Polishing.

Add additional tests, add Javadoc to explain isEnclosingClassParameter() behavior.

See #3038
Original pull request: #3039

Author: mp911de

src/main/java/org/springframework/data/mapping/Parameter.java

@@ -156,10 +156,8 @@ public boolean equals(@Nullable Object o) {
 			return false;
 		}
 
-		return Objects.equals(this.name, that.name)
-				&& Objects.equals(this.type, that.type)
-				&& Objects.equals(this.key, that.key)
-				&& Objects.equals(this.entity, that.entity);
+		return Objects.equals(this.name, that.name) && Objects.equals(this.type, that.type)
+				&& Objects.equals(this.key, that.key) && Objects.equals(this.entity, that.entity);
 	}
 
 	@Override
@@ -183,6 +181,15 @@ boolean maps(PersistentProperty<?> property) {
 		return property.equals(referencedProperty);
 	}
 
+	/**
+	 * Returns whether this parameter is a candidate for the enclosing class by checking the parameter type against
+	 * {@link Class#getEnclosingClass()} and whether the defining class is an inner non-static one.
+	 * <p>
+	 * Note that for a proper check the parameter position must be compared to ensure that only the first parameter (at
+	 * index {@code 0}/zero) qualifies as enclosing class instance parameter.
+	 *
+	 * @return {@literal true} if this parameter is a candidate for the enclosing class instance.
+	 */
 	boolean isEnclosingClassParameter() {
 		return enclosingClassCache.get();
 	}

src/test/java/org/springframework/data/mapping/ParameterUnitTests.java

@@ -162,7 +162,7 @@ class ClassMember {
 	static class StaticType {
 
 		class NonStaticInner {
-			NonStaticInner(StaticType outer) {}
+			NonStaticInner() {}
 		}
 
 		static class StaticInner {

src/test/java/org/springframework/data/mapping/PreferredConstructorDiscovererUnitTests.java

@@ -22,6 +22,7 @@
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 import java.util.Iterator;
+import java.util.List;
 
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Value;
@@ -99,8 +100,9 @@ void discoversInnerClassConstructorCorrectly() {
 
 		assertThat(constructor).isNotNull();
 
-		Parameter<?, P> parameter = constructor.getParameters().iterator().next();
-		assertThat(constructor.isParentParameter(parameter)).isTrue();
+		List<Parameter<Object, P>> parameters = constructor.getParameters();
+		assertThat(constructor.isParentParameter(parameters.get(0))).isTrue();
+		assertThat(constructor.isParentParameter(parameters.get(1))).isFalse();
 	}
 
 	@Test // DATACMNS-1082, DATACMNS-1126
@@ -231,6 +233,7 @@ static class Outer {
 
 		class Inner {
 
+			public Inner(Outer outer) {}
 		}
 	}