Include line and column position in error messages.

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

@@ -204,6 +204,14 @@ public final class JsonReader implements Closeable {
   private int pos = 0;
   private int limit = 0;
 
+  /*
+   * Track the number of newlines and columns preceding the current buffer. To
+   * compute the line and column of a position in the buffer, compute the line
+   * and column in the buffer and add the preceding values.
+   */
+  private int bufferStartLine;
+  private int bufferStartColumn;
+
   private final List<JsonScope> stack = new ArrayList<JsonScope>();
   {
     push(JsonScope.EMPTY_DOCUMENT);
@@ -817,6 +825,16 @@ public final class JsonReader implements Closeable {
    * false.
    */
   private boolean fillBuffer(int minimum) throws IOException {
+    // Before clobbering the old characters, update where buffer starts
+    for (int i = 0; i < pos; i++) {
+      if (buffer[i] == '\n') {
+        bufferStartLine++;
+        bufferStartColumn = 0;
+      } else {
+        bufferStartColumn++;
+      }
+    }
+
     if (limit != pos) {
       limit -= pos;
       System.arraycopy(buffer, pos, buffer, 0, limit);
@@ -835,6 +853,28 @@ public final class JsonReader implements Closeable {
     return false;
   }
 
+  private int getLineNumber() {
+    int result = bufferStartLine;
+    for (int i = 0; i < pos; i++) {
+      if (buffer[i] == '\n') {
+        result++;
+      }
+    }
+    return result + 1; // the first line is '1'
+  }
+
+  private int getColumnNumber() {
+    int result = bufferStartColumn;
+    for (int i = 0; i < pos; i++) {
+      if (buffer[i] == '\n') {
+        result = 0;
+      } else {
+        result++;
+      }
+    }
+    return result + 1; // the first column is '1'
+  }
+
   private int nextNonWhitespace() throws IOException {
     while (pos < limit || fillBuffer(1)) {
       int c = buffer[pos++];
@@ -1110,7 +1150,7 @@ public final class JsonReader implements Closeable {
    * with this reader's content.
    */
   private IOException syntaxError(String message) throws IOException {
-    throw new MalformedJsonException(message + " near " + getSnippet());
+    throw new MalformedJsonException(message + " @" + getLineNumber() + ":" + getColumnNumber());
   }
 
   private CharSequence getSnippet() {

gson/src/test/java/com/google/gson/stream/JsonReaderTest.java

@@ -18,6 +18,7 @@ package com.google.gson.stream;
 
 import java.io.IOException;
 import java.io.StringReader;
+import java.util.Arrays;
 import junit.framework.TestCase;
 
 public final class JsonReaderTest extends TestCase {
@@ -763,4 +764,35 @@ public final class JsonReaderTest extends TestCase {
     } catch (IOException expected) {
     }
   }
+
+  public void testFailWithPosition() throws IOException {
+    JsonReader reader = new JsonReader(new StringReader("[\n\n\n\n\n0,}]"));
+    reader.beginArray();
+    reader.nextInt();
+    try {
+      reader.peek();
+      fail();
+    } catch (IOException expected) {
+      assertEquals("Expected literal value @6:3", expected.getMessage());
+    }
+  }
+
+  public void testFailWithPositionGreaterThanBufferSize() throws IOException {
+    String spaces = repeat(' ', 8192);
+    JsonReader reader = new JsonReader(new StringReader("[\n\n" + spaces + "\n\n\n0,}]"));
+    reader.beginArray();
+    reader.nextInt();
+    try {
+      reader.peek();
+      fail();
+    } catch (IOException expected) {
+      assertEquals("Expected literal value @6:3", expected.getMessage());
+    }
+  }
+
+  private String repeat(char c, int count) {
+    char[] array = new char[count];
+    Arrays.fill(array, c);
+    return new String(array);
+  }
 }