Warn when using jsonAdd with schemas

Using the jsonAdd feature with the Smithy to OpenAPI converter is
probably never what you actually want to do. It means that clients,
servers, and other artifacts generated from the Smithy model don't know
about the shapes being defined only in OpenAPI. This PR adds a severe
log warning when this is detected.

smithy-openapi/src/main/java/software/amazon/smithy/openapi/fromsmithy/mappers/OpenApiJsonAdd.java

@@ -58,6 +58,14 @@ public ObjectNode updateNode(Context<? extends Trait> context, OpenApi openapi,
         for (Map.Entry<String, Node> entry : add.entrySet()) {
             try {
                 LOGGER.info(() -> "OpenAPI `jsonAdd`: adding `" + entry.getKey() + "`");
+
+                if (entry.getKey().startsWith("/components/schemas")) {
+                    LOGGER.severe("Adding schemas to the generated OpenAPI model directly means that "
+                                  + "clients, servers, and other artifacts generated from your Smithy "
+                                  + "model don't know about all of the shapes used in the service. You "
+                                  + "almost certainly should not do this.");
+                }
+
                 result = NodePointer.parse(entry.getKey())
                         .addWithIntermediateValues(result, entry.getValue().toNode())
                         .expectObjectNode();

smithy-openapi/src/test/java/software/amazon/smithy/openapi/fromsmithy/mappers/OpenApiJsonAddTest.java

@@ -15,7 +15,11 @@
 
 package software.amazon.smithy.openapi.fromsmithy.mappers;
 
+import java.util.logging.Handler;
+import java.util.logging.LogRecord;
+import java.util.logging.Logger;
 import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 import software.amazon.smithy.model.Model;
 import software.amazon.smithy.model.node.Node;
@@ -26,16 +30,22 @@
 import software.amazon.smithy.openapi.fromsmithy.OpenApiConverter;
 
 public class OpenApiJsonAddTest {
-    @Test
-    public void addsWithPointers() {
-        Model model = Model.assembler()
+
+    private static Model MODEL;
+
+    @BeforeAll
+    public static void before() {
+        MODEL = Model.assembler()
                 // Reusing another test cases's model, but that doesn't matter for the
                 // purpose of this test.
                 .addImport(RemoveUnusedComponentsTest.class.getResource("substitutions.smithy"))
                 .discoverModels()
                 .assemble()
                 .unwrap();
+    }
 
+    @Test
+    public void addsWithPointers() {
         ObjectNode addNode = Node.objectNodeBuilder()
                 .withMember("/info/description", "hello")
                 .withMember("/info/foo", "bar")
@@ -49,7 +59,7 @@ public void addsWithPointers() {
 
         ObjectNode openApi = OpenApiConverter.create()
                 .config(config)
-                .convertToNode(model);
+                .convertToNode(MODEL);
 
         String description = NodePointer.parse("/info/description").getValue(openApi).expectStringNode().getValue();
         String infoFoo = NodePointer.parse("/info/foo").getValue(openApi).expectStringNode().getValue();
@@ -61,4 +71,45 @@ public void addsWithPointers() {
         Assertions.assertEquals("nested", infoNested);
         Assertions.assertEquals("custom", infoTitle);
     }
+
+    private static final class SearchingHandler extends Handler {
+        boolean found;
+        String searchString;
+
+        SearchingHandler(String searchString) {
+            this.searchString = searchString;
+        }
+
+        @Override
+        public void publish(LogRecord record) {
+            if (record.getMessage().contains(searchString)) {
+                found = true;
+            }
+        }
+
+        @Override
+        public void flush() {}
+
+        @Override
+        public void close() throws SecurityException {}
+    }
+
+    @Test
+    public void warnsWhenAddingSchemas() {
+        Logger logger = Logger.getLogger(OpenApiJsonAdd.class.getName());
+        SearchingHandler handler = new SearchingHandler("Adding schemas to the generated OpenAPI model directly");
+        logger.addHandler(handler);
+
+        ObjectNode addNode = Node.objectNode()
+                .withMember("/components/schemas/Merged", Node.objectNode().withMember("type", "string"));
+
+        OpenApiConfig config = new OpenApiConfig();
+        config.setService(ShapeId.from("smithy.example#Service"));
+        config.setJsonAdd(addNode.getStringMap());
+        ObjectNode openApi = OpenApiConverter.create().config(config).convertToNode(MODEL);
+        NodePointer.parse("/components/schemas/Merged").getValue(openApi).expectObjectNode();
+        logger.removeHandler(handler);
+
+        Assertions.assertTrue(handler.found);
+    }
 }