Add setting for leniency on Gson instance.

Add a JsonReader factory (for parity with the JsonWriter one) which provides a configured instance using the Gson settings.

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

@@ -101,6 +101,12 @@
  */
 public final class Gson {
   static final boolean DEFAULT_JSON_NON_EXECUTABLE = false;
+  static final boolean DEFAULT_LENIENT = false;
+  static final boolean DEFAULT_PRETTY_PRINT = false;
+  static final boolean DEFAULT_ESCAPE_HTML = true;
+  static final boolean DEFAULT_SERIALIZE_NULLS = false;
+  static final boolean DEFAULT_COMPLEX_MAP_KEYS = false;
+  static final boolean DEFAULT_SPECIALIZE_FLOAT_VALUES = false;
 
   private static final String JSON_NON_EXECUTABLE_PREFIX = ")]}'\n";
 
@@ -124,6 +130,7 @@ public final class Gson {
   private final boolean htmlSafe;
   private final boolean generateNonExecutableJson;
   private final boolean prettyPrinting;
+  private final boolean lenient;
 
   final JsonDeserializationContext deserializationContext = new JsonDeserializationContext() {
     @SuppressWarnings("unchecked")
@@ -177,22 +184,24 @@ public final class Gson {
    */
   public Gson() {
     this(Excluder.DEFAULT, FieldNamingPolicy.IDENTITY,
-        Collections.<Type, InstanceCreator<?>>emptyMap(), false, false, DEFAULT_JSON_NON_EXECUTABLE,
-        true, false, false, LongSerializationPolicy.DEFAULT,
-        Collections.<TypeAdapterFactory>emptyList());
+        Collections.<Type, InstanceCreator<?>>emptyMap(), DEFAULT_SERIALIZE_NULLS,
+        DEFAULT_COMPLEX_MAP_KEYS, DEFAULT_JSON_NON_EXECUTABLE, DEFAULT_ESCAPE_HTML,
+        DEFAULT_PRETTY_PRINT, DEFAULT_LENIENT, DEFAULT_SPECIALIZE_FLOAT_VALUES,
+        LongSerializationPolicy.DEFAULT, Collections.<TypeAdapterFactory>emptyList());
   }
 
   Gson(final Excluder excluder, final FieldNamingStrategy fieldNamingPolicy,
       final Map<Type, InstanceCreator<?>> instanceCreators, boolean serializeNulls,
       boolean complexMapKeySerialization, boolean generateNonExecutableGson, boolean htmlSafe,
-      boolean prettyPrinting, boolean serializeSpecialFloatingPointValues,
+      boolean prettyPrinting, boolean lenient, boolean serializeSpecialFloatingPointValues,
       LongSerializationPolicy longSerializationPolicy,
       List<TypeAdapterFactory> typeAdapterFactories) {
     this.constructorConstructor = new ConstructorConstructor(instanceCreators);
     this.serializeNulls = serializeNulls;
     this.generateNonExecutableJson = generateNonExecutableGson;
     this.htmlSafe = htmlSafe;
     this.prettyPrinting = prettyPrinting;
+    this.lenient = lenient;
 
     List<TypeAdapterFactory> factories = new ArrayList<TypeAdapterFactory>();
 
@@ -704,6 +713,15 @@ public JsonWriter newJsonWriter(Writer writer) throws IOException {
     return jsonWriter;
   }
 
+  /**
+   * Returns a new JSON writer configured for the settings on this Gson instance.
+   */
+  public JsonReader newJsonReader(Reader reader) {
+    JsonReader jsonReader = new JsonReader(reader);
+    jsonReader.setLenient(lenient);
+    return jsonReader;
+  }
+
   /**
    * Writes the JSON for {@code jsonElement} to {@code writer}.
    * @throws JsonIOException if there was a problem writing to the writer
@@ -795,7 +813,7 @@ public <T> T fromJson(String json, Type typeOfT) throws JsonSyntaxException {
    * @since 1.2
    */
   public <T> T fromJson(Reader json, Class<T> classOfT) throws JsonSyntaxException, JsonIOException {
-    JsonReader jsonReader = new JsonReader(json);
+    JsonReader jsonReader = newJsonReader(json);
     Object object = fromJson(jsonReader, classOfT);
     assertFullConsumption(object, jsonReader);
     return Primitives.wrap(classOfT).cast(object);
@@ -822,7 +840,7 @@ public <T> T fromJson(Reader json, Class<T> classOfT) throws JsonSyntaxException
    */
   @SuppressWarnings("unchecked")
   public <T> T fromJson(Reader json, Type typeOfT) throws JsonIOException, JsonSyntaxException {
-    JsonReader jsonReader = new JsonReader(json);
+    JsonReader jsonReader = newJsonReader(json);
     T object = (T) fromJson(jsonReader, typeOfT);
     assertFullConsumption(object, jsonReader);
     return object;

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

@@ -16,6 +16,7 @@
 
 package com.google.gson;
 
+import com.google.gson.stream.JsonReader;
 import java.lang.reflect.Type;
 import java.sql.Timestamp;
 import java.text.DateFormat;
@@ -31,6 +32,14 @@
 import com.google.gson.internal.bind.TypeAdapters;
 import com.google.gson.reflect.TypeToken;
 
+import static com.google.gson.Gson.DEFAULT_COMPLEX_MAP_KEYS;
+import static com.google.gson.Gson.DEFAULT_ESCAPE_HTML;
+import static com.google.gson.Gson.DEFAULT_JSON_NON_EXECUTABLE;
+import static com.google.gson.Gson.DEFAULT_LENIENT;
+import static com.google.gson.Gson.DEFAULT_PRETTY_PRINT;
+import static com.google.gson.Gson.DEFAULT_SERIALIZE_NULLS;
+import static com.google.gson.Gson.DEFAULT_SPECIALIZE_FLOAT_VALUES;
+
 /**
  * <p>Use this builder to construct a {@link Gson} instance when you need to set configuration
  * options other than the default. For {@link Gson} with default configuration, it is simpler to
@@ -74,15 +83,16 @@ public final class GsonBuilder {
   private final List<TypeAdapterFactory> factories = new ArrayList<TypeAdapterFactory>();
   /** tree-style hierarchy factories. These come after factories for backwards compatibility. */
   private final List<TypeAdapterFactory> hierarchyFactories = new ArrayList<TypeAdapterFactory>();
-  private boolean serializeNulls;
+  private boolean serializeNulls = DEFAULT_SERIALIZE_NULLS;
   private String datePattern;
   private int dateStyle = DateFormat.DEFAULT;
   private int timeStyle = DateFormat.DEFAULT;
-  private boolean complexMapKeySerialization;
-  private boolean serializeSpecialFloatingPointValues;
-  private boolean escapeHtmlChars = true;
-  private boolean prettyPrinting;
-  private boolean generateNonExecutableJson;
+  private boolean complexMapKeySerialization = DEFAULT_COMPLEX_MAP_KEYS;
+  private boolean serializeSpecialFloatingPointValues = DEFAULT_SPECIALIZE_FLOAT_VALUES;
+  private boolean escapeHtmlChars = DEFAULT_ESCAPE_HTML;
+  private boolean prettyPrinting = DEFAULT_PRETTY_PRINT;
+  private boolean generateNonExecutableJson = DEFAULT_JSON_NON_EXECUTABLE;
+  private boolean lenient = DEFAULT_LENIENT;
 
   /**
    * Creates a GsonBuilder instance that can be used to build Gson with various configuration
@@ -351,6 +361,19 @@ public GsonBuilder setPrettyPrinting() {
     return this;
   }
 
+  /**
+   * By default, Gson is strict and only accepts JSON as specified by
+   * <a href="http://www.ietf.org/rfc/rfc4627.txt">RFC 4627</a>. This option makes the parser
+   * liberal in what it accepts.
+   *
+   * @return a reference to this {@code GsonBuilder} object to fulfill the "Builder" pattern
+   * @see JsonReader#setLenient(boolean)
+   */
+  public GsonBuilder setLenient() {
+    lenient = true;
+    return this;
+  }
+
   /**
    * By default, Gson escapes HTML characters such as &lt; &gt; etc. Use this option to configure
    * Gson to pass-through HTML characters as is.
@@ -544,7 +567,7 @@ public Gson create() {
 
     return new Gson(excluder, fieldNamingPolicy, instanceCreators,
         serializeNulls, complexMapKeySerialization,
-        generateNonExecutableJson, escapeHtmlChars, prettyPrinting,
+        generateNonExecutableJson, escapeHtmlChars, prettyPrinting, lenient,
         serializeSpecialFloatingPointValues, longSerializationPolicy, factories);
   }
 

gson/src/main/java/com/google/gson/stream/JsonReader.java

@@ -294,7 +294,7 @@ public JsonReader(Reader in) {
   }
 
   /**
-   * Configure this parser to be  be liberal in what it accepts. By default,
+   * Configure this parser to be liberal in what it accepts. By default,
    * this parser is strict and only accepts JSON as specified by <a
    * href="http://www.ietf.org/rfc/rfc4627.txt">RFC 4627</a>. Setting the
    * parser to lenient causes it to ignore the following syntax errors:

gson/src/test/java/com/google/gson/functional/LeniencyTest.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2016 The 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.functional;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.reflect.TypeToken;
+import java.util.List;
+import junit.framework.TestCase;
+
+import static java.util.Collections.singletonList;
+
+/**
+ * Functional tests for leniency option.
+ */
+public class LeniencyTest extends TestCase {
+
+  private Gson gson;
+
+  @Override
+  protected void setUp() throws Exception {
+    super.setUp();
+    gson = new GsonBuilder().setLenient().create();
+  }
+
+  public void testLenientFromJson() {
+    List<String> json = gson.fromJson(""
+        + "[ # One!\n"
+        + "  'Hi' #Element!\n"
+        + "] # Array!", new TypeToken<List<String>>() {}.getType());
+    assertEquals(singletonList("Hi"), json);
+  }
+}