Add JsonReader.skipName.

kotlin/src/main/java/com/squareup/moshi/kotlin/KotlinJsonAdapter.kt

@@ -68,7 +68,7 @@ internal class KotlinJsonAdapter<T>(
       val binding = if (index != -1) bindings[index] else null
 
       if (binding == null) {
-        reader.nextName()
+        reader.skipName()
         reader.skipValue()
         continue
       }

moshi/src/main/java/com/squareup/moshi/ClassJsonAdapter.java

@@ -151,7 +151,7 @@ final class ClassJsonAdapter<T> extends JsonAdapter<T> {
       while (reader.hasNext()) {
         int index = reader.selectName(options);
         if (index == -1) {
-          reader.nextName();
+          reader.skipName();
           reader.skipValue();
           continue;
         }

moshi/src/main/java/com/squareup/moshi/JsonAdapter.java

@@ -219,9 +219,9 @@ public abstract class JsonAdapter<T> {
 
   /**
    * Returns a JSON adapter equal to this, but that throws a {@link JsonDataException} when
-   * {@linkplain JsonReader#setFailOnUnknown(boolean) unknown values} are encountered. This
-   * constraint applies to both the top-level message handled by this type adapter as well as to
-   * nested messages.
+   * {@linkplain JsonReader#setFailOnUnknown(boolean) unknown names and values} are encountered.
+   * This constraint applies to both the top-level message handled by this type adapter as well as
+   * to nested messages.
    */
   @CheckReturnValue public final JsonAdapter<T> failOnUnknown() {
     final JsonAdapter<T> delegate = this;

moshi/src/main/java/com/squareup/moshi/JsonReader.java

@@ -279,7 +279,7 @@ public abstract class JsonReader implements Closeable {
   }
 
   /**
-   * Returns true if this parser forbids skipping values.
+   * Returns true if this parser forbids skipping names and values.
    */
   @CheckReturnValue public final boolean failOnUnknown() {
     return failOnUnknown;
@@ -332,6 +332,15 @@ public abstract class JsonReader implements Closeable {
    */
   public abstract int selectName(Options options) throws IOException;
 
+  /**
+   * Skips the next token, consuming it. This method is intended for use when the JSON token stream
+   * contains unrecognized or unhandled names.
+   *
+   * <p>This throws a {@link JsonDataException} if this parser has been configured to {@linkplain
+   * #failOnUnknown fail on unknown} names.
+   */
+  public abstract void skipName() throws IOException;
+
   /**
    * Returns the {@linkplain Token#STRING string} value of the next token, consuming it. If the next
    * token is a number, this method will return its string form.

moshi/src/main/java/com/squareup/moshi/JsonUtf8Reader.java

@@ -562,6 +562,27 @@ final class JsonUtf8Reader extends JsonReader {
     return result;
   }
 
+  @Override public void skipName() throws IOException {
+    if (failOnUnknown) {
+      throw new JsonDataException("Cannot skip unexpected " + peek() + " at " + getPath());
+    }
+    int p = peeked;
+    if (p == PEEKED_NONE) {
+      p = doPeek();
+    }
+    if (p == PEEKED_UNQUOTED_NAME) {
+      skipUnquotedValue();
+    } else if (p == PEEKED_DOUBLE_QUOTED_NAME) {
+      skipQuotedValue(DOUBLE_QUOTE_OR_SLASH);
+    } else if (p == PEEKED_SINGLE_QUOTED_NAME) {
+      skipQuotedValue(SINGLE_QUOTE_OR_SLASH);
+    } else if (p != PEEKED_BUFFERED_NAME) {
+      throw new JsonDataException("Expected a name but was " + peek() + " at path " + getPath());
+    }
+    peeked = PEEKED_NONE;
+    pathNames[stackSize - 1] = "null";
+  }
+
   /**
    * If {@code name} is in {@code options} this consumes it and returns its index.
    * Otherwise this returns -1 and no name is consumed.

moshi/src/main/java/com/squareup/moshi/JsonValueReader.java

@@ -151,6 +151,18 @@ final class JsonValueReader extends JsonReader {
     return -1;
   }
 
+  @Override public void skipName() throws IOException {
+    if (failOnUnknown) {
+      throw new JsonDataException("Cannot skip unexpected " + peek() + " at " + getPath());
+    }
+
+    Map.Entry<?, ?> peeked = require(Map.Entry.class, Token.NAME);
+
+    // Swap the Map.Entry for its value on the stack.
+    stack[stackSize - 1] = peeked.getValue();
+    pathNames[stackSize - 2] = "null";
+  }
+
   @Override public String nextString() throws IOException {
     Object peeked = (stackSize != 0 ? stack[stackSize - 1] : null);
     if (peeked instanceof String) {

moshi/src/test/java/com/squareup/moshi/JsonReaderTest.java

@@ -960,4 +960,23 @@ public final class JsonReaderTest {
     assertThat(value).isEqualTo(
         Collections.singletonMap("pizzas", Arrays.asList("cheese", "pepperoni")));
   }
+
+  @Test public void skipName() throws IOException {
+    JsonReader reader = newReader("{\"a\":1}");
+    reader.beginObject();
+    reader.skipName();
+    assertThat(reader.peek()).isEqualTo(JsonReader.Token.NUMBER);
+    reader.skipValue();
+    reader.endObject();
+  }
+
+  @Test public void skipNameOnValueFails() throws IOException {
+    JsonReader reader = newReader("1");
+    try {
+      reader.skipName();
+      fail();
+    } catch (JsonDataException expected) {
+    }
+    assertThat(reader.nextInt()).isEqualTo(1);
+  }
 }

moshi/src/test/java/com/squareup/moshi/JsonUtf8ReaderTest.java

@@ -994,6 +994,20 @@ public final class JsonUtf8ReaderTest {
     }
   }
 
+  @Test public void failureMessagePathFromSkipName() throws IOException {
+    JsonReader reader = newReader("{\"a\":[42,}");
+    reader.beginObject();
+    reader.skipName();
+    reader.beginArray();
+    reader.nextInt();
+    try {
+      reader.peek();
+      fail();
+    } catch (JsonEncodingException expected) {
+      assertThat(expected).hasMessage("Expected value at path $.null[1]");
+    }
+  }
+
   @Test @Ignore public void strictVeryLongNumber() throws IOException {
     JsonReader reader = newReader("[0." + repeat('9', 8192) + "]");
     reader.beginArray();

moshi/src/test/java/com/squareup/moshi/MoshiTest.java

@@ -910,7 +910,7 @@ public final class MoshiTest {
       adapter.fromJson("{\"diameter\":5,\"crust\":\"thick\",\"extraCheese\":true}");
       fail();
     } catch (JsonDataException expected) {
-      assertThat(expected).hasMessage("Cannot skip unexpected STRING at $.crust");
+      assertThat(expected).hasMessage("Cannot skip unexpected NAME at $.diameter");
     }
   }