GH-1139 Fix function composition with non-existing functions

Resolves #1139

Author: olegz

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistry.java

@@ -144,11 +144,12 @@ public <T> T lookup(Class<?> type, String functionDefinition, String... expected
 				Set<String> functionRegistratioinNames = super.getNames(null);
 				String[] functionNames = StringUtils.delimitedListToStringArray(functionDefinition.replaceAll(",", "|").trim(), "|");
 				for (String functionName : functionNames) {
-					if (functionRegistratioinNames.contains(functionName) && logger.isDebugEnabled()) {
-						logger.debug("Skipping function '" + functionName + "' since it is already present");
+					if (functionRegistratioinNames.contains(functionName)) {
+						if (logger.isDebugEnabled()) {
+							logger.debug("Skipping function '" + functionName + "' since it is already present");
+						}
 					}
 					else {
-
 						Object functionCandidate = this.discoverFunctionInBeanFactory(functionName);
 						if (functionCandidate != null) {
 							Type functionType = null;

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistryTests.java

@@ -29,6 +29,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Set;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
@@ -115,6 +116,30 @@ public void testEmptyPojoConversion() {
 		assertThat(result).isEqualTo("{}");
 	}
 
+	@SuppressWarnings({ "rawtypes", "unchecked" })
+	@Test
+	public void testCompositionWithNonExistingFunction() throws Exception {
+		FunctionCatalog catalog = this.configureCatalog(CompositionWithNullReturnInBetween.class);
+		for (int i = 0; i < 10; i++) {
+			catalog.lookup("echo1|any");
+		}
+		Field functionRegistrationsField =  ReflectionUtils.findField(catalog.getClass(), "functionRegistrations");
+		functionRegistrationsField.setAccessible(true);
+		Set<FunctionRegistration> functionRegistrations = (Set) functionRegistrationsField.get(catalog);
+		assertThat(functionRegistrations.size()).isEqualTo(1);
+		FunctionRegistration registration = functionRegistrations.iterator().next();
+		assertThat(registration.getNames().size()).isEqualTo(1);
+		assertThat(registration.getNames().iterator().next()).isEqualTo("echo1");
+
+		for (int i = 0; i < 10; i++) {
+			catalog.lookup("echo1|any|foo|bar|bye");
+		}
+		assertThat(functionRegistrations.size()).isEqualTo(1);
+		registration = functionRegistrations.iterator().next();
+		assertThat(registration.getNames().size()).isEqualTo(1);
+		assertThat(registration.getNames().iterator().next()).isEqualTo("echo1");
+	}
+
 	@SuppressWarnings({ "rawtypes", "unchecked" })
 	@Test
 	public void testCompositionWithNullReturnInBetween() {