Fix trailing comma in properties call for empty subtypes (#412)

* Fix trailing comma in properties call for empty subtypes

Fixes code generation bug where adapters for sealed interfaces with empty
subtypes generated invalid Java syntax: jsonb.properties("@type", )

- Refactor property name handling to use LinkedHashSet to avoid duplicates
- Convert to stream-based approach for cleaner code
- Add test case for empty sealed interface subtypes

Fixes #410

Author: joaonmatos

blackbox-test/src/main/java/org/example/customer/subtype/Dessendre.java

@@ -0,0 +1,19 @@
+package org.example.customer.subtype;
+
+import org.example.customer.subtype.Dessendre.Alicia;
+import org.example.customer.subtype.Dessendre.Curator;
+import org.example.customer.subtype.Dessendre.Paintress;
+
+import io.avaje.jsonb.Json.SubType;
+
+@io.avaje.jsonb.Json
+@SubType(type = Alicia.class, name = "Maelle")
+@SubType(type = Paintress.class, name = "Aline")
+@SubType(type = Curator.class, name = "Renoir")
+public sealed interface Dessendre {
+  public record Alicia() implements Dessendre {}
+
+  public record Paintress() implements Dessendre {}
+
+  public record Curator() implements Dessendre {}
+}

blackbox-test/src/main/java/org/example/customer/subtype/EmptySupertype.java

@@ -0,0 +1,11 @@
+package org.example.customer.subtype;
+
+import io.avaje.jsonb.Json;
+
+@Json
+@Json.SubType(type = EmptySupertype.SubtypeA.class, name = "a")
+@Json.SubType(type = EmptySupertype.SubtypeB.class, name = "b")
+public sealed interface EmptySupertype {
+  record SubtypeA() implements EmptySupertype {}
+  record SubtypeB() implements EmptySupertype {}
+}

blackbox-test/src/test/java/org/example/customer/subtype/EmptySupertypeTest.java

@@ -0,0 +1,62 @@
+package org.example.customer.subtype;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+import io.avaje.json.JsonAdapter;
+import io.avaje.jsonb.JsonType;
+import io.avaje.jsonb.Jsonb;
+
+class EmptySupertypeTest {
+  Jsonb jsonb = Jsonb.builder().build();
+  JsonAdapter<EmptySupertype> adapter = jsonb.adapter(EmptySupertype.class);
+  JsonType<EmptySupertype> type = jsonb.type(EmptySupertype.class);
+
+  @Test
+  void nullObject() {
+    var object = (EmptySupertype) null;
+    var expected = "";
+    var actual = type.toJson(object);
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  void objectA() {
+    var object = new EmptySupertype.SubtypeA();
+    var expected = "{\"@type\":\"a\"}";
+    var actual = type.toJson(object);
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  void jsonA() {
+    var json = "{\"@type\":\"a\"}";
+    var expected = new EmptySupertype.SubtypeA();
+    var actual = type.fromJson(json);
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  void objectB() {
+    var object = new EmptySupertype.SubtypeB();
+    var expected = "{\"@type\":\"b\"}";
+    var actual = type.toJson(object);
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  void jsonB() {
+    var json = "{\"@type\":\"b\"}";
+    var expected = new EmptySupertype.SubtypeB();
+    var actual = type.fromJson(json);
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  void invalidJsonC() {
+    var json = "{\"@type\":\"c\"}";
+    assertThrows(IllegalStateException.class, () -> type.fromJson(json));
+  }
+}

jsonb-generator/src/main/java/io/avaje/jsonb/generator/ClassReader.java

@@ -7,6 +7,7 @@
 
 import java.lang.reflect.InvocationTargetException;
 import java.util.*;
+import java.util.stream.Collectors;
 
 import javax.lang.model.element.Element;
 import javax.lang.model.element.ElementKind;
@@ -291,47 +292,32 @@ public void writeConstructor(Append writer) {
       }
     }
     writer.append("    this.names = jsonb.properties(");
+    var properties = new LinkedHashSet<String>();
     if (hasSubTypes) {
-      writer.append("\"").append(typeProperty).append("\", ");
+      properties.add('"' + typeProperty + '"');
     }
-    writer.append(propertyNames());
+    properties.addAll(propertyNames());
+    writer.append(String.join(", ", properties));
     writer.append(");").eol();
   }
 
-  private String propertyNames() {
+  private List<String> propertyNames() {
     return readOnlyInterface ? propertyNamesReadOnly() : propertyNamesFields();
   }
 
-  private String propertyNamesFields() {
-    final StringBuilder builder = new StringBuilder();
-    //set to prevent writing same key twice
-    final var seen = new HashSet<String>();
-    for (int i = 0, size = allFields.size(); i < size; i++) {
-      final FieldReader fieldReader = allFields.get(i);
-      if (!seen.add(fieldReader.propertyName())) {
-        continue;
-      }
-      if (i > 0) {
-        builder.append(", ");
-      }
-      if (usesTypeProperty && fieldReader.propertyName().equals(typePropertyKey())) {
-        builder.append(" ");
-        continue;
-      }
-      builder.append("\"").append(fieldReader.propertyName()).append("\"");
-    }
-    return builder.toString().replace(" , ", "");
+  private List<String> propertyNamesFields() {
+    return allFields.stream()
+      .map(FieldReader::propertyName)
+      .map(property -> '"' + property + '"')
+      .filter(property -> !usesTypeProperty || !property.equals(typePropertyKey()))
+      .collect(toList());
   }
 
-  private String propertyNamesReadOnly() {
-    final StringBuilder builder = new StringBuilder();
-    for (int i = 0; i < methodProperties.size(); i++) {
-      if (i > 0) {
-        builder.append(", ");
-      }
-      builder.append("\"").append(methodProperties.get(i).propertyName()).append("\"");
-    }
-    return builder.toString().replace(" , ", "");
+  private List<String> propertyNamesReadOnly() {
+    return methodProperties.stream()
+      .map(MethodProperty::propertyName)
+      .map(property -> '"' + property + '"')
+      .collect(toList());
   }
 
   @Override