Improves generic type support in schema inspection

The fix targets cases when a method's return type has a generic
type, and the generic type is declared inline on the return type.
We need to pass containing class information as a ResolvableType
in order to be able to resolve generic types.

Closes gh-1037

Author: rstoyanchev

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

@@ -93,7 +93,6 @@ public final class SchemaMappingInspector {
 			(!method.getDeclaringClass().equals(Object.class) && !method.getReturnType().equals(Void.class) &&
 					method.getParameterCount() == 0 && Modifier.isPublic(method.getModifiers()));
 
-
 	private final GraphQLSchema schema;
 
 	private final Map<String, Map<String, DataFetcher>> dataFetchers;
@@ -182,13 +181,15 @@ private void checkFieldsContainer(
 			if (resolvableType != null) {
 				PropertyDescriptor descriptor = getProperty(resolvableType, fieldName);
 				if (descriptor != null) {
-					checkField(fieldContainer, field, ResolvableType.forMethodReturnType(descriptor.getReadMethod()));
+					MethodParameter returnType = new MethodParameter(descriptor.getReadMethod(), -1);
+					checkField(fieldContainer, field, ResolvableType.forMethodParameter(returnType, resolvableType));
 					continue;
 				}
 				// Kotlin function?
 				Method method = getRecordLikeMethod(resolvableType, fieldName);
 				if (method != null) {
-					checkField(fieldContainer, field, ResolvableType.forMethodReturnType(method));
+					MethodParameter returnType = new MethodParameter(method, -1);
+					checkField(fieldContainer, field, ResolvableType.forMethodParameter(returnType, resolvableType));
 					continue;
 				}
 			}

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

@@ -310,7 +310,7 @@ void mappedSubscriptionWithUnmappedArgument() {
 
 
 	@Nested
-	class TypesInspectionTests {
+	class SchemaTypeInspectionTests {
 
 		@Test
 		void reportIsEmptyWhenFieldHasMatchingObjectProperty() {
@@ -434,6 +434,25 @@ void reportHasUnmappedFieldOnEagerlyFetchedNestedType() {
 			assertThatReport(report).hasUnmappedFieldCount(1).containsUnmappedFields("Author", "missing");
 		}
 
+		@Test // gh-1037
+		void reportHasUnmappedFieldOnGenericType() {
+			String schema = """
+						type Query {
+							teamContainer: TeamContainer
+						}
+						type TeamContainer {
+							items: [Team]
+						}
+						type Team {
+							name: String
+							missing: String
+						}
+					""";
+
+			SchemaReport report = inspectSchema(schema, TeamController.class);
+			assertThatReport(report).hasUnmappedFieldCount(1).containsUnmappedFields("Team", "missing");
+		}
+
 		@Test
 		void reportWorksWithCyclicRelations() {
 			String schema = """
@@ -680,6 +699,10 @@ public Team team(TeamMember teamMember) {
 			return null;
 		}
 
+		@QueryMapping
+		public ListContainer<Team> teamContainer() {
+			return new ListContainer<>(Collections.emptyList());
+		}
 	}
 
 
@@ -692,4 +715,9 @@ record TeamMember(String name, Team team) {
 
 	}
 
+
+	record ListContainer<T>(List<T> items) {
+
+	}
+
 }