Skip TrivialDataFetcher in ContextDataFetcherDecorator

The `applyDecorator` method is working to exclude things from
graphql-java. The TrivialDataFetcher interface is used to know when
to perform instrumentation and is a part of the public SPI and
should be preserved.

See gh-983

Author: osi

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

@@ -20,6 +20,7 @@
 
 import graphql.ExecutionInput;
 import graphql.GraphQLContext;
+import graphql.TrivialDataFetcher;
 import graphql.schema.DataFetcher;
 import graphql.schema.DataFetchingEnvironment;
 import graphql.schema.FieldCoordinates;
@@ -150,6 +151,9 @@ public TraversalControl visitGraphQLFieldDefinition(
 		}
 
 		private boolean applyDecorator(DataFetcher<?> dataFetcher) {
+			if (dataFetcher instanceof TrivialDataFetcher) {
+				return false;
+			}
 			Class<?> type = dataFetcher.getClass();
 			String packageName = type.getPackage().getName();
 			if (packageName.startsWith("graphql.")) {

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

@@ -27,9 +27,12 @@
 import graphql.GraphQL;
 import graphql.GraphQLError;
 import graphql.GraphqlErrorBuilder;
+import graphql.TrivialDataFetcher;
 import graphql.schema.DataFetcher;
 import graphql.schema.DataFetcherFactories;
+import graphql.schema.FieldCoordinates;
 import graphql.schema.GraphQLFieldDefinition;
+import graphql.schema.GraphQLSchema;
 import graphql.schema.idl.SchemaDirectiveWiring;
 import graphql.schema.idl.SchemaDirectiveWiringEnvironment;
 import io.micrometer.context.ContextRegistry;
@@ -238,4 +241,18 @@ else if (value instanceof Mono) {
 		tester.accept(directiveWiring, env -> Mono.just("hello"));
 	}
 
+	@Test //gh-980
+	void trivialDataFetcherIsNotDecorated() {
+		GraphQL graphQl = GraphQlSetup.schemaContent(SCHEMA_CONTENT)
+									  .queryFetcher("greeting", (TrivialDataFetcher) env -> "hello")
+									  .toGraphQl();
+
+		GraphQLSchema schema = graphQl.getGraphQLSchema();
+		FieldCoordinates coordinates = FieldCoordinates.coordinates("Query", "greeting");
+		DataFetcher<?> dataFetcher = schema.getCodeRegistry()
+										   .getDataFetcher(coordinates, schema.getFieldDefinition(coordinates));
+
+		assertThat(dataFetcher).isInstanceOf(TrivialDataFetcher.class);
+	}
+
 }