LUCENE-4078: PatternReplaceCharFilter assertion error caused by malformed

utf-16. This is most likely a bug in the JDK because a
Pattern("").replaceAll("x") is inserted in between surrogate pair
characters and corrupts strings.

A temporary fix is to check for this at random pattern generator and pick
again if detected.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1343214 13f79535-47bb-0310-9956-ffa450edef68

lucene/analysis/common/src/test/org/apache/lucene/analysis/pattern/TestPatternReplaceCharFilter.java

@@ -23,7 +23,6 @@ import java.io.StringReader;
 import java.util.Random;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
-import java.util.regex.PatternSyntaxException;
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.BaseTokenStreamTestCase;
@@ -306,7 +305,7 @@ public class TestPatternReplaceCharFilter extends BaseTokenStreamTestCase {
     long maxTime = 1000 * 2;
     Random random = new Random(random().nextLong());
     for (int i = 0; i < numPatterns && start + maxTime > System.currentTimeMillis(); i++) {
-      final Pattern p = randomPattern();
+      final Pattern p = _TestUtil.randomPattern(random());
       final String replacement = _TestUtil.randomSimpleString(random);
       Analyzer a = new Analyzer() {
         @Override
@@ -325,14 +324,4 @@ public class TestPatternReplaceCharFilter extends BaseTokenStreamTestCase {
            * time for certain patterns. */ 40, true); // only ascii
     }
   }
-  
-  public Pattern randomPattern() {
-    while (true) {
-      try {
-        return Pattern.compile(_TestUtil.randomRegexpishString(random()));
-      } catch (PatternSyntaxException ignored) {
-        // if at first you don't succeed...
-      }
-    }
-  }
  }

lucene/test-framework/src/java/org/apache/lucene/analysis/MockTokenizer.java

@@ -22,7 +22,6 @@ import java.io.Reader;
 
 import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
 import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
-import org.apache.lucene.util.AttributeSource.AttributeFactory;
 import org.apache.lucene.util.automaton.CharacterRunAutomaton;
 import org.apache.lucene.util.automaton.RegExp;
 

lucene/test-framework/src/java/org/apache/lucene/util/_TestUtil.java

@@ -30,6 +30,8 @@ import java.nio.CharBuffer;
 import java.util.*;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.TimeUnit;
+import java.util.regex.Pattern;
+import java.util.regex.PatternSyntaxException;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 
@@ -900,4 +902,24 @@ public class _TestUtil {
       }
     }
   }
+
+  /**
+   * Returns a valid (compiling) Pattern instance with random stuff inside. Be careful
+   * when applying random patterns to longer strings as certain types of patterns
+   * may explode into exponential times in backtracking implementations (such as Java's).
+   */
+  public static Pattern randomPattern(Random random) {
+    final String nonBmpString = "AB\uD840\uDC00C";
+    while (true) {
+      try {
+        Pattern p = Pattern.compile(_TestUtil.randomRegexpishString(random));
+        // Make sure the result of applying the pattern to a string with extended
+        // unicode characters is a valid utf16 string. See LUCENE-4078 for discussion.
+        if (UnicodeUtil.validUTF16String(p.matcher(nonBmpString).replaceAll("_")))
+          return p;
+      } catch (PatternSyntaxException ignored) {
+        // Loop trying until we hit something that compiles.
+      }
+    }
+  }
 }