fix: Ensure proper merging of Binder default props (#2177)

Fixes #2151.

spring-cloud-gcp-pubsub-stream-binder/src/main/java/com/google/cloud/spring/stream/binder/pubsub/config/ExtendedBindingHandlerMappingsProviderConfiguration.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2017-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.spring.stream.binder.pubsub.config;
+
+import java.util.Collections;
+import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
+import org.springframework.cloud.stream.config.BindingHandlerAdvise.MappingsProvider;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Configuration for extended binding metadata.
+ */
+@Configuration(proxyBeanMethods = false)
+public class ExtendedBindingHandlerMappingsProviderConfiguration {
+
+  @Bean
+  public MappingsProvider pubSubExtendedPropertiesDefaultMappingsProvider() {
+    return () -> Collections.singletonMap(
+        ConfigurationPropertyName.of("spring.cloud.stream.gcp.pubsub.bindings"),
+        ConfigurationPropertyName.of("spring.cloud.stream.gcp.pubsub.default"));
+  }
+}

spring-cloud-gcp-pubsub-stream-binder/src/main/java/com/google/cloud/spring/stream/binder/pubsub/config/PubSubBinderConfiguration.java

@@ -24,14 +24,11 @@
 import com.google.cloud.spring.stream.binder.pubsub.PubSubMessageChannelBinder;
 import com.google.cloud.spring.stream.binder.pubsub.properties.PubSubExtendedBindingProperties;
 import com.google.cloud.spring.stream.binder.pubsub.provisioning.PubSubChannelProvisioner;
-import java.util.Collections;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
-import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
 import org.springframework.cloud.stream.binder.Binder;
-import org.springframework.cloud.stream.config.BindingHandlerAdvise.MappingsProvider;
 import org.springframework.cloud.stream.config.ConsumerEndpointCustomizer;
 import org.springframework.cloud.stream.config.ProducerMessageHandlerCustomizer;
 import org.springframework.context.annotation.Bean;
@@ -71,12 +68,4 @@ public PubSubMessageChannelBinder pubSubBinder(
 
     return binder;
   }
-
-  @Bean
-  public MappingsProvider pubSubExtendedPropertiesDefaultMappingsProvider() {
-    return () ->
-        Collections.singletonMap(
-            ConfigurationPropertyName.of("spring.cloud.stream.gcp.pubsub.bindings"),
-            ConfigurationPropertyName.of("spring.cloud.stream.gcp.pubsub.default"));
-  }
 }

spring-cloud-gcp-pubsub-stream-binder/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -0,0 +1 @@
+com.google.cloud.spring.stream.binder.pubsub.config.ExtendedBindingHandlerMappingsProviderConfiguration