Fix constructor binding of EnumMaps

Fixes gh-41550

Author: wilkinsona

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/MapBinder.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.context.properties.bind;
 
 import java.util.Collection;
+import java.util.EnumMap;
 import java.util.Map;
 import java.util.Properties;
 import java.util.function.Supplier;
@@ -65,8 +66,7 @@ protected Object bindAggregate(ConfigurationPropertyName name, Bindable<?> targe
 				}
 			}
 		}
-		Map<Object, Object> map = CollectionFactory
-			.createMap((target.getValue() != null) ? Map.class : target.getType().resolve(Object.class), 0);
+		Map<Object, Object> map = createMap(target);
 		for (ConfigurationPropertySource source : getContext().getSources()) {
 			if (!ConfigurationPropertyName.EMPTY.equals(name)) {
 				source = source.filter(name::isAncestorOf);
@@ -76,6 +76,15 @@ protected Object bindAggregate(ConfigurationPropertyName name, Bindable<?> targe
 		return map.isEmpty() ? null : map;
 	}
 
+	private Map<Object, Object> createMap(Bindable<?> target) {
+		Class<?> mapType = (target.getValue() != null) ? Map.class : target.getType().resolve(Object.class);
+		if (EnumMap.class.isAssignableFrom(mapType)) {
+			Class<?> keyType = target.getType().asMap().getGeneric(0).resolve();
+			return CollectionFactory.createMap(mapType, keyType, 0);
+		}
+		return CollectionFactory.createMap(mapType, 0);
+	}
+
 	private boolean hasDescendants(ConfigurationPropertyName name) {
 		for (ConfigurationPropertySource source : getContext().getSources()) {
 			if (source.containsDescendantOf(name) == ConfigurationPropertyState.PRESENT) {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/ValueObjectBinder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -25,6 +25,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -156,6 +157,10 @@ private <T> T getNewDefaultValueInstanceIfPossible(Binder.Context context, Resol
 			if (Collection.class.isAssignableFrom(resolved)) {
 				return (T) CollectionFactory.createCollection(resolved, 0);
 			}
+			if (EnumMap.class.isAssignableFrom(resolved)) {
+				Class<?> keyType = type.asMap().getGeneric(0).resolve();
+				return (T) CollectionFactory.createMap(resolved, keyType, 0);
+			}
 			if (Map.class.isAssignableFrom(resolved)) {
 				return (T) CollectionFactory.createMap(resolved, 0);
 			}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/MapBinderTests.java

@@ -20,6 +20,7 @@
 import java.util.AbstractMap;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.EnumMap;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -79,6 +80,9 @@ class MapBinderTests {
 	private static final Bindable<Map<String, String[]>> STRING_ARRAY_MAP = Bindable.mapOf(String.class,
 			String[].class);
 
+	private static final Bindable<EnumMap<ExampleEnum, String>> EXAMPLE_ENUM_STRING_ENUM_MAP = Bindable
+		.of(ResolvableType.forClassWithGenerics(EnumMap.class, ExampleEnum.class, String.class));
+
 	private final List<ConfigurationPropertySource> sources = new ArrayList<>();
 
 	private final Binder binder = new Binder(this.sources);
@@ -637,6 +641,17 @@ void bindToCustomMapWithoutCtorAndConverterShouldResolve() {
 		assertThat(result.getCustomMap().getSource()).isEqualTo("value");
 	}
 
+	@Test
+	void bindToEnumMapShouldBind() {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("props.foo-bar", "value");
+		this.sources.add(source);
+		Binder binder = new Binder(this.sources, null, null, null);
+		EnumMap<ExampleEnum, String> result = binder.bind("props", EXAMPLE_ENUM_STRING_ENUM_MAP).get();
+		assertThat(result).hasSize(1).containsEntry(ExampleEnum.FOO_BAR, "value");
+
+	}
+
 	private <K, V> Bindable<Map<K, V>> getMapBindable(Class<K> keyGeneric, ResolvableType valueType) {
 		ResolvableType keyType = ResolvableType.forClass(keyGeneric);
 		return Bindable.of(ResolvableType.forClassWithGenerics(Map.class, keyType, valueType));

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/ValueObjectBinderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -21,6 +21,7 @@
 import java.nio.file.Paths;
 import java.time.LocalDate;
 import java.util.ArrayList;
+import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -306,6 +307,13 @@ void bindWhenMapParametersWithEmptyDefaultValueShouldReturnEmptyInstance() {
 		assertThat(bound.getMapValue()).isEmpty();
 	}
 
+	@Test
+	void bindWhenEnumMapParametersWithEmptyDefaultValueShouldReturnEmptyInstance() {
+		NestedConstructorBeanWithEmptyDefaultValueForEnumMapTypes bound = this.binder.bindOrCreate("foo",
+				Bindable.of(NestedConstructorBeanWithEmptyDefaultValueForEnumMapTypes.class));
+		assertThat(bound.getMapValue()).isEmpty();
+	}
+
 	@Test
 	void bindWhenArrayParameterWithEmptyDefaultValueShouldReturnEmptyInstance() {
 		NestedConstructorBeanWithEmptyDefaultValueForArrayTypes bound = this.binder.bindOrCreate("foo",
@@ -781,6 +789,20 @@ Map<String, String> getMapValue() {
 
 	}
 
+	static class NestedConstructorBeanWithEmptyDefaultValueForEnumMapTypes {
+
+		private final EnumMap<ExampleEnum, String> mapValue;
+
+		NestedConstructorBeanWithEmptyDefaultValueForEnumMapTypes(@DefaultValue EnumMap<ExampleEnum, String> mapValue) {
+			this.mapValue = mapValue;
+		}
+
+		EnumMap<ExampleEnum, String> getMapValue() {
+			return this.mapValue;
+		}
+
+	}
+
 	static class NestedConstructorBeanWithEmptyDefaultValueForArrayTypes {
 
 		private final String[] arrayValue;