KAFKA-9825 Kafka protocol BNF format should have some way to display tagged fields (#20536)

# Description
The [protocol guide](https://kafka.apache.org/protocol) 1) doesn't
display
tagged fields in BNF, and 2) includes empty tagged fields and redundant
nested tables in tables.

# Change
## BNF
Now tagged fields are displayed as FIELD_NAME<tag number>

Old:  <img width="1316" height="275" alt="Screenshot 2025-09-13 at 5 34
28 PM"

src="https://github.com/user-attachments/assets/c3e59382-7a6b-43f3-bc7a-893fb27d524d"
/>

New:  <img width="1386" height="328" alt="Screenshot 2025-09-24 at 12 50
34 PM"

src="https://github.com/user-attachments/assets/1ddbc95e-b0a7-4cd5-a5e0-e1303ffd2d06"
/>

Array Field: <img width="914" height="275" alt="Screenshot 2025-09-24 at
12 52 19 PM"

src="https://github.com/user-attachments/assets/cfe66a21-0d66-4f23-8e5d-1d5dac8e4c9b"
/>

## Table
Empty tagged fields are removed from the table.

Nested table for tagged fie  Old: <img width="805" height="506"
alt="Screenshot 2025-09-28 at 11 07 01 PM"

src="https://github.com/user-attachments/assets/0669c2f3-150c-479d-b6ff-1d2857540fef"
/>  lds are removed. Tag of the field is shown in the "Field" column.

New:   <img width="1371" height="727" alt="Screenshot 2025-09-28 at 11
10 30 PM"

src="https://github.com/user-attachments/assets/030abde6-60ec-4195-9778-da48ebd01084"
/>

Reviewers: Andrew Schofield <[email protected]>

Author: jack2012aa

clients/src/main/java/org/apache/kafka/common/protocol/Protocol.java

@@ -19,6 +19,7 @@
 import org.apache.kafka.common.message.RequestHeaderData;
 import org.apache.kafka.common.message.ResponseHeaderData;
 import org.apache.kafka.common.protocol.types.BoundField;
+import org.apache.kafka.common.protocol.types.Field;
 import org.apache.kafka.common.protocol.types.Schema;
 import org.apache.kafka.common.protocol.types.TaggedFields;
 import org.apache.kafka.common.protocol.types.Type;
@@ -27,6 +28,7 @@
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
+import java.util.TreeMap;
 
 public class Protocol {
 
@@ -49,7 +51,23 @@ private static void schemaToBnfHtml(Schema schema, StringBuilder b, int indentSi
                     subTypes.put(field.def.name, type.arrayElementType().get());
                 }
             } else if (type instanceof TaggedFields) {
-                b.append("_tagged_fields ");
+                Map<Integer, Field> taggedFields = new TreeMap<>(((TaggedFields) type).fields());
+                taggedFields.forEach((tag, taggedField) -> {
+                    if (taggedField.type.isArray()) {
+                        b.append("[");
+                        b.append(taggedField.name);
+                        b.append("]");
+                        if (!subTypes.containsKey(taggedField.name))
+                            subTypes.put(taggedField.name + "&lt;tag: " + tag.toString() + "&gt;", taggedField.type.arrayElementType().get());
+                    } else {
+                        b.append(taggedField.name);
+                        if (!subTypes.containsKey(taggedField.name))
+                            subTypes.put(taggedField.name + "&lt;tag: " + tag.toString() + "&gt;", taggedField.type);
+                    }
+                    b.append("&lt;tag: ");
+                    b.append(tag);
+                    b.append("&gt; ");
+                });
             } else {
                 b.append(field.def.name);
                 b.append(" ");
@@ -90,6 +108,12 @@ private static void populateSchemaFields(Schema schema, Set<BoundField> fields)
         }
     }
 
+    private static void appendFieldNameToTable(String name, StringBuilder b) {
+        b.append("<td>");
+        b.append(name);
+        b.append("</td>");
+    }
+
     private static void schemaToFieldTableHtml(Schema schema, StringBuilder b) {
         Set<BoundField> fields = new LinkedHashSet<>();
         populateSchemaFields(schema, fields);
@@ -101,28 +125,12 @@ private static void schemaToFieldTableHtml(Schema schema, StringBuilder b) {
         b.append("</tr>");
         for (BoundField field : fields) {
             b.append("<tr>\n");
-            b.append("<td>");
-            b.append(field.def.name);
-            b.append("</td>");
-            b.append("<td>");
             if (field.def.type instanceof TaggedFields) {
                 TaggedFields taggedFields = (TaggedFields) field.def.type;
                 // Only include the field in the table if there are actually tags defined
                 if (taggedFields.numFields() > 0) {
-                    b.append("<table class=\"data-table\"><tbody>\n");
-                    b.append("<tr>");
-                    b.append("<th>Tag</th>\n");
-                    b.append("<th>Tagged field</th>\n");
-                    b.append("<th>Description</th>\n");
-                    b.append("</tr>");
                     taggedFields.fields().forEach((tag, taggedField) -> {
-                        b.append("<tr>\n");
-                        b.append("<td>");
-                        b.append(tag);
-                        b.append("</td>");
-                        b.append("<td>");
-                        b.append(taggedField.name);
-                        b.append("</td>");
+                        appendFieldNameToTable(taggedField.name + "&lt;tag: " + tag.toString() + "&gt;", b);
                         b.append("<td>");
                         b.append(taggedField.docString);
                         if (taggedField.type.isArray()) {
@@ -136,11 +144,10 @@ private static void schemaToFieldTableHtml(Schema schema, StringBuilder b) {
                         b.append("</td>");
                         b.append("</tr>\n");
                     });
-                    b.append("</tbody></table>\n");
-                } else {
-                    b.append(field.def.docString);
                 }
             } else {
+                appendFieldNameToTable(field.def.name, b);
+                b.append("<td>");
                 b.append(field.def.docString);
             }
             b.append("</td>");