RFR: 8375588: Enhanced property metadata [v2]

[John Hendrikx]

On Wed, 21 Jan 2026 01:07:15 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> Implementation of [enhanced property metadata](https://gist.github.com/mstr2/2fec0303fc440b8eaeb126befc76eb5c).
>> 
>> ### New API
>> This PR includes the following API additions:
>> 
>> 1. `ReadOnlyProperty.getDeclaringClass()` and its default implementation.
>> 2. The `javafx.beans.property.AttachedProperty` interface.
>> 3. New constructors for all `Simple<*>Property` and `ReadOnly<*>Wrapper` classes, accepting the declaring class of the property.
>> 
>> The declaring class is stored in a new field in the `Simple<*>Property` classes. If a legacy constructor is used that doesn't specify the declaring class, the `ReadOnlyProperty.getDeclaringClass()` default implementation is called the first time the `Simple<*>Property.getDeclaringClass()` method is called, and its result is stored for future retrieval.
>> 
>> ### Testing
>> For testing, this PR also includes the `test.util.property.PropertyMetadataVerifier` tool. It systematically tests all public and protected properties of a class, and ensures conformance to the following rules:
>> * `ReadOnlyProperty.getBean()` returns the object instance of the enclosing class, or the target object instance if the property is an attached property.
>> *  `ReadOnlyProperty.getName()` returns the name of the property, which must correspond to the name of the property getter (excluding the word "Property").
>> * `ReadOnlyProperty.getDeclaringClass()` returns the enclosing class of the property getter.
>> * The declaring class of a `Simple<*>Property` or `ReadOnly<*>Wrapper` must be specified in the constructor, not resolved at runtime.
>> * `getBean()`, `getName()`, and `getDeclaringClass()` must not be overridden in subclasses of `Simple<*>Property` or `ReadOnly<*>Wrapper`.
>> * An instance property does not implement `AttachedProperty`.
>> * An instance property has a parameterless property getter.
>> * An attached property implements `AttachedProperty`.
>> * An attached property has a static single-argument property getter that accepts the target object.
>> * `AttachedProperty.getTargetClass()` returns the class of the single parameter of the static property getter.
>> * A property getter does not return an instance of `ReadOnly<*>Wrapper`, it returns the result of calling `ReadOnly<*>Wrapper.getReadOnlyProperty()`.
>> 
>> Many properties in existing JavaFX classes violate the `PropertyMetadataVerifier` rules in some way or shape. This PR won't address these issues, this will be done in a future cleanup PR.
>
> Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:
> 
>   ReadOnlyProperty.getDeclaringClass() tests

Perhaps it could help to think of attached properties as simple configuration on the node, not as temporary state owned by a container. You may not know which container a node will end up in, but you can still set things like a margin, or tell it to grow if it’s placed in a VBox. You might do the same for other container types it could live in. When the node is actually added to a parent, that parent just reads the properties it understands and ignores the rest.

>From that point of view, it’s hard to justify why a container should remove properties it didn’t set. Auto-removal makes moving a node between parents lossy and surprising, because you lose configuration that was intentionally added. A simpler rule is: keep attached properties on the node, let containers use what applies to them, and only remove a property if the code that added it explicitly does so.

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PR Comment: https://git.openjdk.org/jfx/pull/2015#issuecomment-3780792738