fix OnionArchitecture losing optionalLayers after as

The `OnionArchitecture.as(..)` method (and transitively `because(..)`) didn't pass the `optionalLayers` property along when creating a `new OnionArchitecture(..)` on return.
Thus, once a test called `as(..)` or `because(..)` on the rule text `optionalLayers` would be reset to `false`.

Signed-off-by: Peter Gafert <peter.gafert@archunit.org>

archunit/src/main/java/com/tngtech/archunit/library/Architectures.java

@@ -790,12 +790,14 @@ private OnionArchitecture(
                 Optional<DescribedPredicate<? super JavaClass>> domainServicePredicate,
                 Optional<DescribedPredicate<? super JavaClass>> applicationPredicate,
                 Map<String, DescribedPredicate<? super JavaClass>> adapterPredicates,
+                boolean optionalLayers,
                 List<IgnoredDependency> ignoredDependencies,
                 Optional<String> overriddenDescription) {
             this.domainModelPredicate = domainModelPredicate;
             this.domainServicePredicate = domainServicePredicate;
             this.applicationPredicate = applicationPredicate;
             this.adapterPredicates = adapterPredicates;
+            this.optionalLayers = optionalLayers;
             this.ignoredDependencies = ignoredDependencies;
             this.overriddenDescription = overriddenDescription;
         }
@@ -1036,8 +1038,8 @@ public void check(JavaClasses classes) {
         }
 
         @Override
-        public ArchRule because(String reason) {
-            return ArchRule.Factory.withBecause(this, reason);
+        public OnionArchitecture because(String reason) {
+            return (OnionArchitecture) Factory.withBecause(this, reason);
         }
 
         /**
@@ -1052,7 +1054,7 @@ public ArchRule allowEmptyShould(boolean allowEmptyShould) {
         @Override
         public OnionArchitecture as(String newDescription) {
             return new OnionArchitecture(domainModelPredicate, domainServicePredicate,
-                    applicationPredicate, adapterPredicates, ignoredDependencies,
+                    applicationPredicate, adapterPredicates, optionalLayers, ignoredDependencies,
                     Optional.of(newDescription));
         }
 

archunit/src/test/java/com/tngtech/archunit/library/OnionArchitectureTest.java

@@ -1,7 +1,10 @@
 package com.tngtech.archunit.library;
 
 import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Stream;
 
 import com.google.common.collect.ImmutableSet;
 import com.tngtech.archunit.core.domain.JavaClasses;
@@ -40,6 +43,7 @@
 import static com.tngtech.java.junit.dataprovider.DataProviders.testForEach;
 import static java.beans.Introspector.decapitalize;
 import static java.lang.System.lineSeparator;
+import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toSet;
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -178,9 +182,24 @@ public void onion_architecture_rejects_empty_layers_by_default() {
         assertFailureOnionArchitectureWithEmptyLayers(result);
     }
 
+    @DataProvider
+    public static List<Object> ruleTextModifications() {
+        return Stream.<Function<OnionArchitecture, OnionArchitecture>>of(
+                Function.identity(),
+                onionArchitecture -> onionArchitecture
+                        .as("Onion architecture consisting of (optional) changed"),
+                onionArchitecture -> onionArchitecture
+                        .because("changed"),
+                onionArchitecture -> onionArchitecture
+                        .as("Onion architecture consisting of (optional) changed")
+                        .because("changed")
+        ).collect(toList());
+    }
+
     @Test
-    public void onion_architecture_allows_empty_layers_if_all_layers_are_optional() {
-        OnionArchitecture architecture = anOnionArchitectureWithEmptyLayers().withOptionalLayers(true);
+    @UseDataProvider("ruleTextModifications")
+    public void onion_architecture_allows_empty_layers_if_all_layers_are_optional(Function<OnionArchitecture, OnionArchitecture> modifyRule) {
+        OnionArchitecture architecture = modifyRule.apply(anOnionArchitectureWithEmptyLayers().withOptionalLayers(true));
         assertThat(architecture.getDescription()).startsWith("Onion architecture consisting of (optional)");
 
         JavaClasses classes = new ClassFileImporter().importPackages(absolute("onionarchitecture"));