Revert "check valid usage depending on interface/class"

This reverts commit f2521d8.

The check would break code that scans all the features, e.g.,
org.eclipse.xtext.findReferences.ReferenceFinder.findLocalReferencesFromElement(Predicate<URI>,
EObject, Resource, Acceptor)

org.eclipse.xtext.common.types.tests/tests/org/eclipse/xtext/common/types/JvmGenericTypeTest.java

@@ -210,7 +210,6 @@ public JvmType apply(JvmTypeReference from) {
 	}
 
 	@Test public void testUpdateInterfacesToExtendUpdatesSuperTypes() {
-		genericType.setInterface(true);
 		JvmTypeReference interface1 = createTypeReference();
 		JvmTypeReference interface2 = createTypeReference();
 		genericType.getInterfacesToExtend().addAll(List.of(interface1, interface2));
@@ -228,7 +227,6 @@ public JvmType apply(JvmTypeReference from) {
 	}
 
 	@Test public void testUpdateSuperTypesUpdatesInterfacesToExtend() {
-		genericType.setInterface(true);
 		JvmTypeReference interface1 = createTypeReference();
 		JvmTypeReference interface2 = createTypeReference();
 		JvmTypeReference anotherType = createTypeReference();
@@ -250,26 +248,6 @@ public JvmType apply(JvmTypeReference from) {
 		assertEquals(0, genericType.getInterfacesToExtend().size());
 	}
 
-	@Test public void testWrongUsageInClass() {
-		IllegalStateException thrown = assertThrows(IllegalStateException.class, () ->
-			genericType.getInterfacesToExtend());
-		assertEquals("interfacesToExtend can only be used in interfaces", thrown.getMessage());
-	}
-
-	@Test public void testWrongUsageInInterface() {
-		genericType.setInterface(true);
-		var expectedMessage = "classToExtend/interfacesToImplement can only be used in classes";
-		var thrown = assertThrows(IllegalStateException.class, () ->
-			genericType.getClassToExtend());
-		assertEquals(expectedMessage, thrown.getMessage());
-		thrown = assertThrows(IllegalStateException.class, () ->
-			genericType.setClassToExtend(null));
-		assertEquals(expectedMessage, thrown.getMessage());
-		thrown = assertThrows(IllegalStateException.class, () ->
-			genericType.getInterfacesToImplement());
-		assertEquals(expectedMessage, thrown.getMessage());
-	}
-
 	private JvmTypeReference createTypeReference() {
 		return createReferenceTo(
 				TypesFactory.eINSTANCE.createJvmGenericType());

org.eclipse.xtext.common.types/src/org/eclipse/xtext/common/types/impl/JvmGenericTypeImplCustom.java

@@ -69,7 +69,6 @@ public boolean isAnonymous() {
 	@Override
 	public void setClassToExtend(JvmTypeReference newClassToExtend) {
 		checkPendingInitialization();
-		checkValidUsage(false);
 		JvmTypeReference oldClassToExtend = classToExtend;
 		super.setClassToExtend(newClassToExtend);
 		super.getSuperTypes().remove(oldClassToExtend);
@@ -81,7 +80,6 @@ public void setClassToExtend(JvmTypeReference newClassToExtend) {
 	@Override
 	public JvmTypeReference getClassToExtend() {
 		checkPendingInitialization();
-		checkValidUsage(false);
 		if (!super.getSuperTypes().contains(classToExtend)) {
 			// some one else removed it via superTypes API
 			super.setClassToExtend(null);
@@ -121,7 +119,6 @@ public EList<JvmTypeReference> getSuperTypes() {
 	@Override
 	public EList<JvmTypeReference> getInterfacesToImplement() {
 		checkPendingInitialization();
-		checkValidUsage(false);
 		var origInterfacesToImplement = super.getInterfacesToImplement();
 		var origSuperTypes = super.getSuperTypes();
 		if (!superTypesSnapshot.equals(origSuperTypes)) {
@@ -138,7 +135,6 @@ public EList<JvmTypeReference> getInterfacesToImplement() {
 	@Override
 	public EList<JvmTypeReference> getInterfacesToExtend() {
 		checkPendingInitialization();
-		checkValidUsage(true);
 		var origInterfacesToExtend = super.getInterfacesToExtend();
 		var origSuperTypes = super.getSuperTypes();
 		if (!superTypesSnapshot.equals(origSuperTypes)) {
@@ -152,14 +148,6 @@ public EList<JvmTypeReference> getInterfacesToExtend() {
 		return origInterfacesToExtend;
 	}
 
-	private void checkValidUsage(boolean expectInterface) {
-		var interf = isInterface();
-		if (expectInterface && !interf)
-			throw new IllegalStateException("interfacesToExtend can only be used in interfaces");
-		if (!expectInterface && interf)
-			throw new IllegalStateException("classToExtend/interfacesToImplement can only be used in classes");
-	}
-
 	private List<JvmTypeReference> createSnapshot(EList<JvmTypeReference> origList) {
 		return new ArrayList<>(origList);
 	}