Handle empty tags with value child of list types correctly.

Changelog.md

@@ -17,6 +17,7 @@ Fixes:
 - Fix handling of empty `@XmlValue` members of string-like type. Also
   collapse whitespace when parsing non-string primitives (per xml
   schema). Strings never ignore whitespace.
+- Fix handling `XmlValue` members of collection type inside an empty tag.
 - Fix parsing of `XmlDefault` attributes if the (effective) type is an
   attribute and it is parsed using as serializable value (rather than)
   directly as primitive.

serialization/src/commonMain/kotlin/nl/adaptivity/xmlutil/serialization/XMLDecoder.kt

@@ -1014,9 +1014,13 @@ internal open class XmlDecoderBase internal constructor(
             // Handle the case of an empty tag for a value child. This is not a nullable item (so shouldn't be
             // treated as such).
             if (valueChild >= 0 && input.peek() is XmlEvent.EndElementEvent && !seenItems[valueChild]) {
-                // This code can rely on seenItems to avoid infinite item loops as it only triggers on an empty tag.
-                seenItems[valueChild] = true
-                return valueChild
+                val valueChildDesc = xmlDescriptor.getElementDescriptor(valueChild)
+                // Lists/maps need to be empty (treated as null/missing)
+                if (valueChildDesc.kind !is StructureKind.LIST && valueChildDesc.kind !is StructureKind.MAP) {
+                    // This code can rely on seenItems to avoid infinite item loops as it only triggers on an empty tag.
+                    seenItems[valueChild] = true
+                    return valueChild
+                }
             }
             for (eventType in input) {
                 when (eventType) {

serialization/src/commonTest/kotlin/nl/adaptivity/xml/serialization/regressions/EmptyTagWithValueChild.kt

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2024.
+ *
+ * This file is part of xmlutil.
+ *
+ * This file is licenced to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You should have received a copy of the license with the source distribution.
+ * Alternatively, you may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package nl.adaptivity.xml.serialization.regressions
+
+import io.github.pdvrieze.xmlutil.testutil.assertXmlEquals
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import nl.adaptivity.xmlutil.serialization.XML
+import nl.adaptivity.xmlutil.serialization.XmlValue
+import nl.adaptivity.xmlutil.util.CompactFragment
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class EmptyTagWithValueChild {
+
+    @Test
+    fun testSerializeStr() {
+        val actual = XML.encodeToString(OuterStr(InnerStr("")))
+        assertXmlEquals("<Outer><Inner /></Outer>", actual)
+    }
+
+
+    @Test
+    fun testSerializeCF() {
+        val actual = XML.encodeToString(OuterFrag(InnerFrag(emptyList())))
+        assertXmlEquals("<Outer><Inner /></Outer>", actual)
+    }
+
+    @Test
+    fun testDeserializeCF() {
+        val expected = OuterFrag(InnerFrag(emptyList()))
+        val actual = XML.decodeFromString<OuterFrag>("<Outer><Inner /></Outer>")
+        assertEquals(expected, actual)
+    }
+
+    @Test
+    fun testDeserializeStr() {
+        val expected = OuterStr(InnerStr(""))
+        val actual = XML.decodeFromString<OuterStr>("<Outer><Inner /></Outer>")
+        assertEquals(expected, actual)
+    }
+
+
+    @Serializable
+    @SerialName("Outer")
+    private data class OuterStr(val inner: InnerStr)
+
+    @Serializable
+    @SerialName("Inner")
+    private data class InnerStr(@XmlValue val value: String)
+
+    @Serializable
+    @SerialName("Outer")
+    private data class OuterFrag(val inner: InnerFrag)
+
+    @Serializable
+    @SerialName("Inner")
+    private data class InnerFrag(@XmlValue val values: List<CompactFragment>)
+}