Fix XSD generator to respect required field attribute

modello-plugins/modello-plugin-xsd/src/main/java/org/codehaus/modello/plugin/xsd/XsdGenerator.java

@@ -87,6 +87,8 @@ private void generateXsd(Map<String, Object> parameters) throws IOException, Mod
 
         // we assume parameters not null
         String xsdFileName = (String) parameters.get(ModelloParameterConstants.OUTPUT_XSD_FILE_NAME);
+        // enforceMandatoryElements parameter is kept for backward compatibility but is no longer used.
+        // Required fields are now always enforced based on field.isRequired() value.
         boolean enforceMandatoryElements =
                 Boolean.parseBoolean((String) parameters.get(ModelloParameterConstants.XSD_ENFORCE_MANDATORY_ELEMENTS));
 
@@ -232,9 +234,7 @@ private void writeComplexTypeDescriptor(
                     }
                     w.startElement("xs:element");
 
-                    if (!enforceMandatoryElements || !field.isRequired()) {
-                        // Usually, would only do this if the field is not "required", but due to inheritance, it may be
-                        // present, even if not here, so we need to let it slide
+                    if (!field.isRequired()) {
                         w.addAttribute("minOccurs", "0");
                     }
                 }

modello-plugins/modello-plugin-xsd/src/test/java/org/codehaus/modello/plugin/xsd/RequiredFieldXsdGeneratorTest.java

@@ -0,0 +1,107 @@
+package org.codehaus.modello.plugin.xsd;
+
+/*
+ * Copyright (c) 2004, Codehaus.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is furnished to do
+ * so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+import javax.inject.Inject;
+import javax.xml.XMLConstants;
+import javax.xml.transform.stream.StreamSource;
+import javax.xml.validation.Schema;
+import javax.xml.validation.SchemaFactory;
+import javax.xml.validation.Validator;
+
+import java.io.File;
+import java.io.StringReader;
+import java.util.Map;
+
+import org.codehaus.modello.AbstractModelloGeneratorTest;
+import org.codehaus.modello.core.ModelloCore;
+import org.codehaus.modello.model.Model;
+import org.codehaus.plexus.testing.PlexusTest;
+import org.junit.jupiter.api.Test;
+import org.xml.sax.SAXParseException;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+/**
+ * Test that verifies required fields are properly enforced in generated XSD schemas
+ * without needing the XSD_ENFORCE_MANDATORY_ELEMENTS parameter.
+ *
+ * @author Modello Team
+ */
+@PlexusTest
+public class RequiredFieldXsdGeneratorTest extends AbstractModelloGeneratorTest {
+    @Inject
+    private ModelloCore modello;
+
+    public RequiredFieldXsdGeneratorTest() {
+        super("required-field");
+    }
+
+    @Test
+    public void testRequiredFieldsEnforcedWithoutParameter() throws Throwable {
+        Model model = modello.loadModel(getXmlResourceReader("/required-field.mdo"));
+
+        // Generate XSD WITHOUT the XSD_ENFORCE_MANDATORY_ELEMENTS parameter
+        Map<String, Object> parameters = getModelloParameters("1.0.0");
+        // Note: NOT setting XSD_ENFORCE_MANDATORY_ELEMENTS parameter
+
+        modello.generate(model, "xsd", parameters);
+
+        SchemaFactory sf = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
+        Schema schema = sf.newSchema(new StreamSource(new File(getOutputDirectory(), "test-1.0.0.xsd")));
+        Validator validator = schema.newValidator();
+
+        // Test 1: Valid XML with all required fields should pass
+        String validXml = "<?xml version=\"1.0\"?>\n"
+                + "<testModel xmlns=\"http://codehaus-plexus.github.io/TEST/1.0.0\">\n"
+                + "  <requiredField>value</requiredField>\n"
+                + "</testModel>";
+
+        validator.validate(new StreamSource(new StringReader(validXml)));
+
+        // Test 2: XML missing required field should fail
+        String missingRequiredXml = "<?xml version=\"1.0\"?>\n"
+                + "<testModel xmlns=\"http://codehaus-plexus.github.io/TEST/1.0.0\">\n"
+                + "  <optionalField>value</optionalField>\n"
+                + "</testModel>";
+
+        try {
+            validator.validate(new StreamSource(new StringReader(missingRequiredXml)));
+            fail("Validation should have failed for XML missing required field");
+        } catch (SAXParseException e) {
+            // Expected - the error should mention the required field
+            assertTrue(
+                    e.getMessage().contains("requiredField") || e.getMessage().contains("expected"),
+                    "Error message should indicate missing required field: " + e.getMessage());
+        }
+
+        // Test 3: XML with optional field omitted should pass
+        String withoutOptionalXml = "<?xml version=\"1.0\"?>\n"
+                + "<testModel xmlns=\"http://codehaus-plexus.github.io/TEST/1.0.0\">\n"
+                + "  <requiredField>value</requiredField>\n"
+                + "</testModel>";
+
+        validator.validate(new StreamSource(new StringReader(withoutOptionalXml)));
+    }
+}

modello-plugins/modello-plugin-xsd/src/test/resources/required-field.mdo

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<model xmlns="http://codehaus-plexus.github.io/MODELLO/2.0.0"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="http://codehaus-plexus.github.io/MODELLO/2.0.0 https://codehaus-plexus.github.io/modello/xsd/modello-2.0.0.xsd"
+       xml.namespace="http://codehaus-plexus.github.io/TEST/${version}"
+       xml.schemaLocation="http://codehaus-plexus.github.io/TEST/${version} http://codehaus-plexus.github.io/test-${version}.xsd">
+  <id>test</id>
+  <name>Test</name>
+  <description>
+    Simple test model for required field validation.
+  </description>
+  <defaults>
+    <default>
+      <key>package</key>
+      <value>org.codehaus.modello.test</value>
+    </default>
+  </defaults>
+  <classes>
+    <class rootElement="true">
+      <name>TestModel</name>
+      <version>1.0.0+</version>
+      <description>
+        A simple model to test required field enforcement.
+      </description>
+      <fields>
+        <field>
+          <name>requiredField</name>
+          <version>1.0.0+</version>
+          <required>true</required>
+          <type>String</type>
+          <description>This field is required and must be present.</description>
+        </field>
+        <field>
+          <name>optionalField</name>
+          <version>1.0.0+</version>
+          <type>String</type>
+          <description>This field is optional and may be omitted.</description>
+        </field>
+      </fields>
+    </class>
+  </classes>
+</model>

src/main/mdo/modello.mdo

@@ -672,7 +672,6 @@
         <field xml.insertParentFieldsUpTo="versionRange">
           <name>type</name>
           <version>1.0.0+</version>
-          <required>true</required>
           <type>String</type>
           <description><![CDATA[
             Simple type for this field (or array of such type). Can be one of : <code>boolean</code>, <code>byte</code>,