Remember annotations when using withExistingValue

Update `Bindable` builder methods so that existing annotations are
retained.

Closes gh-18218

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

@@ -162,7 +162,7 @@ public final class Bindable<T> {
 				existingValue == null || this.type.isArray() || this.boxedType.resolve().isInstance(existingValue),
 				() -> "ExistingValue must be an instance of " + this.type);
 		Supplier<T> value = (existingValue != null) ? () -> existingValue : null;
-		return new Bindable<>(this.type, this.boxedType, value, NO_ANNOTATIONS);
+		return new Bindable<>(this.type, this.boxedType, value, this.annotations);
 	}
 
 	/**
@@ -171,7 +171,7 @@ public final class Bindable<T> {
 	 * @return an updated {@link Bindable}
 	 */
 	public Bindable<T> withSuppliedValue(Supplier<T> suppliedValue) {
-		return new Bindable<>(this.type, this.boxedType, suppliedValue, NO_ANNOTATIONS);
+		return new Bindable<>(this.type, this.boxedType, suppliedValue, this.annotations);
 	}
 
 	/**

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

@@ -160,6 +160,20 @@ public class BindableTests {
 		assertThat(bindable1).isEqualTo(bindable3);
 	}
 
+	@Test // gh-18218
+	public void withExistingValueDoesNotForgetAnnotations() {
+		Annotation annotation = AnnotationUtils.synthesizeAnnotation(TestAnnotation.class);
+		Bindable<?> bindable = Bindable.of(String.class).withAnnotations(annotation).withExistingValue("");
+		assertThat(bindable.getAnnotations()).containsExactly(annotation);
+	}
+
+	@Test // gh-18218
+	public void withSuppliedValueValueDoesNotForgetAnnotations() {
+		Annotation annotation = AnnotationUtils.synthesizeAnnotation(TestAnnotation.class);
+		Bindable<?> bindable = Bindable.of(String.class).withAnnotations(annotation).withSuppliedValue(() -> "");
+		assertThat(bindable.getAnnotations()).containsExactly(annotation);
+	}
+
 	@Retention(RetentionPolicy.RUNTIME)
 	@interface TestAnnotation {