Fix username duplication in chat when defaultRenderer is explicitly set

paper-api/src/main/java/io/papermc/paper/chat/ChatRenderer.java

@@ -26,12 +26,12 @@ public interface ChatRenderer {
     Component render(Player source, Component sourceDisplayName, Component message, Audience viewer);
 
     /**
-     * Create a new instance of the default {@link ChatRenderer}.
+     * Gets the default {@link ChatRenderer}.
      *
-     * @return a new {@link ChatRenderer}
+     * @return the default {@link ChatRenderer}
      */
     static ChatRenderer defaultRenderer() {
-        return new ViewerUnawareImpl.Default((source, sourceDisplayName, message) -> Component.translatable("chat.type.text", sourceDisplayName, message));
+        return ViewerUnawareImpl.Default.INSTANCE;
     }
 
     @ApiStatus.Internal

paper-api/src/main/java/io/papermc/paper/chat/ViewerUnawareImpl.java

@@ -5,13 +5,11 @@
 import org.bukkit.entity.Player;
 import org.jetbrains.annotations.ApiStatus;
 import org.jspecify.annotations.NullMarked;
-import org.jspecify.annotations.Nullable;
 
 @ApiStatus.Internal
 @NullMarked
 sealed class ViewerUnawareImpl implements ChatRenderer, ChatRenderer.ViewerUnaware permits ViewerUnawareImpl.Default {
     private final ViewerUnaware unaware;
-    private @Nullable Component message;
 
     ViewerUnawareImpl(final ViewerUnaware unaware) {
         this.unaware = unaware;
@@ -24,13 +22,12 @@ public Component render(final Player source, final Component sourceDisplayName,
 
     @Override
     public Component render(final Player source, final Component sourceDisplayName, final Component message) {
-        if (this.message == null) {
-            this.message = this.unaware.render(source, sourceDisplayName, message);
-        }
-        return this.message;
+        return this.unaware.render(source, sourceDisplayName, message);
     }
 
     static final class Default extends ViewerUnawareImpl implements ChatRenderer.Default {
+        static final ViewerUnawareImpl.Default INSTANCE = new ViewerUnawareImpl.Default((source, sourceDisplayName, message) -> Component.translatable("chat.type.text", sourceDisplayName, message));
+
         Default(final ViewerUnaware unaware) {
             super(unaware);
         }

paper-server/src/main/java/io/papermc/paper/adventure/ChatProcessor.java

@@ -170,7 +170,7 @@ protected Void evaluate() {
 
     private void readModernModifications(final AbstractChatEvent chatEvent, final ChatRenderer originalRenderer) {
         this.flags.set(MESSAGE_CHANGED, !chatEvent.message().equals(this.paper$originalMessage));
-        if (originalRenderer != chatEvent.renderer()) { // don't set to false if it hasn't changed
+        if (originalRenderer != chatEvent.renderer()) { // don't set to true if it hasn't changed
             this.flags.set(FORMAT_CHANGED, true);
         }
     }