1885995 - [css-properties-values-api] is_discrete_animatable should be more granular for custom properties

Status: NEW

(Core :: CSS Transitions and Animations, enhancement)

Description

[Zach Hoffman [:zrhoffman]]

In bug 1846516, all custom property types were said to be discretely animatable <https://searchfox.org/mozilla-central/rev/529f04f4cd2a/servo/components/style/properties/mod.rs#1043-1044>, which mostly works for discrete animation, for non-transition interpolation, and for discrete transitions.

However, for interpolating custom properties in transitions, if all custom properties are said to be discretely animatable, those custom properties cannot also be said to be transitionable without additional logic being added <https://searchfox.org/mozilla-central/rev/529f04f4cd2a/servo/ports/geckolib/glue.rs#1216>.

Instead, registered custom property types that can interpolate should return false for is_discrete_animatable.