Fix package tangle with configuration properties

Fix a package tangle that was introduced when we added cache bypass to
`SpringIterableConfigurationPropertySource`. Ideally we should have
been able to depend on `env` from `context` but unfortunately the
`EnvironmentPostProcessor` interface references `SpringApplication`
which needs to use the Binder.

The `isImmutable` method has now been moved to `OriginLookup` which
removes the immediate tangle.

Closes gh-18393

Author: philwebb

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

@@ -25,7 +25,7 @@
 import java.util.Set;
 import java.util.stream.Stream;
 
-import org.springframework.boot.env.OriginTrackedMapPropertySource;
+import org.springframework.boot.origin.OriginLookup;
 import org.springframework.core.env.EnumerablePropertySource;
 import org.springframework.core.env.MapPropertySource;
 import org.springframework.core.env.PropertySource;
@@ -236,8 +236,8 @@ static CacheKey get(EnumerablePropertySource<?> source) {
 		}
 
 		private static boolean isImmutable(EnumerablePropertySource<?> source) {
-			if (source instanceof OriginTrackedMapPropertySource) {
-				return ((OriginTrackedMapPropertySource) source).isImmutable();
+			if (source instanceof OriginLookup) {
+				return ((OriginLookup<?>) source).isImmutable();
 			}
 			if (StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME.equals(source.getName())) {
 				return source.getSource() == System.getenv();

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/OriginTrackedMapPropertySource.java

@@ -22,7 +22,6 @@
 import org.springframework.boot.origin.OriginLookup;
 import org.springframework.boot.origin.OriginTrackedValue;
 import org.springframework.core.env.MapPropertySource;
-import org.springframework.core.env.PropertySource;
 
 /**
  * {@link OriginLookup} backed by a {@link Map} containing {@link OriginTrackedValue
@@ -52,6 +51,7 @@ public OriginTrackedMapPropertySource(String name, Map source) {
 	 * @param name the property source name
 	 * @param source the underlying map source
 	 * @param immutable if the underlying source is immutable and guaranteed not to change
+	 * @since 2.2.0
 	 */
 	@SuppressWarnings({ "unchecked", "rawtypes" })
 	public OriginTrackedMapPropertySource(String name, Map source, boolean immutable) {
@@ -77,11 +77,7 @@ public Origin getOrigin(String name) {
 		return null;
 	}
 
-	/**
-	 * Return {@code true} if this {@link PropertySource} is immutable and has contents
-	 * that will never change.
-	 * @return if the property source is read only
-	 */
+	@Override
 	public boolean isImmutable() {
 		return this.immutable;
 	}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/origin/OriginLookup.java

@@ -35,6 +35,16 @@ public interface OriginLookup<K> {
 	 */
 	Origin getOrigin(K key);
 
+	/**
+	 * Return {@code true} if this lookup is immutable and has contents that will never
+	 * change.
+	 * @return if the lookup is immutable
+	 * @since 2.2.0
+	 */
+	default boolean isImmutable() {
+		return false;
+	}
+
 	/**
 	 * Attempt to lookup the origin from the given source. If the source is not a
 	 * {@link OriginLookup} or if an exception occurs during lookup then {@code null} is