Remove service renames after flattenNamespaces (#2109)

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 +149,52 @@ 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()