Enforce HiddenGroupRef not being model group of Complex Type

daffodil-core/src/main/scala/org/apache/daffodil/core/dsom/ModelGroup.scala

@@ -189,6 +189,7 @@ object ModelGroupFactory {
     // a SequenceGroupRef or ChoiceGroupRef, with isHidden = true. So this
     // temporary sequence will be discarded after this.
     seq.checkHiddenGroupRefHasNoChildren
+    seq.checkHiddenGroupRefNotChildOfComplexType
     //
     // construct the group ref XML, then recursively process that,
     // but set flag so it will be hidden.

daffodil-core/src/main/scala/org/apache/daffodil/core/dsom/SequenceGroup.scala

@@ -285,6 +285,17 @@ trait SequenceDefMixin
     }
   }
 
+  lazy val checkHiddenGroupRefNotChildOfComplexType: Unit = {
+    if (hiddenGroupRefOption.isDefined) {
+      optLexicalParent.collect { case _: ComplexTypeBase =>
+        schemaDefinitionError(
+          "A complex type cannot have a sequence with a hiddenGroupRef as its model group. " +
+            "Wrap the hiddenGroupRef sequence in an empty sequence instead."
+        )
+      }
+    }
+  }
+
   final lazy val hiddenGroupRefXML = LV('hiddenGroupRefXML) {
     val Found(qname, _, _, _) = hiddenGroupRefOption
     // synthesize a group reference here.

daffodil-core/src/test/scala/org/apache/daffodil/core/dsom/TestRefMap.scala

@@ -163,7 +163,9 @@ class TestRefMap {
         </xs:group>
           <xs:element name="r1" type="ex:ct1"/>
         <xs:complexType name="ct1">
-          <xs:sequence dfdl:hiddenGroupRef="ex:g1"/>
+          <xs:sequence>
+            <xs:sequence dfdl:hiddenGroupRef="ex:g1"/>
+          </xs:sequence>
         </xs:complexType>
         <xs:group name="g1">
           <xs:choice>
@@ -176,7 +178,7 @@ class TestRefMap {
     val sset = compiler.compileNode(testSchema).sset
     val root = sset.root
     val comps = root.allComponents
-    assertEquals(14, comps.length)
+    assertEquals(15, comps.length)
     val refMap = root.refMap
     val numEntries = refMap.size
     assertEquals(6, numEntries)
@@ -189,8 +191,8 @@ class TestRefMap {
     val gref = rootDecl.complexType.modelGroup.asInstanceOf[ChoiceGroupRef]
     val Seq((grefSSCD, gdRefSpecs)) = refMap.get(gref.groupDef).get
     assertEquals(gref.shortSchemaComponentDesignator, grefSSCD)
-    assertEquals(14, root.numComponents)
-    assertEquals(14, root.numUniqueComponents)
+    assertEquals(15, root.numComponents)
+    assertEquals(15, root.numUniqueComponents)
   }
 
   @Test def testRefMapNonExplosion1(): Unit = {

daffodil-test/src/test/resources/org/apache/daffodil/section14/sequence_groups/HiddenSequences.tdml

@@ -282,4 +282,32 @@
     </tdml:errors>
   </tdml:unparserTestCase>
 
+  <tdml:defineSchema name="ComplexTypeWithHiddenGroupRefSequence">
+    <xs:include
+        schemaLocation="/org/apache/daffodil/xsd/DFDLGeneralFormat.dfdl.xsd" />
+    <dfdl:format ref="ex:GeneralFormat" lengthKind="delimited" />
+
+    <xs:group name="s4">
+      <xs:sequence>
+        <xs:element name="f" type="xs:int" dfdl:outputValueCalc="{6}"/>
+      </xs:sequence>
+    </xs:group>
+    <xs:element name="e1">
+      <xs:complexType>
+        <xs:sequence dfdl:hiddenGroupRef="ex:s4"/>
+      </xs:complexType>
+    </xs:element>
+  </tdml:defineSchema>
+
+  <tdml:parserTestCase name="ComplexTypeWithHiddenGroupRefSequence1" root="e1"
+      model="ComplexTypeWithHiddenGroupRefSequence">
+    <tdml:document>7</tdml:document>
+    <tdml:errors>
+      <tdml:error>Schema Definition Error</tdml:error>
+      <tdml:error>complex type cannot have</tdml:error>
+      <tdml:error>sequence with a hiddenGroupRef</tdml:error>
+      <tdml:error>model group</tdml:error>
+    </tdml:errors>
+  </tdml:parserTestCase>
 </tdml:testSuite>
+

daffodil-test/src/test/resources/org/apache/daffodil/section14/sequence_groups/SequencesWithHiddenRefs.dfdl.xsd

@@ -82,7 +82,9 @@
           <xs:sequence>
             <xs:element name="h">
               <xs:complexType>
-                <xs:sequence dfdl:hiddenGroupRef="ex:s1" />
+                <xs:sequence>
+                  <xs:sequence dfdl:hiddenGroupRef="ex:s1" />
+                </xs:sequence>
               </xs:complexType>
             </xs:element>
           </xs:sequence>

daffodil-test/src/test/resources/org/apache/daffodil/section15/choice_groups/ChoicesInHiddenContexts.dfdl.xsd

@@ -106,7 +106,9 @@
               dfdl:outputValueCalc="{ 1 }" />
             <xs:element name="h">
               <xs:complexType>
-                <xs:sequence dfdl:hiddenGroupRef="ex:c1" />
+                <xs:sequence>
+                  <xs:sequence dfdl:hiddenGroupRef="ex:c1" />
+                </xs:sequence>
               </xs:complexType>
             </xs:element>
           </xs:choice>
@@ -119,7 +121,9 @@
               dfdl:outputValueCalc="{ 'hello' }" />
             <xs:element name="h">
               <xs:complexType>
-                <xs:sequence dfdl:hiddenGroupRef="ex:c1" />
+                <xs:sequence>
+                  <xs:sequence dfdl:hiddenGroupRef="ex:c1" />
+                </xs:sequence>
               </xs:complexType>
             </xs:element>
           </xs:choice>
@@ -160,7 +164,9 @@
             <xs:sequence>
               <xs:element name="g">
                 <xs:complexType>
-                  <xs:sequence dfdl:hiddenGroupRef="ex:c3" />
+                  <xs:sequence>
+                    <xs:sequence dfdl:hiddenGroupRef="ex:c3" />
+                  </xs:sequence>
                 </xs:complexType>
               </xs:element>
             </xs:sequence>
@@ -178,7 +184,9 @@
             <xs:sequence>
               <xs:element name="g">
                 <xs:complexType>
-                  <xs:sequence dfdl:hiddenGroupRef="ex:c1" />
+                  <xs:sequence>
+                    <xs:sequence dfdl:hiddenGroupRef="ex:c1" />
+                  </xs:sequence>
                 </xs:complexType>
               </xs:element>
             </xs:sequence>

daffodil-test/src/test/resources/org/apache/daffodil/section23/dfdl_functions/Functions.tdml

@@ -4919,7 +4919,9 @@
                   <xs:element name="name" type="xs:string" dfdl:lengthKind="delimited"/>
                   <xs:element name="data">
                     <xs:complexType>
-                      <xs:sequence dfdl:hiddenGroupRef="ex:hiddenData"/>
+                      <xs:sequence>
+                        <xs:sequence dfdl:hiddenGroupRef="ex:hiddenData"/>
+                      </xs:sequence>
                     </xs:complexType>
                   </xs:element>
                 </xs:sequence>

daffodil-test/src/test/scala/org/apache/daffodil/section14/sequence_groups/TestHiddenSequences.scala

@@ -78,4 +78,8 @@ class TestHiddenSequences {
   @Test def test_invalidGroupDefWithHiddenSequenceModelGroup(): Unit = {
     runnerNoValidate.runOneTest("invalidGroupDefWithHiddenSequenceModelGroup")
   }
+
+  @Test def test_ComplexTypeWithHiddenGroupRefSequence1(): Unit = {
+    runnerNoValidate.runOneTest("ComplexTypeWithHiddenGroupRefSequence1")
+  }
 }