Avoid dependency on Spring Data for Kotlin apps

Prior to this commit, Kotlin applications would require
"spring-data-commons" on the classpath to get the invocation method
support.

This commit removes the dependency on Spring Data's
`KotlinReflectionUtils` and use a local implementation instead.

Fixes gh-1397

Author: bclozel

spring-graphql/src/main/java/org/springframework/graphql/data/method/InvocableHandlerMethodSupport.java

@@ -27,11 +27,14 @@
 
 import graphql.GraphQLContext;
 import io.micrometer.context.ContextSnapshot;
+import kotlin.jvm.JvmClassMappingKt;
+import kotlin.reflect.KFunction;
+import kotlin.reflect.jvm.KTypesJvm;
+import kotlin.reflect.jvm.ReflectJvmMapping;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.CoroutinesUtils;
 import org.springframework.core.KotlinDetector;
-import org.springframework.data.util.KotlinReflectionUtils;
 import org.springframework.graphql.execution.ContextPropagationHelper;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -47,6 +50,8 @@ public abstract class InvocableHandlerMethodSupport extends HandlerMethod {
 
 	private static final Object NO_VALUE = new Object();
 
+	private static final boolean KOTLIN_REFLECT_PRESENT = KotlinDetector.isKotlinReflectPresent();
+
 
 	@Nullable
 	private final Executor executor;
@@ -137,6 +142,7 @@ protected Object doInvoke(GraphQLContext graphQLContext, Object... argValues) {
 	private static Object invokeSuspendingFunction(Object bean, Method method, Object[] argValues) {
 		Object result = CoroutinesUtils.invokeSuspendingFunction(method, bean, argValues);
 
+		Assert.state(KOTLIN_REFLECT_PRESENT, "Missing org.jetbrains.kotlin:kotlin-reflect dependency");
 		// Support use of DataLoader from suspending function
 		Class<?> returnType = KotlinReflectionUtils.getReturnType(method);
 		if (CompletableFuture.class.isAssignableFrom(returnType)) {
@@ -210,4 +216,15 @@ protected Mono<Object[]> toArgsMono(Object[] args) {
 		});
 	}
 
+	static class KotlinReflectionUtils {
+
+		static Class<?> getReturnType(Method method) {
+			KFunction<?> kotlinFunction = ReflectJvmMapping.getKotlinFunction(method);
+			if (kotlinFunction == null) {
+				throw new IllegalArgumentException(String.format("Cannot resolve %s to a KFunction", method));
+			}
+			return JvmClassMappingKt.getJavaClass(KTypesJvm.getJvmErasure(kotlinFunction.getReturnType()));
+		}
+	}
+
 }