Improve "Connection" Java type checks

ConnectionFieldTypeVisitor now also checks if the container type
ends on "Connection", and if so it lets it pass through.

See gh-709

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/data/pagination/CompositeConnectionAdapter.java

@@ -62,15 +62,15 @@ public String cursorAt(Object container, int index) {
 	}
 
 	private ConnectionAdapter getRequiredAdapter(Object container) {
-		ConnectionAdapter adapter = getAdapter(container);
+		ConnectionAdapter adapter = getAdapter(container.getClass());
 		Assert.notNull(adapter, "No ConnectionAdapter for: " + container.getClass().getName());
 		return adapter;
 	}
 
 	@Nullable
-	private ConnectionAdapter getAdapter(Object container) {
+	private ConnectionAdapter getAdapter(Class<?> containerType) {
 		for (ConnectionAdapter adapter : this.adapters) {
-			if (adapter.supports(container.getClass())) {
+			if (adapter.supports(containerType)) {
 				return adapter;
 			}
 		}

spring-graphql/src/main/java/org/springframework/graphql/data/pagination/ConnectionFieldTypeVisitor.java

@@ -195,19 +195,24 @@ else if (result instanceof CompletionStage<?> stage) {
 			}
 		}
 
-		@SuppressWarnings("unchecked")
-		private <T> Connection<T> adapt(@Nullable Object container) {
-			if (container instanceof Connection<?> connection) {
-				return (Connection<T>) connection;
+		private <T> Object adapt(@Nullable Object container) {
+			if (container == null) {
+				return EMPTY_CONNECTION;
 			}
 
-			Collection<T> nodes = (container != null ?
-					this.adapter.getContent(container) : Collections.emptyList());
+			if (container instanceof Connection<?>) {
+				return container;
+			}
 
-			if (nodes.isEmpty()) {
-				return (Connection<T>) EMPTY_CONNECTION;
+			if (!this.adapter.supports(container.getClass())) {
+				if (container.getClass().getName().endsWith("Connection")) {
+					return container;
+				}
+				throw new IllegalStateException(
+						"No ConnectionAdapter for: " + container.getClass().getName());
 			}
 
+			Collection<T> nodes = this.adapter.getContent(container);
 			int index = 0;
 			List<Edge<T>> edges = new ArrayList<>(nodes.size());
 			for (T node : nodes) {

spring-graphql/src/test/java/org/springframework/graphql/data/pagination/ConnectionFieldTypeVisitorTests.java

@@ -34,6 +34,7 @@
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.io.Resource;
+import org.springframework.graphql.Book;
 import org.springframework.graphql.BookSource;
 import org.springframework.graphql.ExecutionGraphQlResponse;
 import org.springframework.graphql.GraphQlSetup;
@@ -51,7 +52,7 @@ public class ConnectionFieldTypeVisitorTests {
 
 
 	@Test
-	void paginationDataFetcher() {
+	void paginatedTypeIsAdapted() {
 
 		ListConnectionAdapter adapter = new ListConnectionAdapter();
 		adapter.setInitialOffset(30);
@@ -83,6 +84,39 @@ void paginationDataFetcher() {
 		);
 	}
 
+	@Test // gh-709
+	void customConnectionTypeIsPassedThrough() {
+
+		List<MyEdge<Book>> edges = BookSource.books().stream().map(book -> new MyEdge<>("0_" + book.getId(), book)).toList();
+		MyPageInfo pageInfo = new MyPageInfo(edges.get(0).cursor(), edges.get(edges.size() - 1).cursor, true, true);
+		MyConnection<Book> connection = new MyConnection<>(edges, pageInfo);
+
+		Mono<ExecutionGraphQlResponse> response = GraphQlSetup.schemaResource(BookSource.paginationSchema)
+				.dataFetcher("Query", "books", env -> connection)
+				.connectionSupport(new ListConnectionAdapter())
+				.toGraphQlService()
+				.execute(BookSource.booksConnectionQuery(null));
+
+		ResponseHelper.forResponse(response).assertData(
+				"{\"books\":{" +
+						"\"edges\":[" +
+						"{\"cursor\":\"0_1\",\"node\":{\"id\":\"1\",\"name\":\"Nineteen Eighty-Four\"}}," +
+						"{\"cursor\":\"0_2\",\"node\":{\"id\":\"2\",\"name\":\"The Great Gatsby\"}}," +
+						"{\"cursor\":\"0_3\",\"node\":{\"id\":\"3\",\"name\":\"Catch-22\"}}," +
+						"{\"cursor\":\"0_4\",\"node\":{\"id\":\"4\",\"name\":\"To The Lighthouse\"}}," +
+						"{\"cursor\":\"0_5\",\"node\":{\"id\":\"5\",\"name\":\"Animal Farm\"}}," +
+						"{\"cursor\":\"0_53\",\"node\":{\"id\":\"53\",\"name\":\"Breaking Bad\"}}," +
+						"{\"cursor\":\"0_42\",\"node\":{\"id\":\"42\",\"name\":\"Hitchhiker's Guide to the Galaxy\"}}" +
+						"]," +
+						"\"pageInfo\":{" +
+						"\"startCursor\":\"0_1\"," +
+						"\"endCursor\":\"0_42\"," +
+						"\"hasPreviousPage\":true," +
+						"\"hasNextPage\":true}" +
+						"}}"
+		);
+	}
+
 	@Test // gh-707
 	void nullValueTreatedAsEmptyConnection() {
 
@@ -226,4 +260,14 @@ public String cursorAt(Object container, int index) {
 
 	}
 
+
+	private record MyConnection<T>(List<MyEdge<T>> edges, MyPageInfo pageInfo) {
+	}
+
+	private record MyEdge<T>(String cursor, T node) {
+	}
+
+	private record MyPageInfo(String startCursor, String endCursor, boolean hasPreviousPage, boolean hasNextPage) {
+	}
+
 }