Omit the stacktrace for JOniException

src/org/joni/Config.java

@@ -74,6 +74,11 @@ public interface Config extends org.jcodings.Config {
     int CHECK_STRING_THRESHOLD_LEN            = ConfigSupport.getInt("joni.check_string_threshold_len", 7);
     int CHECK_BUFF_MAX_SIZE                   = ConfigSupport.getInt("joni.check_buff_max_size", 0x4000);
 
+    // Whether JOniException and its subclasses record a stack trace when thrown.
+    // Filling in the stack trace is expensive and the Java stack trace is rarely useful
+    // (e.g. for a regexp syntax error), so it is disabled by default.
+    boolean ENABLE_STACK_TRACE                = ConfigSupport.getBoolean("org.joni.enableStackTrace", false);
+
     PrintStream log = System.out;
     PrintStream err = System.err;
 

src/org/joni/exception/JOniException.java

@@ -19,10 +19,24 @@
  */
 package org.joni.exception;
 
+import org.joni.Config;
+
 public class JOniException extends RuntimeException{
     private static final long serialVersionUID = -6027192180014164667L;
 
     public JOniException(String message) {
         super(message);
     }
+
+    // The stacktrace is not very useful and is very expensive,
+    // for example for Regexp#to_s on a Regexp like /(?i:a)|(?i:b)/,
+    // so it is omitted unless -Dorg.joni.enableStackTrace=true
+    @Override
+    public final Throwable fillInStackTrace() {
+        if (Config.ENABLE_STACK_TRACE) {
+            return super.fillInStackTrace();
+        } else {
+            return this;
+        }
+    }
 }