Merge branch '2.6.x' into 2.7.x

Closes gh-29411

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertySources.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -87,15 +87,16 @@ public final class ConfigurationPropertySources {
 		Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
 		MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
 		PropertySource<?> attached = getAttached(sources);
-		if (attached != null && attached.getSource() != sources) {
+		if (attached != null) {
+			if (attached instanceof ConfigurationPropertySourcesPropertySource
+					&& ((SpringConfigurationPropertySources) attached.getSource()).isUsingSources(sources)) {
+				return;
+			}
 			sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
-			attached = null;
 		}
-		if (attached == null) {
 		sources.addFirst(new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
 				new SpringConfigurationPropertySources(sources)));
 	}
-	}
 
 	static PropertySource<?> getAttached(MutablePropertySources sources) {
 		return (sources != null) ? sources.get(ATTACHED_PROPERTY_SOURCE_NAME) : null;

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertySourcesTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -71,6 +71,19 @@ class ConfigurationPropertySourcesTests {
 		assertThat(child.getProperty("my.example-property")).isEqualTo("1234");
 	}
 
+	@Test
+	void attachWhenAlreadyAttachedWithSameSourcesShouldReturnExistingInstance() {
+		ConfigurableEnvironment environment = new StandardEnvironment();
+		MutablePropertySources sources = environment.getPropertySources();
+		sources.addLast(new SystemEnvironmentPropertySource("system", Collections.singletonMap("SERVER_PORT", "1234")));
+		sources.addLast(new MapPropertySource("config", Collections.singletonMap("server.port", "4568")));
+		ConfigurationPropertySources.attach(environment);
+		Iterable<ConfigurationPropertySource> first = ConfigurationPropertySources.get(environment);
+		ConfigurationPropertySources.attach(environment);
+		Iterable<ConfigurationPropertySource> second = ConfigurationPropertySources.get(environment);
+		assertThat(first).isSameAs(second);
+	}
+
 	@Test
 	void getWhenNotAttachedShouldReturnAdapted() {
 		ConfigurableEnvironment environment = new StandardEnvironment();