Gson respects the lenient flag

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

@@ -102,7 +102,7 @@
  */
 public final class Gson {
   static final boolean DEFAULT_JSON_NON_EXECUTABLE = false;
-  static final boolean DEFAULT_LENIENT = false;
+  static final boolean DEFAULT_LENIENT = true;
   static final boolean DEFAULT_PRETTY_PRINT = false;
   static final boolean DEFAULT_ESCAPE_HTML = true;
   static final boolean DEFAULT_SERIALIZE_NULLS = false;
@@ -847,15 +847,15 @@ private static void assertFullConsumption(Object obj, JsonReader reader) {
    * Reads the next JSON value from {@code reader} and convert it to an object
    * of type {@code typeOfT}. Returns {@code null}, if the {@code reader} is at EOF.
    * Since Type is not parameterized by T, this method is type unsafe and should be used carefully
-   *
+   * <p>
+   * The leniency of the reader passed in is respected. See {@linkplain JsonReader#setLenient(boolean)}
+   * </p>
    * @throws JsonIOException if there was a problem writing to the Reader
    * @throws JsonSyntaxException if json is not a valid representation for an object of type
    */
   @SuppressWarnings("unchecked")
   public <T> T fromJson(JsonReader reader, Type typeOfT) throws JsonIOException, JsonSyntaxException {
     boolean isEmpty = true;
-    boolean oldLenient = reader.isLenient();
-    reader.setLenient(true);
     try {
       reader.peek();
       isEmpty = false;
@@ -877,8 +877,6 @@ public <T> T fromJson(JsonReader reader, Type typeOfT) throws JsonIOException, J
     } catch (IOException e) {
       // TODO(inder): Figure out whether it is indeed right to rethrow this as JsonSyntaxException
       throw new JsonSyntaxException(e);
-    } finally {
-      reader.setLenient(oldLenient);
     }
   }
 

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

@@ -363,13 +363,23 @@ public GsonBuilder setPrettyPrinting() {
   }
 
   /**
-   * 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.
+   * By default, Gson is liberal in what it accepts. Setting lenient to false causes Gson to
+   * only accept JSON as specified by 
+   * <a href="http://www.ietf.org/rfc/rfc4627.txt">RFC 4627</a>.
    *
    * @return a reference to this {@code GsonBuilder} object to fulfill the "Builder" pattern
    * @see JsonReader#setLenient(boolean)
    */
+  public GsonBuilder setLenient(boolean lenient) {
+    this.lenient = lenient;
+    return this;
+  }
+
+  /**
+   * Gson is lenient by default. Use {@link #setLenient(boolean)} if
+   *             you wish to change the leniency
+   * @return a reference to this {@code GsonBuilder} object to fulfill the "Builder" pattern
+   */
   public GsonBuilder setLenient() {
     lenient = true;
     return this;

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

@@ -17,30 +17,91 @@
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonSyntaxException;
 import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+
 import java.util.List;
 import junit.framework.TestCase;
 
 import static java.util.Collections.singletonList;
 
+import java.io.StringReader;
+import java.lang.reflect.Type;
+
 /**
  * Functional tests for leniency option.
  */
 public class LeniencyTest extends TestCase {
 
-  private Gson gson;
+  private Gson lenientGson;
+  private Gson strictGson;
 
   @Override
   protected void setUp() throws Exception {
     super.setUp();
-    gson = new GsonBuilder().setLenient().create();
+    lenientGson = new GsonBuilder().create();
+    strictGson = new GsonBuilder().setLenient(false).create();
   }
 
   public void testLenientFromJson() {
-    List<String> json = gson.fromJson(""
+    final String testString = ""
+        + "[ # One!\n"
+        + "  'Hi' #Element!\n"
+        + "] # Array!";
+    final String expectedResult = "Hi";
+    Type type = new TypeToken<List<String>>() {}.getType();
+
+    JsonReader reader = new JsonReader(new StringReader(testString));
+    reader.setLenient(true);
+    // fromJson(JsonReader, Type) should respect the leniency of 
+    // the JsonReader
+    List<String> json = strictGson.fromJson(reader, type);
+    assertEquals(singletonList(expectedResult), json);
+
+    // the factory method should set the leniency of the created factory 
+    // to be the same as the leniency of the Gson instance
+    reader = lenientGson.newJsonReader(new StringReader(testString));
+    assertTrue(reader.isLenient());
+    // fromJson(JsonReader, Type) should respect the leniency of 
+    // the JsonReader
+    json = strictGson.fromJson(reader, type);
+    assertEquals(singletonList(expectedResult), json);    
+
+    json = lenientGson.fromJson(testString, type);
+    assertEquals(singletonList(expectedResult), json);
+  }
+
+  public void testStrictFromJson() {
+    final String testString = ""
         + "[ # One!\n"
         + "  'Hi' #Element!\n"
-        + "] # Array!", new TypeToken<List<String>>() {}.getType());
-    assertEquals(singletonList("Hi"), json);
+        + "]";
+    Type type = new TypeToken<List<String>>(){}.getType();
+
+    try {
+      // JsonReader is strict by default
+      JsonReader reader = new JsonReader(new StringReader(testString));
+      // fromJson(JsonReader, Type) should respect the leniency of 
+      // the JsonReader
+      lenientGson.fromJson(reader, type);
+      fail();
+    } catch (JsonSyntaxException expected) { }
+
+    try {
+      // the factory method should set the leniency of the created factory 
+      // to be the same as the leniency of the Gson instance
+      JsonReader reader = strictGson.newJsonReader(new StringReader(testString));
+      assertFalse(reader.isLenient());
+      // fromJson(JsonReader, Type) should respect the leniency of 
+      // the JsonReader
+      lenientGson.fromJson(reader, type);
+      fail();
+    } catch(JsonSyntaxException expected) { }
+
+    try {
+      strictGson.fromJson(testString, type);
+      fail();
+    } catch (JsonSyntaxException expected) { }
   }
 }

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

@@ -18,6 +18,7 @@
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonIOException;
 import com.google.gson.JsonPrimitive;
 import com.google.gson.JsonSyntaxException;
 import com.google.gson.LongSerializationPolicy;
@@ -556,7 +557,7 @@ public void testUnquotedStringDeserializationFails() throws Exception {
     try {
       gson.fromJson(value, String.class);
       fail();
-    } catch (JsonSyntaxException expected) { }
+    } catch (JsonIOException expected) { }
   }
 
   public void testHtmlCharacterSerialization() throws Exception {