constant);
+          stringToConstant.put(toStringVal, constant);
           constantToName.put(constant, name);
         }
       } catch (IllegalAccessException e) {
@@ -820,7 +824,9 @@ public EnumTypeAdapter(final Class<T> classOfT) {
         in.nextNull();
         return null;
       }
-      return nameToConstant.get(in.nextString());
+      String key = in.nextString();
+      T constant = nameToConstant.get(key);
+      return (constant == null) ? stringToConstant.get(key) : constant;
     }
 
     @Override public void write(JsonWriter out, T value) throws IOException {
@@ -928,4 +934,4 @@ public static <T1> TypeAdapterFactory newTypeHierarchyFactory(
       }
     };
   }
-}
+}