Inspect bean class if it is available

Avoids instantiating beans if not necessary, and allows user to
provide Function as a @SpringBootApplication (for instance), or
more generally as a source to the application context (as opposed
to being component scanned).

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/config/ContextFunctionCatalogAutoConfigurationTests.java

@@ -123,6 +123,20 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 				.isEqualTo(Foo.class);
 	}
 
+	@Test
+	public void configurationFunction() {
+		create(FunctionConfiguration.class);
+		assertThat(context.getBean("foos")).isInstanceOf(Function.class);
+		assertThat(catalog.<Function<?, ?>>lookup(Function.class, "foos"))
+				.isInstanceOf(Function.class);
+		assertThat(inspector.getInputType(catalog.lookup(Function.class, "foos")))
+				.isEqualTo(String.class);
+		assertThat(inspector.getOutputType(catalog.lookup(Function.class, "foos")))
+				.isEqualTo(Foo.class);
+		assertThat(inspector.getInputWrapper(catalog.lookup(Function.class, "foos")))
+				.isEqualTo(Flux.class);
+	}
+
 	@Test
 	public void dependencyInjection() {
 		create(DependencyInjectionConfiguration.class);
@@ -558,6 +572,22 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 		}
 	}
 
+	@EnableAutoConfiguration
+	@Configuration("foos")
+	protected static class FunctionConfiguration
+			implements Function<Flux<String>, Flux<Foo>> {
+
+		@Override
+		public Flux<Foo> apply(Flux<String> flux) {
+			return flux.map(foo -> new Foo(value() + ": " + foo.toUpperCase()));
+		}
+
+		@Bean
+		public String value() {
+			return "Hello";
+		}
+	}
+
 	@EnableAutoConfiguration
 	@Configuration
 	@ComponentScan(basePackageClasses = FooConfiguration.class)