Synchronize Log4jLogEvent-related changes from 2.x

This updates `Log4jLogEvent` and its builder class to work similarly to
what is in 2.25.0. The previously added `MementoLogEvent` class can be
removed as the builder can make memento copies better.

Author: jvz

log4j-async-logger/src/main/java/org/apache/logging/log4j/async/logger/RingBufferLogEvent.java

@@ -25,7 +25,6 @@
 import org.apache.logging.log4j.core.ReusableLogEvent;
 import org.apache.logging.log4j.core.async.InternalAsyncUtil;
 import org.apache.logging.log4j.core.impl.ContextDataFactory;
-import org.apache.logging.log4j.core.impl.Log4jLogEvent;
 import org.apache.logging.log4j.core.impl.MementoMessage;
 import org.apache.logging.log4j.core.time.Clock;
 import org.apache.logging.log4j.core.time.Instant;
@@ -495,38 +494,4 @@ private void clearContextData() {
             }
         }
     }
-
-    /**
-     * Initializes the specified {@code Log4jLogEvent.Builder} from this {@code RingBufferLogEvent}.
-     * @param builder the builder whose fields to populate
-     */
-    @Override
-    public void initializeBuilder(final Log4jLogEvent.Builder builder) {
-        // If the data is not frozen, make a copy of it.
-        // TODO: merge with MementoLogEvent#memento
-        final StringMap oldContextData = this.contextData;
-        final StringMap contextData;
-        if (oldContextData != null && !oldContextData.isFrozen()) {
-            contextData = ContextDataFactory.createContextData(oldContextData);
-        } else {
-            contextData = oldContextData;
-        }
-        builder.setContextData(contextData) //
-                .setContextStack(contextStack) //
-                .setEndOfBatch(endOfBatch) //
-                .setIncludeLocation(includeLocation) //
-                .setLevel(getLevel()) // ensure non-null
-                .setLoggerFqcn(fqcn) //
-                .setLoggerName(loggerName) //
-                .setMarker(marker) //
-                .setMessage(memento()) // ensure non-null & immutable
-                .setNanoTime(nanoTime) //
-                .setSource(location) //
-                .setThreadId(threadId) //
-                .setThreadName(threadName) //
-                .setThreadPriority(threadPriority) //
-                .setThrown(getThrown()) //
-                .setInstant(instant) //
-        ;
-    }
 }

log4j-core-test/src/test/java/org/apache/logging/log4j/core/impl/Log4jLogEventTest.java

@@ -16,10 +16,10 @@
  */
 package org.apache.logging.log4j.core.impl;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
-import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -326,9 +326,7 @@ public void testEquals() {
         different("null fqcn", builder(event).setLoggerFqcn(null), event);
 
         different("different name", builder(event).setLoggerName("different"), event);
-        assertThrows(
-                NullPointerException.class,
-                () -> different("null name", builder(event).setLoggerName(null), event));
+        different("null name", builder(event).setLoggerName(null), event);
 
         different("different marker", builder(event).setMarker(MarkerManager.getMarker("different")), event);
         different("null marker", builder(event).setMarker(null), event);
@@ -365,6 +363,6 @@ private void different(final String reason, final Log4jLogEvent.Builder builder,
     @Test
     public void testToString() {
         // Throws an NPE in 2.6.2
-        assertNotNull(Log4jLogEvent.newBuilder().build().toString());
+        assertDoesNotThrow(() -> new Log4jLogEvent().toString());
     }
 }

log4j-core/src/main/java/org/apache/logging/log4j/core/LogEvent.java

@@ -19,9 +19,10 @@
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.Marker;
 import org.apache.logging.log4j.ThreadContext;
-import org.apache.logging.log4j.core.impl.MementoLogEvent;
+import org.apache.logging.log4j.core.impl.Log4jLogEvent;
 import org.apache.logging.log4j.core.time.Instant;
 import org.apache.logging.log4j.message.Message;
+import org.apache.logging.log4j.message.ReusableMessage;
 import org.apache.logging.log4j.util.ReadOnlyStringMap;
 import org.jspecify.annotations.Nullable;
 
@@ -40,6 +41,7 @@ public interface LogEvent {
      * Returns an immutable version of this log event, which MAY BE a copy of this event.
      *
      * @return an immutable version of this log event
+     * @since 2.8.1
      */
     LogEvent toImmutable();
 
@@ -48,9 +50,18 @@ public interface LogEvent {
      * <p>
      *     Location information for both events might be computed by this method.
      * </p>
+     * <p>
+     *   <strong>Warning:</strong> If {@code event.getMessage()} is an instance of {@link ReusableMessage}, this method
+     *   remove the parameter references from the original message. Callers should:
+     * </p>
+     * <ol>
+     *   <li>Either make sure that the {@code event} will not be used again.</li>
+     *   <li>Or call {@link LogEvent#toImmutable()} before calling this method.</li>
+     * </ol>
+     * @since 3.0.0
      */
     default LogEvent toMemento() {
-        return new MementoLogEvent(this);
+        return new Log4jLogEvent.Builder(this).build();
     }
 
     /**

log4j-core/src/main/java/org/apache/logging/log4j/core/ReusableLogEvent.java

@@ -19,7 +19,6 @@
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.Marker;
 import org.apache.logging.log4j.ThreadContext;
-import org.apache.logging.log4j.core.impl.Log4jLogEvent;
 import org.apache.logging.log4j.core.time.Instant;
 import org.apache.logging.log4j.message.Message;
 import org.apache.logging.log4j.util.StringMap;
@@ -62,10 +61,4 @@ public interface ReusableLogEvent extends LogEvent {
     void setThreadPriority(final int threadPriority);
 
     void setNanoTime(final long nanoTime);
-
-    /**
-     * Initializes the specified {@code Log4jLogEvent.Builder} from this {@code ReusableLogEvent}.
-     * @param builder the builder whose fields to populate
-     */
-    void initializeBuilder(final Log4jLogEvent.Builder builder);
 }

log4j-core/src/main/java/org/apache/logging/log4j/core/async/InternalAsyncUtil.java

@@ -22,6 +22,7 @@
 import org.apache.logging.log4j.core.util.Constants;
 import org.apache.logging.log4j.message.AsynchronouslyFormattable;
 import org.apache.logging.log4j.message.Message;
+import org.apache.logging.log4j.util.InternalApi;
 import org.apache.logging.log4j.util.StackLocatorUtil;
 import org.jspecify.annotations.Nullable;
 
@@ -31,13 +32,14 @@
  *     Consider this class private.
  * </p>
  */
+@InternalApi
 public final class InternalAsyncUtil {
 
     private InternalAsyncUtil() {}
 
     /**
      * Returns the specified message, with its content frozen unless system property
-     * {@code log4j.format.msg.async} is true or the message class is annotated with
+     * {@code log4j.async.formatMessagesInBackground} is true or the message class is annotated with
      * {@link AsynchronouslyFormattable}.
      *
      * @param msg the message object to inspect, modify and return