Configure GraphQlProperties even if GraphQlSource is defined

Prior to this commit, the main GraphQL auto-configuration would be
guarded with a condition on a `GraphQlSource` bean being missing. While
we want to prevent the auto-configuration from registering such a bean
if the user configuration already did so, we should still contribute the
`GraphQlProperties` bean to the context, as it is required for other
purposes.

This commit moves the condition directly on the bean method to avoid
this.

Fixes gh-186

graphql-spring-boot-starter/src/main/java/org/springframework/graphql/boot/GraphQlAutoConfiguration.java

@@ -50,13 +50,13 @@ import org.springframework.graphql.execution.RuntimeWiringConfigurer;
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnClass({GraphQL.class, GraphQlSource.class})
-@ConditionalOnMissingBean(GraphQlSource.class)
 @EnableConfigurationProperties(GraphQlProperties.class)
 public class GraphQlAutoConfiguration {
 
 	private static final Log logger = LogFactory.getLog(GraphQlAutoConfiguration.class);
 
 	@Bean
+	@ConditionalOnMissingBean
 	public GraphQlSource graphQlSource(ResourcePatternResolver resourcePatternResolver, GraphQlProperties properties,
 			ObjectProvider<DataFetcherExceptionResolver> exceptionResolversProvider,
 			ObjectProvider<Instrumentation> instrumentationsProvider,

graphql-spring-boot-starter/src/test/java/org/springframework/graphql/boot/GraphQlAutoConfigurationTests.java

@@ -28,6 +28,7 @@ import org.springframework.graphql.execution.GraphQlSource;
 import org.springframework.graphql.execution.MissingSchemaException;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link GraphQlAutoConfiguration}
@@ -74,6 +75,15 @@ class GraphQlAutoConfigurationTests {
 				});
 	}
 
+	@Test
+	void shouldBackOffWithCustomGraphQlSource() {
+		this.contextRunner.withUserConfiguration(CustomGraphQlSourceConfiguration.class)
+				.run((context) -> {
+					assertThat(context).getBeanNames(GraphQlSource.class).containsOnly("customGraphQlSource");
+					assertThat(context).hasSingleBean(GraphQlProperties.class);
+				});
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class CustomGraphQlBuilderConfiguration {
 
@@ -84,4 +94,14 @@ class GraphQlAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class CustomGraphQlSourceConfiguration {
+
+		@Bean
+		GraphQlSource customGraphQlSource() {
+			return mock(GraphQlSource.class);
+		}
+
+	}
+
 }