Add comments to warning suppressions and small fixes

Author: ppkarwasz

log4j-api/src/main/java/org/apache/logging/log4j/message/ReusableMessageFactory.java

@@ -30,6 +30,10 @@
  * @since 2.6
  */
 @PerformanceSensitive("allocation")
+/*
+ * https://errorprone.info/bugpattern/ThreadLocalUsage
+ * Instance thread locals are not a problem here, since this class is almost a singleton.
+ */
 @SuppressWarnings("ThreadLocalUsage")
 public final class ReusableMessageFactory implements MessageFactory2, Serializable {
 
@@ -127,43 +131,43 @@ public Message newMessage(final String message, final Object p0, final Object p1
 
     @Override
     public Message newMessage(final String message, final Object p0, final Object p1, final Object p2,
-            final Object p3) {
+                              final Object p3) {
         return getParameterized().set(message, p0, p1, p2, p3);
     }
 
     @Override
     public Message newMessage(final String message, final Object p0, final Object p1, final Object p2, final Object p3,
-            final Object p4) {
+                              final Object p4) {
         return getParameterized().set(message, p0, p1, p2, p3, p4);
     }
 
     @Override
     public Message newMessage(final String message, final Object p0, final Object p1, final Object p2, final Object p3,
-            final Object p4, final Object p5) {
+                              final Object p4, final Object p5) {
         return getParameterized().set(message, p0, p1, p2, p3, p4, p5);
     }
 
     @Override
     public Message newMessage(final String message, final Object p0, final Object p1, final Object p2, final Object p3,
-            final Object p4, final Object p5, final Object p6) {
+                              final Object p4, final Object p5, final Object p6) {
         return getParameterized().set(message, p0, p1, p2, p3, p4, p5, p6);
     }
 
     @Override
     public Message newMessage(final String message, final Object p0, final Object p1, final Object p2, final Object p3,
-            final Object p4, final Object p5, final Object p6, final Object p7) {
+                              final Object p4, final Object p5, final Object p6, final Object p7) {
         return getParameterized().set(message, p0, p1, p2, p3, p4, p5, p6, p7);
     }
 
     @Override
     public Message newMessage(final String message, final Object p0, final Object p1, final Object p2, final Object p3,
-            final Object p4, final Object p5, final Object p6, final Object p7, final Object p8) {
+                              final Object p4, final Object p5, final Object p6, final Object p7, final Object p8) {
         return getParameterized().set(message, p0, p1, p2, p3, p4, p5, p6, p7, p8);
     }
 
     @Override
     public Message newMessage(final String message, final Object p0, final Object p1, final Object p2, final Object p3,
-            final Object p4, final Object p5, final Object p6, final Object p7, final Object p8, final Object p9) {
+                              final Object p4, final Object p5, final Object p6, final Object p7, final Object p8, final Object p9) {
         return getParameterized().set(message, p0, p1, p2, p3, p4, p5, p6, p7, p8, p9);
     }
 

log4j-api/src/main/java/org/apache/logging/log4j/message/SimpleMessage.java

@@ -19,6 +19,7 @@
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
+import java.util.Objects;
 
 import org.apache.logging.log4j.util.StringBuilderFormattable;
 
@@ -100,7 +101,13 @@ public boolean equals(final Object o) {
 
         final SimpleMessage that = (SimpleMessage) o;
 
-        return !(charSequence != null ? !charSequence.equals(that.charSequence) : that.charSequence != null);
+        /*
+         * https://errorprone.info/bugpattern/UndefinedEquals
+         *
+         * If the char sequences are different, we fall back on string comparison.
+         */
+        return Objects.equals(this.charSequence, that.charSequence)
+                || Objects.equals(this.getFormattedMessage(), that.getFormattedMessage());
     }
 
     @Override

log4j-api/src/main/java/org/apache/logging/log4j/status/StatusData.java

@@ -144,6 +144,11 @@ public String getFormattedStatus() {
             sb.append(SPACE);
             final ByteArrayOutputStream baos = new ByteArrayOutputStream();
             t.printStackTrace(new PrintStream(baos));
+            /*
+             * https://errorprone.info/bugpattern/DefaultCharset
+             *
+             * Since Java 9 we'll be able to provide a charset.
+             */
             sb.append(baos.toString());
         }
         return sb.toString();

log4j-api/src/main/java/org/apache/logging/log4j/util/LowLevelLogUtil.java

@@ -32,6 +32,11 @@
  */
 final class LowLevelLogUtil {
 
+    /*
+     * https://errorprone.info/bugpattern/DefaultCharset
+     *
+     * We intentionally use the system encoding.
+     */
     @SuppressWarnings("DefaultCharset")
     private static PrintWriter writer = new PrintWriter(System.err, true);
 
@@ -69,6 +74,11 @@ public static void logException(final String message, final Throwable exception)
      */
     @SuppressWarnings("DefaultCharset")
     public static void setOutputStream(final OutputStream out) {
+        /*
+         * https://errorprone.info/bugpattern/DefaultCharset
+         *
+         * We intentionally use the system encoding.
+         */
         LowLevelLogUtil.writer = new PrintWriter(Objects.requireNonNull(out), true);
     }
 

log4j-api/src/main/java/org/apache/logging/log4j/util/PropertiesUtil.java

@@ -653,7 +653,10 @@ private enum TimeUnit {
         HOURS("h,hour,hours", ChronoUnit.HOURS),
         DAYS("d,day,days", ChronoUnit.DAYS);
 
-        // descriptions is effectively immutable
+        /*
+         * https://errorprone.info/bugpattern/ImmutableEnumChecker
+         * This field is effectively immutable.
+         */
         @SuppressWarnings("ImmutableEnumChecker")
         private final String[] descriptions;
         private final ChronoUnit timeUnit;

log4j-api/src/main/java/org/apache/logging/log4j/util/Unbox.java

@@ -62,6 +62,10 @@ public class Unbox {
      * Such memory leaks will not occur if only JDK classes are stored in ThreadLocals.
      * </p>
      */
+    /*
+     * https://errorprone.info/bugpattern/ThreadLocalUsage
+     * Instance thread locals are not a problem here, since this class is a singleton.
+     */
     @SuppressWarnings("ThreadLocalUsage")
     private static class WebSafeState {
         private final ThreadLocal<StringBuilder[]> ringBuffer = new ThreadLocal<>();

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

@@ -18,7 +18,6 @@
 
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.Logger;
-import org.apache.logging.log4j.core.util.Loader;
 import org.apache.logging.log4j.status.StatusLogger;
 import org.apache.logging.log4j.util.LoaderUtil;
 import org.apache.logging.log4j.util.PropertiesUtil;

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

@@ -23,7 +23,6 @@
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
 import org.apache.logging.log4j.core.config.plugins.validation.constraints.Required;
-import org.apache.logging.log4j.core.util.Loader;
 import org.apache.logging.log4j.status.StatusLogger;
 import org.apache.logging.log4j.util.LoaderUtil;
 

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

@@ -24,7 +24,6 @@
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.core.util.Constants;
 import org.apache.logging.log4j.core.util.Integers;
-import org.apache.logging.log4j.core.util.Loader;
 import org.apache.logging.log4j.status.StatusLogger;
 import org.apache.logging.log4j.util.LoaderUtil;
 import org.apache.logging.log4j.util.PropertiesUtil;

log4j-core/src/main/java/org/apache/logging/log4j/core/config/LoggerConfig.java

@@ -51,11 +51,9 @@
 import org.apache.logging.log4j.core.lookup.StrSubstitutor;
 import org.apache.logging.log4j.core.util.Booleans;
 import org.apache.logging.log4j.core.util.Constants;
-import org.apache.logging.log4j.core.util.Loader;
 import org.apache.logging.log4j.message.Message;
 import org.apache.logging.log4j.util.LoaderUtil;
 import org.apache.logging.log4j.util.PerformanceSensitive;
-import org.apache.logging.log4j.util.PropertiesUtil;
 import org.apache.logging.log4j.util.StackLocatorUtil;
 import org.apache.logging.log4j.util.Strings;