Schema inspection handles List from Subscription

Normally a multivalue Publisher is collected to a List, so we can treat
it as a match for a List field. For subscriptions, however, such a
Publisher is left as an infinite stream, and we should not treat as a
match for a List, but rather expect it to be a stream of List items.

Discovered while working on gh-674, which is closely related.

Author: rstoyanchev

Diff for: spring-graphql/src/main/java/org/springframework/graphql/execution/SchemaMappingInspector.java

@@ -112,14 +112,14 @@ private SchemaMappingInspector(GraphQLSchema schema, RuntimeWiring runtimeWiring
 	 */
 	public Report inspect() {
 
-		inspectSchemaType(this.schema.getQueryType(), null);
+		inspectSchemaType(this.schema.getQueryType(), null, false);
 
 		if (this.schema.isSupportingMutations()) {
-			inspectSchemaType(this.schema.getMutationType(), null);
+			inspectSchemaType(this.schema.getMutationType(), null, false);
 		}
 
 		if (this.schema.isSupportingSubscriptions()) {
-			inspectSchemaType(this.schema.getSubscriptionType(), null);
+			inspectSchemaType(this.schema.getSubscriptionType(), null, false);
 		}
 
 		inspectDataFetcherRegistrations();
@@ -128,7 +128,7 @@ public Report inspect() {
 	}
 
 	@SuppressWarnings("rawtypes")
-	private void inspectSchemaType(GraphQLType type, @Nullable ResolvableType resolvableType) {
+	private void inspectSchemaType(GraphQLType type, @Nullable ResolvableType resolvableType, boolean subscription) {
 		Assert.notNull(type, "No GraphQLType");
 
 		type = unwrapNonNull(type);
@@ -138,7 +138,7 @@ private void inspectSchemaType(GraphQLType type, @Nullable ResolvableType resolv
 		}
 		else if (type instanceof GraphQLList listType) {
 			type = unwrapNonNull(listType.getWrappedType());
-			resolvableType = nestForList(resolvableType, type);
+			resolvableType = nestForList(resolvableType, type, subscription);
 		}
 		else {
 			resolvableType = (resolvableType != null ? nestIfReactive(resolvableType) : null);
@@ -177,7 +177,9 @@ else if (resolvableType != null && resolvableType.resolve(Object.class) == Objec
 			if (dataFetcherMap.containsKey(fieldName)) {
 				DataFetcher<?> fetcher = dataFetcherMap.get(fieldName);
 				if (fetcher instanceof SelfDescribingDataFetcher<?> selfDescribingDataFetcher) {
-					inspectSchemaType(field.getType(), selfDescribingDataFetcher.getReturnType());
+					inspectSchemaType(
+							field.getType(), selfDescribingDataFetcher.getReturnType(),
+							(type == this.schema.getSubscriptionType()));
 				}
 				else if (isNotScalarOrEnumType(field.getType())) {
 					if (logger.isDebugEnabled()) {
@@ -228,15 +230,15 @@ private ResolvableType nestIfReactive(ResolvableType type) {
 		return type;
 	}
 
-	private ResolvableType nestForList(@Nullable ResolvableType type, GraphQLType graphQlType) {
+	private ResolvableType nestForList(@Nullable ResolvableType type, GraphQLType graphQlType, boolean subscription) {
 		Assert.state(type != null, "No Java type for " + getTypeName(graphQlType));
 		ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(type.resolve(Object.class));
 		if (adapter != null) {
-			if (adapter.isMultiValue()) {
-				return type.getNested(2);
-			}
 			Assert.state(!adapter.isNoValue(), "Expected List compatible type: " + type);
 			type = type.getNested(2);
+			if (adapter.isMultiValue() && !subscription) {
+				return type;
+			}
 		}
 		Assert.state(type.isArray() || type.hasGenerics(), "Expected List compatible type: " + type);
 		return type.getNested(2);

Diff for: spring-graphql/src/test/java/org/springframework/graphql/execution/SchemaMappingInspectorTests.java

@@ -219,7 +219,7 @@ void reportContainsUnmappedSubscription() {
 							greeting: String
 						}
 						type Subscription {
-							bookSearch(author: String) : Book!
+							bookSearch(author: String) : [Book!]!
 						}
 						
 						type Book {
@@ -238,7 +238,7 @@ void reportIsEmptyWhenSubscriptionIsMapped() {
 							greeting: String
 						}
 						type Subscription {
-							bookSearch(author: String) : Book!
+							bookSearch(author: String) : [Book!]!
 						}
 						
 						type Book {
@@ -259,7 +259,7 @@ void reportWorksForSubscriptionWithExtensionType() {
 						type Subscription {
 						}
 						extend type Subscription {
-					    	bookSearch(author: String) : Book!
+					    	bookSearch(author: String) : [Book!]!
 					 	}
 					 	type Book {
 							id: ID
@@ -493,7 +493,7 @@ void reportUnmappedField() {
 							createBook: Book
 						}
 						type Subscription {
-							bookSearch(author: String) : Book!
+							bookSearch(author: String) : [Book!]!
 						}
 						type Book {
 							id: ID
@@ -598,7 +598,7 @@ public Book createBook() {
 		}
 
 		@SubscriptionMapping
-		public Flux<Book> bookSearch(@Argument String author) {
+		public Flux<List<Book>> bookSearch(@Argument String author) {
 			return Flux.empty();
 		}
 	}