RFR: JDK-8245919: Region#padding property rendering error

[John Hendrikx]

On Mon, 27 Mar 2023 23:05:00 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

> Fix bug in CSS caching code that could reset values on unrelated nodes.
> 
> The bug occurs due to a cache entry being constructed incorrectly when the initial node that triggered the cache entry creation has user set values. The calculated values for properties with a user set value were omitted in the cache entry, and other nodes that later share the same entry would incorrectly assume the omitted property was unstyled and were therefore reset to their default values.

Note for reviewers:

The problem of one Node affecting another unrelated Node is because all properties of the same type, at the same level and same pseudo state set share a cache entry. When the cache entry is constructed based on a Node with an overridden property, the calculated value for the overridden property would be omitted incorrectly -- it is incorrect because other Nodes that would share the same entry may not have this property overridden!  The cache entry always should have a complete set of calculated values, regardless of which Node was used to construct the initial cache entry.

I removed the user overridden property check in `lookup`. I think this is harmless because both callers of `lookup` do the same check themselves again to avoid applying a style that would override a user set value.  However, in `transitionToState` this is just **after** the calculated value is added to the cache, which is exactly what you want.  A test verifies that the fix works.

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PR Comment: https://git.openjdk.org/jfx/pull/1072#issuecomment-1485983070