Remove service renames after flattenNamespaces

flattenNamespaces applies all service renames to disambiguate shapes
that could be in conflict after flattening. But when consumers try to
reload the transformed model, they get an error like:
```
"Service rename for `foo` does not actually change the name from `bar`"
```
because the rename has already been applied. This commit changes
FlattenTransformer to also update the service shape by removing all renames,
so consumers of a flattened model don't run into validation issues.

smithy-build/src/main/java/software/amazon/smithy/build/transforms/FlattenNamespaces.java

@@ -28,8 +28,8 @@
 import software.amazon.smithy.model.shapes.ServiceShape;
 import software.amazon.smithy.model.shapes.Shape;
 import software.amazon.smithy.model.shapes.ShapeId;
-import software.amazon.smithy.model.transform.ModelTransformer;
 import software.amazon.smithy.utils.FunctionalUtils;
+import software.amazon.smithy.utils.ListUtils;
 import software.amazon.smithy.utils.Pair;
 
 /**
@@ -120,9 +120,23 @@ protected Model transformWithConfig(TransformContext context, Config config) {
             throw new SmithyBuildException(
                     "'namespace' and 'service' properties must be set on flattenNamespace transformer.");
         }
+
         Model model = context.getModel();
+        if (!model.getShape(config.getService()).isPresent()) {
+            throw new SmithyBuildException("Configured service, " + config.getService()
+                    + ", not found in model when performing flattenNamespaces transform.");
+        }
+
         Map<ShapeId, ShapeId> shapesToRename = getRenamedShapes(config, model);
-        return ModelTransformer.create().renameShapes(model, shapesToRename);
+        model = context.getTransformer().renameShapes(model, shapesToRename);
+
+        // Remove service renames since they've now been applied, so consumers don't fail service shape validation
+        ShapeId updatedServiceId = shapesToRename.get(config.getService());
+        ServiceShape updatedService = model.expectShape(updatedServiceId, ServiceShape.class)
+                .toBuilder()
+                .clearRename()
+                .build();
+        return context.getTransformer().replaceShapes(model, ListUtils.of(updatedService));
     }
 
     @Override
@@ -131,11 +145,6 @@ public String getName() {
     }
 
     private Map<ShapeId, ShapeId> getRenamedShapes(Config config, Model model) {
-        if (!model.getShape(config.getService()).isPresent()) {
-            throw new SmithyBuildException("Configured service, " + config.getService()
-                    + ", not found in model when performing flattenNamespaces transform.");
-        }
-
         Map<ShapeId, ShapeId> shapesToRename = getRenamedShapesConnectedToService(config, model);
         Set<ShapeId> taggedShapesToInclude = getTaggedShapesToInclude(config.getIncludeTagged(), model);
 

smithy-build/src/test/java/software/amazon/smithy/build/transforms/FlattenNamespacesTest.java

@@ -16,11 +16,13 @@
 package software.amazon.smithy.build.transforms;
 
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.anEmptyMap;
 import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.not;
 
 import java.nio.file.Paths;
 import java.util.List;
+import java.util.Optional;
 import java.util.stream.Collectors;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
@@ -31,7 +33,11 @@
 import software.amazon.smithy.model.node.ExpectationNotMetException;
 import software.amazon.smithy.model.node.Node;
 import software.amazon.smithy.model.node.ObjectNode;
+import software.amazon.smithy.model.shapes.ServiceShape;
 import software.amazon.smithy.model.shapes.Shape;
+import software.amazon.smithy.model.shapes.ShapeId;
+import software.amazon.smithy.model.validation.ValidatedResult;
+import software.amazon.smithy.model.validation.ValidationEvent;
 import software.amazon.smithy.utils.FunctionalUtils;
 
 public class FlattenNamespacesTest {
@@ -143,6 +149,48 @@ public void supportsRenamesOnService() throws Exception {
                 "ns.bar#Widget", "foo.example#Widget")));
     }
 
+    @Test
+    public void removesServiceRenames() {
+        Model model = Model.assembler()
+                .addImport(getClass().getResource("flatten-namespaces-with-renames.json"))
+                .assemble()
+                .unwrap();
+        TransformContext context = TransformContext.builder()
+                .model(model)
+                .settings(Node.objectNode()
+                        .withMember("namespace", "ns.qux")
+                        .withMember("service", "ns.foo#MyService"))
+                .build();
+        Model result = new FlattenNamespaces().transform(context);
+        ShapeId transformedServiceId = ShapeId.from("ns.qux#MyService");
+        assertThat(result.getShape(transformedServiceId), not(Optional.empty()));
+        assertThat(result.expectShape(transformedServiceId, ServiceShape.class).getRename(), anEmptyMap());
+    }
+
+    @Test
+    public void serviceShapeIsValidAfterTransform() {
+        Model model = Model.assembler()
+                .addImport(getClass().getResource("flatten-namespaces-with-renames.json"))
+                .assemble()
+                .unwrap();
+        TransformContext context = TransformContext.builder()
+                .model(model)
+                .settings(Node.objectNode()
+                        .withMember("namespace", "ns.qux")
+                        .withMember("service", "ns.foo#MyService"))
+                .build();
+        Model result = new FlattenNamespaces().transform(context);
+        ValidatedResult<Model> validatedResult = Model.assembler()
+                .addModel(result)
+                .assemble();
+        List<ShapeId> validationEventShapeIds = validatedResult.getValidationEvents().stream()
+                .map(ValidationEvent::getShapeId)
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .collect(Collectors.toList());
+        assertThat(validationEventShapeIds, not(containsInAnyOrder(ShapeId.from("ns.qux#MyService"))));
+    }
+
     @Test
     public void throwsWhenServiceIsNotConfigured() {
         Model model = Model.assembler()