Ensure descendants are always recalculated on cache refresh

Fix `SpringIterableConfigurationPropertySource` to ensure that cached
descendants are always updated on a refresh.

The cache implementation assumes that it is safe to reuse previous
`mappings` and `reverseMappings` data since it doesn't matter if
superfluous values are included. For `descendants` however, we always
want to recalculate values so that we don't get false positives.

Unfortunately, prior to this commit, we only updated the descendants
if a reverseMapping was added. The meant that on a cache refresh,
existing descendants were removed.

Fixes gh-45639

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

@@ -274,11 +274,13 @@ class SpringIterableConfigurationPropertySource extends SpringConfigurationPrope
 						if (configurationPropertyName != null && !configurationPropertyName.isEmpty()) {
 							add(mappings, configurationPropertyName, propertyName);
 							reverseMappings.put(propertyName, configurationPropertyName);
-							addParents(descendants, configurationPropertyName);
 						}
 					}
 				}
 			}
+			for (String propertyName : propertyNames) {
+				addParents(descendants, reverseMappings.get(propertyName));
+			}
 			ConfigurationPropertyName[] configurationPropertyNames = this.immutable
 					? reverseMappings.values().toArray(new ConfigurationPropertyName[0]) : null;
 			lastUpdated = this.immutable ? null : propertyNames;
@@ -296,7 +298,7 @@ class SpringIterableConfigurationPropertySource extends SpringConfigurationPrope
 		}
 
 		private void addParents(Set<ConfigurationPropertyName> descendants, ConfigurationPropertyName name) {
-			if (descendants == null || name.isEmpty()) {
+			if (descendants == null || name == null || name.isEmpty()) {
 				return;
 			}
 			ConfigurationPropertyName parent = name.getParent();

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

@@ -239,6 +239,21 @@ class SpringIterableConfigurationPropertySourceTests {
 				"test.map.bravo", "test.map.charlie", "test.map.delta");
 	}
 
+	@Test
+	void cacheRefreshRecalculatesDescendants() {
+		// gh-45639
+		Map<String, Object> map = new LinkedHashMap<>();
+		map.put("one.two.three", "test");
+		EnumerablePropertySource<?> source = new OriginTrackedMapPropertySource("test", map, false);
+		SpringIterableConfigurationPropertySource propertySource = new SpringIterableConfigurationPropertySource(source,
+				false, DefaultPropertyMapper.INSTANCE);
+		assertThat(propertySource.containsDescendantOf(ConfigurationPropertyName.of("one.two")))
+			.isEqualTo(ConfigurationPropertyState.PRESENT);
+		map.put("new", "value");
+		assertThat(propertySource.containsDescendantOf(ConfigurationPropertyName.of("one.two")))
+			.isEqualTo(ConfigurationPropertyState.PRESENT);
+	}
+
 	/**
 	 * Test {@link PropertySource} that's also an {@link OriginLookup}.
 	 *