Don't detect private constructors on member classes for binding

Refine constructor binding detection logic so that `private`
constructors on member classes are no longer automatically picked for
constructor binding. This provides users a way of signalling that
they wish to use the constructor directly.

Closes gh-32639

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessorTests.java

@@ -31,6 +31,7 @@ import org.springframework.boot.configurationsample.simple.DescriptionProperties
 import org.springframework.boot.configurationsample.simple.HierarchicalProperties;
 import org.springframework.boot.configurationsample.simple.HierarchicalPropertiesGrandparent;
 import org.springframework.boot.configurationsample.simple.HierarchicalPropertiesParent;
+import org.springframework.boot.configurationsample.simple.InnerClassWithPrivateConstructor;
 import org.springframework.boot.configurationsample.simple.NotAnnotated;
 import org.springframework.boot.configurationsample.simple.SimpleArrayProperties;
 import org.springframework.boot.configurationsample.simple.SimpleCollectionProperties;
@@ -459,4 +460,11 @@ class ConfigurationMetadataAnnotationProcessorTests extends AbstractMetadataGene
 		assertThat(metadata).doesNotHave(Metadata.withProperty("multi.some-integer"));
 	}
 
+	@Test
+	void innerClassWithPrivateConstructor() {
+		ConfigurationMetadata metadata = compile(InnerClassWithPrivateConstructor.class);
+		assertThat(metadata).has(Metadata.withProperty("config.nested.name"));
+		assertThat(metadata).doesNotHave(Metadata.withProperty("config.nested.ignored"));
+	}
+
 }

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/simple/InnerClassWithPrivateConstructor.java

@@ -0,0 +1,56 @@
+/*
+ * 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.
+ * 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 org.springframework.boot.configurationsample.simple;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+
+/**
+ * Nested properties with a private constructor.
+ *
+ * @author Phillip Webb
+ */
+@ConfigurationProperties(prefix = "config")
+public class InnerClassWithPrivateConstructor {
+
+	private Nested nested = new Nested("whatever");
+
+	public Nested getNested() {
+		return this.nested;
+	}
+
+	public void setNested(Nested nested) {
+		this.nested = nested;
+	}
+
+	public static final class Nested {
+
+		private String name;
+
+		private Nested(String ignored) {
+		}
+
+		public String getName() {
+			return this.name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+	}
+
+}